Rates of uptake of dissolved amino acids were determined for axenic veliger larvae of the bivalve Crassostrea gigas (70 km 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 substrate concentration of 100 n M each, valine had the hlghest rate of uptake at 70 fmol larva-' h-', and arginine the lowest at 4 fmol larva-' h-' 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 pm01 larva-' h-') even though isotope experiments revealed an influx of 0.32 pm01 larva-' h-' Efflux of taurine was also observed for nonaxenic veligers. Axenic veligers had a K, (substrate concentration at half J,,,) of 11.4 pM and a J,,, (maximum transport capacity) of 4.6 pm01 larva-' h-' for alanine; for leucine, the corresponding values were 7.1 pM and 2.2 pm01 larva-' h-' At substrate concentrations near the K, values (on the order of 10 l t 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.

A method for the direct measurement of picomole amounts of mono-, di-, and trisaccharides in seawater was developed by combining high-performance liquid chromatography (HPLC) with amperometric detection. This new method is described and then applied to the study of sugar uptake from seawater into veliger larvae of a bivalve (Crassostrea gigas) and a gastropod (Haliotis rufescens). Bivalve veligers take up glucose, maltose, cellobiose, and cellotriose but not L-rhamnose, isomaltose, maltotriose, or isomaltotriose. Similarly, gastropod veligers take up glucose and maltose, but not L-rhamnose or maltotriose. Glucose and maltose are transported into the bivalve veligers by separate pathways and the influx of "C-labeled glucose is a good measure of the net flux (measured by HPLC) The uptake of complex sugars, in addition to monosacchai-ides, permits inolluscan larvae to utilize a greater part of the dissolved organic material in the sea as a source of nutrition

Variation in growth and survival of planktonic larvae has profound effects on marine population abundance. Environmental causes of differential larval growth and mortality are well studied, but genetic variation in these traits is less well understood. Here, we reveal genetic variation in survival and growth of full-sib larvae of the Pacific oyster Crassostrea gigas reared under identical conditions. We size-selected 1.42 million, 24 d old larvae to produce small, medium, and large size classes, constituting 93% of the population. Parental tissues and a total of 144 larvae sampled from each size class were individually genotyped with a panel of 45 mapped DNA markers. Consistent with previous work, 11 markers had genotypic frequencies that differed significantly from their Mendelian expectations and, upon mapping, are explained by 6 viability quantitative trait loci (vQTL). Notably, shell-length variance among size classes maps to 6 major growth QTL (gQTL), with just 2 collectively explaining 18% of the variance. We found little overlap between vQTL and gQTL, suggesting that variation in these larval traits is controlled by different genes. This study demonstrates the feasibility of genotyping single larvae for the identification of multiple QTL. Understanding genetic variation in larval biology is important for a comprehensive understanding of marine recruitment.