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

Abstract

The calcareous tube-building polychaete Hydroides elegans (Haswell) is a major fouling organism in tropical waters around the world. In the marine environment, larvae of H. elegans rapidly settle and metamorphose in response to acceptable surface-bound bio-organic films. In addition to biological inducers, previous investigations by our group have indicated chemical inducers for larval settlement and metamorphosis in H. elegans. Crude samples derived from adult H. elegans and colonies of the bryozoan Bugula neritina induced a high percentage of larval metamorphosis in laboratory assays. Here, we describe a bioassay-guided isolation and purification of larval metamorphic inducers originating from these samples. Biologically active HPLC-purified fractions of both samples were composed of free amino acids. The entire free amino acid composition was determined by quantitation with ortho-phthaldialdehyde (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 μM (histidine) to 5.6 μM (taurine). In the laboratory assay, the larval metamorphic response to an artificially prepared sample in identical concentrations of these amino acids was very similar to the natural isolates.