Xjenza Vol. 12 - 2007 - Needs Cover

Xjenza 12 (2007)

Article No. 120201

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Review A look at the Chiropteran Fauna of the Maltese Islands: Towards an effective Action Plan for their conservation Byron Baron * Anatomy and Cell Biology Department, University of Malta, Msida MSD2080, Malta.

Summary. The Maltese Islands are home to ten microchiropteran species, which cover a good proportion of micro-bat diversity. However, very little is currently known about the local ecology and requirements of these species. This review is intended to give an overview of the local bat scene with respect to biology and protection and goes on to present some recommendations which would help in the drawing up of an action plan that is specific to Maltese bats.

By emphasising local research and legal obligations throughout this work it is hoped that the multitude of gaps in the available data and protection become obvious and encourages further work. The overall aim is to have enough reliable data to be able to produce an action plan with a solid foundation of local knowledge. Such a document is urgently required, before the present populations decline beyond a point of recovery.

Keywords: Bats, Chiroptera, Conservation, Genetics, Ecology Received: 24 June 2007

Introduction Bats are classified in a single order, the Chiroptera, with over 1000 recorded species worldwide. This order is split into two sub-orders, the Megachiroptera (consisting of the Old World fruit bats) and the Microchiroptera (all other bat species).

In general, microchiropterans are more diverse in form than megachiropterans due to the variety of habitats and food sources they have taken advantage of. Around three quarters of microchiropterans are insectivorous (feeding on insects and other arthropods), and yet there are some that feed on amphibians, fish, small birds or mammals, blood, fruit or nectar. Similarly, they take advantage of a number of different habitats ranging from trees to caves and even human structures. Because of this great diversity they have a global distribution (excluded the Arctic, Antarctic and a few oceanic islands). According to ‘The 2000 IUCN Red List of Threatened Species’, over 21% of michrochiropterans are threatened and a further 23% are considered Near Threatened and are thus of conservation concern.

Taking a look at Europe, 45 species of bats have been identified so far. Of these, 44 are insectivorous michrochiropterans, while the last one is a fruit-eating megachiropteran (the Egyptian fruit bat, Rousettus aegyptiacus). Presently in Malta there is a total of 10 microchiropteran species, five residents and five rare or irregular migrants. The resident species are: Rhinolophus hipposideros minimus, Myotis punicus, Plecotus austriacus, Pipistrellus pygmaeus and Pipistrellus kuhlii.

The rare migrant species are: Rhinolophus ferrumequinum, Eptesicus serotinus, Nyctalus noctula and Miniopterus schreibersi; Tadarida teniotis is a rare winter visitor (Borg et al., 1997; Falzon, 1999; Jones, 1999; Baron and Vella, 2007).

Ecology Habitat Selection for Roosting and Feeding Microchiropteran bats use a variety of habitats for roosting and feeding. The ones which are of greatest relevance to the Maltese Islands are the garigue, maquis and aquatic habitats. The garigue and maquis are characterised by sparse vegetation, aromatic shrubs and small trees, which offer open spaces for hunting. Aquatic habitats such as streams and water pools are favoured as feeding areas because they sustain a variety of insects.

Some bat species have adapted well to urban environments and feed under light sources which also attract many insects.

Certain landscape features such as tree lines, hedgerows, and canals are used regularly by bats when moving between roosts and feeding grounds (Verboom, 1998).

The abundance of flight paths is proportional to the amount of landscape features, with species such as Myotis daubentonii and Rhinolophus hipposideros taking detours to follow hedgerows rather than cross open areas while travelling to a feeding area (Racey, 1998). Such behaviour is thought to act as an anti-predator strategy as well as allowing feeding on the way, since windbreakers may provide shelter for insects (Gaisler and Kolibac, 1992).

In Malta, a multitude of sites are used by bats for roosting ranging from caves to man-made structures namely water-tunnels, catacombs, Second World War underground shelters, bastions, fortification walls and inuse and abandoned residences. In a study covering 10 years and including 28 roosting sites for Myotis punicus it was found that caves were the only type of roost used throughout the year (Borg, 1998). Other studies (Jones, 1999; Baron, 2006) have described the habitats

* Corresponding Author: e-mail: bbar002@um.edu.mt Tel:+356 21639913. Previous Address: Conservation Biology Research Group, Department of Biology, University of Malta, Msida MSD2080, Malta.

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surrounding some of the 28 roosts mentioned above.

Although caves provide ideal natural conditions for hibernation and nursing, some species such as Pipistellus pygmaeus in Malta rely almost exclusively on man-made sites for roosting and breeding.

Bats tend to migrate to meet their roosting or feeding requirements. These migrations can vary from daily movements between the roosts and foraging areas to longer migrations for over-wintering or having young. In Malta the recorded migrations associated with both roosting and feeding are relatively short compared to other European countries, where bats may cover thousands of kilometres and even cross borders. For the local Myotis punicus it is only the females that annually migrate long distances, to the nursery for hibernation, giving birth and rearing young. However, a male covered the longest recorded distance for this species in Malta from Chadwick Lakes, Malta (trapped in November 1993) to Ghar Siekel, Gozo (September, 1996) (Borg, 1998).

The diet of insectivorous bats consists of a multitude of insects, including Coleoptera, Diptera, Ephemeroptera, Lepidoptera, Neuroptera, and Trichoptera (Best et al., 1997). In the Maltese Islands, a study of the diet of Myotis punicus, carried out using faecal material from below feeding perches, showed that the main prey species were of three insect orders: Orthoptera, Coleoptera and Lepidoptera (Borg, 1998). Many bats use echolocation to locate their prey although some take advantage of the sounds made by their prey as the means of locating them.

Certain bats catch their prey in flight, while others called gleaning bats take their prey from surfaces such as foliage or the ground. Prey may be eaten on the wing or from a perch.

Reproductive biology Maltese bats, like all other European bats are monoestrous. This is due to the adverse winter conditions in the region, when food is scarce and temperatures are low. To cope with such conditions these bats have evolved an interrupted reproductive cycle where females are in oestrous from late summer to the end of autumn with copulation also starting in late summer and may even continue into winter. Then, depending on the species, fertilisation, implantation or post-implantation development are delayed until spring (Altringham, 1996).

As for other temperate bats, local bats species usually give birth to a single young each year in spring, which develop during the early summer months (June and July), when temperatures are high and food is plentiful (Racey, 1982). For the first couple of weeks young bats are carried by their mothers during feeding forages, and when they are over three weeks old that they are left in the nurseries until old enough to hunt by themselves. They then return with the mother to the summer roosts. These juveniles then reproduce after one or two years. Bats are relatively long-lived and in Malta, for example, the longest-lived recorded Myotis punicus male was first

ringed in 1988 and last re-trapped in 2000 (i.e. over 12 years of age) (Borg, 2002).

With respect to the local nurseries, very little is as yet known. A couple of nurseries are known for Pipistellus pigmaeus. The only known nursery for Myotis punicus, which was Ghar il-Friefet (limits of Birzebbuga), has been abandoned by the resident bats and till now the location of the present nursery is unknown. This is because the low numbers make it impossible to follow swarming bats into the nursery. A nursery may eventually be found by chance as has happened with the discovery of a Myotis punicus roost in a complex of World War II shelters in Gozo during some excavations during November 2007. This discovery points towards the need of continued research, monitoring and conservation (MEPA, 2007).

Importance of bats There are several ways in which various species of bats can be considered to be of economic importance.

Pollination and seed dispersal, especially in the tropics, are major ecological services. Insectivorous bats are the primary consumers of nocturnal insects and many species feed on medical or agricultural pests. Guano (bat droppings) is considered to be an economically important product as it is a highly prized fertiliser in developing countries that can not rely on chemical fertilisers.

Insectivorous species consume large quantities of a variety of insects including a number of important agricultural pests on crops such as vines, cucurbits and potatoes (Whitaker, 1993). In the Maltese Islands, Plecotus austriacus was found to feed on at least 23 different moth species of which at least 8 are known pests. Pest species identified included Autographa gamma, Chrysodeixis chalcites and Spodoptera exigua, which feed on a variety of wild and cultivated plants and Galleria mellonella, a pest in apiculture (Borg and Sammut, 2002).

Threats to Maltese Bats and their habitats One of the best documented declines in Europe is that of its five Rhinolophus species, which has been attributed to increased disturbance to their roost sites (mainly caves) and to changes to their foraging habitats over the past years (Ransome and Hutson 2000). While in some countries only a restricted distribution with a handful of bats remains, in others they have gone extinct (EUROBATS National Reports; Ransome and Hutson 2000). Interestingly, the dramatic decline in Rhinolophus hipposideros populations may have been a result of competition rather than direct human impact. This is due to the almost complete overlap in the diet (same type and size range of prey) of this bat with that of Pipistrellus pipistrellus where these two species are found sympatrically (Arlettaz et al., 2000).

In their natural habitat, bats do fall prey to a number of species, the most noteworthy being birds of prey (such as

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owls, hawks and falcons) and snakes. However, they are not generally the main prey species of these animals as has been shown for owls with only few individuals taken (Baker, 1962; Barclay et al., 1982; Speakman, 1991; Borg, 1998). Of interest is the fact that the decline or extinction of certain bat populations has been brought about by introduced predators such as cats and rats as well as certain invasive plant species (O'Donnell, 2000; Gerlach and Taylor, 2006) which leads again to human interference with natural systems.

