Induction of larval attachment and metamorphosis in the serpulid polychaete Hydroides elegans by dissolved free amino acids: isolation and identification

The calcareous tube-building polychaete Hydroides elegans (Haswell) is a ma jor fouling organism in tropical waters around the world. In the marine env ironment, larvae of H. elegans rapidly settle and metamorphose in response to acceptable surface-bound bio-organic films. In addition to biological in ducers, previous investigations by our group have indicated chemical induce rs for larval settlement and metamorphosis in H. elegans. Crude samples der ived from adult H. elegans and colonies of the bryozoan Bugula neritina ind uced a high percentage of larval metamorphosis in laboratory assays. Here, we describe a bioassay-guided isolation and purification of larval metamorp hic inducers originating from these samples. Biologically active HPLC-purif ied fractions of both samples were composed of free amino acids. The entire free amino acid composition was determined by quantitation with ortho-phth aldialdehyde (OPA) and was found to be comprised of aspartic acid, glutamic acid, serine, histidine, glycine, arginine, alanine, asparagine, glutamine and taurine in concentrations ranging from 0.2 mu M (histidine) to 5.6 mu M (taurine). In the laboratory assay, the larval metamorphic response to an artificially prepared sample in identical concentrations of these amino ac ids was very similar to the natural isolates.