Larvae of the rock crab Cancer irroratus were cultured under specific environmental regimes to examine the influence of temperature and salinity on respiration and excretion rates during development. In addition, the type of biochemical substrate used for energy production was determined. The allometric relationship between oxygen consumption and body weight (VO2) was found to be affected by temperature but not by salinity. The data suggest that the successful development and recruitment of rock crab larvae is influenced by environmental conditions within their tolerance limits where physiological performance is impaired to such an extent that they are less fit to effectively compete within the zooplankton community.