Do transparent exopolymeric particles (TEP) derived from Phaeocystis globosa bloom impact the physiological performances of European sea bass juveniles

A mesocosm experiment (1m3 enclosures) was carried out over 28days to evaluate the effect of Transparent Exopolymer Particles (TEP) derived from decaying Phaeocystis globosa colonies on the physiological performance and mortality of European sea bass juveniles (35mm in length and 113days old). Accordingly, sea bass juveniles were exposed to high TEP concentrations derived from both a culture of decaying P. globosa colonies (7634.27±3514.41μgXGeqL−1) and freshly sea foam (932.54±341.21μgXGeqL−1). During the experiment, environmental parameters (pH, dissolved oxygen, temperature and salinity) were stable, similar among treatments and not limiting for growth. Only TEP concentration varied between treatments. Fish mortality rate was relatively low (0 to 2%d−1) and mostly occurred during the first week when TEP concentrations were relatively low. Despite high and varying TEP concentrations, juvenile sea bass physiological performances (growth in length and weight, Fulton condition index and RNA–DNA ratio) did not differ between replicates and treatments. In addition, juvenile sea bass increased both in size by 7.2mm (growth rate of 0.26mmd−1) and weight by 708mg (growth rate of 25.29mgd−1) during the 28days of the experiment. Altogether, these results showed clearly that TEP derived from decaying P. globosa bloom and foam accumulation have no negative effect on juvenile sea bass physiological performances and survival if water dissolved oxygen is maintained high. Despite being one of the most recurrent phytoplankton blooms recorded in the northwest European shelf seas and forms large blooms in the coastal waters during spring, we suggest that Phaeocystis bloom has no deleterious effect on marine coastal fish aquaculture activities. •We examine the effect of Phaeocystis globosa bloom on juvenile sea bass.•Fishes were exposed to high concentration of transparent exopolymeric particles (TEP).•TEP have no negative effect on sea bass physiological performances and survival.