Settlement inducers for larvae of the tropical fouling serpulid, Spirobranchus kraussii (Baird, 1865) (Polychaeta: Annelida)

Calcareous tubeworms are one of the most abundant fouling organisms found on substrates submerged in marine environments. Research has clearly shown that tubeworms select surfaces with a biofilm, and attachment and adhesion strength is enhanced in the presence of a biofilm. Studies have also shown that abiotic materials in the environment are strongly linked to proliferation of aquatic benthic microbes, which in turn may influence larval recruitment. Soil-derived nutrients are capable of supporting large, diverse bacterial communities and have been used to encourage growth of heterotrophic microbes. In this study we investigate the effect of organic nutrient-rich extract derived from sediments on larval settlement of the fouling calcareous polychaete, Spirobranchus kraussii (Baird, 1865). Application of a soil extract, as used in the preparation of GSe microalgal culture media, induced larval settlement within 24 h in laboratory assays. Our observations suggest that soil extract promoted the growth of an inductive biofilm from microbiota present on the larvae during the incubation period. However, the presence of a chemical inducer could not be conclusively discounted.