HEMOLYMPH RESPIRATORY GAS, ACID-BASE, AND ION STATUS OF THE AMPHIBIOUS PURPLE SHORE CRAB LEPTOGRAPSUS VARIEGATUS (FABRICIUS) DURING IMMERSION AND ENVIRONMENTAL HYPOXIA

Abstract

ABSTRACT The ability of Leptograpsus variegatus to respire in water was assessed in laboratory simulations. The hemolymph respiratory gas, acid-base, ionic status, and metabolic status was assessed in acclimation conditions (access to air or water), during 12-h immersion and for 6 h after return to acclimation conditions. The importance of environmental O2 was subsequently determined by lowering water PO2. Submergence of Leptograpsus elicited a significant decrease in hemolymph PCO2 between 1- and 2-h immersion but neither CO2 content nor pH reflected this fluctuation. There was a significant a-v difference in hemolymph oxygenation which was maintained throughout the water-breathing phase. Both venous and arterial PO2 were significantly elevated from the initial value between 0.5 and 2 h of immersion. There was no decrease in O2 content or Hc-O2 unloading during immersion and hemolymph L-lactate remained below 1.5 mmol·l-1. Hemolymph osmotic pressure remained largely constant while Cl concentrations showed a brief increase 30 min after submergence. The K in hemolymph of L. variegatus increased steadily during immersion but was restored by the end of the recovery phase. In hypoxic water (20 torr), hemolymph lactate increased to 18 mol·l-1, while pH and PO2 were largely unchanged. The CO2 and Hc-O2 were maintained at a higher level than in normal water. Venous PCO2 and CCO2 increased progressively in response to hypoxia. The Ca and Mg were greater in the hemolymph of hypoxic crabs than in the normoxic crabs. Sustained immersion of Leptograpsus has no observable acid-base consequences, while O2 delivery was maintained, but with some reduction, in hemolymph oxygenation. Changes in strong ion concentrations are not important to acid-base balance in immersed L. variegatus. In hypoxic water, L. variegatus shows increased lactate production and compensatory increases in bicarbonate. Thus, Leptograpsus is suited to air-breathing, but is able to respire in water for at least 12 h and is thus truly amphibious.