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Estuarine, Coastal and Shelf Science xxx (2012) 1e9

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Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring Javier Atalah a, b, *, Tasman P. Crowe a a b

School of Biology and Environmental Science, Science Centre West, University College Dublin, Belfield, Dublin 4, Ireland Cawthron Institute, 98 Halifax Street East, Nelson 7010, Private Bag 2, Nelson 7042, New Zealand

a r t i c l e i n f o

a b s t r a c t

Article history: Received 9 May 2011 Accepted 27 December 2011 Available online xxx

Consideration of the impacts of pollutants on elements of biodiversity and the development of costeffective biomonitoring tools to measure those impacts are essential to coastal biodiversity conservation. To examine the effects of nutrient enrichment and to develop biomonitoring tools, a network of 11 rocky intertidal sites differing in nutrient contamination levels was established on the west coast of Ireland. Communities of molluscs on the lower shore were sampled at the sites and a range of physicochemical variables was measured to characterize levels of contamination on the shores. Total abundance and number of taxa of molluscs were reduced in contaminated sites compared to control sites. Multivariate analyses showed that the structure of the molluscan assemblages differed between contaminated and control sites, discriminating between species that were more abundant at contaminated sites and those that were more abundant at control sites. Multivariate multiple regression analysis showed that nitrite, phosphate and ammonia levels in seawater accounted for more than 45% of the variability in the community structure of molluscs. This study suggests that molluscan assemblages could be a cost-effective tool to monitor and detect changes induced by nutrient enrichment in coastal areas. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: pollution environmental status Fucus serratus ecological indicators intertidal assemblages

1. Introduction The present major impact of human activities on marine biodiversity is expected to increase during the coming decades (Halpern et al., 2008). Urban, industrial and agricultural developments have contaminated estuaries and coastal waters by a variety of effluents (Valiela, 2006). Contamination can encompass substantial loads of various nutrients, organic matter, sediments, heavy metals and hydrocarbons, which provide single or combined stressors to coastal areas (Crowe et al., 2000). Eutrophication, in particular, is of major concern (Valiela, 2006), leading to changes in the structure and functioning of communities and ecosystems (Kautsky et al., 1986). Documented effects of nutrient enrichment on rocky shores include a decline in the abundance of perennial macroalgae, mainly the brown algae Fucus vesiculosus L. (Schramm, 1996), but also Fucus serratus L (Kraufvelin et al., 2006, 2010), and increases in the cover of ephemeral algae (Worm et al., 1999). In recent years, the development of indicators of environmental quality has been driven by several global and regional initiatives on

* Corresponding author. Cawthron Institute, 98 Halifax Street East, Nelson 7010, Private Bag 2, Nelson 7042, New Zealand. E-mail address: javier.atalah@cawthron.org.nz (J. Atalah).

sustainable development (UN WSSD, 2002), climate change (IPCC, 2007), the conservation of biological diversity (UN CBD, 1992) and integrated water resource management (EC, 2000), with a shift towards using environmental indicators of anthropogenic impact within a regulatory framework. The EU Directive 2000/60/EC (The Water Framework Directive, WFD) requires considerations of impacts of contamination on elements of marine biodiversity and the development of cost-effective biomonitoring. An ideal contamination indicator should be linked to a specific stressor, capable of providing meaningful information to decision-making that is sufficiently sensitive and reliable, robust to confounding factors, applicable over a range of spatial and temporal scales, easy to measure, cost-effective, non-destructive and scientifically defensible (UNESCO, 2006). Although a range of biological assemblages has been used to monitor and assess changes in coastal areas, most have involved subtidal soft-bottom assemblages (Borja et al., 2003). Assessment tools using intertidal rocky shore assemblages are less common (Benedetti-Cecchi and Osio, 2007). The use of macroalgal assemblages is explicitly required by the WFD and recommended by other researchers as a potential cost-effective biomonitoring tool for assessing the impacts of contamination (Wells et al., 2007). In considering alternative approaches, molluscs are frequently described as potentially reliable bioindicators (Espinosa et al., 2007). They inhabit almost all marine environments, often with high

0272-7714/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2011.12.034

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


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J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

diversity and abundance, and their taxonomy, biology, ecology and distribution are well known in many coastal zones, including Europe. Moreover, many molluscan species function as ecosystem engineers, providing structurally complex habitat for other species to inhabit and seek refuge from predators (Koivisto and Westerbom, 2010); in addition, their taxonomy is well known. Contamination can cause changes in abundance and the composition and structure of communities of molluscs (Terlizzi et al., 2005b), which generally reflect changes in overall species richness in intertidal rocky shore environments (Smith, 2005). Studies that have used molluscs to assess urban contamination have been restricted mostly to subtidal environments (Terlizzi et al., 2005b) or to the use of a specific molluscan group (e.g. Patellidae, Espinosa et al., 2007). This study compared the diversity and structure of macroalgal and molluscan assemblages associated with the F. serratus canopy on rocky shores subject to differing intensities of nutrient enrichment. In particular, the study tested the relationship between concentrations of nutrients (nitrate, nitrite, phosphate and ammonia) and aspects of assemblage structure, in order to develop relevant biomonitoring techniques. F. serratus was chosen as the focal habitat because the following features make it well suited for biomonitoring: it is widely distributed around the north Atlantic Ocean, it is ubiquitous on hard substrata and restricted to the lower shore (ensuring limited variation in the tidal level of different sites sampled), it is easily recognised and constitutes a species-rich habitat. 2. Methods 2.1. Study sites Molluscan assemblages associated with >80% coverage of F. serratus were sampled at eleven sites, differing in concentrations of nitrate, nitrite, ammonia and phosphate, along the west coast of Ireland (Fig. 1). Sites were in fully marine rocky intertidal habitats, sheltered from wave action and with a substratum comprising a mix of granite bedrock and large boulders of low slope (>120 ).

