THE EFFECTS OF SALINITY STRESS ON THE RATES OF AEROBIC RESPIRATION AND PHOTOSYNTHESIS IN THE HERMATYPIC CORAL SIDERASTREA SIDEREA.

Corals are reputed to have low tolerance to salinity fluctuations. Yet the scleractinian coral Siderastrea siderea commonly inhabits reef zones and nearshore areas that experience salinity fluctuations of 5 to l0%. Small colonies of this species were subjected to both long-term and sudden decreases or increases in salinity. Their rates of aerobic respiration and photosynthesis, measured as changes in oxygen concentration, were followed for up to 144 hours after the sudden changes. Normal salinities of coastal waters near Panacea, Florida, are 28 to 30% but S. siderea was able to acclimate to 42% when salinity was increased slowly over a 30-day period. Neither respiratory nor photosynthetic rates of S. siderea were affected by changes in salinity of less than 10% above or below the acclimation salinity. Greater changes in salinity (either up or down) caused decreases in respiratory and photosynthetic rates proportional to the magnitude of the salinity change. Decreases in chborophyll per algal cell and in assimilation number were associated with and possibly responsible for some of the decreases in photosynthetic rates. These results show that S. siderea is able to withstand sudden and prolonged, environmentally realistic changes in salinity without measurable whole-animal effects. Further studies are needed to determine whether this species is remarkable in its ability to tolerate salinity change, or whether reef corals are more tolerant to salinity change than is generally believed.