Differential processing of anthropogenic carbon and nitrogen in benthic food webs of A Coruña (NW Spain) traced by stable isotopes

Author's Accepted Manuscript Differential processing of anthropogenic carbon and nitrogen in benthic food webs of A Coruña (NW Spain) traced by stable isotopes Antonio Bode, Consolación Fernández, Carmen Mompeán, Santiago Parra, Fernando Rozada, Joaquín Valencia-Vila, Inés G. Viana PII: S0967-0645(13)00374-3 DOI: http://dx.doi.org/10.1016/j.dsr2.2013.09.033 Reference: DSRII3520 To appear in: Deep-Sea Research II Cite this article as: Antonio Bode, Consolación Fernández, Carmen Mompeán, Santiago Parra, Fernando Rozada, Joaquín Valencia-Vila, Inés G. Viana, Differential processing of anthropogenic carbon and nitrogen in benthic food webs of A Coruña (NW Spain) traced by stable isotopes, Deep-Sea Research II, http://dx.doi.org/10.1016/j.dsr2.2013.09.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. www.elsevier.com/locate/dsr2 1  Differential processing of anthropogenic carbon and nitrogen in benthic food webs of A Coruña (NW Spain) traced by stable isotopes Antonio Bode*1, Consolación Fernández2, Carmen Mompeán1, Santiago Parra1, Fernando Rozada1,3, Joaquín Valencia-Vila1 and Inés G. Viana1 * e-mail: antonio.bod[email protected] 1 Instituto Español de Oceanografía. Centro Oceanográfico de A Coruña. Apdo. 130. 15080 A Coruña, Spain 2 Unidad de Ecología. Departamento de Biología de Organismos y Sistemas. Universidad de Oviedo. 33071 Oviedo, Spain 3 Present address: Instituto de Ganadería de Montaña, CSIC-Universidad de León, Finca Marzanas, Ctra. Grulleros, 24346 León, Spain Abstract In this study the effect of inputs of organic matter and anthropogenic nitrogen at small spatial scales were investigated in the benthos of the Ria of A Coruña (NW Spain) using stable carbon and nitrogen isotopes. This ria is characteristically enriched in nutrients provided either by marine processes (as coastal upwelling) or by urban and agricultural waste. Stable isotope composition in trophic guilds of infaunal benthos revealed spatial differences related to their nutrient inputs. The main difference was the presence of an additional chemoautotrophic food web at the site with a large accumulation of organic matter. The enrichment in heavy nitrogen isotopes observed in most compartments suggests the influence of sewage-derived nitrogen, despite large inputs of marine nitrogen. Macroalgae (Fucus vesiculosus) resulted significantly enriched at the site influenced by estuarine waters. In contrast, no differences were found in mussels (Mytilus galloprovincialis), thus suggesting a major dependence on marine nutrient sources for this species. However, the estimations of anthropogenic influence were largely dependent on assumptions required to model the different contributions of sources. The 2  measurement of stable isotope signatures in various compartments revealed that, despite anthropogenic nutrients are readily incorporated into local food webs, a major influence of natural marine nutrient sources cannot be discarded. Keywords: δ15N, δ13C, subtidal, intertidal, wastewater, upwelling, chemoautotrophy 1. Introduction Coastal food webs are increasingly altered by pressures from eutrophication and pollution as most of the human population concentrates near the coast. Anthropogenic nutrients, as those derived from urban and agricultural wastewaters have been identified as one of the main causes of changes in the structure and composition of food webs because of their impact in the nutrient cycles (McClelland and Valiela, 1998; Castro et al., 2007). The excess nutrients may lead to large increases in primary production and clear signs of eutrophication, including hypoxia when the remineralisation of the produced organic matter exhausts the oxygen in the water, but often the changes remain unnoticed because some coastal ecosystems are already highly productive. Estuaries, for instance, display enhanced production and specific food webs related to their