The Western Rock Lobster (Panulirus cygnus George) is the most valuable single species fishery in Australia with an annual value in excess of $250 000 000. Consequently, there has been a substantial research effort geared towards gaining a better understanding of the basic biology of this species which has resulted in a comprehensive management programme by the Fisheries Department of Western Australia. This research effort has revealed, amongst other results, a correlation between the relative strength of post-larval recruitment and inter-annual variation in oceanographical processes. More specifically, the strength of puerulus settlement has been shown to correlate positively with the relative strength of flow of the Leeuwin Current as inferred by mean monthly sea level (Pearce & Phillips 1988). There is as yet no strong evidence to suggest a mechanism which might account for this con-elation. This is due largely to the scarcity of information available regarding the pelagic larval phase of the Western Rock Lobster's life cycle.

The bulk of our knowledge concerning the pelagic larval phase of the life cycle emanates from a series of oceanographical surveys conducted by the CSIRO in the 1970's which documented the horiwntal and vertical distribution of phyllosomata off the coast of Western Australia. The results of these surveys suggested that phyllosomata may modify patterns of daily vertical migration in order to take advantage of surface and subsurface circulation features such that horizontal transport conducive to recruitment is achieved (Rimmer & Phillips 1979). Correlational evidence suggests further that light may play an important role in regulating the depth distribution of phyllosomata and also that larval response to light may change with development These investigations did not, however, address the relative role of the Leeuwin Current in larval recruitment dynamics.

There is no laboratory based information available on the relative effect of light and temperature on phyllosoma behaviour and physiology due largely to the difficulties associated with reliable larval culture. Such information is vital to a comprehensive understanding of the possible mechanisms by which inter-annual oceanographic variation may affect larval growth and, ultimately, post-larval recruitment. The purpose of the present study was to investigate the behavioural ressponse to light and the physiological response to temperature of early and mid­stage phyllosomata cultured in the laboratory. The study was made possible because of recent advances in larval culture technology developed at the Marine Biology Laboratory of the Department of Zoology, University of Western Australia.