Mussel beds were absent. The overall study comprised clusters of sites in Connemara, Galway and Shannon, to account for possible regional or biogeographical differences (Fig. 1). Within each cluster, we used existing data from a long-term monitoring programme (Toner et al., 2005) to identify two sites with high levels of nutrients and two sites considered to represent conditions of low impact (control sites). In Connemara, the two contaminated sites were Kilkieran (5319.20 N, 9 43.90 W) and Rossaveal (5316.20 N, 9 33.40 W) and the two control sites were Ballynahown (5314.20 N, 9 33.20 W) and Mweenish Island (5317.50 N, 09 50.30 W). The Kilkieran site was located next to the outfall of a seaweed meal production plant discharging untreated waste water directly into the bay. Rossaveal is directly affected by untreated industrial effluents coming from a harbour. Within the Galway area, it was not possible to find two contaminated sites with similar abiotic characteristics, and only one contaminated site, Mutton Island (5315.1 N, 9 03.00 W), was sampled. This was located in the vicinity of an outfall discharging secondary treated sewage from Galway City. The two control sites were Parkmore (5310.20 N, 8 58.00 W) and Rinville (5316.00 N, 9 02.50 W). In the Shannon coastal region, the two contaminated sites were Kilrush (52 37.40 N, 09 29.30 W) and Fenit (5216.60 N, 09 50.30 W), with control sites at Rinevella Point (52 34.90 N, 9 44.60 W) and Carrigaholt (52 36.00 N, 09 42.10 W). Both of the contaminated sites are near to outfalls from which untreated or partially treated urban waste water effluents are discharged. In each cluster, contaminated and control sites were chosen so that they were geographically interspersed. When possible, sites were chosen randomly from a larger pool of candidate sites. At each site, an area was selected from among several suitable areas on the low-shore. The areas chosen were 30 m long, 20 m wide and parallel to the coast line along a conspicuous F. serratus fringe. 2.2. Water chemistry In order to establish a more detailed profile of the contemporary nutrient status of the sites than was available through existing data,

Fig. 1. Map showing the location of the eleven study sites in the west coast of Ireland. Two contaminated (black symbols) and two control sites (grey symbols) were sampled at each of the clusters Connemara and Shannon. In the Galway cluster, one polluted site and two control sites were sampled (see Methods section for details). The panel on the lower left corner shows the location of the region relative to the island of Ireland.

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

water samples were collected on two occasions during the winter when nutrient concentrations are likely to be maximal (Levinton, 2001). At each site, triplicate water samples were taken with 500 mL opaque HDPE plastic bottles. Sample bottles were acid washed and thoroughly rinsed with deionised water before use, and rinsed with sample water before filling with sample. Ammonium concentrations were determined within 24 h after collection, while samples for measurement of nitrite, nitrate and phosphate were stored at 30  C for subsequent analysis. Standard spectrophotometric methods were used to measure levels nitrite (NO 2,  3 mg N/L), nitrates (NO 3 þ NO2 , mg N/L), phosphate (PO4 , mg P/L) and ammonia (NH3, mg N/L) (Hansen et al., 2007). Salinity (PSU) was measured using Star-Oddi salinity loggers that were fastened to rocks at the sites for a week, recording values every hour. 2.3. Sampling of molluscs In June and July (summer) 2006, molluscs were sampled at low tide from five randomly positioned 0.25 m2 quadrats within each site. Sampling at each site took one day and sites were visited in a random order to avoid temporal confounding of comparisons of nutrient status and region. All loose molluscs found inside a quadrat were collected and placed inside buckets. Then all specimens of the canopyforming species (mainly F. serratus, but also Ascophyllum nodosum and F. vesiculosus) whose holdfasts were inside the quadrat were cut and placed in buckets, for later washing to remove animals. Additionally, one half of each quadrat was randomly selected and all organisms were cleaned off the rock using a paint scraper. The epifauna and the scraping samples were stored in labelled jars, preserved in 5% formaldehyde. Molluscs were later sorted, counted and identified to species or genera. The protocols were based on those developed by O. Mulholland (University College Dublin unpubl.) and are known to be effective at removing of molluscs from macroalgae on rocky shores. 2.4. Statistical analysis Differences in assemblage structure between contaminated and control sites were tested using a distance-based permutational analysis of variance (PERMANOVA, Anderson, 2001a) using BrayeCurtis similarities of the square-root transformed data. The design comprised three factors: Cluster (random, with three levels: Connemara, Galway and Shannon), Nutrient status (fixed, with two levels: contaminated and control, and crossed with factor Cluster) and Sites (random, with two levels, and nested in factor Nutrient status). One cluster (Galway) only had one contaminated site (see study sites section above), thus resulting in an asymmetrical design for this cluster. Routines in PERMANOVAþ (Anderson and Gorley, 2007), an add-on to Version 6 of the PRIMER computer program (Clarke and Gorley, 2006) were used to partition multivariate variability according to the full experimental design and dealt appropriately with asymmetry. Differences in community structure among treatment levels were visualized by principal coordinate (PCO) analyses on the basis of BrayeCurtis similarities of the square-root transformed data. Similarity Percentage Analysis (SIMPER, Clarke, 1993) was used to identify the percentage contribution of each species (or taxon) to observed differences between communities at the contaminated and control sites. For this, the ratio Diss/SD was used to indicate the consistency with which a given species contributed to the average dissimilarity between samples from contaminated and control sites. Values 1 indicated a high degree of consistency. Taxa that consistently discriminated between treatments are displayed as vectors in the PCO plots. Univariate permutational analyses of variance (Anderson, 2001b) were carried out on several variables to test for

