MEPS 294:109-116 (2005)  -  doi:10.3354/meps294109

ABSTRACT: Extracellular polymers (EPS) produced by diatoms have been demonstrated as potent mediators of larval settlement in Hydroides elegans. Few studies have addressed the importance of environmental parameters (e.g. temperature and salinity) on quantity and quality of diatom EPS as larval settlement cues. The growth rates of the benthic pennate diatoms Achnanthes sp. and Nitzschia constricta reached a maximum and a minimum level at high and low temperature and salinity, respectively. A positive correlation was observed between the growth rate of diatoms and their production of EPS. In order to decouple the quantitative effect of diatom films from the potential qualitative effect of diatom EPS on larval settlement, the same amount of diatom EPS obtained from different growth conditions were immobilized in hydrogels and investigated in larval settlement assays. The diatom EPS obtained from high temperature treatments were more inductive to larval settlement than the low-temperature treatments, irrespective of the salinity setting. The qualitative differences of the diatom EPS samples under investigation were further analyzed by bioassay-guided gel-chromatography. The bioactive EPS fraction of Achnanthes sp. mainly consisted of large macromolecules, while the bioactive EPS fraction of N. constricta consisted of both large and small macromolecules. Due to their sensitivity to changes in environmental parameters, diatoms may serve as small scale proxies of substratum suitability for larval settlement of benthic marine invertebrates, analogous to the reported role of bacteria in marine biofilms.

KEY WORDS: Extracellular polymers (EPS) · Larvae settlement · Temperature · Salinity · Hydroides elegans · Diatoms · Biofilms