Impact of parasites on the reproduction and fecundity of the blue sand crab Portunus pelagicus from Moreton Bay, Australia

Abstract

The rhizocephalan Sacculina granifera had a marked effect on the gonad development and growth of its host Portunus pelagicus. Crabs were frequently castrated by the parasite but, in some cases, castration was incomplete, ie the reproductive potential of the infected host is not necessarily zero. Crabs were susceptible to infection by the parasite at any size/age, but juvenile crabs were more frequently infected. The abundance of the egg predator Carcinonemertes mitsukurii was correlated with salinity and temperature, but not with egg mortality on the host. Hence, the worms had little impact on host fecundity. The nicothoid copepod Choniosphaera indica was the major source of egg mortality on P. pelagicus. Mean mortality due to the copepod was 2.4% (range 0-19.6%). While the copepod may be capable of rapid development and infection of crab clutches, it had a negligible effect on host fecundity because it occurred at relatively low intensities (1-1821 copepods host-1). The parasite and egg predators exhibited seasonal patterns in their infections of the host population. Seasonal patterns were found in the molting, mating, gonad development, breeding, and sex ratios of crabs. -from Authors