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differences between contaminated and control sites, using the same experimental design as described above for the multivariate analyses. The variables were: number of taxa, total abundance, salinity, nitrate, nitrite, phosphate and ammonia. Univariate analyses were performed using PERMANOVA, with Euclidean distances as the measure of similarity. This is preferable to traditional ANOVA, because PERMANOVA calculates P-values using permutations, rather than relying on tabled P-values, which assume normality. Additionally, as mentioned above, the PERMANOVA analysis can deal appropriately with asymmetric designs. Levene’s test based on the median was used to check the assumption of homogeneity of variances. Total abundance data were ln(x) transformed to remove heterogeneous variances, to achieve approximate unimodal symmetry and to avoid skewness. The relationship between species data and environmental variables was analysed using multivariate multiple regression (McArdle and Anderson, 2001), more specifically the DISTLM routine in the PRIMER 6 & PERMANOVA (Anderson and Gorley, 2007). A marginal test was used where individual variables were fitted separately to test their relationship with the molluscan assemblage data (ignoring other variables), followed by a forward-selection procedure, conditional on variables already included in the model. The conditional test identifies the subset of variables that best predicts the species data. Both the conditional and marginal tests were done using 4999 permutations. Tests were based on BrayeCurtis dissimilarities of the untransformed molluscan abundance data. Environmental variables used in the analyses were nitrite, nitrates, phosphate and ammonia. Salinity did not vary significantly among sites and was not used in these analyses. 3. Results 3.1. Water chemistry Nitrate levels varied significantly among clusters (Table 1, Fig. 2a), but no significant differences between contaminated and control sites were found in any of the three clusters (Table 1, Fig. 2a). Nitrate mean concentration ranged from a minimum of 66.22 mg/L (2.92 SE) at the Connemara cluster to a maximum of 539.16 (22.59 SE) at the Galway cluster. Nitrite levels were higher at contaminated sites compared to control, but only in two of the geographical clusters, namely Connemara and Shannon (Table 1, Fig. 2b). Ammonia concentration was on average w2.5 fold higher at contaminated sites compared with control sites in all three clusters (Table 1, Fig. 2c), this pattern was encountered despite significant site-to-site variability (Table 1, Fig. 2c). There tended to be higher levels of phosphates at contaminated sites compared to control sites in all three clusters, but this was not significant (Table 1, Fig. 2d). Median salinity ranged between 26 and 37 PSU, but did not vary significantly either with contamination status or among geographical clusters (Table 1, Fig. 2e). 3.2. Molluscan assemblage structure Thirty-five mollusc species were found across all sites and were included in the analyses (Table 2). The molluscan assemblages differed significantly among the three geographical clusters (Table 3) and between contaminated and control sites (Table 3). The PCO plots (Fig. 3) illustrate this pattern, showing a separation between assemblages from the three different clusters and at contaminated and control sites. SIMPER analysis indicated that variation in the abundance of thirteen taxa contributed >75% of the difference between assemblages in contaminated and control sites. Lacuna pallidula, Rissoa parva, Bittium reticulatum, Littorina spp., Gibbula umbilicalis, Gibbula cineraria, Nucella lapillus and

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


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J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

Table 1 Permutational ANOVAs for the environmental variables based on Euclidean distance of the untransformed data. Source of variation

df

Cluster Contamination Cluster  contamination Sites (cluster  contamination) Res Total

2 1 2 5 55 65

Nitrates

Ammonia

Phosphates

Nitrites

Salinity

F

P

F

P

F

P

F

P

F

P

12.3 0.3 0.7 1.00Eþ10

0.01 0.60 0.55 1.00

0.1 26.1 0.2 8.5Eþ06

0.93 0.03 0.84 0.00

3.5 0.9 0.3 1.0Eþ10

0.13 0.39 0.76 1.00

15.8 0.7 3.9 1.0Eþ10

0.01 0.44 0.09 1.00

1.1 1.4 0.7 1.0Eþ10

0.40 0.28 0.52 1.00

(mean ¼ 33.8  6.8 SE) sites. On the other hand Odostomia scalaris, Mytilus edulis individuals or juveniles, Littorina littorea, Rissoa lilacina and Cingula cingulus tended to be more abundant at contaminated sites (Table 4). From these taxa, Littorina littorea had

Ansates pellucida tended to be more abundant at control sites. L. pallidula had the highest contribution to the observed dissimilarities and consistency (Diss/SD ratio) to the differences between contaminated (mean ¼ 3.7  1.77 SE) and control

a

b 700 Contamined Control

16

Contamined Control

14

600 12

Nitrite (µg/L)

Nitrate (µg/L)

500

400

300

8 6

200

4

100

2 0

0 Connemara

c

10

80

Galway

Connemara

Shannon

Galway

Shannon

d 30

Contamined Control

Contamined Control

25

Phosphate (µg/L)

Ammonia (µg/L)

60

40

20

15

10

20 5 0 Connemara

Galway

Shannon

0 Connemara

Galway

Shannon

e 40 Contamined Control

Salinity (PSU)

30

20

10

0 Connemara

Galway

Shannon

Fig. 2. Mean (þSE) nitrates (a), nitrites, (b) ammonia (c), phosphate (d) and salinity (e) in each of the three clusters at contaminated (filled bars) and control sites (empty bars).

