A COMPARATIVE STUDY OF THE NET METABOLIC BENEFITS DERIVED FROM THE UPTAKE AND RELEASE OF FREE AMINO ACIDS BY MARINE INVERTEBRATES

Abstract

A comparative study was undertaken to evaluate the overall significance of free amino acid (FAA) uptake and release in the biology of 21 species of marine invertebrates, representing 7 phyla. Measurements of transport fluxes were made in defined media using the fluorescamine method, corrected for ammonia excretion, and related to measured metabolic rates and natural environmental levels. Except for arthropods, in which net uptake was negligible, all the animals exhibited influx of FAA at rates dependent on media levels, and low, constant efflux. Equilibrium concentrations were always found to be less than the mean minimum bay water concentrations. Thus, all must derive benefit to commonly support at least 3-10% of their metabolism—approximately sufficient to provide for the needs of epidermal and associated tissues, including ciliary pumping over gills, tube feet activity, etc. Certain forms, including a sand dollar and brittlestar, appear to have become particularly adapted to make use of this resource, which may provide them more sustenance than ingested food. Yet other species support lesser, but still substantial, proportions of their metabolic requirements through these mechanisms. It is concluded that net uptake of FAA is an essentially universal property of soft-bodied marine invertebrates, and it plays an important part in their well-being, especially by providing for much of the energy needs of superficial structures and aiding in metabolite retention.