Ontogenic Changes in the Rates of Amino Acid Transport from Seawater by Marine Invertebrate Larvae (Echinodermata, Echiura, Mollusca)

¹ Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371

Transport rates of amino acids were determined for larvae of different ages of the echiuran worm Urechis caupo, the gastropod Haliotis rufescens, the bivalve Crassostrea gigas, and the sea urchin Strongylocentrotus purpuratus. All larval forms showed an increase in the transport rate of amino acids during development. Trochophores of U. caupo increased their rate of net flux for each of 5 amino acids (100 nM each) by a factor of 1.6 and 2.2 during 1-3 days and 4-8 days, respectively, for two independent cultures. In H. rufescens, the maximum transport capacity (J_max) for alanine increased 3-fold during the 24 h required for the trochophore to develop into a veliger. In C. gigas veligers, there was a 9-fold increase in the maximum transport capacity for alanine during larval development from an 80 µm to a 300 µm larva. In sea urchins, the prism-stage larvae (2-day-old) had an alanine transport system with a K_t of 1.9 µM and a J_max of 8.1 pmol larva^-1h^-1. The kinetics of alanine transport in the pluteus-stage (4-day-old) were best described by two systems (System I: K_t = 1.0 µM with a J_max of 5.6 pmol larva^-1h^-1; System II: K_t = 132.0 µM with a J_max of 8.4 pmol larva^-1h^-1). In larvae of C. gigas, the relationship between the rate of alanine transport and body size was described by the equation, log J_max (pg larva^-1h^-1) = 1.6894(X) + (-0.5937), where X is the shell length in µm. It is illustrated that the allometric increase in respiration rates, during the growth of bivalve larvae, is matched by an ontogenic increase in amino acid transport capacity.

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