Metabolic response of the grass shrimp Palaemonetes kadiakensis Rathbun, to acute exposure of sublethal changes in pH

Abstract

The effects of sublethal changes in environmental pH on the grass shrimp Palaemonetes kadiakensis were determined using changes in metabolic rate and critical oxygen concentration as indicators of stress. Oxygen consumption was measured using a computer automated intermittent flow respirometer which allowed multiple sampling of a single individual without exposing it to prolonged oxygen stress. Metabolic rate and critical oxygen concentration were determined using a quadratic model with plateau nonlinear regression procedure. Sublethal changes in pH (6.5, 9.0) did not have a significant effect on metabolic rate. Temporary disturbances in hemolymph acid-base status caused by acute pH stress, may not elicit a metabolic response when not accompanied by necrosis of the gill epithelium. There was an effect of pH on critical oxygen concentration, with pH 6.5 significantly higher than the control (pH 7.8), and pH 9.0 significantly lower than the control. Shifts in critical oxygen concentration were attributed to changes in blood oxygen affinity caused by hemolymph acidosis or alkalosis.