diverse inputs of nutrients from marine and terrestrial sources. Similarly, coastal upwelling causes elevated levels of primary production by the input of significant amounts of nutrients from deep waters. The Galician coast (NW Spain) is one paradigmatic region to study the effects of the anthropogenic and natural sources of nutrients. It is located at the northern limit of the eastern boundary upwelling system of the N Atlantic and characterised by high primary production due to the input of nutrient-rich deep ocean waters near the coast (Alvarez-Salgado et al., 2002). The fertilising effect of the upwelling is amplified by the rias and bays that retain and exchange water with the shelf and favour rapid mineralisation of the produced organic matter (AlvarezSalgado et al., 1997). Estuarine zones in the rias are generally small because of the low flow of most rivers in this region (Rio Barja and Rodriguez Lestegás, 1996) and upwelling dynamics 3  dominate nutrient fluxes (Nogueira et al., 1997). However, most of the urban and industrial population of Galicia concentrates near the rias. Near 57% of a total population of 1.5 million inhabitants lives in the two major urban areas of Vigo and A Coruña (Precedo Ledo et al., 2008) located inside two of the main rias. The Ria of A Coruña is formed by a bay of 15.7 km2 and a small estuarine zone (Ria do Burgo) in the mouth of the river Mero (Cosme de Avilés and Prego, 1995). The river basin drains 385 km2 but its mean annual flow is only 6.6 m s-1. The marine influence is high in the bay (Cabanas et al., 1987) reflecting the nutrient dynamics driven by the winter mixing and summer upwelling in the nearby shelf (Casas et al., 1997; Bode et al., 2004a, b). The influence of estuarine waters is restricted to the inner bay where there was also an effect of the harbour infrastructures causing enhanced nutrient and phytoplankton concentrations (Varela et al., 1994; Varela and Prego, 2003). Urban population near the ria amounts ca. 250,000 inhabitants according to the Spanish Official Population Census (http://www.ine.es/inebase) thus having a large potential impact on nutrient inputs to coastal waters. Urban and industrial developments in the area collect and treat wastewater in a water treatment plant recently improved with secondary and tertiary treatment (http://augasdegalicia.xunta.es/es/edars/ACOR.html). This plant is designed for a population of up to 600,000 inhabitants and the treated waters reach the open ocean through a submarine outfall located outside and 7.5 km west of the mouth of the bay. Nevertheless the possible influence of diffuse inputs of nutrients to the ria by local point sources, occasional leaks in the sanitation system or overflows during storms is not known. Discrimination between nutrient sources for species or food webs can be made by measuring the natural abundance of stable isotopes. As light isotopes are mobilised faster in chemical reactions than heavy ones, each molecule has a characteristic isotopic signature reflecting the pathways followed in its formation. The reactants are progressively enriched in heavy isotopes while the products are relatively depleted. The isotope enrichment of the reactant (ε) is characteristic of each reaction (Mariotti et al., 1981; Ruby et al., 1987; Wasser et al., 1998; Needoba et al., 2004) and allows for a differentiation of nutrients with different origins (Heaton, 1986). Nitrogen from 4  urban and agricultural wastewaters is generally enriched in heavy isotopes because of the large fractionation associated with nitrification (Mariotti et al., 1981). This feature was employed in numerous studies to determine the influence of wastewater in coastal systems (McClelland and Valiela, 1998; Savage and Elmgren, 2004; Castro et al., 2007; Bode et al., 2011; Viana et al., 2011; Viana and Bode, 2013). Similarly carbon isotopic signatures reflect the origin of the organic matter in marine food webs (Spiro et al., 1986; Cifuentes et al., 1988; Dando and Spiro, 