Locally, the best documented decline is that of Myotis punicus over the past 30 years. Although a decline has been observed in roosts all over the Maltese Islands (Borg, 1998), the worst case was that at Ghar il-Friefet, (limits of Birzebbugia) which resulted in a complete abandonment of the only known nursery in Malta.

Between March and September of the early years in which the use of this cave was recorded (between 1987 and 1996) up to 89% of the 80 to 100 individuals present were females (Borg, 1998). Numbers fell from 200 to just 12 individuals in 1990 (Borg, 1998). Recent studies have also recorded this abandonment (Jones, 1999; Baron and Vella, 2007).

Although bats face a multitude of threats, most can be linked to human activities as shown by the above declines. Bats are exceptionally vulnerable to human disturbance in their nursery and hibernation roosts because it leads to their arousal, often at great energetic cost (Thomas et al., 1990), which may be fatal (Tuttle, 1991). In Malta, as in most other countries, land is taken for development to accommodate a growing human population. According to the IUCN, “In Malta, bats are threatened through increasing urbanisation coupled with tourist development schemes” (Hutson et al., 2001). This results in the degradation and destruction of habitats such as garigue and maquis which offer bats ideal sites for both roosting and feeding (Jones, 1999).

As illustrated by a CORINE 2000 land cover map in the MEPA’s State of the Environment Report 2005, 23% of the Maltese Islands are urbanised while another 49% are occupied by agriculture. Although species such as pipistrelles can take advantage of urban and open habitat such as arable land and degraded habitats, gleaners such as Myotis punicus and Rhinolophus hipposideros tend to prefer hunting over dense vegetation and woodland edges in preference to degraded or modified terrains (Borg, 1998; Falzon, 1999; Jones, 1999; Bontadina et al., 2002; Motte and Libois, 2002; Beuneux, 2004; Aulagnier and Juste, 2004; Jacobs et al., 2004; Aulagnier and Benda, 2004). Arable land in Malta, being not so intensively cultivated offers bats a number of linear landscape elements. However, the percentage of arable land keeps decreasing, as more land is taken up for developments and the agricultural land that remains is cultivated more intensively with greater amounts of chemical fertilisers and pesticides used. Although there is as yet little information on the effects of pesticides on bats, the

effects can be divided into reduction of insect numbers and diversity (affecting diet) and accumulation of sublethal doses in fat, which during periods of use of these reserves such as hibernation or migration are released at lethal doses (Ducummon, 2000).

Walsh and Harris (1996a) have shown that insect decline occurs where there is reduction in area of water bodies which is the case when these are drained, obstructed or modified to fit some embellishment project. Studies on other species suggest that there is a decline in prey species because pesticides indiscriminately kill all insects including species fed upon by bats. Among such studies are Aebischer (1991), Feber et al. (1997), Chamberlain, Wilson & Fuller (1999), Ormerod & Watkinson (2000), Ambrosini et al. (2002), Benton et al. (2002), and di Giulio, Edwards & Meister (2001). Even British authors, with a wealth of data to draw upon due to the efforts of the BCT and DEFRA in the form of projects and surveys state “However, there are few data to show the impact of agricultural intensification on bat numbers” (Wickramasinghe et al. 2003). These authors showed the negative impact of pesticides by comparing abundances (through flight passes) between organic and conventional farming. Because bats tend to have a regional diet and having no quantitative or even qualitative Maltese data concerning the use of pesticides and their effects on animals, it is difficult to tackle this issue and thus such a local study should be given priority because it has an impact on all biodiversity.

Underground sites, both natural (e.g. caves) and manmade (e.g. shelters and fortifications), are crucial to the survival of many bat species since they provide conditions suitable for hibernation and breeding. Caves are a delicate and essential part of the bats’ habitat. In fact, 8 out of the 10 recorded Maltese species roost in caves and these are being threatened by a number of human activities including limestone quarrying and road building (Borg, 1998; Jones, 1999; Baron, 2006). The former has great bearing in Malta and is responsible for both disturbance and destruction of key roosting caves.

The damage is not only caused by blasting and transit of heavy machinery used, that send shockwaves throughout the cave and may lead to the collapse of certain overhangs or entrances, but also through settling of fine dust throughout the cave including resting bats.

Cave disturbance may also take other forms. Some caves are used by farmers as storage areas and are closed or modified by means of lights, stonework, doors, gates, etc.

Such modifications lead to exclusion of bats through the presence of a physical barrier or changes in the internal environment. Concerns over public safety have led to the sealing of underground sites (e.g. the shelters in Zebbug, Gozo). In most cases, such action is not a deliberate attempt to exclude bats since their presence may not be known. On odd occasions bats may be disturbed by tourists or amateur explorations as well as cook-outs where fires are lit in the caves.

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Deliberate disturbance is usually due to fear or prejudice due to a combination of inaccurate information coupled with perceived risks of damage or disease, which trigger eradication campaigns. Worst of all is disturbance by vandals who burn caves, spray or paint graffiti on the walls, throw objects at the bats or in rare cases even set caves on fire. Although such acts are infrequent, they can be very destructive.

Besides caves, residential buildings together with churches and historical buildings in Malta are important roosting sites for Rhinolophus hipposideros minimus, Myotis punicus and pipistrelles especially where these have underground extensions dug in rock or offer high, deep cavities which mimic natural structures and can offer a constant environment (Borg, 1998; Jones, 1999; Baron and Vella, 2007). In some cases there may be conflicts between the owners and bats. Renovation of buildings can lead to the loss of these roost sites. In Malta, a number of historical buildings with bat colonies have been restored and the bats excluded. The number of large, undisturbed rooms in houses is declining because of the trend towards improved use of space and the demolishing of old buildings. Occupancy of public buildings, including churches, should be the least problematic since they fall under a central entity. Many such buildings are considerably old and often house longestablished populations and possibly maternity roosts.

Legislation, Protection and Conservation Legal protection for bats can be of two forms, international or national. International treaties which include bats and their habitats are not usually specific to them but include them together with other flora and fauna such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora 1973 (CITES), the Convention on the Conservation of Migratory Species of Wild Animals 1979 (Bonn Convention), the Convention on the Conservation of European Wildlife and Natural Habitats 1979 (Bern Convention), the European Communities Council Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora 1992 (The EEC Habitats and Species Directive) and the Convention on Biological Diversity 1992 (The Rio Convention). Maltese bats are included in the latter four conventions and thus Malta endorses these international agreements.

The Bonn Convention provides protection for Malta’s five migrant chiropterans (listed in Appendix II since they would ‘significantly benefit from the international co-operation that could be achieved by an international agreement’). The Bern Convention provides protection for all of Malta’s bats under Appendix II as ‘strictly protected fauna species’. The EEC Habitats and Species Directive includes three of Malta’s chiropterans in Annex II as ‘species of community interest and in need of strict protection’, while including all Maltese bats in Annex IV as ‘species of community interest whose taking in the

wild and exploitation may be subject to management measures and the populations of which should be maintained at a “favourable” status’. The Rio Convention helps Maltese bats by imposing measures for the rehabilitation and restoration of degraded ecosystems and promoting the recovery of threatened species through appropriate legislation and management plans.

The Agreement on the Conservation of Bats in Europe (EUROBATS) was created under the Bonn Convention and is the only specific convention for European bats and thus includes all of Malta’s species. It covers 48 Range States in Europe and through its conservation and management plan, aims towards bat conservation through legislation, education, conservation measures and international co-operation.

Although upon signing EUROBATS each country is bound to protect the listed bat species, there is no strict rules as to how this should be done and national legal protection for bats varies greatly between the EU member states such that while in some countries bats are well cared for and integrated into action plans, in others they receive no tangible protection. In some cases, the bats themselves may be protected but their roosting or feeding habitats are not. In others, though legislation may in theory be adequate, often the resources are not available to ensure proper enforcement.

The first hint of protecting bats through local legislation in Malta came in the Environment Protection Act of 1991 and then in the Environment Protection Act of 2001.

From these came the following legal notices, which offer specific protection. The Flora and Fauna Protection Regulations, 1993 (Legal Notice 49 of 1993) specifically mentions all local microchiroptera as being protected in Schedule II. It clearly states all the prohibitions and repercussions of such actions i.e. it is illegal to take, kill, possess, sell, exchange, import or export any specimens of bats as well as disturb them particularly during periods of breeding, rearing or hibernation. Fines and imprisonment are the penalties set for breaking this law (MEPA, 1993). The Flora and Fauna Protection (Amendment) Regulations of 1999 (Legal Notice 161 of 1999) maintain the status of local bat species as in L.N. 49 of 1993 (MEPA, 1999). The Flora, Fauna and Natural Habitats Protection Regulations of 2003 (Legal Notice 257 of 2003) not only recognises local bat species as being in need of protection but also as requiring particular areas as part of their conservation. Thus it provides for the protection of habitats that are important for bats, including caves and other roosts (MEPA, 2003). Permits issued for research on local bat species cite this legal notice as their main basis such that both the species and its habitat are disturbed as little as possible. The next step in such legislation is the protection of areas known to be important feeding sites. Presently these three legal notices have been incorporated into L.N. 311 of 2006 (MEPA, 2006).

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Recommendations for a local Action Plan In order to better safeguard Malta’s chiroptera and make sure that they are not lost in the near future it is essential to draw up and implement an action plan on a national level. The creation of such an action plan is in line with the Rio Convention, which requires the preparation of a national biodiversity strategy. To aid in the preparation of an effective action plan, in which each species gets the conservation attention it requires, it is useful to take example from other countries and use their successes as a basis for local action.

