Page 1

109

RARE STONEWORTS

THE DISCOVERY & CONSERVATION OF RARE STONEWORTS IN SUFFOLK’S FARMLAND PONDS 2019 JULIET HAWKINS Introduction Stoneworts, or charophytes, are an advanced group of green algae that have a complex structure and, to the non-botanist, a resemblance to aquatic vascular plants. They grow underwater in freshwater and brackish habitats, mostly standing water but occasionally in moving. The majority, but not all, of species are confined to calcareous or brackish situations. This article is primarily about the discovery and conservation of rare stoneworts found in Suffolk’s chalky boulder clay farmland ponds. The original UK Biodiversity Action Plan (UK BAP) list of priority species, created between 1995 and 1999, included eight stonewort species for which Species Action Plans (SAPs) existed, with an additional four species possessing Species Statements. In 2007, a review of UK BAP priority species and habitats increased the number of stonewort species to eleven. It is estimated that over half of Britain’s 28 or 29 native stonewort species are listed in the Red Data Book (Stewart & Church, 1992) or are Nationally Scarce (Pond Conservation, 2010). Sanford and Fisk list 18 stonewort species that have been recorded in Suffolk and highlight the paucity of records received (Sanford & Fisk, 2010). Thus, it is interesting to discover several nationally rare or uncommon spring-fruiting stoneworts where concentrated survey efforts have been made on 50 neglected and restored farm ponds - ‘befores and afters’ - in Bramfield and Walpole parishes in North-east Suffolk a high density ‘pondscape’. Limited survey time was targeted at getting a snapshot of a range of taxa: amphibians in early spring, dragonflies and flowering plants later in the year, and opportunistic samples of aquatic invertebrates as part of these surveys. Of the 50 farm ponds surveyed in Bramfield and Walpole parishes in 2019, 45 were ancient (i.e. pre-1900 and often much earlier) and five were newly created in 2009. Seven ancient ponds had been completely or partially restored over winter 2018/19; six ponds are minimally but regularly disturbed by watering livestock; 24 ponds were completely unmanaged; and 12 ponds were periodically cleaned out. Of the seven restored ponds, five supported one or more very rare stoneworts and in total they hosted six stonewort species. The 2019 discovery of Nitella capillaris (Slimy-fruited Stonewort), thought to have been extinct in the UK since 1959, together with both Tassel and Clustered Stonewort in these two parishes demonstrated the wider benefits of sympathetic farmland pond restoration for priority conservation stoneworts beyond improving habitat for the more obvious amphibians and aquatic invertebrates. Earlier, restoration of ponds at Suffolk Wildlife Trust’s Grove Farm Nature Reserve at Thurston (now Black Bourne Valley Nature Reserve) resulted in the discovery of the Endangered Tolypella intricata (Tassel Stonewort) in May 2011 for which there had been only one other known site in Suffolk, followed by the discovery of the Nationally Scarce Tolypella glomerata (Clustered Stonewort) in one of the Trust’s newly created ponds there. The Pond Conservation Trust (now known as Freshwater Habitats Trust)

Trans. Suffolk Nat. Soc. 55 (2019)