1993; Machas et al., 2003; Martineau et al., 2004; Bode et al., 2006; Malet et al., 2008; Sakamaki and Richardson, 2008; Bode et al., 2011). However, previous studies focus on a few species or benthic compartments, thus limiting the generalisation of their conclusions to the whole ecosystem. The objective of the present study is to determine the effect of inputs of organic matter and anthropogenic nitrogen at small spatial scales in the Bay of A Coruña (NW Spain). For this purpose the natural abundance of stable carbon and nitrogen isotopes was examined in different compartments, including water, seston, subtidal sediments and infauna and intertidal organisms. Each compartment was selected as representative of nutrient effects at instantaneous (surface water) or longer time-scales (sediments and benthic organisms). Intertidal benthos was chosen as indicator of the contribution of different nutrient sources in surface water, while subtidal infauna was intended to reflect nutrient sources near the sediment. The seasonal variability was taken into account by sampling across annual seasons and the estimations of anthropogenic contributions included variations in isotopic fractionation. 2. Methods 2.1 Subtidal sediments and infauna Samples of subtidal sediments and infauna were collected bimonthly (January 2010 to November 2011) at stations B2 (9 m depth) and DB (17 m depth) using R/V Lura (Fig. 1). These stations we representative of the spatial variability of infaunal benthos in the area (LópezJamar and Mejuto, 1985). At each sampling date five box-core samples (Bouma-type box-corer, 5  sampling area = 0.0175 m2) were pooled to obtain representative estimates of infaunal species composition and biomass (López-Jamar et al., 1986). The upper 2 cm of the core sample sediments were analysed for total organic matter content (ash-free dry weight) and granulometric characteristics (Buchanan, 1984). In addition particulate organic carbon and nitrogen concentrations (POC and PON) and stable isotope abundance were determined in subsamples of these sediments. The infaunal samples were sieved through a 0.5 mm mesh, anaesthetized with magnesium chloride (7% w/v), and then preserved in 5% buffered formaldehyde previously containing Rose Bengal as a staining agent to facilitate the sorting of organisms. Specimens intended for stable isotope determinations were obtained from additional box-core samples, sorted immediately after sampling in the laboratory and kept for 24 h in small aquaria containing filtered seawater to facilitate evacuation of gut contents. For trophic analysis species were classified in trophic guilds (filter feeders, deposit feeders, omnivores and carnivores) from the information provided in the literature. 2.2. Water Temperature, salinity and chlorophyll-fluorescence profiles of water above each subtidal sediment stations were obtained at each sampling date using a CTD SBE-25. Fluorescence was converted to chlorophyll-a concentrations after calibration with acetonic extracts of discrete water samples collected with Niskin bottles. In addition, surface water nutrients were determined in samples collected monthly during 2011 at stations W1 and W2, located near the sediment stations and, according to previous studies (Cabanas et al., 1987; Varela et al., 1994; Varela and Prego, 2003), representative of marine and estuarine end-members, respectively (Fig. 1). Additional water samples were collected near the coast concurrently with samples of intertidal organisms. Dissolved nitrate, nitrite and ammonium concentrations were determined by segmented-flow analysis (Casas et al., 1997). 6  2.3. Intertidal benthos Samples of the brown alga Fucus vesiculosus and the mussel Mytilus galloprovincialis were collected monthly during 2010 and 2011 at two intertidal sites (Fig. 1). Mera was located at the outer bay in the less urbanized part of the study area. In contrast, Ria do Burgo was located in the area of direct estuarine influence and heavy urban population. Algal samples for stable isotope determinations were collected from the apical 2 cm of the thallus of 25-35 cm long specimens, while mussel samples were collected from the adductor muscle of 40-50 cm (shell length) individuals at both sites. 