Stable Isotope Analysis of Oysters as a Tool for Environmental Monitoring in a Marine Extractive Reserve

ABSTRACT The stable isotopes δ 13 C and δ 15 N are widely recognized and utilized as biomarkers for analysing trophic links, paleoenvironmental reconstruction, biogeography and nutrient sources. However, it is essential to further develop their applications, as their use in marine environmental monitoring is not as prominent. 13 C and 15 N have distinct signatures in organic compounds, which can be utilized to identify potential carbon and nitrogen sources. Marine bivalves are often employed in environmental studies as efficient bioindicators because sessile filter feeders tend to bioaccumulate pollutants. The present study analysed δ 13 C and δ 15 N in seston and oysters inhabiting two areas with different environmental conditions in a marine extractive reserve. The isotopic values were compared for two trophic levels and three oyster tissues, resulting in a broad view of local dynamics. Seston samples from Forno Beach (FB) exhibited depleted δ 13 C values, possibly reflecting a terrigenous carbon contribution in this area. Considering oyster tissues, δ 13 C and δ 15 N values in the hepatopancreas were similar to seston, possibly due to oysters' role as filter feeders, supporting the use of digestive tissues for assessing short‐term changes of environmental conditions. Moreover, isotope values for oyster gills and muscles suggest long‐term homogeneous conditions for Anjos Beach (AB) and FB, with a predominance of marine carbon and nitrogen sources. Our results underline the relevance of analysing bivalve tissues separately because they display different turnover rates and depict variable time frames of environmental conditions. This article provides valuable information on the variables that must be considered when applying stable isotope analysis in coastal environmental monitoring, highlights knowledge gaps and recommends best practices for future work in this area.