The green alga Caulerpa racemosa is a non-native, invasive species in the Mediterranean, and an
important stressor for several native organisms. The algal capacity to produce secondary metabolites has
been suggested to modulate success of the C. racemosa invasion, although many of potentially involved
biological pathways still remain unexplored.
In this respect, the aim of the present study was to investigate some molecular and cellular effects in
the white seabream Diplodus sargus, an ecologically key species, which included the alien C. racemosa in
its diet. Organisms were sampled in 2 seasonal periods from 3 locations of Southern Italy, each characterized
by different levels of algal abundance.
The level of caulerpin, one of the main secondary algal metabolites, in fish tissues has been used as an
indicator of the trophic exposure to the seaweed and related with molecular and cellular responses.
Chemical analyses indicated that fish from invaded sites can accumulate caulerpin, with liver concentrations
ranging from a few up to hundreds of mg/g. Biomarkers analyses revealed only limited alterations
of the main antioxidant defences, such as glutathione reductase and levels of glutathione; on the other
hand, increased enzymatic activities of cytochrome P450, glutathione S-transferases and acyl CoA oxidase,
as well as enhanced gene transcription for peroxisome proliferator-activated receptor alpha, cytochrome
P4501A and vitellogenin 1 were observed in fish more exposed to C. racemosa as indicated by
liver concentrations of caulerpin higher than 50 mg/g.
Despite a direct molecular relationship with this algal metabolite could not be established, our results
suggest that a C. racemosa enriched diet can modulate biotransformation and fatty acids metabolism of
D. sargus. Assessing whether similar effects represent short- or long-term effects will be of crucial
importance to understand consequences on the general health status and reproductive performance of
exposed key fish species in the Mediterranean region.
