Biochemical composition, metabolism, and amino acid transport in planula-larvae of the soft coral Heteroxenia fuscescens

We determined the monthly percentage of biochemical components in planulae of the soft coral Heteroxenia fuscescens, for a 3-year period, and evaluated the findings in relation to seasonal fluctuations in water temperature. We determined the biochemical profile and metabolic rate of aging planulae and examined the possible absorption of dissolved organic material (DOM) from the water by the planulae. Our study is the first to present a long-term biochemical profile of planulae. They contained an average of 2.2% ash, 51.5% lipid, 33.6% protein, and 1.3% carbohydrate. Calculation of the average energetic content of a planula revealed a value of 1.63 J planula^-1. Significant seasonal differences in planulae weight were noted between the summer and the other seasons. A significant decrease (41%) from the initial weight, 0.029 mg, took place in the planulae dry weight within 15 days. Significant decreases over time were also found in lipid (50%) and carbohydrate (83%) concentration but not in protein (20%). Metabolic rates of a planula was 0.06 μl O₂ planula^-1 hr^-1. The study shows for the first time that a soft coral planulae can take up dissolved free amino acids from seawater. Even though each of the amino acids was initially present at equimolar concentrations, there was a much faster uptake for the neutral, nonpolar amino acids, than for polar and basic ones. The potential contribution to the metabolic demand of planulae, from the uptake of amino acids, is estimated to be 11%. It is suggested that this uptake does not appear to be due to energetic considerations, but may have a more significant impact on their nitrogen budget. (C) Wiley-Liss, Inc.