Laboratory larval growth and settlement of the tube worm hydroides elegans (polychaeta: serpulidae)

Aim of this work was to use the different stages of Hydroides elegans life- cycle for toxicity and settlement tests. In this perspective the influence of some cultural parameters (temperature and food) on larval growth and the importance of a substrate pre-treatment for the settlement of competent larvae (metatrochophores) have been investigated. Trochophores, obtained through artificial fertilization, were reared at 20° and 25°C and fed with three species of planktonic unicellular algae, Pavlova lutheri Droop, Isochrysis galbana Parke and Tetraselmis suecica Kylin Butcher, until the three setigers metatrochopore stage was achieved. Periodical measurements of larvae collected from the different groups allowed us to determine different growth rates. Then, competent larvae were added to replicate Petri dishes, previously subjected to different biofilm treatment (Sea Water Biofilm and Algal Biofilm), in order to check their settlement behaviour. The same kind of substrata treatment were utilised in a settlement test to asses the efficacy of experimental antifouling booster biocide. Larvae reared at 20°C, fed with Pavlova lutheri have been the most reliable in terms of stage homogeneity and have shown the highest growth rate. The settlement behaviour of competent larvae is deeply influence by the presence of biofilm and the biofilm obtained by immersion in natural unfiltered sea water attract a greater number of larvae than the other; moreover significant differences in antifouling performance, expressed as settlement percentage, have been observed between substrata biofilmed in different ways.