110

Suffolk Natural History, Vol. 55

subsequently funded a translocation experiment of the Tassel Stonewort into five new ponds on the reserve in 2017. Time and monitoring will tell whether it is successful but so far no plants have been recorded. The discovery of these rare spring-fruiting stoneworts raises several questions: • Are ‘rare’ stoneworts really rare with very demanding habitat requirements? • Are stoneworts very poorly recorded in Suffolk? • If rare stoneworts with demanding habitat requirements are found in Suffolk farmland ponds, what is the best way to safeguard their future? Are ‘rare’ stoneworts really rare? There is no shortage of waterbodies in Suffolk in which to look for stoneworts: the county has a very high pond density relative to other parts of the UK with an estimated 22,000+ ponds (Sibbett, 1996), as well as large areas of wet fens in the Waveney Valley and coastal water in nature reserves. Stoneworts, like flowering plants, have habitat preferences: some species prefer peaty fens such as Redgrave and Lopham Fens and Hopton Fen and others prefer brackish or calcareous conditions. However, many of the UK’s 28 or 29 species have quite broad habitat requirements, living in small ponds or large lakes, permanent and temporary, freshwater or brackish. But whatever the waterbody, stoneworts are exacting ‘connoisseurs of clean water’ (Stewart, 1996) and mineral substrates. In the calcareous soils of Suffolk, an important factor for stonewort survival is probably the increased levels of dissolved bicarbonate ions, which stoneworts use as a carbon source in photosynthesis. As a by-product of this reaction many stoneworts secrete calcium carbonate as an encrustation which gives them their crunchy, brittle ‘stonewort’ texture. (Stewart, 1996). Stoneworts are very good colonisers of new and recently restored ponds with bare areas of substrate. The newly exposed substrates result in a flush of minerals which early annual stonewort species utilise. After the initial appearance of these annual species, perennial stoneworts take over and more competitive vascular plants begin to colonise and out-compete the stoneworts, especially as organic matter begins to accumulate on the pond floor. Stoneworts are also sensitive to herbicide and fertiliser pollution. Farmland ponds are vulnerable to herbicide spray drift and ditch inflows that take leachates from adjacent arable fields. Stoneworts are particularly vulnerable to enrichment from phosphates and nitrates. Phosphates are particularly damaging and levels as low as 20micrograms per litre have been shown to inhibit some species (Stewart, 1996). Both Lambert (2007) and Lambert and Davy (2010) suggest nitrate is more important than phosphate in suppressing stonewort populations, mainly by stimulating growth of epiphytic and benthic competition (in the form of other algae such as diatoms). Thus, in Suffolk’s wider farmland, estimated at 78% of the county’s land use, waterbodies may be too nutrient-rich and high in phosphates and nitrates for stonewort species that cannot compete in such conditions. Additionally, most ponds on farmland are not managed, so they contain an accumulation of vegetation and leaf litter, creating eutrophic conditions which are unfavourable to stoneworts.

Trans. Suffolk Nat. Soc. 55 (2019)


RARE STONEWORTS

111

The ability of stoneworts to survive at depth is largely a function of water quality as they can grow at greater depth if there is better light penetration. The more nutrient-enriched the water is the poorer the light penetration due to diatoms (singlecelled algae). Where ponds have a varied underwater topography and plenty of shallow shelves at the margins or shallow zones within the water, small species such as Nitella capillaris and Tolypella glomerata can thrive in the 0-50cm depth of water. However, if ponds are over deepened, the resulting water depth is likely to be too deep (and too dark) for them to thrive except in drought years or at the pond margins. Lack of rotational cutting back of shading vegetation or traditional livestock access, or traditional rotational pond cleaning allows succession by more dominant, aquatic and emergent vegetation and shading trees and shrubs. As pioneer species, stoneworts flourish best in recently disturbed water bodies, and are highly vulnerable to successional communities of emergent vegetation at the pond edges such as reedmace or branched bur-reed, or dominant and shading stands of aquatic plants such as broadleaved pondweed. Left unmanaged, and undisturbed by livestock, ponds are gradually filled by emergent species and eventually in later succession, both are shaded out by naturally regenerating trees and shrubs. Stoneworts are able to spread where movement of animals such as deer or livestock help transport oospores between ponds. Thus, well-connected habitat with waterbodies close to each other, such as fen pools, or farmland ponds with corridors such as hedges and margins where wild animals or farm livestock move between ponds, provides more opportunities for stonewort dispersal and increases the chance of stonewort survival. Are ‘rare’ stoneworts simply under-recorded? Are ‘rare’ stoneworts simply under-recorded because they are difficult to survey due to growing in inaccessible places and difficult to identify? Martin Sanford, Suffolk’s Plant Recorder, says that aquatic plants are the most under-recorded habitat group they are difficult to access, they involve the use of difficult keys, expensive books and often microscopes. In turn, of the aquatic flora, Characeae are the most underrecorded with only 570 county records submitted since 1750 (SBIS, 2019). The records are predominantly from fenland nature reserve sites. In Suffolk, few people currently record stoneworts other than myself, despite the fact that there are plenty of botanists surveying sites and newt surveyors who might have good aquatic plant knowledge and must be regularly surveying ponds. The 13% of Suffolk county stonewort records I have made are from predominantly chalky boulder clay farmland ponds in 20+ parishes, reflecting the fact that my surveys of c1,500 ponds since 2004 as Suffolk Wildlife Trust’s Pond Adviser have been primarily focussed on great crested newt conservation on farmland. The rare, spring-fruiting Tolypella and Nitella species are visible in spring when surveying for great crested newts and are distinctively different - so I would have noticed them and recorded them along with all other plants listed on my survey sheets. I was ‘stonewort-trained’ by Tim Pankhurst at Plantlife back in 2008 and have participated in various training