Although the details of this action plan must be drawn up with the participation and co-operation of all experts in the concerned fields, a few essential recommendations will be listed below based on what has been noted during local studies and what essential information still needs to be collected. The action plan should focus on three main areas namely research, legislation and management, and education.

Research Although 10 species have been recorded in the Maltese Islands (Borg et al., 1997; Falzon, 1999; Jones, 1999; Baron and Vella, 2007), there are still a number of gaps in the known biology and ecology of a number of these.

Without basic local knowledge regarding each species, including its genetic diversity, ecology, feeding, it is very difficult to draw up legislation and a management plan to effectively protect bats, their roosts and foraging habitats.

Funds should be allocated for research into population studies, habitat requirements and diet.

Population studies should be carried out to determine the status and distribution of each species including any seasonal movements. The primary target should be to review the systematics and determine which sub-species actually inhabit the Maltese Islands using morphometrics, echolocation calls and molecular techniques. The variety of markers and studies that can be carried out on bats has been outlined by Burland and Worthington Wilmer (2001). The importance of an integrated approach can be seen in studies where the use of mitochondrial DNA and echolocation calls in determining that individuals classified as Pipistrellus pipistrellus in fact constituted two cryptic species namely P. pipistrellus and P. pygmaeus (Jones and Van Parijs, 1993; Barrett et al., 1997). Population studies of Maltese microchiropterans include an investigation of the seasonal changes in abundance, roosting and feeding (through faecal analysis) habits of pipistrelles (Falzon, 1999). Another study analysed the distribution, abundance, behaviours and habitat associations of bat species in Malta using various survey techniques, roost counts and mist netting which recorded Rhinolophus hipposideros, Myotis punicus and pipistrelles (Jones, 1999). A study to determine the population structure of the local Myotis punicus was carried out using cellulose acetate allozyme electrophoresis using a non-lethal sampling technique.

Results showed that the Maltese population of Myotis

punicus is a single breeding population with an indication of inbreeding (Baron and Vella, 2007). Such studies offer valuable and relevant knowledge to update the status of each bat species in the Maltese Red Data Book. The collected data from any of these studies should be considered and forwarded to the IUCN/SSC Chiroptera Specialist Group by local authorities acting as national contacts to improve the evaluation of the status of threat of the local species. Also such research centres focusing on conservation biology research should be funded to increase its effort toward providing the necessary knowledge for effective conservation management.

Further bat species research on roosting habits locally should include the determination of desired characteristics of caves, buildings and other hypogea together with those of their surrounding habitats that are important to each species. This involves the compilation of an inventory of underground habitats used by each species indicating the condition of each roost, key roosts and the current or potential threats faced by such sites. It is also important to have long-term monitoring programmes for key roosts and the legally protected species that inhabit them.

Further bat species research on foraging habits and requirements should focus on the specificity of bat feeding habits and the changes in diet throughout the year. The studies should also be extended to include the importance of linear landscape elements for local bat species, the effect of agriculture and related chemicals on Maltese bats and the adaptation of local bats to changes in landscape if possible.

Detailed nationwide bat population surveys which show how bat species conservation is developed abroad include the ‘Action Plan for the Conservation of Bats in the United Kingdom’ (Hutson, 1993), ‘The status and conservation of horseshoe bats in Britain’ (MitchellJones, 1995), ‘Foraging Habitat Preferences of Vespertilionid Bats in Britain’ (Walsh and Harris, 1996a), ‘Factors Determining the Abundance of Vespertilionid Bats in Britain: Geographical, Land Class and Local Habitat Relationships’ (Walsh and Harris, 1996b) and ‘the UK's National Bat Monitoring Programme: Final Report’ (Walsh, 2001). These works include detailed investigations of large areas and analyse foraging habits, breeding, hibernation, and other roost sites, and population numbers. They then provide recommendations for improved monitoring, protection and conservation.

At an international level, the relevant example of a species action plan is that for the greater horseshoe bat (Rhinolophus ferrumequinum) in Europe, which gives detailed information about all aspects of this bat and puts forward a number of conservation actions (Ransome and Hutson 2000).

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Legislation and management Although all bat species in Malta are protected by law, there is as yet inadequate protection of roosts and their surrounding habitat especially when it comes to manmade structures which might be occupied or in regular use (such as churches or government buildings). At present only 2 caves in the Maltese Islands are to some extent protected in relation to bats: Ghar Hasan and Ghar il-Friefet. In both cases they are protected on paper and have been fitted with bat grilles. However the erection of bat grilles is not enough to safeguard such sites especially if these aren’t even properly maintained.

The nurseries or key roosts of Myotis punicus and Rhinolophus hipposideros minimus could be established as Special Areas of Conservation (SACs) since they are 2 of the 13 bat species listed in Annex II of the EEC Habitat Directive.

Since bats use a range of feeding sites and habitats at different times of the year, it is not enough to protect individual roost but it is equally important to protect foraging habitats and the landscape elements used by bats for commuting (Racey, 1998; Jones, 1999).

Implementation and enforcement are also lacking. If damage to a roost is reported, immediate action is required before that particular roost is lost. In order to be able to detect such threats as soon as they manifest themselves it is essential for roosts to be monitored regularly and checked for signs of disturbance. Besides protective legislation, it is important that there is a speeding up of procedures related to the removal of illegal obstructions to cave entrances (such as meshes or gates) and retraction of quarrying permits.

Education Education is of the utmost importance and the desired educational programme should be primarily aimed at the general public in such a way that it can be applicable to both children and professionals alike. It should encourage an understanding of bats by including various aspects such as their biology, importance to humans, role in the environment, roosting and foraging requirements, use of man-made structures as roosts, major threats, need for protection and the present legal protection provided.

There is a vast amount of information regarding bats, available in the form of leaflets and other educational material that can be used as a basis for local awareness programmes.

The other aspect of education that needs to be considered is formal education, which can be divided into two. The first is to include bats into undergraduate lectures about local ecology and conservation. The other would be to specifically train local bat and conservation experts. The latter would be an investment for the future and should be opted for. Despite its small size, Malta has the human resources to train people who can work on protecting the

rich local biodiversity at all levels. It is never feasible in the long run to have foreign professionals coming for short-term projects when the country already has people and facilities to train the future generation of conservation scientists. All that is needed is funding to push forward and improve the process that is already in progress.

The single most important awareness event is the ‘European Bat Night’, an international public-awareness event organised by EUROBATS that has taken place every year for the past 10 years, with the participation of over 30 countries. During this activity the public is informed about bats through bat walks, leaflets, talks, presentations, workshops and exhibitions. This event is usually planned for the last weekend of August, although the date may vary from one country to another. Malta has taken part in this event in previous years and it can be a very educational event if well-promoted.

Conclusion The Maltese Islands have a diversity of bat species which should be taken care of in the best interest of the nation and the world since some are species restricted to this geographical area. In order to achieve this, an action plan is urgently required, which by implementing the above recommendations and much more can first of all fill in the gaps in the present knowledgebase and ultimately offer local bats and the habitats they require, adequate protection. To reap the maximum benefits from preparing such an action plan it is important to integrate ideas from all participating parties and set up clear, attainable checkpoints and goals in the form of stages to meet both national and international requirements and standards.

The goals should be adaptable to ensure that as the local picture improves, with the completion of each checkpoint within the action plan, the new information is channelled towards refining and better targeting future goals. With such an action plan in place, the framework for better bat research and conservation would have been set. It might also be used as a pilot project for application to other Maltese species requiring critical attention.

Acknowledgements The author would like to thank Dr. Adriana Vella, Ph.D. (Cantab.) and the Conservation Biology Research Group at the University of Malta for providing insight into the fields of conservation and bat population genetics. The author would also like to thank Mr. John J. Borg, Curator of the National Museum of Natural History, for sharing his experience and expertise about local bats.

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42. Racey P.A. (1982). ‘Ecology of bat reproduction’. In: T.H. Kunz (Ed.), Ecology of Bat, Plenum press, New York (1982), pp. 57– 104.

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3, pp. 123-142. 1991.

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Xjenza 11 (2007)

Article No. 120301

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Research Article Burrow density of the endangered Maltese Freshwater Crab Potamon fluviatile lanfrancoi at Lunzjata and Xlendi valleys, Gozo Jacqueline Debrincat and Patrick J. Schembri* Department of Biology, University of Malta, Msida MSD2080, Malta

Summary. The density of burrows of the highly threatened and locally protected freshwater crab Potamon fluviatile lanfrancoi at its only known locality of occurrence on Gozo, the Wied tal-Lunzjata / Wied tax-Xlendi valley system, was surveyed during the 2006-2007 wet season. Of a length of 851m of the main channel of Wied tal-Lunzjata surveyed, 665m had burrows, while of 303m of Wied tax-Xlendi surveyed, only 60m had burrows, giving a mean burrow density of 1.29 and 0.10 burrows per metre, respectively. The highest concentrations of burrows occurred in three areas within Wied tal-Lunzjata: its upper reaches, in the Ta’ Ghajn Tuta area, and in the Wied tas-Saqwi area. Only few burrows occurred in the lower reaches of Wied tax-Xlendi, the only accessible part of this valley that could be surveyed. There was no clear relationship between burrow density and either water depth or flow rate, although there were indications that high flow rates tended to favour high burrow densities. Burrows were invariably excavated in the soil or muddy sediment close to the water level and the availability of muddy sediment was a key factor determining the occurrence of burrows. Burrow occurrence and burrow density did not seem to be affected much by material dumped into the valley, or by moderately poor water quality, but there were clear indications that the crabs may be particularly susceptible to severe changes in water quality and in the hydrologic regime, particularly where this affects the availability of critical habitat.

