Responses of digestive enzyme profiles to various scenarios of food availability in newly-hatched Stage I phyllosoma larvae of the tropical spiny lobster Panulirus ornatus

Stage I phyllosoma larvae of the spiny lobster Panulirus ornatus hatch in tropical oceanic waters with limited and variable food resources. To better understand how these larvae cope with food deprivation, this study examined specific (mU mg⁻¹ protein) and total (mU larva⁻¹) activities of major digestive enzymes (i.e., α-amylase, non-specific esterase, trypsin-like protease) during a series of ex situ experiments. Specifically, temporal changes in enzyme profiles were examined in three experiments simulating scenarios in which phyllosoma hatch and begin development in an environment where (1) prey is either continuously present or absent; (2) prey is initially present, but subsequently absent; (3) prey is initially absent, but subsequently present. Results indicated that the accessibility of suitable prey provides an overarching influence on digestive enzyme activities and substrate utilisation in Stage I phyllosoma of P. ornatus, with enzymatic responses to both intermittent prey availability and food deprivation being influenced by their nutritional history. In the absence of prey, larval digestive enzyme activities (mU larva⁻¹) initially remained static from hatch but eventually declined with extended food deprivation. When prey became available, enzyme activities increased, with delayed access to prey having minimal impact on this enzymatic response. Furthermore, phyllosoma were able to adjust α-amylase and non-specific esterase activities (within 8 h) in response to the disappearance of prey, demonstrating adaptive changes to endure periods of food deprivation that were based on their nutritional history. The ability of phyllosoma to regulate enzyme activities from hatch is an important physiological strategy allowing them to survive in an environment characterised by highly variable zooplankton biomass and abundance, and explains why diets that differ greatly in nutrient composition have consistently been found effective for rearing phyllosoma in captivity.