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

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Table 2 List of the 35 taxa identified and included in the analysis. Species name

Family

Order

Class

Taxonomic authority

Acanthocardia tuberculata Anomiacea sp. Assiminea grayana Bittium reticulatum Odostomia scalaris Buccinum undatum Calliostoma zizyphinum Unidentified Polyplacophora Cingula cingulus Gibbula cineraria Gibbula umbilicalis Goodallia triangularis Ansates pellucida Hiatella arctica Hinia incrassata Hinia reticulatum Lacuna pallidula Lacuna vincta Littorina compressa Littorina littorea Melarhaphe neritoides Littorina spp.a Musculus sp. Mytilus edulis Nucella lapillus Unidentified Nudibranchia Ocenebra erinacea Onchidella celtica Onoba semicostata Patella vulgata Rissoa lilacina Rissoa parva Tricolia pullus Turtonia minuta Venerupis senegalensis

Cardiidae Anomiidae Assimineidae Cerithiidae Pyramidellidae Buccinidae Trochidae Neoloricata Rissoidae Trochidae Trochidae Astartidae Patellidae Hiatellidae Buccinidae Buccinidae Littorinidae Littorinidae Littorinidae Littorinidae Littorinidae Littorinidae Mytilidae Mytilidae Muricidae Nudibranchia Muricidae Onchidiidae Rissoidae Patellidae Rissoidae Rissoidae Tricollidae Turtoniidae Veneridae

Veneroida Pterioida Mesograstropoda Mesogastropoda Heterobranchia Neogastropoda Archaeogastropoda Neoloricata Mesogastropoda Archaeogastropoda Archaeogastropoda Veneroida Archaeogastropoda Myoida Neogastropoda Neogastropoda Mesogastropoda Mesogastropoda Mesogastropoda Mesogastropoda Mesogastropoda Mesogastropoda Mytiloida Mytiloida Neogastropoda Nudibranchia Neogastropoda Systellommatophora Mesogastropoda Archaeogastropoda Mesogastropoda Mesogastropoda Archaeogastropoda Veneroida Veneroida

Bivalvia Bivalvia Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Polyplacophora Gastropoda Gastropoda Gastropoda Veneroida Gastropoda Bivalvia Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Bivalvia Bivalvia Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Gastropoda Bivalvia Bivalvia

Coen, 1915

a

Fleming, 1828 da Costa, 1778 Jeffreys, 1867 MacGillivray, 1843 Linnaeus, 1758 Montagu, 1803 Linnaeus, 1758 da Costa, 1778 Montagu, 1803 Linné, 1758 Linnaeus, 1767 Ström, 1768 Linnaeus, 1758 da Costa, 1778 Montagu, 1803 Jeffreys, 1865 Linnaeus, 1758 Linnaeus, 1758

Linnaeus, 1758 Linnaeus, 1758 Linnaeus, 1758 Cuvier, 1817 Montagu, 1803 Linnaeus, 1758 Récluz, 1843 da Costa, 1778 Linnaeus, 1758 Fabricius O., 1780 Gmelin, 1791

This designation refers to individuals that were either Littorina mariae or Littorina obtusata.

the highest consistency and contribution to the observed dissimilarities between contaminated (mean ¼ 24.4  5.1 SE) and control sites and (mean ¼ 6.1  1.8 SE). Three rare species (Tricolia pullus, Lacuna vincta, Assiminea grayana) present at control sites were not found at contaminated sites. 3.3. Number of taxa and total abundance There was significant variation among clusters in the mean number of molluscan taxa (Table 3 and Fig. 4), ranging from an average of 11.8 ( 0.49 S.E.) taxa in the Connemara cluster to 7.0 ( 0.92 S.E.) taxa in the Galway cluster. Similarly, there was significant spatial variation in the number of taxa of molluscs at the site scale (Table 3), ranging from 6.0 to 12.8 taxa per site on average. Although there was a trend for a reduced number of taxa at contaminated (mean 7.3  0.67 S.E.) compared with control sites (mean 10.5  0.45 S.E.) in all three clusters (Fig. 4), PERMANOVA did not detect significant differences (Table 3).

There was significant spatial variation among clusters and between sites in the total abundance of molluscs (Table 3 and Fig. 4), ranging from an average of 514.7 (68.7 S.E.) individuals in the Connemara cluster to 176.6 (42.3 S.E.) in the Galway Cluster. However, total abundance was significantly reduced at contaminated (mean 183.7  36.6 S.E.) compared with control sites (mean 398.2  51.6 S.E., Table 3 and Fig. 4). In addition, there was significant spatial variation in total abundance of molluscs at the site scale (Table 3), ranging on average from a minimum of 71.8 (6.8 S.E.) to a maximum of 598.8 (83.5 S.E.) individuals per site. 3.4. Relationship between molluscan data and environmental variables The non-parametric multivariate regression analysis showed that each of the four environmental variables (i.e. all variables measured) individually had a significant relationship with molluscan assemblage data (Table 5a), with greatest amount of

Table 3 PERMANOVA of differences in molluscan assemblage structure based on BrayeCurtis similarities of the square-root transformed data and permutational ANOVAs for the number of taxa and total abundance. Source of variation

df

Multivariate MS

F

P

MS

F

P

MS

F

P

Cluster Contamination Cluster  contamination Sites (cluster  contamination) Res Total Transformation

2 1 2 5 44 54

11 756 10 700 2399.8 2839 484.5

4.1 4.4 0.8 5.9

0.003 0.03 0.61 0.00

100 89.157 15.25 7.34 3.6273

13.6 5.9 2.1 2.0

0.02 0.13 0.22 0.10

529.8 311.6 26.9 39.9 11.6

13.3 11.5 0.7 3.4

0.01 0.05 0.53 0.01

Square root

Number of taxa

None

Total abundance

ln(x)

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


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Fig. 3. Principal Coordinates Ordination (PCO) plots of molluscan assemblages in each cluster: a) Connemara, b) Galway and c) Shannon e Tralee at both contaminated (filled symbols) and control sites (empty symbols) on the basis of BrayeCurtis similarities of the square-root transformed data.

variation explained by nitrite (13.0%), ammonia (12.5%) and phosphate (11.7%). The sequential model using the forward-selection method showed that the four variables together explained 45.0% of the total variation of the molluscan assemblage structure (Table 5b). The percentage of variation in the biotic data explained by ammonia and phosphates was increased after fitting the nitrite data and, conversely, the amount of variation explained by nitrate was greatly reduced after fitting the other three variables (Table 5b).

