. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 344 H. A. WOODS AND R. L. DeSILETS. JR. we weighed it (± g) and determined its volume (± ml) by the displacement of 5 ml of seawater in a 10-ml graduated cylinder (Booth. 1995). Effects of gradual versus abrupt salinity change We compared the survival of degelled embryos ex- posed to abrupt and gradual salinity changes. Ten egg masses were degelled. five with pre-kidney-spot embryos and five with kidney-spot veligers. The capsules from each of these masses were split into three groups: one group maintained in full-st
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 344 H. A. WOODS AND R. L. DeSILETS. JR. we weighed it (± g) and determined its volume (± ml) by the displacement of 5 ml of seawater in a 10-ml graduated cylinder (Booth. 1995). Effects of gradual versus abrupt salinity change We compared the survival of degelled embryos ex- posed to abrupt and gradual salinity changes. Ten egg masses were degelled. five with pre-kidney-spot embryos and five with kidney-spot veligers. The capsules from each of these masses were split into three groups: one group maintained in full-strength seawater for the dura- tion of the experiment; a second group exposed abruptly to 5%c for 1 h by the method described above; and a third group exposed to a gradual decline in salinity before exposure to 5%c for 1 h. Egg capsules of the third group were initially in 5 ml of water in a 25-ml glass vial. Four times at intervals of 20 min we added 5 ml of fresh water to the vials. After each step, the measured salinity in the vial deviated from the calculated salinity by less than 1%C. Capsules were left at 5%c for 1 h. During this time, after the capsules had settled to the bottom of the vial, we removed all except 5 ml of water. We increased the salin- ity to full strength (30%P) over 20 min in three steps by adding ml and then ml of full-strength seawa- ter, then finally filtering the capsules into seawater. We scored individuals 6 days later, by which time all embryos had become veligers or died. Results Gelled versus degelled capsules The effect of different salinities on gelled and degelled capsules is shown in Figure 1. The fraction of embryos GO c § .75 .5 .25. Degelled egg capsules 10 15 30 Salinity (%o) Figure 1. Survival of Melanochlamys diomedea embryos after im- mersion in various salinities for 3 h. Survival was scored 3 days after exposure to the test salinity. Filled squares (•) indicate embryos in egg masses, open squares (D) degelled embryos
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