Trans. Suffolk Nat. Soc. 55 (2019)


112

Suffolk Natural History, Vol. 55

J. Hawkins

days on them since by various stonewort experts including Nick Stewart, the National Charophyte recorder. Thus, whilst aware of stoneworts and noting them as Chara sp, I have only latterly become more confident in my identification skills. Analysis of about one thousand pond surveys (2004-2006) revealed that 78% were shaded or suffering from some form of poor water quality and stoneworts were rarely found fruiting in these unsuitable ponds (Suffolk Pond Project Report July 2004 – October 2006, Hawkins 2006) - although it is possible that their oospores were lying dormant in the organic matter at the bottom of the pond. A second short phase of surveys involved a limited, but more targeted, return to some of the restored ponds to assess the re-colonisation by great crested newts. These restored ponds would have been more likely to support stoneworts due to the removal of accumulated organic material and the flush of minerals caused by exposing the substrates. It was at these, mainly restored, ponds that I first started recording more stonewort species including rare and uncommon ones from 2011 onwards - more aware, better trained and better armed with identification keys.

We know so little about rare stoneworts in Suffolk that a conservation strategy is difficult to formulate. Increased research, and monitoring of ponds, may help guide pond management that benefits stoneworts as well as other priority pond wildlife. Tim Pankhurst of Plantlife, and Dorothy Casey of Suffolk Wildlife Trust, discuss management issues at one of the Walpole ponds supporting Tolypella intricata.

Trans. Suffolk Nat. Soc. 55 (2019)


RARE STONEWORTS

113

The conservation of rare stoneworts in ancient farmland ponds The Freshwater Habitats Trust provides excellent advice on the creation of stonewort habitat in new ponds and mineral extraction sites - see their Stonewort Dossier at https://freshwaterhabitats.org.uk/wp-content/uploads/2013/09/Stonewort_V2Feb15.pdf My experience is that these rare stoneworts have been recorded, and probably ‘re-appeared’, in restored or disturbed ancient farmland ponds where there are often other conservation priorities to consider such as amphibians, aquatic invertebrate and even birds. So for those involved in pond conservation what might be good practice to ensure stoneworts are not sidelined by other more charismatic species? If we do find rare stoneworts with demanding habitat requirements in Suffolk ponds, what is the best way to safeguard their future? To fruit and set oospores, stoneworts need very clean water, exposed mineral substrates and plenty of light. Using the combined wisdom and experience of stonewort and rare plant experts, I suggest that periodic fruiting of stoneworts is required to ensure a reservoir/seedbank of the species’ long-lived oospores. So pond restoration, or partial restoration, that removes organic matter and lets in light for other target species such as amphibians is likely to benefit long-dormant stoneworts. This sort of disturbance happened regularly in the past when ponds were an important part of farm management. Historically, Suffolk farm ponds were disturbed regularly or periodically to keep them functional. Ponds used for watering livestock or collecting clean drinking water for humans were disturbed daily - some would have been turbid through intense disturbance but most would probably have had one or two poached, muddy margins at entry points with browsed emergent and aquatic vegetation over the part of the pond that livestock could reach - and possibly for only part of the year as they rotationally grazed different pastures. This would leave ponds, or part of the ponds, with areas of bare substrate, sunny and without shading plant competition - good conditions for stoneworts. Other ponds would have been periodically disturbed as a valuable source of organic matter with which to manure or ‘marl’ the heavy clay arable fields. Thomas Tusser, who farmed in Suffolk in the 1550s, wrote Five Hundred Points of Good Husbandry, an expanded version of his original title, A Hundreth Good Pointes of Husbandrie (1557) and advised his fellow farmers on pond cleaning or ‘saying’ in September: Such muddy deep ditches and pits in the field, That all a dry summer no water will yield By saying and casting that mud upon heaps, Commodities many the husbandman reaps And Tusser advised to “sew ponds and amend dams” every year. Thus, pond ‘cleaning’ would have been a regular part of a farmer’s calendar and ensured that ponds stayed open, sunny and accessible for livestock to drink from and relatively free of organic matter as this was useful on the soil as a fertiliser or improver. As ‘pioneer species’, stoneworts would have had good periodic opportunities to germinate after a pond cleaning, fruit and set their oospores. Trans. Suffolk Nat. Soc. 55 (2019)


