Changes in Food Selection through Ontogeny in Crassostrea gigas Larvae

Bivalves are some of the most important suspension feeders in aquatic systems. Much research has been conducted on the feeding mechanisms of adult molluscan suspension feeders, but less is known about the feeding mechanisms of their larval stages. To date, the general consensus is that veligers are restricted to collecting particles 4-20 μm in size and that food selection is indiscriminate within this size range, but this hypothesis remains to be directly tested. Therefore, we experimentally assessed this assumption by quantifying microalgal particle capture rates for the larvae of the Pacific oyster (Crassostrea gigas) when fed five different microalgal species individually and in combination. We then tested whether factors such as cell size affected capture rate and consumption, as well as whether capture rate was affected by the presence of other microalgal species. We found evidence of food preference that was not simply a function of size or relative nutritional quality for C. gigas veligers. Further, we found that food selectivity changed through ontogeny. To our knowledge, the changes in selection that we observed through ontogeny have not been previously reported. Interestingly, there was also a sharp decrease in the variability among replicates in consumption rate as the larvae aged. Whether this is a function of velar structure or larval size remains to be tested. Our results suggest some underlying process resulting in certain species of microalgae being captured and consumed at significantly different rates than others.