2.4. Stable isotope analysis Sediment and biological samples for stable isotope determination were dried (50 ⁰C, 24 h), ground to a fine powder and weighted (± 0.002 mg). The isotopic composition of total nitrate (NO3 -+NO2 -) was determined by previous conversion into ammonium and later recovery of ammonium on a solid phase (Ahad et al., 2006). The procedure is an adaptation of the diffusion method (Sigman et al., 1997) involving the incubation of samples in two steps. First, aliquots of the samples were incubated (50 °C, 1 week) in the same collecting flask without cap to reduce the volume and concentrate nitrate. Ashed MgO was added to raise pH above 9.7 to remove ammonia by volatilization. In the second step (50 °C, 2 weeks), ashed Devarda´s alloy was added to the reduced volume sample to convert nitrate and nitrite into ammonium. The high pH (>11) of the mixture ensured also the conversion of ammonium into ammonia gas that was collected on a sterilized glass-fibre disk (Whatman, GF/F), acidified with 0.5 ml of 0.25N H2SO4 and hooked on a needle fixed to the inner side of the flask (Slawyk and Raimbault, 1995). After the incubation, the disk filters containing ammonium sulphate were dried and prepared for isotopic analysis. The stable isotope composition of ammonium was determined in another aliquot of the water samples by an adaptation of the diffusion method (Holmes et al., 1998). This method involves gas-phase diffusion as described for the second step of the total 7  nitrate extraction. In all cases corrections for isotopic fractionation during the whole incubation and diffusion steps were made (Holmes et al., 1998). Samples were placed in tin capsules and introduced into an isotope-ratio mass spectrometer (Thermo Finnigan Mat Delta Plus) via an element analyser (Carlo Erba CHNSO 1108). Isotopic results are expressed in delta notation (δ15N or δ13C) relative to atmospheric N or VPDB ( Bode et al., 2011). Precision (SE of 5 replicates) was better than 0.05 ‰ for either δ15N or δ13C. The coefficient of variation of triplicate sample aliquots was always <2%. Precision for δ15N determinations in both nitrate and ammonium was better than 0.4 ‰. The contributions of anthropogenic (fa) and marine (1-fa) sources to nitrogen composition of primary producers (δ15NP) were estimated using a mixing model of two end members: δ15NP = fa δ15Na + (1-fa) δ15Nm - ε where δ15NP is the isotopic composition of phytoplankton, microphytobenthos or macroalgae, estimated from the analysis of seston, surface sediments or F. vesiculosus, respectively. The isotopic composition of nitrogen sources was represented by the mean value of total nitrate in surface marine waters (δ15Nm) or anthropogenic nitrogen (δ15Na). As it was difficult to obtain representative samples from the diffuse sources of anthropogenic nitrogen in the study area, we used a mean δ15Na value obtained from measurements in samples of urban wastewater released from several water treatment plants in the study region (17.8±0.6‰ se, n=7). The model included an isotopic enrichment factor (ε) between the source (nitrate) and the product (primary producer nitrogen). Several values of ε were employed to constrain the estimated contributions. 2.5. Statistical analysis Differences between stations in the values of the environmental variables were determined using non parametric ANOVA (Mann-Whitney U) while differences in isotopic composition among trophic guilds were analysed using parametric ANOVA and a posteriori tests (Dunnett C). As the main objective of this study is to compare different locations in the study area, all values 8  from the same sampling site were averaged. The species composition of the infaunal communities in subtidal sediments was analysed using a cluster analysis (Bray-Curtis distance, group average method) on log-transformed species biomass for each sampling date. Only species contributing >0.1% to total biomass were selected for this analysis. The contribution of species to similarity within each station was determined using the procedure SIMPER of PRIMER statistical package (Clarke and Warwick, 2001). 