Andrisoa A., Stieglitz Thomas, Raimbault P., Rodellas V., Lartaud F. (2023). Tracing groundwater sources in coastal food webs : nitrogen and carbon isotope values in mussels in a Mediterranean lagoon. Estuaries and Coasts, [Early access], [14 p.]. ISSN 1559-2723.
Titre du document
Tracing groundwater sources in coastal food webs : nitrogen and carbon isotope values in mussels in a Mediterranean lagoon
Andrisoa A., Stieglitz Thomas, Raimbault P., Rodellas V., Lartaud F.
Source
Estuaries and Coasts, 2023,
[Early access], [14 p.] ISSN 1559-2723
While the role that groundwater discharge plays in supporting primary production in coastal ecosystems is well recognized, there is still limited evidence on its impacts higher up the food chain. In this study, we investigate the role of groundwater discharge in supplying nitrogen and carbon to the Mediterranean mussels (Mytilus galloprovincialis) in the Salses-Leucate lagoon (France). Nitrogen (delta N-15) and carbon (delta C-13) isotope values in the mantle and gill tissues of Mediterranean mussels are used to trace nitrogen and carbon sources at groundwater-exposed sites and a control site. Our results show similar isotope values for mantle and gill tissues, likely due to relatively stable environmental conditions in the study sites and to the biochemical composition of tissues. Diet shift, fractionation, and the physiological function of tissues could also explain this observation. delta N-15 values in mussel tissues increase overall in winter at both the groundwater-influenced sites (4.9 to 7.8 parts per thousand) and the control site (3.4 to 8.5 parts per thousand) in comparison with those in autumn (3.5 to 7.4 parts per thousand at the groundwater-influenced sites and 4.5 to 6.9 parts per thousand at the control site), likely due to reduced food supply and slower metabolism in winter, resulting in N-15 enrichment. In contrast, mussel delta C-13 values decrease in winter at the groundwater-influenced sites (- 23.4 to - 21.6 parts per thousand) and the control site (- 22.0 to - 19.0 parts per thousand), suggesting input from C-13-depleted sources originating from groundwater input. The comparison of the isotopic values of mussel tissues and potential food sources indicates that the main diet of M. galloprovincialis in the Salses-Leucate lagoon is a mixture of groundwater particulate organic matter (POM), lagoon POM, and marine POM (POM as a proxy of phytoplankton). Depleted delta C-13 values in mussel tissues, particularly at groundwater-exposed sites, provide evidence of uptake of groundwater-derived nutrients. The ecological benefit of groundwater input on filter feeders results from local increases in food availability (mainly phytoplankton), supported by groundwater-derived nitrogen and carbon. In summary, this study shows the combined (a) indirect effect of groundwater discharge on mussel growth via uptake of their food, phytoplankton, and (b) the likely direct feeding of groundwater POM by M. galloprovincialis. It thus shows the important ecological implication of groundwater inputs in coastal lagoon food webs.
Plan de classement
Sciences du milieu [021]
;
Limnologie biologique / Océanographie biologique [034]
