The effect of picoplankton and nanoplankton food on growth and settlement of early D-shaped larvae of the scallop Argopecten ventricosus

The D-shaped larvae of the Pacific calico scallop, Arogopecten ventricosus, were fed five picoplankton species (< 0.2-4.0mum) and two nanoplankton species (>4.0 mum) to test whether a specific, smaller diet compared to the larger, more typical, nanoplankton diet would improve growth and settlement. Larvae were offered these food items during the first two days of larval life, after which all groups were provided a standard larval diet. Ingestion and digestion were quantified using epifluoresence, and growth measurements were taken through day 25. Ingestion results showed that larvae ingest picoplankton species at a higher percentage than they ingest nanoplankton species during the first day of larval life (P≤0.05). Picoplankton food items took a longer time to digest than nanoplankton species and this was interpreted as providing better digestion profiles than nanoplankton species. Growth measurements the first week indicated larvae that were fed the picoplankton species Micromonas pusilla and Imantonia rotunda grew faster untill day 5 than larvae fed the various other diets; by day 25, however, no growth differences were detectable. Differences in settlement success (survival) after 25 days of culture varied 25 to 40% between treatments and were not significant (P>0.05). These results indicate that the picoplankton species Imantonia rotunda was readily ingested the first day of larval life, provided a good digestion profile, and boosted growth rates of scallop larvae in early larval life. The implication of these findings is that this species of microalgae should be incorporated into commercial diets of A. ventricosus to increase larval production.