114

Suffolk Natural History, Vol. 55

So, my advice for rare stonewort conservation is to periodically open up, ‘clean’ or patch-scoop parts of long-neglected, shaded ponds full of organic matter where the water source is reliable and very clean - ponds at the top of slopes and ponds buffered by organic grassland or generous margins. Stonewort oospores are believed to survive for 100+ years buried in sediment. Where the oospores exist, this patchrestoration of clean water ponds could result in a flush of fruiting stonewort. Pond restoration should take care to avoid introducing anything that could adversely affect stoneworts or other native wildlife. Pond diggers should be washed down prior to work to avoid inadvertently introducing alien invasive plants such as New Zealand pygmyweed. Coarse fish increase turbidity and should not be introduced and for the same reasons duck should not be encouraged. Pond plants should not be introduced as the pond’s natural stonewort and plant community would be irreversibly altered. It is important not to compromise the historic shape and bank profile of ancient ponds with their own cultural history (Friday ponds, laundry ponds, retting ponds etc) by digging deeper or steeper than the original profile. Suffolk Wildlife Trust is currently exploring funding opportunities with Natural England for the Bramfield Farm Cluster farmers working together on the rotational pond management for conservation of rare stoneworts, and other priority species, together with training botanists and a monitoring programme. The Natural History Museum is working on the DNA of Tolypella and Nitella stonewort species and there are many research questions for those with an interest in ponds and stoneworts. The unknowns for research The temptation for advisers with a limited budget is not to return at all to admire the restored ponds or return several years later to monitor for newts, dragonflies and aquatic plants ‘after it has settled down’. It is important to monitor the following spring and summer after restoration for the presence of stoneworts as it is often only in that first year or two that they are easy to see, access and sample before other aquatic plant species take over. More information is needed to understand the status and ecology of Suffolk’s stoneworts. Will we discover that the ‘rare’ ones are far more widespread than hitherto thought? Will we find that actually the rare ones are so sensitive to enriched water that they are only found at the top of slopes, buffered by wide margins against modern agriculture, where the water source is simply rainfall? Should we look further back into pastoral history to see whether livestock droving routes and pond density influence stonewort distribution? Should we look deeper than the chalky boulder clay into the sub-surface geology at the gravels and sands that might influence stonewort distribution? We don’t know the longevity of different species or under what conditions the oospores survive. Is oospore longevity related to how unpolluted the sediment they are deposited in or covered by, or other factors such as whether the pond dries out for long periods? Once a pond has been ‘restored’ and resulted in a flush of fruiting stonewort, is the stonewort more vulnerable without increased levels of buffering? Buried under layers of deep organic matter in neglected ponds, the oospores have been protected

Trans. Suffolk Nat. Soc. 55 (2019)


RARE STONEWORTS

115

from modern artificial fertiliser and herbicides, but once ‘exposed’ the stoneworts become potentially vulnerable to: • phosphates and nitrates, principally from agricultural run-off, fertiliser application and where ponds receive ditch inflow water that takes leachates from adjacent arable fields. Those at the top of slopes are the least vulnerable to leaching nutrients or ditch inflows • breakdown of nutrients in leaf litter from trees and shrubs • periodic algal blooms that reflect nutrient loading and can overwhelm stoneworts and rooted macrophyte vegetation

