Picophytoplankton contribution to Mytilus edulis growth in an intensive culture environment

Autotrophic picoplankton (<= 2.0 mu m) is one of the most abundant phytoplankton components in marine ecosystems. The contribution of picophytoplankton to blue mussel (Mytilus edulis) growth was investigated in eastern Prince Edward Island, where the bulk of the Canadian suspended mussel industry is located. Field trials using flow cytometry were used to determine the ability of mussels to retain picophytoplankton (0.2-2.0 mu m) and nanophytoplankton (2.0-20.0 mu m). Size-fractionated phytoplankton biomass (chl-a) and mussel growth (shell height and tissue weight) were also measured. Mussel retention efficiencies (RE) for picophytoplankton and nanophytoplankton averaged 20 +/- 2.0 and 60 +/- 3.5 %, respectively. Estimates of RE and phytoplankton biomass were integrated into a dynamic energy budget (DEB) model to investigate the contribution of picophytoplankton to mussel growth during the post-spring bloom period. When DEB simulations excluded picophytoplankton (RE = 0 %), the predicted reduction in mussel growth ranged between 14 and 29 %. It is concluded that the contribution of <2.0-mu m phytoplankton to the mussel's energy budget is non-negligible and should be taken into account when investigating interactions between bivalve farming and phytoplankton dynamics.