Determinants of food selection by bivalve larvae

Selection of food particles for consumption by larvae impacts nutritional gain needed for growth, development, and metamorphosis. Past work has suggested that molluscan larvae are capable of collecting food within a narrow size range. Recent studies have found evidence of size-independent food selection in molluscan larvae, but relatively little is known about the characteristics of particles that larvae preferentially capture. Therefore, we conducted experiments with the larvae of two mussels, Mytilus trossulus and Mytilus edulis, to determine whether they are selective feeders, and if so, whether we could determine the characteristics of particles selected as food. We fed larvae microalgae and polystyrene microspheres of different sizes, nutritional content, surface charge, and hydrophobicity. We found that for both species, there was no effect of size on particle selection for particles 2–8 μm, but, surprisingly, these two congeners preferentially captured particles with different characteristics. Larvae of M. trossulus preferentially captured particles that were more hydrophilic and had a more negative surface charge, but there was no effect of nutritional content. The larvae of M. edulis showed a different pattern; they preferentially captured particles with low surface charge and greater food value, but hydrophobicity did not affect selection. Larvae of these two congeners are indeed selective in which particles they collect but appear to be using different rules for selection. More work is needed to determine whether there are any general patterns that govern particle selection for larvae and mechanisms that could produce the observed patterns. Such work is needed to help us to determine whether individual species use different rules or whether there are general patterns in the types of particles larvae select.