Keywords: Crustacea, Decapoda, Potamidae, Malta, conservation.

Received: 10 October 2007 Introduction The only freshwater crabs currently occurring in Europe belong to the Eurasian genus Potamon. Three species are presently recognised as valid (Fauna Europaea, 2004): Potamon ibericum (Bieberstein, 1809), the most widespread, occurring in Romania, Bulgaria, Ukraine, Greece, some Aegean islands, and Turkey, and introduced into France; Potamon fluviatile (Herbst, 1785) occurring in Italy, Sardinia, Croatia, Albania, Greece and Malta (and in North Africa); and Potamon potamios (Olivier, 1804), which is found in Cyprus, Crete, some Aegean islands, and the southwestern and southern parts of Turkey (and in Syria, Israel and Palestine) (Pretzmann, 1980; 1983; Fauna Europaea, 2004; Crustikon, undated).

However, other species of uncertain validity have been instituted [for example, Potamon rhodium (Parisi, 1913), supposedly endemic to a few Greek islands (Pretzmann, 1980; Brandis et al., 2000)], as well as a large number of subspecific and infrasubspecific taxa for the three accepted species (see for example Pretzmann, 1962; 1980; 1983), most of which are not considered valid.

Records of a freshwater crab in Malta date back to at least 1647, and this species has been recorded in the literature as Thelphusa fluviatilis, Potamon edulis and Potamon fluviatile (Capolongo & Cilia, 1990). Thelphusa Latreille, 1819 and edulis Latreille, 1818 are junior synonyms of Potamon Savigny, 1816 and fluviatile Herbst, 1785, respectively. In 1990, on the basis of small morphometric and morphological differences between Maltese populations and Italian (Potamon fluviatile fluviatile) and

North African (Potamon fluviatile algeriense) populations of this species, Capolongo & Cilia (1990) described a new subspecies from Malta: Potamon fluviatile lanfrancoi.

In the semi-arid Maltese Islands, Potamon fluviatile is limited to localities with perennially available freshwater, and on the island of Malta it has been recorded from Marsa, San Martin and It-Tilliera (near Il-Wardija), Wied il-Gnejna and Bingemma (both near Mgarr), Wied ilBahrija and L-Imtahleb (both on the outskirts of Rabat), and from Il-Wied ta' Gordajna (between L-Imtahleb and Wied il-Bahrija), while in Gozo it is only known from IlWied tal-Lunzjata (on the outskirts of Kercem) (Pace, 1974; Schembri, 1983; Schembri et al., 1987; Capolongo & Cilia, 1990; Cachia, 1997; Camilleri & Cachia, 2000).

All these localities are (or were) characterised by more or less perennial freshwater springs. The population at Marsa was extirpated when the marshes there were drained in the 1850s, while it seems that the population at Bingemma has also been lost (Capolongo & Cilia, 1990; Camilleri & Cachia, 2000). Although no quantitative estimates exist, there is general agreement among all authors that have studied the Maltese Potamon fluviatile populations, that these are suffering a general decline, which has been attributed to a variety of factors, including: loss of habitat due to agriculture and urbanization, excessive extraction of water, diversion of springs, pesticide use, over-collecting, human persecution, and unusually hot and dry summers (Schembri, 1983; Schembri et al., 1987; Capolongo &

* Corresponding Author: e-mail: patrick.j.schembri@um.edu.mt Telephone: +356 23402789 Fax: +356 2132 3781.

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

Cilia, 1990; Cachia, 1997). The 1989 Red Data Book for the Maltese Islands listed Maltese populations of this species as ‘Endangered’ (using the pre-1994 IUCN Red List criteria); a more recent re-assessment made using the 2001 IUCN Red List categories and criteria applied as per the most recent guidelines (IUCN, 2006) lists Maltese populations as CR (Critically Endangered) under B1ab (ADI & Ecoserv, 2005; MEPA, 2007).

Spearheaded by the efforts of a local environmentalist and a local environmental non-governmental organization, Potamon fluviatile lanfrancoi has become a conservation icon in Malta (Lanfranco, 1975; Schembri, 1983; Capolongo & Cilia, 1990) and has been legally protected since 1993. Under present legislation it is listed in Schedules III (Animal and plant species of national interest whose conservation requires the designation of special areas of conservation) and VI (Animal and plant species of national interest in need of strict protection) of the Flora, Fauna and Natural Habitats Protection Regulations, 2006 (Legal Notice 311 of 2006 published in the Supplement to the Malta Government Gazette of 7th December 2006).

Given its position in Malta as a highly threatened, protected species, it is very surprising that no overall assessment of the actual status of the populations of the crab on the Maltese Islands have been made. As far as we are aware, the only information available is the estimate of the population density in the San Martin area made by Cachia (1997). This author recorded population densities of between 125 crabs/ha and 350 crabs/ha along a 600m strip of watercourse, depending on season. No population density estimates for the only Gozitan population of Potamon fluviatile lanfrancoi exist, however, according to Capolongo & Cilia (1990), this population is concentrated along a length of watercourse of only 150m in the upper reaches of the Wied tal-Lunzjata valley.

Against this background of fragmentary information on the status of Potamon fluviatile lanfrancoi in Gozo, we have made surveys along as much of the Wied talLunzjata/Wied tax-Xlendi valley system (Figure 1) as was accessible to us. Normally, much of the valley bed along this system is choked by dense reed beds that make it impenetrable; however, we took advantage of the fact that one of us (JD) was based in Gozo so that when farmers cropped reed beds along different sections of the valley, surveys could be made while the watercourse was accessible.

Methods used Surveys were made during the 2006-2007 wet season, between December 2006 and April 2007. We surveyed Wied tal-Lunzjata from its headwaters at Ta’ Wied Hmar at Kercem, south to Ta’ Wistin Farun, limits of Munxar (Figure 2), a total distance of 973m; however, we did not survey a 120m section west of Fontana (section L20; see Table 1 and Figure 2) for health and safety reasons. We surveyed Wied tax-Xlendi from a point 140m west of

2

where the small tributary known as Wied il-Gharab joins Wied tax-Xlendi up till that part of the mouth of Wied tax-Xlendi which has been developed into a car park at the head of Il-Bajja tax-Xlendi (Figure 3); this section measured 303m. We could not survey the middle section of the Wied tal-Lunzjata/Wied tax-Xlendi valley system between Ta’ Wistin Farun and where the tributary known as Wied ta’ l-Ghancija joins up with Wied tal-Lunzjata to become Wied tax-Xlendi, and between this point and the Wied il-Gharab area, because the valley system in this section is gorge-like and has very steep sides, making the watercourse inaccessible without the use of specialised rock climbing techniques, and even so, it is not possible to walk along the watercourse as it is choked by dense reed beds. The section that was not surveyed measured 788m. The tributary valleys of Wied ta’ l-Ghancija and Wied il-Gharab were not surveyed for similar reasons.

The tributaries feeding Wied tal-Lunzjata further upstream than the Ta’ Wied Hmar area were also not surveyed. Although some burrows occurred in farmland in the Ta’ Ghajn Tuta area, this land was also not surveyed as it is heavily cultivated, making access problematic. The tributary of Wied tas-Saqwi was surveyed but no traces of burrows were found. This tributary is mostly cultivated and does not appear to retain water for any great length of time following rainfall episodes.

The number of Potamon burrow openings was counted along sections of the watercourse by first measuring a section using a surveyor’s measuring tape, or where it was not possible to stretch the tape, by pacing, and then counting the number of active burrows on both banks of the watercourse. Where burrows were noted, 4-20m sections were measured, but where there were no burrows, longer sections were measured. Active burrows were taken as those that did not have the mouth clogged with soil, stones or debris. Water depth in each section was measured at the deepest point using a graduated rod.

The speed of flow of the water was noted (as nil, low, medium or high) but was not quantified.

Results A total length of 1154m of the main channel of the Wied tal-Lunzjata/Wied tax-Xlendi valley system was surveyed; this represents 56% of the main channel (that is, excluding tributary valleys) of the system. The density of burrows in different sections of the valley bed is given in Table 1, which also provides information on water depth, flow rate and general environmental conditions at the time of survey. Overall, out of a total length of 851m of Wied tal-Lunzjata surveyed, (excluding section L20, which was not surveyed), 665m (78.2%) had burrows. A total of 303m of Wied tax-Xlendi was surveyed, but only 60m (19.8%) had burrows. The mean burrow densities in the lengths of valley surveyed were 1.29 burrows per metre at Wied tal-Lunzjata, and 0.10 burrows per metre at Wied tax-Xlendi.

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

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Fig. 1. Location of the Wied tal-Lunzjata / Wied tax-Xlendi system on Gozo (indicated by the rectangle on the contour map of Gozo). Š Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

4

Fig. 2: The Wied tal-Lunzjata watercourse (shaded) showing the sections investigated in this study (L1 to L41). For clarity not all sections are labelled; arrows point to the midpoint of each labelled section. Locality codes: GhT – Ta’ Ghajn Tuta; WF - Ta’ Wistin Farun; WGh - Wied ta’ l-Ghancija; WH - Ta’ Wied Hmar; WS - Wied tas-Saqwi; WX Wied tax-Xlendi.

Fig. 3: The lower reaches of the Wied tax-Xlendi watercourse (shaded) showing the sections investigated in this study (X1 to X9). For clarity not all sections are labelled; arrows point to the midpoint of each labelled section. Locality codes: BX – Bajja tax-Xlendi; CP – carpark; WA - Wied il-Gharab.

