Can a marine pest reduce the nutritional value of Mediterranean fish flesh?

Biological invasions are deemed as one of the most severe threats to biodiversity and can result in huge economic impacts on natural resources. Many studies have assessed structural changes caused by the introduction of nonindigenous species, but urgent questions remain to be answered about the complex indirect effects of invasive pests on marine biodiversity at the species and ecosystem level. Previous investigations focusing on the biological invasion by Caulerpa racemosa in the Mediterranean indicated that the lipophilic algal metabolite caulerpin accumulates in the tissues of the native edible white sea bream Diplodus sargus feeding on the exotic alga. The level of caulerpin in D. sargus has been thus used as an indicator of the trophic exposure of the fish to the seaweed and related with adverse effects on the fish health. In the present study, we show that the C. racemosa-based diet can also alter muscle fatty acids composition in the white sea bream by reducing the percentage of polyunsaturated fatty acids of the n-3 and n-6 series, such as eicosapentaenoic (C20:5), docosahexaenoic (C22:6) and arachidonic acids (C20:4). This represents both a real threat to the health of fish unable to biosynthesize these essential fatty acids and an impoverishment of an important source of essential fatty acids for human nutrition, which helps to prevent cardiovascular diseases, diabetes, hepatic steatosis, cancer and neurological disorders. On the whole, this work sheds light on an unexplored and critical aspect of biological invasions with implication on the health of both humans and the environment.