Combined effects of salinity, temperature and food on early development of the polychaete Hydroides elegans

Effects of salinity, temperature and food concentration on early development of the polychaete Hydroides elegans (Haswell) were examined in 4 laboratory experiments. Three 2-factor experlments tested the effects of salinity (15 to 35sl,,] and temperature (15 to 30°C ) on the survival and duration of development of H elegans from newly-released oocyte to 2-cell, 2-cell to blastula, and blastula to trochophore stages respectively. A fourth 3-factor experiment tested the effects of salinity (15 to 35%0) , temperature (15 to 30°C ) , and concentration of the single-cell alga Isochrysis galbana (0 to 10h cells ml-') on survival, settlement, and duration of development from trochophore to newly-settled juvenile. Within the experimental range, temperature had no effect on survivorship, but low temperature led to longer duration of development. Low salinity reduced survivorship and settlement, and lengthened the duration of development. Low food concentration reduced survivorship and settlement. and lengthened the duration of development from trochophore to newly-settled juvenile. At concentrations <103 cells ml-', >35% larvae survived through the 10 d experiment but lost their ability to become competent Percentages of trochophores reaching settlement were similar at 104, 105, and 10%ells ml-l. Duration of development was shortest at concentrations of 10' cells ml-l, while trochophores at 104 and 106 cells ml-' had slmllar but longer durations of development. Our data suggest that in Hong Kong waters, the decrease in salinity during the summer seems to override the benefits of high temperature and to be responsible for the decline in H. eleganssettlement. The increase in phytoplankton concentration from early spring to early summer may contribute to the formation of settlement peaks. Temperature, however, does not seem to be a limiting factor for early development and settlement of H. elegans.