Physiological energetics of Japanese scallop Patinopecten yessoensis larvae

Abstract

Growth and ingestion rates were determined for Japanese scallop Patinopecten yessoensis larvae reared at temperatures between 10 and 18 °C and fed concentrations of Isochrysis aff. galbana (clone T-ISO) cells between 5 and 30 cells · μl −1 to gain insight into energy balance. Veliger larvae were held in experimental chambers at densities of 0.5–100 · ml −1 to assess the influence of crowding on growth, respiratory and feeding rates. Long-term growth studies lasting 28 days indicated that growth was most rapid at highest food concentrations of 30 cells · μl −1 despite indications from short-term feeding studies that ingestion was at a maximum and independent of concentration between 15 and 30 cells · μl −1. Growth and ingestion are both reduced as the density of larvae increases. Feeding rates (6 h) remained fairly constant between densities of 1–5 larvae · ml −1 if food availability was increased proportionately. However, growth experiments lasting 28 days revealed extremely low survivorship if larvae are reared at densities of >1 2 · ml −1. Respiratory rates were higher than previously reported for bivalve larvae and reaching values of 13 nl · h −1 or 13–29 ml O 2 · g −1 [AFDW] · h −1. Oxygen consumption was reduced ≈ 35% at larval densities between 5 and 25 · ml −1 which are typical densities used when measuring metabolic rates of veliger larvae. Assimilation efficiencies between ≈ 55 and 80% were comparable to published values for mussel and oyster larvae but higher respiratory demand and comparatively slow growth rates for this species were reflected in lower growth efficiencies than those previously reported for bivalve larvae. Japanese scallop larvae apparently require a minimum food concentration of 7–15 cells · μl −1 (depending on size) to gain sufficient energy to support respiration and growth. Despite morphological similarities between species of bivalve larvae they may differ in their rates of energy acquisition and utilization.