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

5

Section

Length of section (m)

No. of burrows per metre of valley bed

Water depth (m)

Water flow

Notes

L1

30

0

0

dry

Rocky bed with shingle; abundant dumped rubbish

L2

15

0

0.20

nil

Turbid water; rocks on bed

L3

18

0.06

0.25

nil

Turbid water; rocks on bed

L4

10

2.70

0.58

nil

Greenish-grey water

L5

14.4

2.30

0.11

nil

Greenish-grey water

L6

11.2

1.80

0.90

low

L7

12

0.70

0.80

low

L8

14

0.40

0.20

medium

L9

15

0.70

0.30

low

Turbid water; reed debris

L10

11

0.50

0.15

nil

Foul-smelling, turbid water

L11

8

0

0.15

nil

Foul-smelling, turbid water

L12

19

0.20

0.10

low

Rocky bed; banks almost dry

L13

20

1.10

0.10

low

Turbid water; rocky bed

L14

29

0.70

0.32

nil

L15

44

0

0.10

low

L16

15

0

0.18

low

L17

53

0.10

0.20

low

Clear water; dumped rubbish

L18

26

0.10

0.28

low

Clear water; dumped rubbish

L19

35

0.10

0.20

nil

122

?

?

low

L21

35

0.70

0.35

low

L22

24

0.20

0.35

nil

L23

23

1.70

0.16

medium

L24

23

0.04

0.16

medium

Clear water; dumped rubbish Clear water; one bank covered by cut reeds

L20

Moderately clear water; some dumped rubbish decomposing dumped vegetable waste and dumped rubbish Turbid water; rocks on bed; dumped rubbish; vegetated banks

Turbid water; dumped rubbish Paved bed; dumped rubbish and reed debris; banks consist of ashlar walls Turbid water; dumped rubbish; banks consist of ashlar walls

Sewage pumping station on east bank; turbid water; dumped rubbish Foul smelling, turbid water; not surveyed for health and safety reasons Foul-smelling, turbid water (but clear water discharge from fields); anoxic sediment on valley bed; Foul-smelling, turbid water; anoxic sediment on valley bed Clear water; dumped rubbish

L25

40

0.60

0.23

medium

L26

30

0.30

0.25

low

Clear water

medium

Clear water; bed choked with debris

L27

30

0

0.14

(cont.)…

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

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… (cont.)

L28

26

0.30

0.17

medium

L29

11

4.20

0.35

low

Slightly turbid water; parts of watercourse obstructed by cut reeds; dumped rubbish Clear water Very clear water; dumped rubbish; narrow watercourse (1m) Very clear water; very narrow watercourse (0.9m) Clear water; very narrow watercourse (0.5m) Clear water; very narrow watercourse (0.5m) Deepest part not accessible to measure water depth; turbid water; heavily littered Turbid water; dumped rubbish; rubble walls on west bank Clear water; parts of watercourse obstructed by cut reeds

L30

15

2.00

0.20

high

L31

9

2.40

0.10

high

L32

4

10.00

0.15

high

L33

4.5

4.70

0.15

high

L34

9

0

>0.2

low

L35

23

0.40

0.25

low

L36

11

1.50

0.15

low

L37

17

0.30

0.40

low

Grey to black sediment on bed

L38

12

0.40

0.20

nil

Foul-smelling, turbid water; dumped rubbish

L39

47

0.04

0.65

low

Clear water; pebbly substratum

L40

23

0.04

0.70

nil

L41

35

0.0

0.5

low

788

?

?

?

X1

56

0

0.10

low

X2

21

0

0.05

low

X3

30

0.10

0.12

low

X4

30

0.10

0.12

low

X5

30

0

0.12

low

Dumped rubbish

X6

30

0

0.20

low

Yellowish-green water

X7

38

0

0.20

low

Yellowish-green water

X8

30

0

0.50

nil

X9

38

0

0.30

nil

Turbid water; parts of watercourse obstructed by cut reeds Very turbid water; drop-off to gorge-like section of valley beyond this point Inaccessible deep gorge-like section of valley; dense reed beds Dry muddy banks; rocky bed Very shallow pebbly watercourse Clear water with dense algal growth; thick vegetation on banks Wet muddy banks with vegetation

Concrete bank on east side of watercourse; cut reeds floating in greyish-green water Concrete bank on east side of watercourse; cut reeds floating in greyish-green water

Table 1: Counts of the density of Potamon burrows along the Wied tal-Lunzjata/Wied tax-Xlendi valley system made between December 2006 and April 2007. The ‘Length of section’ column represents the measured lengths of different sections of Wied tal-Lunzjata (sections coded ‘L’; Fig. 2) and Wied tax-Xlendi (sections coded ‘X’; Fig. 3), while the ‘No. of burrows’ column represents the number of burrows in that section standardized to ‘per metre of valley bed’; note that burrows on both banks of the watercourse were counted and used for the burrow density estimations.

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

These data were explored by inspection and graphically.

In general, there was no obvious relationship between water depth, flow rate, and burrow density with increasing distance from the ‘source’ (that is, the start of section L1). Neither was there any clear relationship between burrow density and either water depth or flow rate, although there was a tendency for the highest burrow densities to occur where the flow rate was high (for example, in sections L30-L33). Although it would be reasonable to assume that water is more abundant towards the head of the valley system, where springs run into the channel, and least abundant towards the mouth, in effect, the water supply depends also on the contribution from tributary valleys that join the main channel at various points along its course, on drainage from fields situated adjacent to the valley banks (as for example, in section L21), and on localised sources of water input, including leakage and overflow from farmers’ irrigation canals and from the sewage pumping station in section L19. The depth of water depended mostly on the availability of water at particular points along the valley and on the microtopography of the watercourse. Thus, water tended to accumulate in localised depressions in the valley bed, irrespective of where these occurred along the valley. Similarly, the rate of water flow was determined primarily by the rainfall and the local gradient and microtopography of the different sections of the valley system, as well as by any obstruction of the watercourse.

Potamon burrows were invariably excavated in the soil or muddy sediment on the banks of the valley, usually close to the water level (normally ± 10cm from the water surface), but occasionally below it and sometimes up to 80cm above it. It was obvious that the availability of muddy sediment was a key factor determining the occurrence of burrows; thus, burrow density was least where there was little muddy sediment available (for example, sections L1 and L2), and there were no burrows where there was no sediment, for example, where the banks were constructed of either ashlar limestone blocks (sections L15 and L16) or of concrete (sections X8 and X9), irrespective of the availability of water. In some places, burrows were observed to have been excavated in the soil-filled spaces in dry stone (rubble) walls when these were present close to the water (for example, in section L35). A second key factor was the wetness of the mud. Burrows were excavated where the mud was wet and burrows in dry mud seemed to be abandoned.

Provided that the sediment was wet, water depth did not seem to affect the occurrence of burrows, however, more burrows tended to occur where the flow rate was high. In this regard, it is also worth noting that burrows occurred close to irrigation canals carrying clear, fast-flowing water in agricultural land in the Ta’ Ghajn Tuta area.

It is not clear what effect water quality has on occurrence or density of burrows. Burrows were found where the water was clear as well as where it was turbid and where there were clear signs of mild eutrophication (for example, in sections L4 and L5). It was only where the

7

water was highly eutrophicated that burrows were absent or present in low densities (for example, in sections L19, L21, L22, L37 and L38). However, these results need to be interpreted with caution since the crabs may be responding to localised micro-environmental conditions rather than to the overall state of the valley section. Thus, for example, although the water in section L21 was overall foul smelling and turbid, the majority of burrows were actually clustered around an outlet delivering clear water discharge from fields bordering the valley banks.

Burrow occurrence and burrow density did not seem to be affected much by material dumped into the valley. This material ranged from vegetable waste, to rags, metal cans, plastic containers, plastic pipes, building waste, household white-goods and discarded farm tools. Most sections of the valleys had dumped material of this type and parts were heavily dumped.

In general, the highest burrow densities (2-10 burrows per metre) were recorded in sections L29-L33, which are located in that part of Wied tal-Lunzjata where the tributary known as Wied tas-Saqwi joins the main channel. Moderate burrow densities were recorded in sections L4-L10 (0.4-2.7 burrows per metre) and in L13L14 (0.7-1.1 burrows per metre), all of which are in the upper reaches of Wied tal-Lunzjata. Another stretch with a medium to low burrow density occurred in sections L21-L28 (0.2-1.7 burrows per metre, except L24 and L27) in the Ta’ Ghajn Tuta area, and in L35-L38 (0.3-1.5 burrows per metre) in the Wied tas-Saqwi area. It thus appears that there are three regions of the main channel of Wied tal-Lunzjata where substantial concentrations of Potamon burrows occur: the upper reaches, the Ta’ Ghajn Tuta area, and the Wied tas-Saqwi area. Wied tax-Xlendi had very low to zero burrow densities and this part of the Wied tal-Lunzjata/Wied tax-Xlendi system cannot be considered a good habitat for Potamon fluviatile.

Discussion With a native range limited to North Africa, Italy, Malta, and the southwestern Balkan area (although there is some recent molecular evidence to suggest that Potamon fluviatile was actually introduced to Italy at least twice by historic human transport; Jesse, 2007), the Mediterranean freshwater crab Potamon fluviatile does not have a wide global distribution. If the various subspecies that have been described are accepted as valid, then the range of some of these is very limited indeed, with that of Potamon fluviatile lanfrancoi being arguably the most limited, since this subspecies occurs only in the Maltese Islands, and therein, in a very restricted number of localities and in a habitat (valleys fed by perennial springs) that is not only rare but also threatened. The designation of these populations as ‘Critically Endangered’ is almost self-evidently justified, even if no overall quantitative assessment of the Maltese population has been made.

