Feeding, assimilation, and growth of mud snail larvae, Nassarius obsoleyus (Say), on three different algal diets

Nassarius obsoletus (Say) veliger larvae were fed three different phytoplankton diets in the laboratory: Isochrysis galbana Parke, Thalassiosira pseudonana (Hust.) Hasle & Heimdal, and Dunaliella tertiolecta Butcher. The relationship between growth rate and ability of the larvae to ingest and assimilate the different algae was investigated. To properly design the assimilation experiments, certain basic aspects of the feeding biology of the gastropod larvae were studied: the relationship between container size and feeding rate, light level and feeding rate, rate of gut evacuation in the presence and absence of food, and filtration and ingestion rates as a function of food concentration. Growth rates, ingestion rates, and efficiencies of carbon retention varied with the algal species provided, although relative growth could not be predicted from measurements of relative rates of carbon uptake from the different phytoplankton species. Larval growth rates are probably determined primarily by the abilities of the different algal species used in our experiments to provide necessary micro-nutrients. Retention efficiencies (carbon retained/carbon ingested) were low, ranging between ≈9 and 17%. Estimates of maximum assimilation efficiencies for young Nassarius obsoletus veligers are also much lower than most values reported for other Zooplankton.