The Tassel Stonewort translocation experiment at Black Bourne Valley Nature Reserve will be interesting to monitor. Will translocation to the bare substrate of new ponds fail because there is something about the timing and method of moving the oospores that the stonewort does not respond to? Or because the stonewort prefers something in the water of the ancient ponds that the new ponds have not yet acquired? Or will it take many years for the oospores to germinate in response to specific climatic conditions? Conclusions Rare stoneworts are uncommon because they require very exacting conditions: clean water, lack of other plant competition, sunlight and in Suffolk’s calcareous soils, increased levels of dissolved bicarbonate ions - and probably more we don’t yet understand. Stoneworts are rarely recorded because in addition to being rare, their habitats are difficult to survey and they require specialist identification skills. Many rare spring-fruiting species have only a small window for being recorded but happily, this period coincides with optimum timing for great crested newt eDNA and traditional surveys. Targeted stonewort identification training for great crested newt surveyors, interested botanists and aquatic invertebrate surveyors, could result in many more records and a greater understanding of stoneworts. We currently believe that periodic fruiting of stoneworts in response to disturbance is required to ensure a reservoir/seedbank of the species’ long-lived oospores. Disturbance could be small scale or prolonged such as may be created by livestock watering in a pond and poaching the margins - something that has gone on since humans have farmed livestock. Alternatively, it could be larger scale periodic disturbance by a machine which removes organic matter from a part of a pond - akin to 16th century rotational pond cleaning. This regular or occasional disturbance has benefits in re-setting all or part of ponds to the early stages of succession which benefits other groups such as dragonflies, water beetles and great crested newts. When everyday farming management, such as watering livestock, involves disturbance to the pond substrate, it is relatively easy and cheap to achieve conservation benefits. Where ponds no longer have a farming function, there needs to be another mechanism to ensure appropriate management. Current codes of good agricultural practise and cross compliance may help safeguard water quality on commercial farmland but extra stewardship incentives are required to buffer

Trans. Suffolk Nat. Soc. 55 (2019)


116

Suffolk Natural History, Vol. 55

farmland ponds more effectively from nitrates, phosphates and pesticides, and to occasionally intervene with disturbance in the absence of livestock or wild animals. Beyond the current legislative sticks and financial incentives, Conservation Covenants are being proposed for landowners who wish to protect special features on their land through ongoing appropriate management after they sell or gift it. It may be that these covenants will help ensure that as our understanding of stoneworts (and other pond wildlife) increases, we will be able to conserve them appropriately. I have been lucky to be Suffolk Wildlife Trust’s Pond Project adviser and to see hundreds of ancient neglected ponds restored by farmers, and especially those in Countryside Stewardship schemes, for wildlife conservation. These priority stoneworts have benefited from this and are very much a part of the pond community which provide underwater shelter and breeding opportunities for aquatic invertebrates, snails, amphibians - which in turn provide food for grass snakes, mammals and farmland birds. Acknowledgements Thank you to Sir Simon Robey, Richard Symes, Shauna Waterer and Simon Roberts, the landowners/farmers of Bramfield who funded this survey work on their farms, and for their enthusiasm in pond conservation - and for stoneworts. Thanks to Nick Stewart, National Charophyte Recorder, who verified my stonewort discoveries and shared my excitement and his knowledge. Thanks to Tim Pankhurst, Regional Conservation Manager at Plantlife, for providing helpful advice and throwing up lots of ideas for further research. Thanks also to Chris Carter who has taken so many incredible photographs of these rare stoneworts, and for putting them onto www.Algaebase.org for those working on stoneworts throughout Europe to use. Thanks to John Baker for helpful editing. Thank you to Martin Sanford for providing SBIS’s stonewort records for reference and for pointing me in the right direction.

