The effect of salinity on larval survival and development in the sea urchin Echinometra lucunter

Reductions in salinity can have adverse effects on larval development and l arval survival in some invertebrate taxa but not others. Salinity tolerance of larvae may be particularly important in echinoderms because they are bo th poor ion regulators and stenohaline. I examined the effect of six levels of salinity (15, 18, 21, 24, 27 and 33 PSU) on survival and rate of develo pment of larvae in the subtropical sea urchin Echinometra lucunter. In the short-term, mortality rate was significantly lower in 33 PSU than in all ot her salinities except 27 PSU, and it was significantly greater in 15 and 18 PSU than in all higher salinities. In the long-term, daily and cumulative mortality were significantly greater in 15 PSU than in most other salinitie s over 11 days of development (except for cumulative mortality in 18 PSU). They were significantly greater in 18 PSU than in 21 PSU or 33 PSU over a p eriod of 13 days. Furthermore, daily mortality was significantly greater in 18 PSU than in 24 PSU or 27 PSU at 13 d after fertilization. Daily and cum ulative mortality were significantly lower in 33 PSU than in 21, 24 or 27 P SU over a period of 17 days. Although in the control (33 PSU) 75% of larvae completed development to the 8-arm stage at 35 d, no larvae developed furt her than the 4-arm stage in 18, 21, 24 or 27 PSU; in 15 PSU, similar to 60% of larvae did not develop further than swimming blastulae. Since prolonged exposure to salinities as high as 27 PSU (frequently recorded in the adult habitat) can result in great larval losses, adaptive behaviours that preve nt larvae from entering water layers of low salinity will enhance their cha nce for survival.