COMBINED EFFECTS OF SALINITY AND TEMPERATURE ON JUVENILE SURVIVAL, GROWTH AND MATURATION IN THE POLYCHAETE HYDROIDS ELEGANS

Effects of salinity (15 to 35 parts per thousand) and temperature (15 to 30 degrees C) on the survival and growth of juvenile polychaete Hyd roides elegans (Haswell), and on their subsequent reproduction, were e xamined in 2 laboratory experiments. Within the experimental range, te mperature did not influence survivorship. However, low salinity reduce d surivorship: at 15 parts per thousand, all juveniles died within 8 d ; at 20 parts per thousand, about 30% of the individuals died within 8 d, but almost all remaining individuals survived throughout the follo wing 17 d of the experiment. At higher salinities, over 95% of the ind ividuals survived throughout the experiment. Juveniles were more vulne rable to low salinity (20 parts per thousand) within 1 dof settlement than at older ages. Both low temperature and low salinity led to slowe r growth and subsequently to a longer time to maturation. At greater t han or equal to 25 parts per thousand and greater than or equal to 20 degrees C, first spawning occurred on Day 16 of the experiment. More t reatments 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 0.2 5 to 3.0 and appeared to be independent of salinity and temperature co nditions. Average fecundity ranged from 1100 to 9050 oocytes per femal e and seemed unaffected by temperature. Average fecundity was similar at salinities greater than or equal to 25 parts per thousand but was l ower at the lowest survival salinity (20 parts per thousand). 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. Th e results also support the ideas that early developmental stages are m ore sensitive to environmental stress than late juveniles and adults, and that juveniles are most vulnerable at the onset of benthic life.