The dominant food sources of benthic suspension feeding bivalves living in shallow coastal areas have been known to be phytoplankton and microphytobenthos. However, there has been considerable debate over which is the primary food source. In this paper, we reviewed previous studies that deal with microalgae (i.e. phytoplankton and microphytobenthos) as a food source for benthic suspension feeding bivalves living in shallow coastal areas. Results of previous studies examining the stable carbon isotope composition of the cockle, Cerastoderme edule, in various coastal areas showed that the main food source for C. edule varied spatially. We estimated the main food source for the clam, Ruditapes philippinarum, on a tidal flat at the mouth of the Midori River. We concluded that R. philippinarum was predominantly feeding on the microphytobenthos. In our sampling station, the annual mean micropytobenthos biomass of the sediment was 30.2±10.2 mgChl-a m-2; this was approximately three times higher than that of phytoplankton in the overlying water column. The high biomass of the microphytobenthos coupled with high tidal and turbulent flow at the mouth of the Midori River results in resuspension and high relative abundance of the microphytobenthos to the overlying phytoplankton. This resuspension provides access to the microphytobenthos as the dominant food for R. philippinarum. To clarify whether the relative importance of phytoplankton and microphytobenthos as food for benthic suspension feeding bivalves living in shallow coastal areas, we need to understand the environmental factors influencing their main food source; additional case studies in this regard is necessary.