Stoneworts in the ponds of the Bramfield Farm Cluster Three landowners in the parish of Bramfield (and a couple of fields in Walpole parish), referred to informally as the Bramfield Farm Cluster, got together in 2018 to work jointly with Suffolk Wildlife Trust (SWT) in assessing wildlife and priority species in the area. SWT’s Farm Conservation Adviser, Juliet Hawkins, co-ordinated various baseline surveys to guide conservation management and against which future comparative surveys can be carried out in the future. The pond surveys of 2018 and 2019 resulted in some exciting discoveries of three rare stoneworts including the Slimy-fruited Stonewort, thought to be extinct in the UK since 1959 and two other rare stoneworts - Tassel and Clustered stonewort - in several of the Bramfield and Walpole ponds. This total (and minimum) of eight stoneworts makes the ponds in Bramfield and Walpole parishes of sufficient quality to have qualified as an Important Stonewort Area in 2004 as defined by Plantlife (Stewart, 2004).

Trans. Suffolk Nat. Soc. 55 (2019)


117

RARE STONEWORTS

Table 1: Stoneworts recorded in Bramfield & Walpole parishes 2019 with British conservation status. Common name

Latin name

Conservation status in Britain*

Location in new or ancient ponds

Slimy-fruited stonewort

Nitella capillaris

Thought to have been Extinct. Only location a ditch near Sutton, Cambs. at end of 19th C, and again in 1959 but not since.

2 ancient restored arable field edge ponds

Tassel stonewort

Tolypella intricata

Endangered species with very restricted distribution. Strongholds Glos/Oxon, but also found in Cambridgeshire, Suffolk, Norfolk, Somerset, Worcs.

2 ancient restored arable field edge ponds 1 plant only in a neglected arable field edge pond

Clustered stonewort

Tolypella glomerata

Nationally Scarce species. Widely scattered in areas of calcareous geology, including sand dunes.

1 ancient restored arable field edge pond 1 regularly disturbed livestock pond Probably introduced at new ponds not surveyed in 2019**

Rough stonewort (prob introduced)

Chara aspera

Occasional species but fairly widespread

Probably introduced at new ponds not surveyed in 2019**

Bristly stonewort (prob introduced)

Chara hispida

Occasional species, relatively widespread but most frequent in East Anglia

Probably introduced at new ponds not surveyed in 2019**

Fragile stonewort

Chara globularis

Occasional species, relatively widespread

2 new ponds created in 2009 next to ancient livestock ponds

Delicate stonewort

Chara virgata

Frequent species, relatively widespread

2 ancient restored ponds

Common stonewort

Chara vulgaris

Frequent species, widespread

4 new ponds 6 ancient restored ponds

*Conservation status in Britain source: Pond Conservation (2010). **Six species of stoneworts were recorded in Bramfield and Walpole parishes in 2019 on three farms. An additional two species are known to exist at the mosaic of 15 or so closely located ponds at a nearby smallholding surveyed by the national Charophyte recorder Nick Stewart several years ago.

Trans. Suffolk Nat. Soc. 55 (2019)


118

Suffolk Natural History, Vol. 55

Slimy-fruited Stonewort Nitella capillaris

C. Carter

Status in the UK (Stewart 2007) - previously considered Extinct The Slimy-fruited Stonewort was last seen in Britain in 1959 and was, until now considered extinct here (Stewart & Church 1992). It was only ever recorded with certainty from the upper Ouse Washes in Cambridgeshire (near Sutton Gault) where it was discovered by Alfred Fryer of Chatteris in 1885. It was recorded regularly until 1899 but the site has been surveyed several times since 1959, including in the last ten years and is believed to be truly extinct there as the area has deteriorated and now looks unsuitable. Records from elsewhere in Britain have either been shown to be errors or lack any voucher material to support the records (Source: update on Nitella capillaris Nick Stewart, 2007). Outside Britain this species is widespread in Europe and the northern hemisphere (Stewart & Church 1992). The plant is best looked for between late April and mid June and can be identified by the lack of stem cortex (i.e. each internode is a single cell) and by the fruiting structures (antheridia and oogonia) being enveloped in mucus (see photos below). The stonewort is thought to reach its optimum development in early spring and then disappears in summer. It is mainly found in shallow ponds, probably the shallow zones of lakes, ditches, and peat diggings. The ecological requirements have not yet been fully recognized. (Source: Urbaniak & GÄ…bka, 2014.)