4. Discussion We found consistent differences in molluscan diversity and assemblage structure associated with nutrient enrichment. This indicates that molluscan assemblages can potentially provide a robust indication of contamination in coastal areas, despite high inherent spatial variability. The observed differences in molluscan assemblage structure were underpinned by changes in the relative abundance of several taxa between contaminated and control sites

Table 4 SIMPER analysis results for contributions from most important taxa to the BrayeCurtis dissimilarity distinguishing the two groups of sites, based on the squared root transformed data. Taxon

Av. abundance contaminated sites

Av. abundance control sites

Av. dissimilarity contributed by each taxon

Diss/SD

% Contribution

Cum.%

Lacuna pallidula Rissoa parva Odostomia scalaris Bittium reticulatum Mytilus edulis Littorina littorea Littorina spp. Gibbula umbilicalis Gibbula cineraria Nucella lapillus Ansates pellucida Rissoa lilacina Cingula cingulus

0.57 1.62 1.34 0.92 1.31 1.86 2.64 1.23 0.35 0.54 0.21 0.57 0.45

1.85 2.17 0.6 1.3 0.85 1 3.52 1.47 0.94 1 0.79 0.53 0.32

4.63 4.28 3.8 3.75 3.59 3.53 3.43 2.99 2.63 2.4 2.31 2.11 1.66

1.49 1.28 1.17 1.24 1.18 1.32 1.29 1.23 1.12 1.21 1.06 0.94 0.68

8.7 8.03 7.14 7.04 6.74 6.64 6.44 5.62 4.94 4.5 4.33 3.96 3.12

8.7 16.73 23.87 30.91 37.65 44.29 50.73 56.35 61.29 65.79 70.12 74.08 77.19

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

Fig. 4. Mean (þSE) number of taxa and total abundance in each of the three clusters at contaminated (filled bars) and control sites (empty bars).

and by differences in assemblage composition (the identities of species present), owing to the absence of three rare species at contaminated sites (Tricolia pullus, L. vincta, A. grayana). Reduced numbers of taxa, recognised as a symptom of nutrient enrichment in hard bottom habitats (Terlizzi et al., 2005b), was apparent as a trend across all geographical clusters in this study, but it was not statistically significant. Increases in the concentrations of organic and inorganic compounds and the uptake of contaminants by marine organisms have been suggested by some authors as potentially altering the abundance and structure of invertebrate assemblages (Otway et al., 1996). Ecological effects of nutrient enrichment can result from eutrophication caused by the excessive proliferation of primary producers, while high levels of toxic nutrient levels (e.g. nitrite or ammonia) can have toxicological effects by reducing the ability of aquatic animals to survive, grow and reproduce. Significantly higher concentrations of ammonia were measured in contaminated compared with controls sites. Ammonia is highly toxic to marine organisms (Chen et al., 2008) and there are few studies on the effect of ammonia on molluscs. For the marine bivalves Crassostrea virginica and Mercenaria mercenaria, lethal threshold values for ammonia range from 3.3 to 6.0 mg L1 and thresholds for sublethal effects are around 280 mg L1 (Epifanio and Srna, 1975). C. virginica and M. mercenaria are considered very tolerant. It is of note that ammonia concentrations found in this study were below these threshold values. Although none of the

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other individual nutrients varied significantly and/or consistently between contaminated and control sites, each of them explained a significant proportion of the variation in molluscan community structure shown by multivariate regression, together accounting for 45% of that variation. They may therefore act in combination as part of a mixture of generalised urban pollutants from a range of sources. It is important to note, however, that this was an observational study and thus the data presented do not allow the inference of causal mechanisms for the observed differences in molluscan community structure. A series of controlled experimental manipulations would be needed to determine the underlying mechanisms causing changes in molluscan assemblages associated with contamination. It is important to recognise that the patterns described above are correlative and there may be other factors that may also be influencing the molluscan assemblages. There is a considerable amount of literature that has shown the effects of urban contamination on the diversity and structure of temperate hard substratum communities in both subtidal (Terlizzi et al., 2005a, 2005b) and intertidal habitats (Archambault et al., 2001; Bishop and Kelaher, 2007; Crowe et al., 2004; Espinosa et al., 2007) and a range of potential mechanisms that may be responsible for these effects. Urban contamination can increase the amount of suspended solids in the water column, and modify the rate of sedimentation. The effects of sedimentation on rocky shore assemblages, both algae and invertebrate, are well documented (Airoldi, 2003). The abundance of key gastropods grazers can be directly reduced by sedimentation (Airoldi and Hawkins, 2007). Changes to gastropod grazer communities often affect the structure and growth of algal assemblages (Lubchenco and Gaines, 1981) and this can translate to changes in ecosystem functioning (O’Connor and Crowe, 2005). Contamination can also reduce light penetration in the water column and this can also influence benthic assemblage structure (Saunders and Connell, 2001). The high variation of molluscan assemblages, abundance and number of taxa within and among sites and geographical clusters likely reflects both regional biogeography and variation in the magnitude of anthropogenic pressure. The Galway and Shannon and Tralee sites are adjacent to relatively large urban centres compared with those in Connemara. It has been suggested that anthropogenic disturbances can decrease or increase the spatial variation in abundance of marine assemblages and populations (Warwick and Clarke, 1993). Although this study was not specifically designed to test for changes in the spatial variability due to contamination, the observed extent of spatial variation at the scale

