Temporal and spatial distribution and abundance of blue swimmer crab (Portunus pelagicus) larvae in a temperate gulf

A plankton-sampling programme for blue swimmer crab (Portunus pelagicus) larvae was conducted in the temperate waters of Gulf St Vincent, South Australia, to investigate: (1) if larval hatching is seasonal; (2) if larvae are restricted to surface waters; (3) if larvae are hatched offshore; and (4) if larval development occurs offshore. The temporal and spatial distribution and abundance of larvae indicated that hatching and zoeal development occur mainly in deeper offshore waters during the warmer months of November to March, and that zoeal development occurs in a range of depths from the neuston to at least 14 m. Although peaks in abundance usually occurred in the upper 3 m, zoeae were distributed throughout the water column, with the majority occurring in sub-surface waters below 1 m depth. There was no evidence for a daylight ontogenetic or tidal vertical migration in the four zoeal stages. Limited sampling revealed no evidence for a diurnal vertical migration in stage-1 zoea. Although the seasonal and inshore-offshore patterns of hatching observed in the study were typical for a portunid species, the broad vertical distribution differed from that observed for P. pelagicus in previous studies.