Even if Potamon fluviatile lanfrancoi is not considered to be a valid taxon, the Maltese populations may

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

nonetheless qualify as an ‘evolutionarily significant unit’ (ESU) sensu Waples (1991) (populations that are reproductively separate from other populations and have unique or different adaptations), certainly as far as reproductive isolation is concerned, although whether Potamon fluviatile lanfrancoi has unique genes or gene combinations has yet to be determined; the Maltese populations also qualify as a ‘management unit’ sensu Moritz (1994) (sets of populations that are currently demographically independent) for conservation management purposes. In this respect, the Gozo population of Potamon fluviatile lanfrancoi is a completely demographically enclosed one and as such is of intrinsic conservation value, quite apart from its cultural importance.

The present study has provided the first data on the distribution and abundance of burrows of the only known population of Potamon fluviatile lanfrancoi in Gozo.

Contrary to the statement made by Capolongo & Cilia (1990), the Gozitan Potamon population is not restricted to a stretch of some 150m in the upper reaches of Wied tal-Lunzjata but occurs throughout the length of this valley from south of Ta’ Wied Hmar to the Ta’ Wistin Farun area, with three concentrations – in the upper reaches of Wied tal-Lunzjata, in the Ta’ Ghajn Tuta area, and in the Wied tas-Saqwi area – at least on the basis of the occurrence of burrows; the highest concentration was in the Wied tas-Saqwi area. A few burrows also occur in the lower reaches of Wied tax-Xlendi, whereas the situation in the upper reaches of this segment (that is, between the Ta’ Wistin Farun and the Wied il-Gharab areas) is not known as this part of the valley was not surveyed due to its inaccessibility.

It is important to note that our assessment was based on the density of burrows and not on actual counts of the live crabs, although crabs were seen in some stations during the survey (in particular in sections L4, L5, L26, L32, L35 and L39); Potamon fluviatile is mostly active at night (Gherardi et al., 1988) and therefore very difficult to survey directly, especially given the mostly inaccessible localities where it occurs in Gozo.

Although it is reasonable to assume that the density of burrows is proportional to the density of live crabs, there are a number of problems with this assumption, the chief of which is that where many burrow openings occurred next to each other, it was not possible to determine if these represent different burrows or single burrows with multiple openings. Burrows with more than one opening were reported by Pace et al. (1976), while by casting burrows, Cachia (1997) demonstrated that these tend to be U-shaped with one arm of the U sometimes forming a second opening to the same burrow. If this was common in the valley system we investigated, than the actual population density of crabs may be considerably lower than the burrow density. On the other hand, there is also the possibility of different burrows sharing a common opening, although this has never been shown to occur.

8

Additional sources of error are related to the dense reed beds along the valley floor making it hard to spot burrows along the banks, even when the reeds were cut (since the stem bases still remain and cut reeds are left on the banks). Thick vegetation growing on the banks also made counting burrows difficult. Burrows constructed in rubble walls were sometimes hard to distinguish as burrows.

Submerged burrows were also not easy to spot and count, particularly where the water was relatively deep and turbid. All these cases result in underestimates of burrow density and hence of crab density. Yet another source of error was that in recently dry areas, it was difficult to say if burrows were active or abandoned. Given these problems, our results need to be interpreted with caution and should probably be considered only as indicative of the actual population density of live crabs.

Observations made in this study agree very well with those made by Cachia (1997) in his study of Potamon fluviatile lanfrancoi from San Martin (on Malta). As at San Martin, the critical habitat for the freshwater crab in the Wied tal-Lunzjata/Wied tax-Xlendi system is wet and muddy valley banks; this includes spaces filled with wet soil at the base of dry stone walls close to the watercourse. Again as at San Martin, most burrows are constructed just above the water level and are abandoned if the sediment dries out. Also as at San Martin, burrows were found in agricultural land away from the watercourse, although always in close association with irrigation canals carrying flowing water. At both San Martin and in the Wied tal-Lunzjata/Wied tax-Xlendi system, the crabs appear to be very tolerant of human presence. In the Wied tal-Lunzjata/Wied tax-Xlendi system the crabs constructed burrows in heavily littered sections of the watercourse as well as those that were not littered; burrows were constructed at the base of rubble walls, within spaces between their stones, and close to irrigation canals, as already stated. The crabs were also tolerant of suboptimal water quality and burrows were present in sections where the water was turbid, where it was moderately eutrophic, and where there appeared to be mild contamination from sewage and from dumped decomposing organic material, although in such areas burrows may have been constructed where very localised pockets of better water quality occurred.

The resilience of the crab and its opportunistic habits probably account for its survival in spite of the heavy human use of the sites where it occurs and the frequent and often intense natural and anthropogenic disturbances.

However, continued survival of the crab in the Maltese Islands depends on careful management since in spite of its resistance to disturbance and its tolerance to moderately poor water quality, nonetheless the crabs seem to be susceptible to severe changes in water quality and in the hydrologic regime. Factors that cause such changes need to be addressed with top priority in any conservation management plan for the species and there is obviously the need for more research on the ecology of Potamon fluviatile in the Maltese Islands as well as for monitoring the existing populations.

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Debrincat, J and Schembri, P.J.: Burrow density of Potamon at Lunzjata and Xlendi valleys, Gozo.

Acknowledgments We are grateful to a number of farmers who cultivate land at Wied tal-Lunzjata for kindly informing us about the occurrence of freshwater crabs in their fields, and to Ms Marija Sciberras (Department of Biology, University of Malta) for her help in the preparation of this paper. We thank the Nature Protection Unit, Malta Environment and Planning Authority (MEPA) for making available their unpublished datasheet on the freshwater crab and for other information.

References ADI & Ecoserv (2005). Threatened and/or endemic invertebrates of the Maltese Islands, excluding insects. Malta: ADI & Ecoserv, study and database commissioned by the Nature Protection Unit, Malta Environment and Planning Authority. [Publication forthcoming] Brandis D., Storch, V. & Turkay, M. (2000). Taxonomy and zoogeography of the freshwater crabs of Europe, North Africa, and the Middle East.

Senckenbergiana Biologica, 80, 5-56.

Cachia S. (1997). Aspects of the behavioural ecology of the freshwater crab Potamon fluviatile lanfrancoi in the Maltese Islands. Unpublished BSc Dissertation.

Department of Biology, University of Malta; x + 178pp.

Camilleri A. & Cachia, S. (2000). The freshwater crab Potamon fluviatile lanfrancoi: a newly discovered locality at Il-Wied ta' Gordajna, and a clarification of records from L-Imtahleb. The Central Mediterranean Naturalist [Malta], 3(2), 79-84.

Capolongo D. & Cilia J.L. (1990). Potamon fluviatile lanfrancoi, a new subspecies of a Mediterranean freshwater crab from the Maltese Islands (Crustacea, Decapoda, Potamidae).

Annalen Naturhististorisches Museum, Wien, 91B, 215-224.

Crustikon. Crustacean photographic website. Tromsø Museum, University of Tromsø (Website created and managed by Dr. Cédric d'Udekem d'Acoz).

Pictorial guide to the Crustacea Decapoda of the Eastern Atlantic, the Mediterranean Sea and the adjacent continental waters. Available online at http://www.tmu.uit.no/crustikon/Decapoda/Decapod a.htm [last accessed 10 Sept. 2007] Fauna Europaea Web Service (2004). Fauna Europaea version 1.3; last updated 19 April 2007. Available online at http://faunaprod.uva.sara.nl/ [last accessed 09 Sept. 2007] Gherardi F., Messana G., Ugolini A. & Vannini M. (1988). Studies on the locomotor activity of the freshwater crab, Potamon fluviatile. Hydrobiologia, 169, 241-250.

IUCN (2006). Guidelines for using the IUCN Red List categories and criteria: version 6.1. Prepared by the Standards and Petitions Working Group for the IUCN SSC Biodiversity Assessments SubCommittee in July 2006. Gland, Switzerland and Cambridge, UK: Species Survival Commission, IUCN, 60 pp.

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Jesse R. (2007). Phylogeography of the freshwater crab Potamon fluviatile in Italy and on the Balkans: present results and future research plans. p.28 In: 13th Annual European Meeting of PhD Students in Evolutionary Biology, Lund, Sweden, August 2007.

[Abstract] Lanfranco, G.G. (1975) A petition for the protection of the freshwater crab in Malta. Malta: Natural History Society of Malta, 4pp.

MEPA [Malta Environment and Planning Authority] (2007). Request for information on Potamon fluviatile. Malta: Nature Protection Unit, Environment Protection Directorate of the Malta Environment & Planning Authority; Unpublished note, 2pp.

Moritz C. (1994). Defining ‘Evolutionarily Significant Units’ for conservation. Trends in Ecology and Evolution, 9, 373-375.

Pace F. (1974). A study of the development of Potamon edulis. Unpublished MSc thesis. Department of Biology, Royal University of Malta.

Pace F., Harris R.R., & Jaccarini V. (1976). The embryonic development of the Mediterranean Freshwater Crab Potamon edulis (= P. fluviatilis) (Crustacea: Decapoda: Potamonidae). Journal of Zoology, London, 180, 93-106.

Pretzmann G. (1962). Die mediterranen und vorderasiatischen Süsswasserkrabben (Potamiden).

