Horizontal distributions of Dungeness crab (Cancer magister) and red rock crab (Cancer productus) larvae in the Strait of Georgia, British Columbia

The supply of planktonic larvae to adult populations is an important contributor to the spatial and temporal variability of benthic marine organisms. The ability to predict spatial patterns of larvae and recruits from the physical and biological processes that facilitate dispersal is required in order to advise and evaluate conservation and fisheries management decisions. In the present study, the horizontal distribution of Dungeness crab (Cancer magister) and red rock crab (Cancer productus) zoeae was described from surveys conducted in the Strait of Georgia in the spring of 2009 and 2010. Processes that may be responsible for generating spatial variability of larvae were evaluated based on (i) horizontal overlap between larvae and water properties, (ii) spatial dependence of larvae and water properties, and (iii) changes in the dispersion of stage-specific distributions. Interspecific variability between horizontal patterns of the first and second larval stages was primarily attributed to differences in the distribution of larval release locations, which appeared to be restricted to the southern and central strait for C. magister. Potential effects of physical processes on larval distributions are also discussed.

Physiological responses of postprandial red rock crabs (Cancer productus) during emersion

The physiological responses of unfed and postprandial red rock crabs ( Cancer productus J.W. Randal, 1840) were investigated during periods of emersion. During aerial exposure, oxygen uptake quickly fell to very low levels and was no longer detectable in the haemolymph after 12 h. The resulting anaerobic respiration led to a build up in lactic acid and the resulting acidosis was more pronounced in the postprandial crabs. There was also a concomitant rise in PCO2 and CCO2, and in both cases these were higher in postprandial animals. Higher ammonia levels in postprandial crabs showed that cellular activities were still proceeding anaerobically, suggesting that although crabs can delay mechanical digestion during emersion, once intracellular digestion occurs they may be committed to these processes. Increased mortality rates of postprandial animals were probably due to a combination of the high lactate and CO2 levels coupled with an increased ammonia concentration. For C. productus stranded in the intertidal zone there may be little effect of feeding, as they are only exposed for short periods and recovery occurs during re-immersion. The crabs are more likely to become moribund and death ensue during longer term exposure such as commercial live shipment.