Biochemical evidence for absence of feeding in puerulus larvae of the Western rock lobster Panulirus cygnus (Decapoda: Palinuridae)

Abstract

Changes in energy-reserves during the transition from phyllosoma through peurulus to juvenile in the Western rock lobster Panulirus cygnus (George, 1962) were studied by means of carbon: nitrogen analysis. Specimens were collected by means of plankton nets and puerulus collectors along the Western Australian coastline between July 1992 and January 1993. Reserves are accumulated during the last phyllosoma stage and are consumed during the puerulus stage. These observations support the hypothesis that the puerulus is a non-feeding stage. Based on basal metabolic rate and observed changes in reserves, the natant puerulus stage is calculated to last a maximum of ∼21.6d. When the estimated cost of swimming is taken into account, the duration is reduced to perhaps a week. The latter time-span corre-sponds with field observations that both abundance of planktonic pueruli in oceanic waters and inshore settlement of pueruli peak in the week around new moon. At 18°C, the puerulus metamorphoses to the first juvenile stage within 12.8 d after settlement; at 23°C this is reduced to ∼8.3 d. After settlement, puerulus larvae have an energetic advantage at elevated temperatures; the increased cost of metabolism is compensated by an accelerated development. The natant puerulus, however, appears to be slightly disadvantaged energetically at elevated temperatures; both C:N ratio and ash-free dry weight of pueruli just after settlement show a decreasing trend as the water temperature increases. The effect of water temperature and the distance from the edge of the continental shelf to the shore on consumption of energy reserves might provide a mechanism to partially explain temporal and spatial patterns in puerulus settlement.