Nitella capillaris female (left) and male (right) plants. It is dioecious with its gametangia (sexual reproductive organs) on different plants. Scale bars 10 Âľm

Trans. Suffolk Nat. Soc. 55 (2019)


119

C. Carter

RARE STONEWORTS

C. Carter

Nitella capillaris antheridia (male sex organ of algae) Mucus surrounding the antheridia is evident (see also cover photo).

Left: a male plant with orange antheridia. Right top: a split antheridium pouring forth its sperm. Right bottom: close up of Nitella capillaris sperm.

Trans. Suffolk Nat. Soc. 55 (2019)


Suffolk Natural History, Vol. 55

C. Carter

120

J. Hawkins

Nitella capillaris oogonium (female sex organ of algae) enclosing the egg cells and close-up showing mucus surrounding.

The Slimy-fruited stonewort (Nitella capillaris), thought to be extinct since 1959, was found growing in clean, clear water in this arable field edge pond on Earlsway Farm, Bramfield - the other pond site it was found in was 1.6km away in Walpole. It was growing around a perimeter section 8m long x 1m wide, on a 0-40cm deep underwater shelf/sloping profile at the northern pond edge (i.e. south-facing) where the pond had been ‘patch-scooped’ in winter 2018/2019 to remove invasive reedmace at the edge and some of the broadleaved pondweed further in. The stonewort persisted in fruiting until the last spring/early summer visit in mid-June 2019. This ancient, sunny pond is at the top of a slope and buffered from arable to the south by a hedge and rough grass and to the north by a 6m grass margin. The pond has had a history of occasional management that has involved removing organic matter from nearby tree and shrub leaf litter.

Trans. Suffolk Nat. Soc. 55 (2019)


121

RARE STONEWORTS

Tassel Stonewort Tolypella intricata

C. Carter

Status in the UK - Endangered Tassel Stonewort has a very restricted distribution with strongholds in Gloucestershire and Oxfordshire but it is also found in Cambs, Norfolk, Somerset and Worcestershire. It is believed to be limited by the availability of open water habitat in early stages of succession and other factors we do not wholly understand. Waterbodies need to be mesotrophic, clay based and with shallow edges that are extensively grazed and poached - and often dry up in the summer. Tassel stonewort was found in an ancient pond at SWT’s Black Bourne Valley Nature Reserve (BBVNR) in 2011 (J. Hawkins), but not confirmed again until 2017 (Nick Stewart). In Suffolk, it has been recorded in a ditch in Mickfield in 1998 and in in Bury St Edmunds in 1889. Thus, to find it in three ancient ponds in Bramfield is very exciting. At BBVNR Suffolk Wildlife Trust has an ongoing translocation project where it is hoped to secure more metapopulations by translocating small amounts of mud material, which is hoped to contain spores, to four new ponds. Tassel stonewort is a winter annual which usually germinates in autumn, overwinters in a vegetative state, and is visible between April and June when the spores ripen; the plant has usually disappeared by July. It is not considered competitive and benefits from disturbance which suppresses other vegetation. It sometimes appears in quantity for a year or two. (Source: Stewart - various).

Tolypella intricata specimens collected at Broad Oak Farm, Walpole, Pond 4. Trans. Suffolk Nat. Soc. 55 (2019)


Suffolk Natural History, Vol. 55

J. Hawkins

122

A huge stand of the Endangered Tassel Stonewort (Tolypella intricata), was found in this newly restored arable field edge pond in Walpole parish on Broad Oak Farm which had previously been shaded by scrub and full of organic matter. Later, Slimyfruited Stonewort was found here too. Another restored farm pond about 200m to the east also supported Tassel Stonewort, taking the total number of ponds known to host this species to four, three in this Bramfield Farm Cluster (and the other at Suffolk Wildlife Trust’s Black Bourne Valley Nature Reserve). Already, just a few months after restoration, invasive emergent vegetation is established. Without livestock disturbance or periodic machine intervention, the pond will become dominated by emergent vegetation and other aquatic plants, shading out the stonewort.

