Response of European flat oyster ( Ostrea edulis) hemocytes to acute salinity and temperature changes

Abstract

European flat oysters, Ostrea edulis, were exposed in aquaria to an acute decrease in salinity or increase in temperature. Oysters were removed at timed intervals and hemolymph withdrawn by cardiac puncture. Hemocytes were measured in vitro for their ability to adhere fluorescent 2-μm latex microspheres (beads). Measurements were made with an epifluorescent microscope by counting the number of beads attached to the hemocytes, which were settled, fixed and stained on glass slides. Oysters maintained at 20°C and 30 ppt salinity were exposed to water at 15 ppt salinity. The ability of their hemocytes to adhere fluorescent beads decreased at 4 h and 8 h after immersion, but returned to control levels by 24 h. When temperature was increased to 25°C (30 ppt salinity), a similar pattern was found; a decrease in the ability to adhere beads at 4 h and 8 h, but a return to control levels by 24 h. Oysters maintained at 15°C then immersed in water at 20 and 25°C (30 ppt salinity) supported these results: bead adherence decreased after 6 h at the warmer temperatures, but was greater at 24 h and 72 h. These results indicate that acute temperature and salinity changes in oyster environments create changes in hemocyte activity and may be reflected by in vitro measurements of bead adherence.