Field and Laboratory Avoidance Reactions by Blue Crabs (Callinectes sapidus) to Storm Water Runoff

Abstract A combined field and laboratory study was conducted to determine the avoidance reactions of blue crabs (Callinectes sapidus) to highly colored, acidic runoff from clear-cut timber areas above a productive north Florida estuary. Blue crabs of two age groups showed marked laboratory avoidance of runoff (pH 4.6, 5.8) and of test water with experimentally reduced pH. Within the pH range 4.5-7.0, there was an inverse relationship between pH and avoidance. Water color appeared to play a minor role in the avoidance reactions. Field data gave divergent results. Small crabs were abundant in areas characterized by pH levels strongly avoided under laboratory conditions. Large crabs, however, were conspicuously absent from such areas in the field, indicating possible avoidance. Factors other than pH were thought to be functional in the field distribution of the crabs. This study indicates that laboratory experiments without associated field studies may cause misleading results if they are applied to a determ...