Trans. Suffolk Nat. Soc. 55 (2019)


123

RARE STONEWORTS

Clustered Stonewort Tolypella glomerata

C. Carter

Status in the UK - Nationally Scarce Clustered stonewort is widely scattered in areas of calcareous geology including sand dunes. It is the most commonly recorded Tolypella species recorded in Britain. It has been found in three other locations in Suffolk - Betty’s Fen, Thelnetham (2010), Peto’s Marsh, Oulton (2017) and SWT’s Black Bourne Valley Nature Reserve (2017). Where the water body is fairly stable, Clustered Stonewort may be a summer annual and can develop rapidly, from germination to oospore production in 3 months (May-July). Where sites dry up in the summer, but are flooded in winter, the plants germinate in autumn, and over-winter, producing oospores as early as May or June as in Bramfield. (Source: Stewart - various).

Clustered stonewort with its characteristically tightly bundled ‘heads’. Trans. Suffolk Nat. Soc. 55 (2019)


Suffolk Natural History, Vol. 55

C. Carter

124

J. Hawkins

Clustered stonewort with its characteristically tightly bundled ‘heads’.

One small fragment of Nationally Scarce Clustered Stonewort (Tolypella glomerata) was found at Brights Farm, Bramfield ancient Bulls Field pond where cattle have regular access to the margins. Trans. Suffolk Nat. Soc. 55 (2019)


RARE STONEWORTS

125

References Hawkins, J. (2006). Suffolk Pond Project Report July 2004 – October 2006. Internal Suffolk Wildlife Trust report. Hawkins, J. (2019). The Conservation of rare Stoneworts in Bramfield & Walpole Parishes report. Suffolk Wildlife Trust report for Bramfield Farm Cluster. Lambert, S. J. (2007). The Environmental Range and Tolerance Limits of British Stoneworts (Charophytes). Thesis submitted for PhD at University of East Anglia. Lambert, S. J. & Davy, A. J. (2010). Water quality as a threat to aquatic plants: discriminating between the effects of nitrate, phosphate, boron and heavy metals on charophytes. New Phytologist 189 (4): 1051-9. Moore, J. A. (1986). Charophytes of Great Britain & Ireland, BSBI Handbook 5. Pond Conservation (2010). Creating ponds and lakes for stoneworts. Million Pond Project. Sanford, M. & Fisk, R. (2010). A Flora of Suffolk. DK & MN Sanford. Sibbett, N. (1996). The distribution and abundance of ponds in Suffolk. English Nature Research Report 333. Stewart, N. F. (1996). Stoneworts - Connoisseurs of Clean Water. British Wildlife 8 (2): 92-99. Stewart, N. F. (2004). Important Stonewort Areas. An assessment of the best areas for stoneworts in the United Kingdom (summary). Plantlife International, Salisbury, UK. Stewart, N. F. (2007). Slimy-fruited Stonewort (Nitella capillaris) (Krocker) J. Groves & Bullock-Webster) in Britain. Unpublished report. Stewart, N. F. & Church, J. M. (1992). Red Data Books of Britain & Ireland: Stoneworts. JNCC, Peterborough. Urbaniak, J. & Gąbka, M. (2013). Polish Charophytes - An Illustrated Guide to Identification. Wydawnictwo Uniwersytetu Przyrodniczego we Wrocławiu. Juliet Hawkins Milden Hall Milden Brent Eleigh Sudbury CO10 9NY gfhawkins@btconnect.com

Trans. Suffolk Nat. Soc. 55 (2019)

Profile for Suffolk Naturalists' Society

The discovery and conservation of rare stoneworts in Suffolk’s farmland ponds 2019  

J. Hawkins

The discovery and conservation of rare stoneworts in Suffolk’s farmland ponds 2019  

J. Hawkins

Recommendations could not be loaded

Recommendations could not be loaded

Recommendations could not be loaded

Recommendations could not be loaded