Effect of marennine produced by the blue diatom Haslea ostrearia on behavioral, physiological and biochemical traits of juvenile Mytilus edulis and Crassostrea virginica

•Effect of marennine on the functional response of mussel and oyster was studied.•A curtailed valve opening was detected at the higher marennine concentration.•Marennine significantly decreased scope for growth of both bivalve species.•Marennine interfered with the accumulation of energy reserves in mussels.•Marennine increased the concentration of unsaturated fatty acids in oyster gills.

Haslea ostrearia is a marine diatom that synthesizes and releases marennine, a water-soluble blue-green pigment responsible for the greening of the gills and labial palps of bivalves. The present study evaluated the effect of different marennine concentrations (0, 0.5, 1.0 and 2.0 mg l− 1) on the behavior (valve opening), physiology (clearance rates, oxygen consumption, assimilation efficiency and scope for growth) and biochemistry (fatty acid composition of neutral and polar lipids) of two commercially important bivalves, the blue mussel Mytilus edulis and the eastern oyster Crassostrea virginica. Under short-term (< 1 day) exposure, the concentration of marennine found on the gills of both species was positively correlated to the concentration of dissolved marennine in the water medium. However, a behavioral response was detected at the higher marennine concentration (2.0 mg l− 1) and both species displayed curtailed valve opening compared to control groups. Under longer-term (8 weeks) exposure, marennine (at 2 mg l− 1) significantly decreased scope for growth by 58% and 85% (ANOVA; F3, 31 = 3.39, P = 0.034 and F3, 31 = 3.08, P = 0.044) for M. edulis and C. virginica respectively. The greening process had an effect on total fatty acids contained in the digestive gland of mussels only, suggesting that marennine interferes with the accumulation of energy reserves in this bivalve. In the polar lipids of the gills, greening increased the concentration of unsaturated fatty acids of C. virginica but not M. edulis, suggesting a possible regulatory mechanism counteracting the marennine effect in oysters. In conclusion, marennine is currently viewed as a non-toxic compound produced by a non-toxic algae species, yet our results show that the substance impairs the biology of bivalves. Such effects should therefore be taken into consideration before the application of mareninne in aquaculture settings.