3. Results 3.1. Water and sediments Surface water from the station W2 was significantly less saline than water from W1 but otherwise both stations have similar mean values of SST, nitrogenous nutrients or chlorophyll (Table 1). The influence of the estuarine waters was more evident in the seston composition, as POC and PON values at W2 waters were ca. 2.5 times higher than those of W1, having also an excess of carbon as indicated by the C:N ratio. However, there were no significant differences in the average isotopic composition of seston or water at both stations. The water collected at both intertidal sampling sites did not show either differences in the water variables analysed, except in the δ15N values of nitrate that were significantly lower at the estuarine site (Table 1). Similar results were found when comparing water characteristics above both infauna sampling stations, as both have equivalent temperature, salinity, and integrated chlorophyll values (Table 2). The only significant difference was in the average amount of light reaching the sediment surface (21% at St. B2 and 7% at St. DB). Despite the similarities in water-column properties, there were large differences in sediments from the infaunal stations (Table 3). Sediments from St. DB showed a mixture of sands but were characterised mainly by a larger fraction of mud and organic matter than those from St. B2. Total organic matter (%AFDW), carbon (%Ctotal) and nitrogen content at St. DB were >5, 15  Nitrate derived from wastewaters and manure is characteristically enriched in 15N because of the large fractionation associated with nitrification and dinitrification processes (Mariotti et al., 1981) with both nitrate and ammonium δ15N generally above 10‰ (Tucker et al., 1999; Savage and Elmgren, 2004). The value assumed for δ15Na is comparable with that found in wastewaters from other areas even it exceeded our measurements in the water, sediments or biota. This would indicate that there were no large inputs from urban or agricultural wastewaters to the bay, despite of the large urban population. This is supported by the small enrichment in 15N (<2‰) found between nitrate, seston and surface sediments (Tables 1 and 3). However, there were relatively high enrichments in some guilds (e.g. DF) or species (F. vesiculosus), suggesting the potential impact of nitrogen from wastewater, at least in the inner zone of the bay. The enrichment could be explained by the accumulation of heavy nitrogen in structural tissues with low turnover rates while light nitrogen is rapidly exchanged with the water, as found in other studies (Savage and Elmgren, 2004). In addition, diffuse sources of heavy nitrogen may affect benthic organisms at small spatial scales. Recent measurements of δ15N in nitrate from interstitial waters in upper 10 cm of sediments from the inner estuary (unpub. results) produced values (mean±se 17.2±0.9‰, n=3) which were close to those found in wastewaters. This suggests that estuarine sediments play a major role of in the remineralisation of diffuse inputs of wastewater nitrogen. Our estimations indicate an average low input of wastewater (anthropogenic) nitrogen for seston or sediments, and even for F. vesiculosus in the estuarine zone, but these estimations were largely dependent on the isotopic fractionation employed. Assimilation of nitrate is generally associated with isotopic fractionation factors between 020‰, both in phytoplankton (Waser et al., 1998; Needoba et al., 2004) and macroalgae (Naldi and Wheeler, 2002) but most estimates are near 5‰. In contrast assimilation of ammonium is assumed to have almost no fractionation at the low ambient concentrations