Tight coupling between primary productivity, export production, and the growth of benthic scallops in the coastal region of the Okhotsk Sea along Hokkaido

Scallop culture is conducted worldwide, nonfeeding and depending on the natural phytoplankton production for the diet. It is necessary for sustainable culture of this species to understand how the phytoplankton production and subsequent vertical transport to the bottom (export production) are regulated by environmental factors. A 3-year time series monitoring of chlorophyll and temperature, as well as sinking particle flux, was conducted to elucidate the relationship between surface primary production, the subsequent export, and the growth of benthic cultured scallops in spring in the coastal region of the Okhotsk Sea along Hokkaido, Japan. Five times larger export fluxes were observed in 2013 than those in other years. Coscinodiscus spp., diameter >200 mu m, was the quantitatively dominant phytoplankton in 2013. This species contributed to the high export flux due to a higher settling velocity. The sudden drops in temperature by >2 degrees C were observed during the study period. These indicated that the supply of nutrients from Intermediate Cold Water (ICW), a cold and nutrients rich water mass, accelerated the primary productivity in this area. This intensity was strongest in 2013, contributing to the high export flux. The large export flux in 2013 provided a more sufficient food to the benthic cultured scallops, resulting in a two times higher growth of the scallops than in other years. This study demonstrated that the size of the dominant diatom species and the supply from ICW strongly influenced the export ratio and the growth of cultured scallops.