Table 5 Results of non-parametric multiple regression of molluscan assemblage data on individual environmental variables for (a) each variable taken individually (ignoring other variables) and (b) forward-selection of variables, where amount explained by each variable added to model is conditional on variables already in the model (i.e. those variables listed above it). %Var: percentage of variance in species data explained by that variable; Cum. (%): cumulative percentage of variance explained. Variable a) Marginal test Nitrite Ammonia Phosphate Nitrate b) Sequential test Nitrite Ammonia Phosphate Nitrate

% variability

F

P

12.98 12.54 11.74 8.85

7.91 7.60 7.05 5.14

<0.001 <0.001 <0.001 <0.001

12.98 12.66 16.91 2.47

7.91 8.86 15.02 2.25

<0.001 <0.001 <0.001 <0.05

Cum (%)

12.98 25.65 42.56 45.03

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


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J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9

of sites was not significantly different between contaminated and control sites. The results here agree with several other studies that have advocated molluscs as useful general surrogates for ecological assessment. For example, Skilleter (1996) demonstrated that molluscan assemblages responded to human impacts in mangrove forests, with patterns of community structure significantly correlated with levels of habitat damage associated with human activity. Terlizzi et al. (2005a,b) have shown that molluscan assemblages can be an effective indicator of the impacts of contamination in rocky subtidal habitats. Smith (2005) showed that variation in assemblages of prosobranch molluscs reflected patterns in the broader intertidal community and provided an accurate prediction of overall diversity. The observed compromise between tolerant and sensitive molluscan species allowed the identification of potential bioindicator taxa, for example the abundance of taxa highly correlated with total abundance, nutrient status or nutrient concentration. In the current study, contaminated sites were characterised by a significant reduction in molluscan total abundance and higher abundance of the gastropods O. scalaris and L. littorea and the bivalve M. edulis. The pyramidellids, such as O. scalaris, are common ectoparasites in many marine communities, but little is known about their biology and life histories (Collin and Wise, 1997), perhaps making their responses difficult to interpret. L. littorea is much better known, is tolerant to high levels of contamination and has also previously been shown to increase in numbers under controlled long-term nutrient enrichment (Kraufvelin et al., 2002); it is increasingly being used as a bioindicator (Jackson, 2008). In this study, its abundance at contaminated sites was on average over 4fold higher control than the control sites. M. edulis can tolerate and accumulate a wide range of contaminants, and is also used extensively as a biomonitor in coastal areas (Widdows and Donkin, 1992). On the other hand, some taxa were consistently more common at control sites, such as L. pallidula, Littorina spp., R. parva, B. reticulatum, G. umbilicalis, Gibbula cineraria, N. lapillus and A. pellucida. Therefore the scarcity of absence of these species can be used an indication of contamination. The largest effect size was observed for the abundance of the gastropods L. pallidula and Littorina spp., that on average were respectively >9 and 3 times more abundant at control sites compared to contaminated ones. The use of macrofauna as a contamination indicator is preferred over chemical analysis, as organisms have an integrating response to their environment and thus, giving a more ecologically relevant indication (Hall et al., 1997). Ideally a good biological indicator should be linked to a specific stressor, be easily identified and applicable to a range of temporal and spatial scales. However, using a single species as an indicator may be contentious, as the presence or absence of individual cannot always be attributed to a particular cause (Fitch and Crowe, 2010). Thus, the potential value of any of these gastropod taxa as indicators for increased levels of nutrient enrichment must be treated with caution. In this context, the multivariate response of molluscan assemblages may provide a more robust indication of contamination. Further research to develop classification tools for rocky shores should include monitoring programmes with larger spatial and temporal scales and an increased range of nutrient concentrations, contaminant types and habitat types (e.g. more exposed shores). The molluscan sampling of this study was undertaken during late spring to early summer as a peak in molluscan abundance and species richness has been shown to occur during this period (Williams, 1996). Hence, the period between late spring and summer are recommended as a suitable time for biological monitoring purposes using these assemblages, although it is recognised that the best period for monitoring may vary in different regions.

Nutrient concentrations were measured only during winter when peak concentrations are more likely to be encountered (Levinton, 2001). This gives a good indication of variation among sites in peak and overall nutrient input, which may strongly influence community structure as it develops over extended periods. It is is important to acknowledge that it would best also to measure nutrients at the same time as the biotic sampling, as this will describe the actual conditions that the organisms are experiencing at the time. For example, some recent nutrient pulses or strong nutrient depletion during of before the sampling time could have affected the molluscan community structure and/or composition. Currently there are no established and widely accepted tools to assess ecological quality of rocky shores based on macroinvertebrates. The approach taken in this study to assess the ecological status of rocky shores was based on comparing the molluscan diversity and assemblage structure of sites with a comparatively high level of nutrient enrichment with that at control sites of the type that could be used to define reference conditions. The WFD requires the classification of water bodies into five ecological quality classes (EC, 2000). In this context, further research is required to develop more detailed classification tools based on the tolerance of molluscan taxa to contamination. For example, it would be valuable to classify taxa into a range of ecological groups based upon previous ecological models (Pianka, 1970) and the stages of their ecological succession in a range of stressed environments (Pearson and Rosenberg, 1978), such that taxa indicative of particular sets of conditions could be nominated and evaluated. Because the habitat sampled in this study, F. serratus on the lower rocky shore, is widespread along the Atlantic coast of Europe and the north-east coast of America, there is a great potential to apply the monitoring methods presented here at a wide range of locations. 5. Conclusions This study shows that nutrient enrichment is associated with changes in the abundance and structure of rocky shore molluscan assemblages. Similar and consistent responses were found at all three of the clusters of sites examined here, representing a broad geographical area and where the sources and amounts of nutrient contamination were quite different from each other. Intertidal habitats are easy to access and molluscs are comparatively easy to identify and so it is suggested that ecological monitoring methods based on molluscs have the potential to provide means for the rapid, wide scale evaluation of rocky shores affected by impacts associated with human activities. Acknowledgements Thanks to Jen Coughlan and Olwyen Mulholland for help with logistics and identification of molluscs. We are grateful to Cristina Armstrong, Maria Buitenhuis and Jayne Fitch for help with fieldwork, and to Rachel Cave (NUI Galway) for help with the nutrient analyses. This study was part of the BioChange project (Biodiversity and Environmental Change: an Integrated Study Encompassing a Range of Scales, Taxa and Habitats) funded by the Irish Environmental Protection Agency under the Strive Programme 2007e2013 (project code 2005-CD-B2_MI). References Airoldi, L., 2003. The effects of sedimentation on rocky assemblages. Oceanography and Marine Biology: An Annual Review 41, 161e236. Airoldi, L., Hawkins, S.J., 2007. Negative effects of sediment deposition on grazing activity and survival of the limpet Patella vulgata. Marine Ecology Progress Series 332, 235e240.

