UPTAKE OF DISSOLVED FREE AMINO ACIDS BY NORTHERN QUAHOGS, MERCENARIA MERCENARIA AND ITS RELATIVE IMPORTANCE TO ORGANIC NITROGEN DEPOSITION IN NARRAGANSETT BAY, RHODE ISLAND.

Studies were undertaken to determine the relationship between size of northern quahogs Mercenaria mercenaria and the rate at which they transport aspartic acid. Quahogs ranging from 25 to 103 mm valve length were collected in Narragansett Bay and placed in seawater aquaria (27 ppt, 20 °C) and allowed to pump water actively. Uptake experiments were carried out using 1 μmol/L C¹⁴ radiolabeled aspartic acid. Aspartate transport rates in μmol/h can be related to valve length by the allometric equation with a = 24.32 and b = 0.905 when valve length is in mm. In May 1990, near-bottom samples of seawater were taken from five locations in Narragansett Bay for analysis of dissolved free amino acids (DFAA) by high-pressure liquid chromatography (HPLC). Results showed that the mean total DFAA concentration was 667.6 nmol/L ± 167.3 SD, with the top five being serine, alanine, aspartic acid, glutamic acid, and glycine. A simple spreadsheet model was used to assess the relative importance of the uptake of DFAA vis-à-vis the filtration of particulate organic matter by M. mercenaria. In the model, environmental DFAA concentrations and uptake rates by quahogs determined in this study are compared with literature values for particulate organic nitrogen concentrations and filtration rates by quahogs. On an annual basis, uptake of DFAA can account for about 14% of the total organic nitrogen uptake by quahogs. Uptake of DFAA by these benthic filter feeders may be a pathway of benthic-pelagic nutrient coupling that is often overlooked in coastal ecosystem analyses. [ABSTRACT FROM AUTHOR]