Growth and reproduction of Halicarcinus australis (Haswell) (Crustacea, Brachyura) in the Swan estuary, Western Australia. II. Larval stages

Abstract

Larvae of Halicarcinus australis (Haswell) were collected in vertical plankton samples from eight stations in the Swan estuary during two summers.

The majority of samples included live and dead larvae; the high proportion of dead larvae shows that there are other important causes of mortality besides predation. Third stage zoeae (the final larval stage) occur over more restricted salinity and temperature ranges than earlier zoeal stages, and their temporal and spatial distributions in the estuary are also more restricted.

Laboratory rearing of H. australis larvae at 16 chlorinity-temperature combinations shows that larvae are less tolerant of extremes of these parameters than crabs. Hydrological conditions unfavourable for larval development occur throughout the estuary in winter and in upstream regions in summer. However, during much of these periods ovigerous females are present in crab populations and larvae are released, thus accounting for some of the mortality apparent from the plankton samples.

Third stage zoeae are found progressively further up stream in summer associated with the advance of favourable salinities and with a zone of plankton abundance. Recruitment into crab populations reflects the time of completion of larval development at each locality.