Please cite this article in press as: Atalah, J., Crowe, T.P., Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2011.12.034


J. Atalah, T.P. Crowe / Estuarine, Coastal and Shelf Science xxx (2012) 1e9 Anderson, M.J., 2001a. A new method for non-parametric multivariate analysis of variance. Austral Ecology 26, 32e46. Anderson, M.J., 2001b. Permutational test for univariate or multivariate analysis of variance and regression. Canadian Journal of Fisheries and Aquatic Sciences 58, 626e639. Anderson, M.J., Gorley, R.N., 2007. PERMANOVAþ for PRIMER: Guide to Software and Statistical Methods. PRIMER-E, Plymouth, UK. Archambault, P., Banwell, K., Underwood, A.J., 2001. Temporal variation in the structure of intertidal assemblages following the removal of sewage. Marine Ecology Progress Series 222, 51e62. Benedetti-Cecchi, L., Osio, G.C., 2007. Replication and mitigation of effects of confounding variables in environmental impact assessment: effect of marinas on rocky-shore assemblages. Marine Ecology Progress Series 334, 21e35. Bishop, M.J., Kelaher, B.P., 2007. Impacts of detrital enrichment on estuarine assemblages: disentangling effects of frequency and intensity of disturbance. Marine Ecology Progress Series 341, 25e36. Borja, A., Muxika, I., Franco, J., 2003. The application of a Marine Biotic Index to different impact sources affecting soft-bottom benthic communities along European coasts. Marine Pollution Bulletin 46, 835e845. Chen, L., Xing, L., Han, L., 2008. Rapid evaluation of poultry manure content using artificial neural networks (ANNs) method. Biosystems Engineering 101, 341e350. Clarke, K.R., 1993. Non-parametric multivariate analyses of changes in community structure. Australian Journal of Ecology 18, 117e143. Clarke, K.R., Gorley, R.N., 2006. PRIMER v6.1.6: User Manual/Tutorial Plymouth, UK. Collin, R., Wise, J.B., 1997. Morphology and development of Odostomia columbiana Dall and Bartsch (Pyramidellidae): implications for the evolution of gastropod development. Biological Bulletin 192, 243e252. Crowe, T.P., Thompson, R.C., Bray, S., Hawkins, S.J., 2000. Impacts of anthropogenic stress on rocky intertidal communities. Journal of Aquatic Ecosystem Stress and Recovery 7, 273e297. Crowe, T.P., Smith, E.L., Donkin, P., Barnaby, D.L., Rowland, S.J., 2004. Measurements of sublethal effects on individual organisms indicate community-level impacts of pollution. Journal of Applied Ecology 41, 114e123. EC, 2000. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for community action in the field of water policy. Official Journal of the European Communities 43, 1e73. Epifanio, C.E., Srna, R.F., 1975. Toxicity of ammonia, nitrate ion, nitrate ion, and orthophosphate to M. mercenaria and C. virginica. Marine Biology 33, 241e246. Espinosa, F., Guerra-Garcia, J.M., Garcia-Gomez, J.C., 2007. Sewage pollution and extinction risk: an endangered limpet as a bioindicator? Biodiversity and Conservation 16, 377e397. Fitch, J.E., Crowe, T.P., 2010. Effective methods for assessing ecological quality in intertidal soft-sediment habitats. Marine Pollution Bulletin 60, 1726e1733. Hall, J.A., Frid, C.L.J., Gill, M.E., 1997. The response of estuarine fish and benthos to an increasing discharge of sewage effluent. Marine Pollution Bulletin 34, 527e535. Halpern, B.S., Walbridge, S., Selkoe, K.A., Kappel, C.V., Micheli, F., D’Agrosa, C., Bruno, J.F., Casey, K.S., Ebert, C., Fox, H.E., Fujita, R., Heinemann, D., Lenihan, H.S., Madin, E.M.P., Perry, M.T., Selig, E.R., Spalding, M., Steneck, R., Watson, R., 2008. A global map of human impact on marine ecosystems. Science 319, 948e952. Hansen, H., Koroleff, F., Grasshoff, K., Kremling, K., Ehrhardt, M., 2007. Determination of Nutrients, Methods of Seawater Analysis. Wiley-VCH Verlag GmbH, pp. 159e228. IPCC, 2007. Fourth Assessment Report: Climate Change 2007. http://www.ipcc.ch/ ipccreports/assessments-reports.htm. Jackson, A., 2008. Littorina Littorea. Common Periwinkle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Marine Biological Association of the United Kingdom, Plymouth. Available from: http://www.marlin.ac.uk/species/Littorinalittorea.htm [cited 09/05/2011]. Kautsky, N., Kautsky, H., Kautsky, U., Waern, M., 1986. Decreased depth penetration of Fucus vesicolosus (L.) since the 1940’s indicates eutrophication of the Baltic Sea. Marine Ecology Progress Series 28, 1e8. Koivisto, M.E., Westerbom, M., 2010. Habitat structure and complexity as determinants of biodiversity in blue mussel beds on sublittoral rocky shores. Marine Biology 157, 1463e1474. Kraufvelin, P., Christie, H., Olsen, M., 2002. Littoral macrofauna (secondary) responses to experimental nutrient addition to rocky shore mesocosms and a coastal lagoon. Hydrobiologia 484, 149e166.