Annalen Naturhististorisches Museum, Wien, 65, 205-240.

Pretzmann G. (1980). Potamiden aus Griechenland (leg.

Malicky, leg Pretzmann.).

Annalen Naturhististorisches Museum, Wien, 83, 667-672.

Pretzmann G. (1983). Die Süsswasserkrabben der Mittelmerrinseln und der westmediterranen Länder.

Annalen Naturhististorisches Museum, Wien, 84B, 369-387.

Schembri P.J. (1983). The Mediterranean freshwater crab: “Il-Qabru”. Civilization [Malta], 7, 182-183.

Schembri P.J., Lanfranco E., Farrugia P., Schembri S. & Sultana J. (1987). Localities with conservation value in the Maltese Islands.

Beltissebh, Malta: Environment Division, Ministry of Education, iii + 27pp.

Waples R.S. (1991). Pacific salmon, Oncorhynchus spp., and the definition of ‘species’ under the Endangered Species Act. Marine Fisheries Review, 53, 11-22.

© Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Xjenza 12 (2007)

Art. No. 120701

1

Comment* Comment on “Model of limestone weathering and damage in masonary”

by P. Gatt, Xjenza vol. 11 (2006).

Jo Ann Cassar** Institute for Masonry and Construction Research, University of Malta, Msida MSD 06, Malta

Keywords: Globigerina Limestone, deterioration, model, characterization Received: 21 January 2007

In his paper, Gatt suggests “a model for fine-grained limestone e.g. Globigerina limestone... based on the nature of the stone and the related mode of weathering … independent of salt load, which is a function of the environment.” He also adds that “it is the mode of weathering which reflects the intrinsic nature of the stone, independently of environment….”. These statements in effect run counter to a corpus of knowledge on stone deterioration (Schaffer, 1932; Price, 1996; Ashurst and Dimes, 1998; Delgado Rodrigues, 2001; Lazzarini, 2002) and including also work quoted by Gatt (e.g. Fitzner et al., 1997), in that no matter what the intrinsic properties of a stone are, the amount of damage and the mode of weathering will always also depend on the surrounding environment; a case in point is the moving of archaeological remains to indoor (and hence sheltered and milder) environments, to slow down deterioration.

Hence, the attempt to develop a model for weathering independent of the environment appears to be misdirected.

The line of research undertaken by Gatt should have also taken into account not only these studies on the deterioration of stone, but also all the empirical studies on Globigerina Limestone which have been conducted locally over the years. The latter has included research on the deterioration of Globigerina Limestone, as well as studies on the chemical and physical properties of Malta’s building stone. These studies have dealt with the characterization of Globigerina Limestone, and have also included an intriguing line of investigation: that of whether the geochemical composition of the insoluble part of Lower Globigerina Limestone can be used to distinguish the durable “franka” from the less durable “soll” This work started with a dissertation by Testa (1989), quoted by Gatt, and culminated in a paper by Cassar and Vella (2003) (not cited by Gatt). In the intervening period, several other dissertations on the subject were written, some of which resulted in a publication by Vella et al. (1997), published in Xjenza.

All of this work has clearly pointed to the fact that the geochemical composition of the insoluble fraction of the Lower Globigerina Limestone can be used to help identify “good” from “bad” stone. A complete list of these, as well as other related dissertations, and published

papers on Globigerina Limestone, can be found in a paper

by Cassar (2004) entitled “Composition and property data of Malta’s building stone for the construction of a database” in a publication by Prikyl & Sigel. A partial list is given below.

Gatt, in his paper, does make reference to another paper

by Cassar (2004) entitled “Comparing visual and geochemical classification of limestone types: the Maltese Globigerina Limestone”. Here, however, Gatt attempts to undermine the sum total of the geochemical work done over the years on Globigerina Limestone, by stating that “Cassar (2004) alleges that marginal noncarbonate geochemical parameters can be used for ‘predicting’ severity of weathering” and “the slight noncarbonate content… has no consequence on salt weathering.” This line of reasoning appears to be contrary to the scientific evidence available to date.

The most succinct way the geochemical information, together with the mineralogical and physical data, as well as information on salt weathering of Globigerina Limestone (including, but not only, that given by Fitzner; see also list of publications given below) are to be interpreted maybe be found in Cassar 2002.

Quoting from the abstract of this paper should greatly clarify matters: “The Globigerina Limestone occurs as two types of building stone: the resistant ‘franka’ and the easily weathering ‘soll’. Research on both fresh and weathered samples has led to an understanding of the main differences in these two types of stones. The causes and mechanisms of deterioration have also been established.

‘Franka’ and ‘soll’ differ in geochemical and mineralogical composition and in physical properties.

The ‘soll’ is richer in the non-carbonate fraction, which occludes some of the pore space, resulting in a lower overall porosity and a higher proportion of small pores.

The ambient local environment, heavily loaded with sea salt, particularly sodium chloride and sulphates, readily induces deterioration in ‘soll’, whereas ‘franka’ tends to resist better in this aggressive environment. The weathering process of Globigerina Limestone in general

* This ‘Comment’ and its ‘Response’ are published ‘as received’ from the respective authors and have not been peer-reviewed. ** Corresponding Author: e-mail: joann.cassar@um.edu.mt Telephone: +356 23402866.

Cassar J: Comment on “Model of limestone weathering and damage in masonary” by P. Gatt, Xjenza vol. 11 (2006).

2

Limestone, Malta, University of Malta.

B.Sc. dissertation (unpublished),

has been explained as a sequence of steps, from the formation of a thick and compact superficial crust, to the loss of this crust, to the initiation of alveolar weathering.

Understanding the deterioration mechanisms of Globigerina Limestone permits criteria for proper conservation treatment to be established.”

However, Gatt states that because “a casual relationship between slight non-carbonate mineral content (e.g. nonswelling kaolinite) and severe weathering forms seen in masonry” was not found, this leads to “eliminating the relevance of geochemical proxies used by Cassar (2004) in “predicting’ weathering in Globigerina Limestone.”

However, the observation that a relationship was not found in itself does not preclude the fact that it does exist. Cassar and Vannucci (2001), state that “the intrinsic clay fraction which, although small, contains minerals such as smectite and illite-smectite which are highly expandible”, are hence “other factors that affect this deterioration process”. Papers by Vannucci et al.

(1994), Vella et al. (1997), Cassar and Vannucci (2001), Cassar (2002) and Cassar (2004), also make it clear that the mineralogical and/or geochemical compositions are in fact important players in the weathering behaviour of the stone. Linking once again the geochemical, mineralogical and physical, Cassar (2004) states that “as “soll” limestone has higher concentrations of phyllosilicates and quartz, it is hypothesised that some of the pore space in this type of stone is occluded by this non-carbonate fraction” which then may give rise to the difference in the intensities of weathering of the two stone types.

Even the use of the words ‘franka’ and ‘soll’ appear to be problematic to Gatt, who states that “an obstacle to the scientific study of Globigerina deterioration is the persistent use in literature of elusive vernacular terms utilised by masons and quarrymen…” It is unfortunate that Gatt thinks this, as in actual fact much of the interest in this work is also, but not only, amongst workers in the building trade, and is due to the fact that this scientific work takes cognizance of the vernacular and as such is richer for having done so. Moreover, what the quarry workers, and builders, have been saying for centuries, is now being substantiated by current research.

In his paper, Gatt borrows extensively from the work by Fitzner, especially his 1997 paper entitled “Model for salt weathering in Maltese Globigerina Limestone” but omits the paper by Vannucci et al., 1994, although Fitzner himself makes reference to this earlier paper, which, for the first time, describes the mode of weathering of Globigerina Limestone.

References/Bibliography Ashurst, J., & Dimes, F.G., (1998), Conservation of building and decorative stone, Butterworth-Heinemann.

Camilleri, A.J., & Tabone Adami, J.P., (1992), Geochemical study of "soll" facies in Lower Globigerina

Cassar, J., (1999), Geochemical and mineralogical characterisation of the Lower Globigerina Limestone of the Maltese Islands with special reference to the “soll” facies, Ph.D. thesis (unpublished), University of Malta.

Cassar, J., (2002), Deterioration of the Globigerina Limestone of the Maltese Islands, Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies, Siegesmund S., Weiss T., & Vollbrecht A. (eds), Geological Society, London, Special Publications, 205, 33-49.

Cassar, J., (2004), Composition and property data of Malta’s building stone for the construction of a database, Architectural and sculptural stone in cultural landscape.

Prikryl, R., and Siegl, P. (eds), The Karolinum Press, 11 – 28.

Cassar, J., (2004), Comparing visual and geochemical classification of limestone types: the Maltese Globigerina Limestone, Stone 2004, 10th International Congress on Deterioration and Conservation of Stone, 27 June-2 July, 2004, Stockholm, Sweden, 569-577.

Cassar, J., (in press), Classifying Maltese prehistoric limestone megaliths by means of geochemical data, 7th International Conference of the Association for the Study of Marble and Other Stones used in Antiquity, ASMOSIA VII, Thassos, Greece 15 – 20 September 2003.

Cassar J., & Vannucci S., (2001), Petrographic and chemical research on the stone of the megalithic temples, Malta Archaeological Review, 5, 40-45.

Cassar, J., & Vella, A.J., (2003), Methodology to identify badly weathering limestone using geochemistry: case study on the Lower Globigerina Limestone of the Maltese Islands, Quarterly Journal of Engineering Geology and Hydrogeology, 36, 85-96.

