Circatidal rhythmicity in the activity of the phenoloxidase enzyme in the common shore crab, Carcinus maenas

Abstract

Specimens of the common shore crab, Carcinus maenas, were entrained to three different tidal regimes in a controlled laboratory environment using a computer-controlled "tidal tank". The first entrainment condition simulated a sinusoidal semi-diurnal tidal excursion of 0.90 m. The second entrainment condition, termed "exposed tidal", used the same tidal excursion as the first but incorporated 2 hr exposure to air around low water. The third system was atidal and acted as a control environment. After 9 days incubation, haemolymph was removed from individual crabs and assayed for phenoloxidase activity. Circatidal rhythmicity in the activity of the phenoloxidase enzyme cascade was demonstrated for the tidally entrained crabs, with peak activities occurring at low water. The converse phase was found for the tidally exposed crabs. The data presented are discussed in terms of the role of phenoloxidase in crustacean host defence and in relation to the location of phenoloxidase within the granulocytes of decapod crustaceans. © 1995.