Amino acid fluxes to and from seawater in axenic veliger larvae of the bivalve (Crassostrea gigas)

Abstract

Rates of uptake of dissolved amino acids were determined for axenic veliger larvae of the bivalve Crassostera gigas (70 .mu.m shell length). Analyses of net fluxes from seawater of amino acids by high-performance liquid chromatography showed a net uptake of all acidic, basic, and neutral amino acids tested. From a subsrate concentration of 100 nM each, valine had the highest rate of uptake at 70 fmol larva-1 h-1, and arginine the lowest at 4 fmol larva-1 h-1. The influx of alanine, arginine, glutamic acid and leucine (measured radiochemically) reflected the net flux (measured by chromatography). However, there was a net efflux of taurine (0.58 pmol larva-1 h-1) even though isotope experiments revealed an influx of 0.32 pmol larva-1 h-1. Efflux of taurine was also observed for nonaxenic veligers. Axenic veligers had a Kt (substrate concentration at half Jmax) of 11.4 .mu.M and a Jmax (maximum transport capacity) of 4.6 pmol larva-1 h-1 for alanine; for leucine, the corresponding values were 7.1 .mu.M and 2.2 pmol larva-1 h-1. At substrate concentrations near the Kt values (on the order of 10 .mu.M), C. gigas larvae could account for 100% of their oxidative needs by the uptake of amino acids from seawater. In most marine environments, such high concentrations are limited to seawater near the sediment. Thus, the overall contribution of dissolved amino acids will depend on the substrate concentration encountered by the larvae in nature.