Characterization of polychaetes inhabiting estuaries and inner bays by composition analysis of amino acids and lactate enantiomers

In this study, we investigated the composition of free amino acids and lactate (Lac) in polychaetes in river estuaries and inner bays using chromatographic techniques. Both l -amino acids and d -amino acids ( d -asparagine, d -alanine ( d -Ala), d -serine, d -aspartic acid, and d -proline ( d -Pro)) were detected, indicating that polychaetes contain some d -amino acids. Some polychaete species exhibited notable amino acid levels, such as glycine in Capitellidae sp. and Thelepus sp., d -Pro in Glycera sp., and β-Ala in Scoletoma nipponica and Scoletoma sp.. High d -Lac levels were detected in Tylorrhynchus osawai and Hediste diadroma , (691 and 797 μmol/100 g-wet, respectively), with the d -form exceeding 98%. T. osawai was dominant in the upper tidal-sensitive zone, wherein other organisms were less abundant because of low salinity (3–8 PSU). Seasonal differences in the concentrations of components in T. osawai were observed, particularly a significant increase in d -Lac in the reproductive period. Notably, the d -Lac concentrations of T. osawai were higher upstream than downstream. Thus, d -Lac might be involved in strategies underlying adaptations to low salinity and reproductive activity. These results suggest that both the d -form of Lac and amino acids may play certain physiological roles in the life of polychaetes.