Effects of tidal fluctuations of salinity on hemolymph composition of the southern oyster drill Thais haemastoma

Abstract

Effects of varying the amplitude and duration of tidal fluctuations of salinity upon the hemolymph osmotic and ionic composition of the southern oyster drill Thais haemastoma were studied. The composition of diluent was varied during one experiment to approximate Mississippi River water. Snails were also subjected to a diurnal 20-10-20%. S fluctuation pattern for two weeks and hemolymph was collected twice daily. Amplitude of hemolymph osmolality and ion fluctuation during tidal fluctuations of salinity was directly related to the amplitude of ambient salinity fluctuation and inversely related to the rate of fluctuation. The rate of hemolymph osmolality and ion change was directly related to the rate of ambient salinity change. Dilution of seawater with simulated river water instead of deionized water resulted in a reduced amplitude of fluctuation of hemolymph osmolality and ion concentration. Most of the hemolymph osmolality fluctuation was due to solute movement and not to shifts in body water. Hemolymph, sodium and chloride level changed in a similar manner throughout all of the experiments except the 10-5-10% S-simulated river-water experiment in which chloride changed much less than sodium. Hemolymph ninhydrinpositive substance (NPS) levels cycled inversely with ambient salinity during the 30-10-30%. and 20-10-20%. S diurnal and the 30-10-30%. S semidiurnal experiments, but did not change during the 10-5-10%. S deionized water or simulated river-water experiment. Snails fed for most of the 2-week 20-10-2%. S diurnal cycle fluctuation experiment and no mortality occurred. Drills were hyperosmotic to the ambient water at all but two sampling periods, when they were isosmotic. Hemolymph NPS levels tended to be higher during low-salinity slack water than during high-salinity slack water. Even small fluctuations of ambient salinity result in fluctuations of hemolymph osmolality and ionic composition which may affect rate functions within the zone of capacity adaptation of the southern oyster drill.