Delgado Rodrigues, J., (2001), Consolidation of decayed stones. A delicate problem with few practical solutions, Historical Constructions, Lourenco, P. B., and Roca, P. (eds), Guimaraes.

Internet address: www.civil.uminho.pt/masonry/Publications/Historical%2 0constructions/page%2003-14_DDelgado.pdf (accessed Nov. 2006) Fassina, V., Mignuci, A., Naccari, A., Stevan, A., Cassar, J., & Torpiano, A., (1996), Investigation on the moisture and salt migration in the wall masonry and on the presence of salt efflorescences on stone surface in the Church of Sta. Marija Ta’ Cwerra at Siggiewi, Malta, Origin, Mechanisms and Effects of Salts on Degradation of Monuments in Marine and Continental Environments.

Zezza, F. (ed), Proceedings, European Commission Research Workshop on Protection and Conservation of

© 2007 Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Cassar J: Comment on “Model of limestone weathering and damage in masonary” by P. Gatt, Xjenza vol. 11 (2006).

3

the European Cultural Heritage, Bari, Italy, Research Report No. 4, 291-308.

the “soll” layers, B.Ed. (Hons.) (unpublished), University of Malta.

Fitzner, B., Heinrichs, K., & Volker, M., (1997), Model for salt weathering at Maltese Globigerina Limestones, Origin, Mechanisms and Effects of Salt on Degradation of Monuments in Marine and Continental Environments.

Zezza, F. (ed), Proceedings, European Commission Research Workshop on Protection and Conservation of the European Cultural Heritage Research Report No. 4, 333-344.

Torfs, K., Van Grieken, R., & Cassar, J., (1996), Environmental effects on deterioration of monuments: Case study of the Church of Santa Marija Ta’ Cwerra, Malta, Origin, Mechanisms and Effects of Salts on Degradation of Monuments in Marine and Continental Environments, Proceedings, European Commission Research Workshop on Protection and Conservation of the European Cultural Heritage, Bari, Italy. Research Report No. 4, 441-451.

Gauci, D.A., & Sapiano, M., (1993), Geochemical anomalies in Globigerina Limestone and the “soll” facies, B.Sc. dissertation (unpublished), University of Malta.

Lazzarini, L., (2002), General issues on the deterioration of stone, The Building Stone in Monuments. Proceedings, Interdisciplinary Workshop, Institute of Geology and Mineral Exploration and Hellenic Section of ICOMOS, Athens-Mytilene, 9-11/11-9-2001, Athens, 149-160.

dissertation

Vannucci, S., Alessandrini, G., Cassar, J., Tampone, G., & Vannucci, M.L., (1994), Templi megalitici preistorici delle isole maltesi: cause e processi di degradazione del Globigerina Limestone, Conservation of Monuments in the Mediterranean Basin, Fassina V., Ott H., and Zezza F. (eds), Proceedings of the 3rd International Symposium, Venice, Italy, 555-565.

Price C.A., (1996), Stone Conservation An Overview of Current Research. The Getty Conservation Institute.

Vella, A.J., Testa, S., & Zammit, C., (1997), Geochemistry of the soll facies of the Lower Globigerina Limestone Formation, Xjenza, Malta, 2 (1), 27-33.

Rizzo, C., & Serracino Inglott, K., (1994), Geochemical study of the Globigerina Limestone formation (Malta), B.Sc. dissertation (unpublished), University of Malta.

Zammit, C.V., (1991), The analysis of Lower Globigerina Limestone for silicon, iron and aluminium, B.Sc. dissertation (unpublished), University of Malta.

Rothert, E., Eggers, T., Cassar, J., Ruedrich, J., Fitzner, B., and Siegesmund, S., (in press), Stone properties and weathering induced by salt crystallisation of Maltese Globigerina Limestone, Geological Society, London, Special Publications, 271, Building Stone Decay: From Diagnosis to Conservation.

Rüdrich, J., Rothert, E., Eggers, T., Cassar, J., Fitzner B., and Siegesmund, S., (2005), Gesteinseigenschaften und salzbedingtes Verwitterungsverhalten maltesischer Globigerinen Kalksteine, STEIN Zerfall und Konservierung Siegesmund, S., Auras, M., and Snethlage, R. (eds), Germany, Edition Leipzig, 194-200.

Schaffer, R.J., (1932, reprinted 1972), The weathering of natural building stones, Department of Scientific and Industrial Research, Building Research Special report No. 18, Building Research Establishment, U.K. Taliana, C., Cassar, J., Vella, A. J., & Ventura, F., (1994), Factors causing deterioration of frescoes within a medieval church in Malta and a proposed solution, Conservation of the Relics of Medieval Monumental Architecture, International Symposium, Warsaw-Lednic, Poland, 24-26 May 1994, 125-130. Also published in Polish (1995): Czynniki powodujace niszczenie freskow w sredniowiecznym kosciele na Malcie, Ochrona Zabytkow, v.1, 85-90.

Testa, S.J., (1989), A down-column geochemical study of Lower Globigerina Limestone with special reference to

© 2007 Xjenza – Journal of the Malta Chamber of Scientists - www.xjenza.com

Xjenza 12 (2007)

Art. No. 120702

1

Response to Comment* Response to Comment by J. Cassar on 'Model of limestone weathering and damage in masonry’, by P.A. Gatt, Xjenza, vol. 11, 2006.

Peter A. Gatt** Dept. of Civil Engineering, University of Malta, Msida , Malta Keywords: Globigerina limestone, non-carbonates, differential weathering, bioturbation

Cassar is thanked for comments focusing only on noncarbonates, referred to in a small section of my paper.

Cassar also comments that the “amount of damage and the mode of weathering will always depend on the surrounding environment”. Actually, ‘mode of weathering’ refers to the style of loss of volume in stone, resulting in a distinct weathered surface independently of salt load which controls rate (amount) of volume loss.

Previous local studies cited by Cassar (e.g. Cassar & Vella, 2003) only confirm already known stratigraphical variations of marginal non-carbonates (<~6% clay/quartz/feldspars) in Globigerina limestone, although their relevance is undermined by the small geographical area sampled and the remarkable omission of geological (textural, depositional and tectonic) controls (Gatt, 2007).

differential weathering extending to >10mm from the surface. Therefore, swelling effect of clay is negligible.

Later, (2) Cassar refers to a different weathering mechanism by invoking salt crystallisation: “the noncarbonate fraction, which occludes some of the pore space, resulting in…higher proportion of small pores”. In fact, porosity in Globigerina limestone masonry is not controlled by marginal non-carbonates but by compaction and the level of calcite cementation/grain size in burrows and matrix, as described in my paper e.g. Sicilian limestone similar to ‘soll’ disintegrates rapidly during laboratory weathering tests because the less (calcite) cemented margins of bioturbation become a conduit for greater evaporation and salt crystallisation (Punturo et al., 2006). Lastly, (3) Cassar & Vella (2003) reject all previous weathering mechanisms by stating that “clay mineral content cannot, however, be utilized to distinguish between franka and soll”.

Conclusions in the previous studies cited by Cassar are problematic because (i) universal limestone nomenclature Therefore, previous local geochemical studies given (i.e. grain size/texture based) is substituted by undefined credence by Cassar are mostly immaterial to studies vernacular terms e.g. ‘soll’, also misconstrued as (including my paper) on weathering of local limestone. synonymous with the ambiguous attribute of “badly weathering stone” (in my paper, ‘soll’ is scientifically classified as an ‘intensely bioturbated packstone facies’).

References Furthermore, (ii) limestone is unusually classified exclusively by its geochemistry, namely the slightly Cassar J. & Vannucci S. (2001) Petrographic and chemical research on the stone of the megalithic temples, Malta higher non-carbonate content in ‘soll’ relative to ‘franka’; Archaeological Review, 5, 40-45. (iii) the non-carbonate fraction in Globigerina limestone is somehow implicated for rapid weathering in ‘soll’, and Cassar concludes that “the causes and mechanism of Cassar, J. & Vella, A.J. (2003), Methodology to identify badly weathering limestone using geochemistry. Journal deterioration have also been established”. of Eng. Geol. and Hydrogeol., 36, 85-96.

Actually, geochemical studies cited by Cassar are unsupported by laboratory weathering tests and fail to Gatt, P.A. (2007) Discussion of “Methodology to identify badly weathering limestone using geochemistry” (J. prove a causal relationship between non-carbonates and Cassar & A. Vella). Journ. of Eng. Geol.& Hydrogeol., weathering. Instead, Cassar’s comments speculatively 40 (in print). forward the following incongruent mechanisms, some uncorroborated by observations of local masonry: Gonzalez Scherer (2004) Effect of swelling inhibitors on the swelling and stress relaxation of clay bearing stones.

(1) Cassar & Vannucci (2001) claim ‘soll’ weathers Environmental Geol. 46, 364-377. rapidly because it “contains minerals such as smectite and illite-smectite which are highly expandable”. Such claybearing rock weathers by the swelling of clay that would Punturo, R., Russo, L. G., Lo Giudice, A., Mazzoleni, P. Pezzino, A. (2006) Building stone in the historical uniformly disrupt only the exterior 1mm (Gonzalez & monuments of E Sicily: the ancient city centre of Catania.

Scherer, 2004). This contrasts with the mode of weathering observed in ‘soll’, dominated by strong Environ. Geol. 50, 156-169. * This ‘Response’ and the original ‘Comment’ are published ‘as received’ from the respective authors and have not been peer-reviewed. ** Corresponding Author: e-mail: mepcons@hotmail.com Telephone: +356 79603783.