Jane Heintz asks why the salinity of the ocean might change from day to day or year to year. It is hard for a doctor to diagnose a patient at a distance, but here is one possibility. Is the ocean near Pawleys Island (South Carolina) normally diluted by fresh water from the mouth of a nearby river? If so, then consider that rivers are abnormally low in the southeastern United States this year because of low rainfall, which is an effect of El Nino. Yes, El Nino is to blame once again! On a day-by-day basis, currents could redirect the plume of fresh water from your part of the shoreline to other areas. As to effects on local mollusks, some species are strongly affected by changes in salinity and others are much less so. I don't know of any molluscan species that can live AND BREED in both fresh and fully marine water. For instance, the bay clam Rangia cuneata (Sowerby, 1831) thrives in the fresh parts of Lake Ponchartrain, Louisiana, growing to an abnormally large size there, but these giants cannot breed in fresh water. What kinds of clams and snails are especially affected by changes in salinity, for instance, during floods and droughts? Andrew K. Rindsberg Geological Survey of Alabama