Spatial heterogeneity in the food web of a heavily modified Mediterranean coastal lagoon: stable isotope evidence

Abstract

International audienceWe investigated the food web structure of the Salses-Leucate Lagoon (northwestern Mediterranean) through delta C-13 and delta N-15 analysis of its benthic macrofauna and potential food sources. This lagoon was heavily human-modified during the 1970s, allowing permanent exchange with the open sea and an increase in salinity from that time. As a result, it exhibits a much less marked salinity gradient than the neighbouring lagoon ecosystems, which Suggests a priori that its food web structure is more homogeneous. In this environmental context, we assessed spatial variability in the isotopic composition of non-vagrant macrofauna in Salses-Leucate in relation to degree of connection with the open sea, anthropogenic inputs and the presence of oyster aquaculture. Overall, the main trophic pathway is based on suspended particulate organic matter and sedimented organic matter. However, there were marked spatial differences (at different scales) in both delta C-13 and delta N-15 values of macrofauna, which suggests an important feeding plasticity within each category of primary consumers at a small spatial scale. delta C-13 data showed that the contributions of the different food sources to the diet of primary consumers changed depending on distance from continental inputs, connection with the open sea and local primary producer coverage. Small-scale delta N-15 variability revealed a very localised influence of anthropogenic nitrogen output. Regarding the possible effect of aquaculture, the isotopic ratios of sediment and macrobenthos were not modified underneath the oyster lines with respect to the neighbouring area. Conversely, the isotopic signature of consumers living on the oyster lines contrasted with those living underneath. Therefore, our results suggest that a decoupling exists between the trophic pathways that occur in the water column and on the soft bottom of this shallow water ecosystem

Heterogeneity in food-web interactions of fish in the Mwanza Gulf, Lake Victoria: a quantitative stable isotope study

“…This approach has been used to compare foodweb structures between ecosystems, seasons and habitats (Carlier et al, 2009;Jackson et al, 2012;Doi et al, 2013;Abrantes et al, 2014), and to study the effects of invasive species on trophic interactions of populations (Jackson et al, 2012).…”

Resource utilization and trophic position of nematodes and harpacticoid copepods in and adjacent to <i>Zostera noltii</i> beds

“…Several studies during the last decade have used natural stable isotope ratios to elucidate the principal food sources of macrobenthos in seagrass beds, stressing the importance of seagrass-associated sources and/or microphytobenthos (MPB) (Lepoint et al, 2000;Kharlamenko et al, 2001;Moncreiff and Sullivan, 2001;Baeta et al, 2009;Carlier et al, 2009;Lebreton et al, 2011;Ouisse et al, 2012;Vafeiadou et al, 2013a). Less information is available for meiobenthos resource utilization in seagrass beds (Vizzini et al, 2000b(Vizzini et al, , 2002aBaeta et al, 2009;Leduc et al, 2009;Lebreton et al, 2011Lebreton et al, , 2012, with none of the studies including meiofauna at the level of feeding types, families, genera or species.…”

Contamination by trace metals and their trophic transfer to the biota in a Mediterranean coastal system affected by gull guano

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