In Situ Variability in Phenoloxidase Activity in the Shore Crab, Carcinus maenas (L.)

Abstract

This paper presents data from a 13-month investigation of the variation in phenoloxidase enzyme activity associated with the changing seasonal conditions in an estuarine ecosystem. Haemolymph samples were collected from shore crabs sampled in the field on alternate spring tides and ancillary measures of water temperature and salinity, total suspended particulate and organic load and bacterial population were made to provide data on the changing nature of the sublittoral ecosystem. Bacterial densities in the water column tended to be low (less than 7500 colonies ml−1) throughout the study except during September and October 1994 when mean recorded densities were 9200 and 12,500 colonies ml−1, respectively. This peak in bacterial abundance correlated (P < 0.05) with the maximum phenoloxidase enzyme activities recorded. Fluctuations in the activity of phenoloxidase were not attributable to changes in the circulating haemocyte population and the collected data is explained in terms of a stimulation of those processes involved in the formation of prophenoloxidase, the zymogen precursor of phenoloxidase, in response to the presence of bacterially derived compounds present in the water column.