Frontiers in Marine Science (Dec 2015)
The use of pelagic fish as proxies of environmental contamination: a case study with sardine populations
Abstract
The use of bioindicators to analyze marine ecosystems contamination is often made difficult due to the absence of appropriate species. Pelagic fish species, captured by commercial fishing fleets around the world, can be successfully used to assess contaminant levels, by determining their body burden in specific compounds. However the study of biological responses elicited by such compounds, through the analysis of biomarkers, is highly dependent on the physiological and reproductive status of the organisms. Such confounding factors elicit seasonal fluctuations that difficult the extrapolation of data. Sardine (Sardina pilchardus) is a marine species common in the North Atlantic Ocean, being easily available through commercial fisheries. The present work intended to explore the potential of this species in biomonitoring studies, by simultaneously using enzymatic biomarkers and condition indices determined in fish landed in three commercial harbors along the west coast of Portugal. This strategy allowed devising spatial and temporal patterns in the sardine metapopulation. Results evidenced significant variability in both biochemical and physiological profiles of the fish, which were coherent among all sampling sites. Throughout the year, large seasonal differences for most markers were reported, which were strongly linked to the reproductive cycle and its physiological consequences (acquisition of energy, mobilization of energy reserves, etc.). It was possible to conclude that seasonality acts as a strong factor underlying chronological physiological adaptations, influencing biochemical markers that are usually employed as indicators of contamination. These effects can limit the usefulness of such a biomarker approach unless seasonality is not accounted for, and if no background values are known from previous studies. In this sense, studies such as this are pivotal to establish a baseline for biomonitoring studies. Also, despite the difficulty in interpreting the obtained biomarker profiles, our data suggest that S. pilchardus may be a successful candidate species to serve as bioindicator in oceanic biomonitoring studies. The use of individuals captured by commercial fisheries is a promising approach for environmental assessments, and studies on other pelagic species should follow.
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