SHORT-TERM EFFECTS OF RAPID SALINITY REDUCTION ON SEED CLAMS (MERCENARIA MERCENARIA)

Abstract

Abstract Sudden salinity drops in Gulf Coast clam growing areas in Florida have been suggested as a cause of seed (juvenile) clam mortality. Laboratory experiments were used to assess short-term impacts of rapid salinity drops on hatchery-produced juvenile northern quahog (=hard clam), Mercenaria mercenaria, in two separate trials. Mortality and condition index (CI) were measured as response parameters. In Trial I, clams were exposed to a salinity drop of 5 ppt, 15 ppt, or 24 ppt over a span of 24 h, and the duration of this exposure was either 3 or 6 days. In Trial II, clams were either immediately immersed or dry-stored for 24 h prior to immersion, representing common treatment patterns by clam growers. In this trial, clams were exposed to acute salinity drops of either 10 ppt or 20 ppt for up to 7 days. Both trials were conducted at ambient seasonal temperatures. Juvenile hard clams were surprisingly robust and resilient to changes in salinity, experiencing less than 5% mortality after relatively abrup...