Comparative study of the uptake of dissolved amino acid in sympatric brittle stars with and without endosymbiotic bacteria

1. 1. Transport rates of dissolved free amino acids for two sympatric ophiuroids were determined to assess differences due to size or life-history traits. 2. 2. Both species of brittle stars demonstrated a net flux of dissolved free amino acids from seawater, while the brooding brittle star Amphipholis squamata had significantly higher rates, greater than twice those of Ophiopholis aculeata. 3. 3. Measured rates of uptake for either species of brittle star contribute less than 5% of the respiratory substrate needed to support aerobic metabolism. 4. 4. For A. squamata, incorporation of dissolved free amino acids into protein appeared to be primarily by its symbiotic subcuticular bacteria. 5. 5. These results suggest that both uptake of amino acids and their subsequent incorporation into bacterial protein are coupled. 6. 6. However, calculations of the maximum potential uptake of dissolved amino acids by the symbiotic bacteria can account for no more than 10% of the total amino acid uptake in A. squamata. 7. 7. At the amino acid concentrations used in this study the maximum uptake of amino acids by bacteria should have been achieved.