normally found in marine waters (Waser et al., 1998). Therefore the use of a mean fractionation factor of 3‰ in our estimates of anthropogenic nitrogen inputs represents a conservative compromise between the assimilation of both nitrate and ammonium by phytoplankton and macroalgae. Notwithstanding the upwelling pulses of nitrate in the study area, studies with isotopic tracers 16  indicated that at least phytoplankton uses equivalent amounts of nitrate and ammonium at seasonal time scales (Bode et al., 2004a). The resulting low influence of anthropogenic nitrogen is consistent with previous studies in the Galician coast (Bode et al., 2006; 2011; Viana et al., 2011; Viana and Bode, 2013). However, the large influence of the value of the isotopic fractionation factor employed in the estimated contribution of different nitrogen sources is not generally acknowledged in pollution studies (Savage and Elmgren, 2004; Lamb et al., 2012) and our results add to the growing evidence that δ15N values alone do not provide an unequivocal proof of a major influence of anthropogenic nitrogen on coastal ecosystems. Acknowledgements We are grateful to the crew of R/V Lura for their collaboration during water and sediment sampling. Nutrient concentrations were determined by R. Carballo and sediment characteristics by J. F. Feijoo. We also acknowledge the participation of A.F. Lamas in sample collection and preparation for stable isotope analysis and of M.C. Vázquez in the analysis of infaunal species. Stable isotope determinations were made by the Servicio de Apoyo a la Investigación of the Universidad de A Coruña (Spain). This research was funded by projects ANILE (CTM200908396 and CTM2010-08804-E) of the Plan Nacional de I+D+i (Spain), and RADIALES of the Instituto Español de Oceanografía (IEO, Spain). C.M. and I.G.V. were supported by FPI fellowships from IEO and from Ministerio de Economía y Competividad (Spain), respectively. References Ahad, J., Ganeshram, R., Spencer, R., Uher, G., Gulliver, P., Bryant, C., 2006. Evidence for anthropogenic 14C-enrichment in estuarine waters adjacent to the North Sea. Geophysical Research Letters 33(8), doi: 10.1029/2006GL025991. Alvarez-Salgado, X.A., Castro, C.G., Pérez, F.F., Fraga, F., 1997. 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Viana, I.G., Bode, A., 2013. Stable nitrogen isotopes in coastal macroalgae: geographic and anthropogenic variability. Science of the Total Environment 443, 887-895. 22  Waser, N.A., Yin, K.D., Yu, Z.M., Tada, K., Harrison, P.J., Turpin, D.H., Calvert, S.E., 1998. Nitrogen isotope fractionation during nitrate, ammonium and urea uptake by marine diatoms and coccolithophores under various conditions of N availability. Marine Ecology Progress Series 169, 29-41. 23  8.44° 8.40° 8.36° 8.32° 43.32° 43.36° 43.40° Mera Ria do Burgo DB B2 W1 W2 A Coruña 8° 4° 0° 36° 40° 44° 48° Iberian Peninsula Figure 1. Location of sampling stations for subtidal infauna (DB and B2), intertidal benthos (Mera and Ria do Burgo) and surface water properties (W1 and W2) in the Bay of A Coruña (NW Spain). 24  Group average DB DB DB DB DB DB B2 B2 B2 B2 B2 B2 Sam p les 100 80 60 40 20 0 Similarity Transform: Log(X+1) Resemblance: S17 Bray Curtis similarity St. DB St. B2 Figure 2. Cluster of infaunal samples (group average method) computed from Bray-Curtis similarity index on log-transformed biomass values of species contributing at least 0.1% to total biomass. 