Evaluating stable isotopic signals in bivalve Pinna nobilis under different human pressures

•Differences between isotopic values of Pinna nobilis in MPAs and non-MPAs•Pinna nobilis has a marked isotopic response to human pressures.•Bivalves in eutrophic environments have higher growth rates but lower survival rates than those in oligotrophic environments.•Pelagic food sources had a major contribution to P. nobilis' diet than benthic.•Benthic filter feeders are suitable indicators in coastal waters.

Increasing human pressures, including recreational boating, on the coastline is a growing sector which has adverse effects on marine biota and habitats. Benthic filter feeders are good indicators of changes in marine ecosystems providing information of biotic response to anthropogenic pressures. This investigation has aimed to evaluate changes in δ13C and δ15N isotopic values, growth and survival rates of Pinna nobilis in different marine environments exposed to distinct human activities. In addition, Bayesian isotopic models have been applied to decipher food sources contributing to the filter feeders' diet. Results have revealed isotopic variation of adductor muscle of P. nobilis according to a human gradient. Similarly, individuals of eutrophic environments showed higher growth rates than those from oligotrophic conditions, however chance of survival in eutrophic environments was lower, especially during the first life stages of P. nobilis. Additionally, similar trends were demonstrated between adductor muscle and mantle tissue of examined individuals, making the latter tissue an appropriate non-lethal sampling technique having implications for environmental and biological assessment and conservation issues. Results have also shown that P. nobilis seems to be relying on pelagic rather than benthic related food sources. Properly assessed, filter feeders can provide information on their interaction with human derived activities, identifying possible alterations of marine systems at an early stage.