Combined effects of salinity and temperature on juvenile survival, growth and maturation in the polychaete Hydroides elegans

Effects of salinity (15 to 35‰) and temperature (15 to 30°C) on the survival and growth of juvenile polychaete Hydroides elegans (Haswell), and on their subsequent reproduction, were examined in 2 laboratory experiments. Within the experimental range, temperature did not influence survivorship. However, low salinity reduced survivorship: at 15‰, all juveniles died within 8 d; at 20‰, about 30% of the individuals died within 8 d, but almost all remaining individuals survived throughout the following 17 d of the experiment. At higher salinities, over 95% of the individuals survived throughout the experiment. Juveniles were more vulnerable to low salinity (20‰) within 1 d of settlement than at older ages. Both low temperature and low salinity led to slower growth and subsequently to a longer time to maturation. At ≤25‰ and ≤20°C, first spawning occurred on Day 16 of the experiment. More treatments were found to have mature worms on Day 25 than on Day 16 of the experiment. Tubes of reproductive individuals were usually longer than 1.2 cm. The male to female ratio varied among treatments from 0.25 to 3.0 and appeared to be independent of salinity and temperature conditions. Average fecundity ranged from 1100 to 9050 oocytes per female and seemed unaffected by temperature. Average fecundity was similar at salinities ≤25‰ but was lower at the lowest survival salinity (20‰). This is the first study to report on growth and maturation of H. elegans under controlled laboratory conditions. It provides information to explain the settlement and population changes of this species in the field. The results also support the ideas that early developmental stages are more sensitive to environmental stress than late juveniles and adults, and that juveniles are most vulnerable at the onset of benthic life.