THE WESTERN ROCK LOBSTER PANULIRUS-CYGNUS (GEORGE, 1962) (DECAPODA, PALINURIDAE) - THE EFFECT OF TEMPERATURE AND DEVELOPMENTAL STAGE ON ENERGY-REQUIREMENTS OF PUERULI

Pueruli of the Western Rock Lobster Panulirus cygnus (George, 1962) ar e thought to be non-feeding. Consequently, the metabolic rate is expec ted to be low during this stage in order to conserve energy reserves. Furthermore, since water temperature potentially has a substantial imp act on energetic needs, the puerulus possibly exhibits mechanisms to r educe the effect of temperature on energy consumption. To test these p ropositions the metabolic rate was measured in post-settlement pueruli and in juveniles at two water temperatures. A respirometer of variabl e volume (10-50 ml) was designed for this purpose, incorporating a Cla rk-type oxygen sensor. Results were compared with data available from the literature. Oxygen consumption in pre-molt pueruli and in intermol t juveniles (1.48 to 5.65 mumol O2.individual-1.h-1 on average) was su bstantially higher than in post-settlement pueruli (1.06-1.41 mumol O2 .ind.-1.h-1). These significant changes could only partly be explained through changes in biomass. Furthermore, no significant effect of an increased water temperature (from 18 to 23-degrees-C) could be detecte d on the metabolic rate in post-settlement pueruli, and the effect is moderate in pre-molt pueruli (Q10 = 1.95). The water temperature has, however, a substantially greater impact on first and second molt juven iles (Q10 = 2.46 to 4.80). The energetic demand was calculated from ox ygen consumption and indicate that energetic needs of post-settlement pueruli is low compared with both pre-molt pueruli and juveniles. A lo w energetic demand and a reduced effect of temperature on energy consu mption is of considerable benefit to a non-feeding larva, and may prov ide the puerulus with a means of extending the duration of the non-fee ding stage and increasing the chance for survival beyond metamorphosis to the first feeding stage. Results indicate that the energetic deman d during metamorphosis may be considerable. It is postulated that ener getic requirements of the planktonic (actively swimming) puerulus larv ae are considerably higher and are likely to be more temperature depen dent.