INFLUENCE OF PHYSICAL AND CHEMICAL FACTORS ON SETTLEMENT AND RECRUITMENT OF THE HYDROID TUBULARIA LARYNX

Field observations using settlement panels, which were carried out in Port Daniel Bay, Bale des Chaleurs, Quebec, Canada, in 1992, showed re cruitment by the hydroid Tubularia larynx to be unevenly distributed w ith depth. Multiple regression on residuals indicated that 2 physical factors, water temperature and light intensity, out of 5 tested explai ned 45% of the observed variance in the recruitment of T. larynx on th e panels. In laboratory experiments, warm temperatures increased settl ement significantly. Contrary to field results, Light intensity did no t seem to influence the settlement of T. larynx in the laboratory. The influence of small scale (<mm) substrate heterogeneity was also teste d in the laboratory. Highest settlement rates occurred on smooth surfa ces, but field experiments carried out in 1993 did not show any hetero geneity preference by T. larynx. The influence of extracts and metabol ites of conspecific adults on larval settlement was also tested in the laboratory and field. Adult extracts had some influence on settlement in some laboratory trials, but not in others. In general, T. larynx s ettled more abundantly on surfaces treated with high concentrations of extract solutions than on other surfaces. As was the case for substra tum heterogeneity, there was no influence of adult extracts detected i n the field. In contrast, adult metabolites showed little influence on settlement under laboratory conditions and no influence on recruitmen t in field experiments.