Spatial and temporal distribution of early-stage phyllosoma of westren rock lobster, Panulirus cygnus

Abstract

Time-series sampling for early-stage phyllosoma of P. cygnus was carried out off the western coast of Australia near the centre of the population of breeding adults. Hatching occurred from November through February in 1973-74 and 1974-75. Spatial distribution of the larvae was similar between the two seasons studied. The density of newly hatched (stage I) phyllosoma was greatest along the off-shore portion of the continental shelf. The majority of larvae moved off shore soon after hatching and the relative abundance of stages 11 and 111 increased with distance off shore. An off-shore extension of the sampling yielded an estimated minimum net rate of off-shore transport of 5.25 km,day for the stage I phyllosoma taken at the station farthest off shore. In 1973-74. larval release increased gradually from a low level in November to a peak in mid January. In 1974-75 larval release commenced at least a month earlier and peaked in late November, tapered off through December, and peaked again in mid January. Water temperature correlated with temporal differences in larval release. Warmer temperatures early in the 1974-75 season apparently induced the onset of breeding early enough to permit a second breeding by some females. There appeared to be no periodicity of hatching related to the lunar cycle. The distribution of early-stage phyllosoma was patchy and the impact of patchiness on quantitative sampling is discussed.