THE EFFECTS OF TEMPERATURE AND SALINITY ON THE OSMOTIC COMPOSITION OF THE SOUTHERN OYSTER DRILL,THAIS HAEMASTOMA

Abstract

1. When Thais haemastoma were acclimated stepwise to constant salinity; hemolymph osmolality, Na+, Mg2+, K+, and Cl- concentrations as well as tissue NPS concentration increased with salinity between 7.5 and 30‰ 10°, 20°, and 30° C. Hemolymph osmolality was significantly greater than that of seawater at 10, 20, 30‰ S and 10°C. Per cent tissue water was unaffected by temperature and decreased with increasing salinity and hemolymph osmolality. The hemolymph concentration of all ions increased with increasing concentrations in seawater. Hemolymph [Cl-] was lower than in seawater at 20° and 30°C but hyperionic to seawater at 20 and 30‰ S and 10°C. Hemolymph [Na+] was greater than in seawater at 10°C but no difference existed at 20° and 30° C. Hemolymph [Mg2+] was significantly greater than in seawater at 10 and 20‰ S at all temperatures. Neither temperature nor salinity significantly affected the hemolymph-to-seawater difference in [K+]. [NPS] in the foot of T. haemastoma increased with salinity and was lower at 10°C than at 20° and 30°C.2. Hemolymph osmolality tracked seawater osmolality less well at 10°C than at 20° and 30° during 30-10-30‰ and 10-30-10‰ diurnal patterns of fluctuating salinity. Reduced tracking at 10°C was due to less decline of hemolymph osmolality during the decreasing-salinity phase of the cycles. Snail hemolymph osmolality also declined less during the decreasing-salinity phase of the 30-10-30‰ S cycle than during the l0-30-10‰ S cycles, indicating that acclimation to different constant salinities prior to the initiation of fluctuating salinity cycles has a significant effect on the response of T. haemastoma to fluctuating salinity. Tissue water in the foot varied inversely with seawater and hemolymph osmolality during fluctuating salinity. The difference in percent tissue water between snails acclimated to 10 and 30‰ S prior to salinity fluctuation was greatest at 30°C, intermediate at 20°C, and least at 10°C. Hemolymph [Na+], [Mg2+], [K+], and [Cl-], tracked ambient salinity least well at 10°C and most closely at 30°C. Passive factors are likely to be responsible for the differences in hemolymph osmotic and ionic fluctuation observed at 10° , 20°, and 30°C. Tissue NPS did not fluctuate with daily salinity cycles in either the 30-10-30‰ or 10-30-10‰ diurnal patterns of fluctuating salinity. Foot tissue NPS of snails acclimated to 30‰ did not change over three weeks of exposure to a 30-10-30‰ S pattern of fluctuating salinity but NPS in the foot of snails acclimated to 10‰ S and subjected to a 10-30-10‰ S pattern of fluctuating salinity increased significantly in 15 days and remained significantly higher on Day 21.