31  SSS 30.4 2.4 34.0 0.6 n.s. NO3 - 38.62 33.77 14.21 10.65 n.s. NO2 - 0.76 0.15 0.53 0.11 n.s. NH4 + 4.72 1.13 3.51 1.32 n.s. δ15NNH4 0.2 0.7 0.2 0.7 n.s. δ15NNO3 3.1 0.2 4.2 0.3 0.007 Table 2. Mean (se: standard error) values of variables measured in the water column above infauna stations (B2 and DB). SST: sea surface temperature (°C), SSS: sea surface salinity, tbottom: temperature 1 m above the bottom (°C), Chlaint: water column integrated chlorophyll-a, %PARbottom: percent of surface irradiance (PAR) at the bottom. number of samples = 12. P: significance of Mann-Whitney U for differences between stations. n.s.: P>0.05 B2 DB mean se mean se P SST 14.95 0.49 14.65 0.52 n.s. SSS 33.82 0.51 34.43 0.59 n.s. tbottom 14.82 0.34 14.34 0.28 n.s. Chlaint 16.01 5.46 45.17 13.96 n.s. %PARbottom 20.81 3.13 6.66 1.37 0.001 Table 3. Mean (se: standard error) values of sediment variables measured at the infauna stations. Q50 φ: median of the distribution of particle diameter (φ = log2(mm)), S0: selection coefficient, %Coarse sand: percent of >500 µm diameter particles (by weight), %Fine sand: percent of 62500 µm diameter particles (by weight), %Mud: percent of <62 µm diameter particles (by weight), %AFDW: percent ash-free dry weight, %Ctotal: percent total carbon (including 32  carbonates), %N: percent nitrogen, C:N: molar C:N ratio, δ13Ctotal: natural abundance of 13C (including carbonates), δ13Corg: natural abundance of 13C (organic matter), δ15N: natural abundance of 15N. number of samples = 9. P: significance of Mann-Whitney U for differences between stations. n.s.: P>0.05. Station B2 DB mean se mean se P Q50 φ 2.95 0.01 3.62 0.08 0.000 S0 1.44 0.01 2.06 0.03 0.000 %Coarse sand 1.02 0.14 3.20 0.37 0.000 %Fine sand 91.19 0.46 56.61 1.74 0.000 %Mud 7.79 0.39 40.19 1.90 0.000 %AFDW 2.07 0.18 10.30 0.55 0.000 %Ctotal 1.90 0.16 4.60 0.12 0.000 %N 0.03 0.00 0.20 0.01 0.000 C:N 76.86 7.97 27.41 1.14 0.001 δ13Ctotal -2.8 0.3 -13.4 0.3 0.000 δ13Corg -25.3 0.1 -24.9 0.1 n.s. δ15N 5.2 0.1 5.1 0.1 n.s. Table 4. Mean (se: standard error) values of δ13C, δ15N and biomass (B, mg fresh weight m-2) for selected infaunal species at stations B2 and DB. The taxonomic group (all species) and trophic guild (only species analysed for stable isotopes) are indicated. %sim: percent contribution of species to Bray-Curtiss similarity for each station (SIMPER analysis, Clarke and Warwick, 2001). n: number of samples (or individuals for stable isotopes). FF: filter feeder, FFs: filter feeder with symbionts, DF: deposit feeder, O: omnivore, P: predator. 33  δ13C δ15N B2 DB Group species Gui ld me an s e me an s e n %si m mea n se n %si m mea n se n Mollusca Pharus legumen FF - 15. 5 0. 17.7 0. 29 16. 8 760 6.2 529 2.4 6 --- --- --- - - - Polychaet a Paradoneis armata --- --- -- - --- -- - - - - 11. 1 416. 8 61.2 6 --- --- --- - - - Mollusca Chamelea gallina FF - 17. 4 0. 37.3 0. 2 1 29.0 228 9.3 138 8.0 5 --- 2.6 --- 1 Others Nemertea --- --- -- - --- -- - - - -8.3 293. 4 215. 7 7 --- 251 6.3 227 1.3 6 Polychaet a Magelona filiformis --- --- -- - --- -- - - - - 7.3 80.5 23.7 6 --- --- --- - - - Mollusca Myrtea spinifera FFs - 27. 5 0. 5 - 1.9 0. 5 1 8 --- --- --- - - - 10. 4 177 5.0 574. 5 6 Polychaet a Notomastus latericeus DF - 17. 5 0. 58.3 0. 4 9 --- 75.5 74.3 4 8.8 435. 1 115. 8 7 Polychaet a Euclymene oerstedi DF - 18. 1 0. 38.7 0. 4 7 --- --- --- - - -8.3 528. 5 233. 6 7 34  Polychaet a Chaetozone gibber DF - 19. 3 0. 47.6 0. 3 8 --- 0.3 --- 1 8.0 792. 6 213. 4 7 Mollusca Nucula sp. --- --- -- - --- -- - - - - --- 69.7 68.9 2 7.4 455. 8 131. 1 6 Polychaet a Chaetozone setosa --- --- -- - --- -- - - - - --- --- --- 0 7.2 100 6.5 808. 8 7 Echinode rmata Leptosynapta bergensis DF - 16. 6 0. 3 11. 8 1. 5 4 --- 155. 1 91.8 6 --- 75.7 28.8 5 Echinode rmata Leptosynapta inhaerens DF - 16. 7 0. 4 10. 8 0. 0 3 --- 99.8 --- 1 --- 362. 8 337. 0 2 Mollusca Abra nitida DF - 18. 1 -- - 6.6 -- - 1--- 0.9 0.64--- 131. 7 71.2 3 Mollusca Corbula gibba FF - 16. 9 0. 27.1 0. 2 8 --- --- --- - - ---- 560. 6 367. 1 3 Mollusca Mactra stultorum FF - 15. 9 0. 17.9 0. 2 7 --- 581 7.6 324 1.4 5 --- 237 9.2 --- 1 Mollusca Nassarius reticulatus O - 16. 5 0. 4 10. 8 0. 3 1 4--- 412 5.4 363. 3 2 --- 100 0.0 465. 5 4 35  Mollusca Thyasira flexuosa FFs - 28. 5 0. 3 - 6.3 0. 7 5 --- 0.3 --- 1 --- 112. 1 32.3 6 Polychaet a Diopatra neapolitana C - 17. 3 0. 3 10. 6 0. 4 5 --- 569. 2 354. 7 3 --- --- --- - - - Polychaet a Glycera sp. C - 17. 5 0. 2 11. 3 0. 6 6 --- 3.7 3.0 3 --- 369. 9 58.5 2 Polychaet a Nephtys hombergii C - 16. 7 0. 49.2 0. 6 6 --- 384. 3 285. 6 6 --- 15.0 11.7 4