The Uptake and Metabolism of Dissolved Amino Acids by Bivalve Larvae

The rates of uptake and metabolism of 14C-labeled glycine and alanine from sea water into larval oysters, Crassostrea gigas (Thunberg) and mussels, Mytilus edulis L. were determined. Kinetic studies showed that both species have a Kt value of 3-4 µM, indicating that bivalve larvae have amino acid transport mechanisms that function efficiently in natural sea water. The Kt values for larvae are similar to those reported for adult bivalves. However, larvae take up dissolved amino acids at approximately ten times the rate reported for adult bivalves on a gram dry weight basis. This difference in uptake capacity presumably reflects the greater absorptive surface area to volume ratio of a larva. Rates of metabolism of absorbed amino acids by larvae were also rapid. Following a 100 min exposure, oyster larvae incorporated 47% of the glycine into protein and 38% was produced as CO2. In comparison to adults, larval bivalves have a more rapid weight-specific uptake and faster rate of utilizing absorbed amino acids. Dissolved nutrients may be of vital importance to larvae when particulate food is scarce since they are often provided with minimal food reserves by the parent.