Growth anomalies in Pecten maximus from coastal waters (Bay of Brest, France): Relationship with diatom blooms

Previous studies carried out with Pecten maximus (Bivalvia: Pectinidae) juveniles in the Bay of Brest have demonstrated that diatom and, more obviously, toxic dinoflagellate blooms could have a negative effect on the daily growth rate. The aim of this study was to characterize the daily shell growth from early 1998 to late spring 1999 with a careful qualitative and quantitative description of the pelagic primary production. Our results, in accordance with previous studies, demonstrate that there are episodic declines in the growth rate. Concurrent events of low growth rate and large bottom-concentrations of algae following diatom blooms (Cerataulina pelagica or Rhizosolenia delicatula), suggests that this high concentration of phytoplankton on the bottom layer, may affect food intake or respiratory activity of the scallops by gill clogging or oxygen depletion. In this study, silicic acid or phosphorus are inferred to be limiting factors responsible for the collapse of the spring bloom. Further, we suggest that, in an N-enriched ecosystem, Si or P-limitation and the changing sinking velocities of phytoplankton, could affect the biology of benthic suspension-feeders.