9

Kraufvelin, P., Moy, F.E., Christie, H., Bokn, T.L., 2006. Nutrient addition to experimental rocky shore communities revisited: Delayed responses, rapid recovery. Ecosystems 9, 1076e1093. Kraufvelin, P., Lindholm, A., Pedersen, M.F., Kirkerud, L.A., Bonsdorff, E., 2010. Biomass, diversity and production of rocky shore macroalgae at two nutrient enrichment and wave action levels. Marine Biology 157, 29e47. Levinton, J.S., 2001. Marine Biology: Function, Diversity and Ecology, second ed. Oxford University Press, Oxford. Lubchenco, J., Gaines, S.D., 1981. A unified approach to marine plant-herbivore interactions. I. Populations and communities. Annual Review of Ecology and Systematics 12, 405e437. McArdle, B.H., Anderson, M.J., 2001. Fitting multivariate models to community data: a comment on distance-based redundancy analysis. Ecology 82, 290e297. O’Connor, N.E., Crowe, T.P., 2005. Biodiversity loss and ecosystem functioning: distinguishing between number and identity of species. Ecology 86, 1783e1796. Otway, N.M., Gray, C.A., Craig, J.R., McVea, T.A., Ling, J.E., 1996. Assessing the impacts of deepwater sewage outfalls on spatially-and temporally-variable marine communities. Marine Environmental Research 41, 45e71. Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology: An Annual Review 16, 229e311. Pianka, E.R., 1970. On r- and K-selection. The American Naturalist 104, 592. Saunders, R.J., Connell, S.D., 2001. Interactive effects of shade and surface orientation on the recruitment of spirorbid polychaetes. Austral Ecology 26, 109e115. Schramm, W., 1996. The Baltic Sea and its transition zones. In: Schramm, W., Nienhuis, P.H. (Eds.), Marine Benthic Vegetation e Recent Changes and the Effects of Eutrophication. Springer, Berlin, pp. 131e164. Skilleter, G.A., 1996. Validation of rapid assessment of damage in urban mangrove forests and relationships with molluscan assemblages. Journal of the Marine Biological Association of the United Kingdom 76, 701e716. Smith, S.D.A., 2005. Rapid assessment of invertebrate biodiversity on rocky shores: where there’s a whelk there’s a way. Biodiversity and Conservation 14, 3565e3576. Terlizzi, A., Benedetti-Cecchi, L., Bevilacqua, S., Fraschetti, S., Guidetti, P., Anderson, M.J., 2005a. Multivariate and univariate asymetrical analyses in environmental impact assessment: a case study of Mediterranean subtidal sessile assemblages. Marine Ecology Progress Series 289, 27e42. Terlizzi, A., Scuderi, D., Fraschetti, S., Anderson, M.J., 2005b. Quantifying effects of pollution on biodiversity: a case study of highly diverse molluscan assemblages in the Mediterranean. Marine Biology 148, 293e305. Toner, P., Bowman, J., Clabby, K., Lucey, J., McGarrigle, M., Concannon, C., Clenaghan, C., Cunningham, P., Delaney, J., O’Boyle, S., MacCárthaigh, M., Craig, M., Quinn, R., 2005. Water Quality in Ireland 2001e2003. Environmental Protection Agency, Wexford, Ireland. UN CBD, 1992. United Nations Convention on Biological Diversity, 1992. Convention Text. http://www.biodiv.org/convention/articles.asp. UN WSSD, 2002. United Nations World Summit on Sustainable Development, 2002. Information Sources. http://www.un.org/esa/sustdev/index.html. UNESCO, 2006. A Handbook for Measuring the Progress and Outcomes of Integrated Coastal and Ocean Management. In: Intergovernmantal Oceanographic Commission Manuals and Guides, vol. 46. ICAM, Dossier, Paris. Valiela, I., 2006. Global Coastal Change. Blackwell Publishing Oxford, UK. Warwick, R.M., Clarke, K.R., 1993. Increased variability as a symptom of stress in marine communities. Journal of Experimental Marine Biology and Ecology 172, 215e226. Wells, E., Wilkinson, M., Wood, P., Scanlan, C., 2007. The use of macroalgal species richness and composition on intertidal rocky seashores in the assessment of ecological quality under the European Water Framework Directive. Marine Pollution Bulletin 55, 151e161. Widdows, J., Donkin, P., 1992. Mussels and environmental contaminants: bioaccumulation and physiological aspects. In: Gosling, E. (Ed.), The Mussel Mytilus: Ecology, Physiology, Genetic and Culture. Elsevier Press, Amsterdam, pp. 383e424. Williams, G.A., 1996. Seasonal variation in a low shore Fucus serratus (Fucales, Phaeophyta) population and its epiphytic fauna. Hydrobiologia 327, 191e197. Worm, B., Lotze, H.K., Boström, C., Engkvist, R., Labanauskas, V., Sommer, U., 1999. Marine diversity shift linked to interactions among grazers, nutrients and propagule banks. Marine Ecology Progress Series 185, 309e314.

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Nutrient enrichment and variation in community structure on rocky shores