Growth and reproduction of Halicarcinus australis (Haswell) (Crustacea, Brachyura) in the Swan estuary, Western Australia. I. Crab instars

Abstract

Populations of Halicarcinus australis (Haswell) were sampled at regular intervals for several years at three localities in the Swan estuary, the water of which is predominately fresh in winter and brackish to marine in summer.

The populations differ consistently in size structure, fecundity, and sex ratio. Some mean values for the three localities, in order from the most downstream, are: proportion of females carrying eggs-0.24, 0.58, and 0.15; proportion of males with pulvini ( ie . fully grown) -0.21, 0.32, and 0.16; and male to female ratio- 1.17, 0.79, and 1.47. A typical postlarval history is: rapid growth from an early crab instar in midsummer to reach maturity shortly before or after winter, copulation, successive ovulations beginning in late winter (females), and death in midsummer. The summer deaths appear to result from postreproductive morbidity rather than from environmental factors. Crab instars are able to survive the environmental extremes in the estuary. They tolerate chlorinities from at least 0.5 to 19.4‰, and they tolerate 33°C for 5 hr when acclimated at 20±1°C and 12‰ chlorinity.

Similarities are noted between the biology and population parameters of postlarvae of H. australis and a mussel, Xenostrobus securis (Lam.), in the Swan estuary. The data for H. australis are also compared with those for a euryhaline marine hymenosomatid, Hymenosoma orbiculare Desm., in the Sand Vlei estuary, South Africa.