The Influence of Metal and Temperature Stress on the Immune System of Crabs

That pollutants render many Crustacea more susceptible to disease implies a stressinduced decrease in immunocompetence. This study examines the effect of heavy metals (20, 50, 500 and 1000 jig 1-1 Cu, 10 and 500 jig 1-1 Cd, and 5 and 50 jig 1-1 Hg) and temperature on the cellular (haemocyte) component of the immune system of the shore crab, Carcinus maenas (L.). Marked fluctuations in circulating haemocyte numbers were observed in control crabs; these appear to correlate with daily changes in tidal height and the spring-neap tidal cycle. No change in haemocyte number was observed in crabs exposed to the metals for up to 30 days. However, Hg (Cu and Cd were not examined) at the highest concentration used, suppressed the tidal influence. A gradual rise in temperature from 10 to 200C significantly increased blood cell numbers although a rapid change initiated no response. In vitro cytotoxicity studies suggest that C. maenas haemocytes are relatively tolerant of metals. Copper had no effect on recognition or phagocytosis of bacteria in vitro although Cd slightly suppressed the latter. It is concluded that the immune system of C. maenas is relatively tolerant of metal stress. Key-words: Carcinus maenas, haemocytes, heavy metals, immunity