The origins, fate, and ecological significance of free amino compounds released by freshwater pulmonate snails

The mass-specific accumulation rates (MSAR) of both total (TFAC) and individual free amino compounds (FAC) in conditioned media were measured by HPLC, using the orthophthaldialdehyde (OPA) methods, in the following cases: (a) laboratory-reared freshwater snails (B. glabrata) with chemosterilized shells; (b) Biomphalaria glabrata with non-chemosterilized shells; (c) B. glabrata faeces; (d) isolated shells of B. glabrata; and (e) 10 other species of freshwater gastropods from the Lewes Brooks, East Sussex, U.K. The MSAR values for B, glabrata show that 95% of thr TFAC's (predominantly ethanolamine, phosphoserine, and the amino acids leucine, isoleucine, valine, aspartic acid, and glycine/threonine) originated from the snails themselves as the faeces and shells contributed only 5.0 and 0%, respectively. In contrast, epizootic organisms on the shells of all 10 snail species from the Lewes Brooks released significant amounts of FAC with the two smallest species (Planorbis vortex and Planorbis contortus) having the highest MSAR values. The MSAR for isolated B. glabrata mucus was 42.45 mu mol . g(-1)h(-1). As 500 mg snails can release 16.67 mg of mucus daily, this could potentially result in the daily loss of 707.5 mu mol of FAC. The cost/benefits of mucus secretion and the various anatomical, physiological, biochemical, and ecological mechanisms which allow freshwater snails to recover FAC's lost as a result, of a high rate of urine production in their hypotonic environment, are discussed. (C) 1998 Elsevier Science Inc.