Effects of light and microhabitat on activity pattern and behaviour of wild and hatchery-reared juveniles ofStichopuscf.horrens

Abstract

Animals develop behavioural strategies throughout life to improve their survival in nature. Juvenile activity and behaviour of the commercial tropical sea cucumberStichopuscf.horrenswere examined considering factors that may influence survival at this critical developmental stage. Wild juveniles were observedin situto describe diel activity and movement. Wild and hatchery-reared juveniles were observed in the laboratory to evaluate the influence of different light-dark cycles and microhabitats on feeding and sheltering behaviour. All juveniles (4–54 g) displayed a distinct nocturnal activity pattern both in the field and laboratory. Nocturnal activity was strongly associated with feeding and locomotion. Wild and hatchery-reared juveniles were most active at night, displayed intermediate activity during twilight, and minimal to no activity during daytime. Movement rates of wild juvenilesin situwere significantly influenced by time and size to a lesser extent. Under constant light and constant dark for 48 h, juvenile feeding rhythm was endogenously controlled and strongly entrained to natural light-dark cycles. Sheltering was directly affected by light and linked to strong phototactic and thigmotactic reflexes. Juveniles preferred vegetation as shelter compared to coral, sand or open space, and showed equal preference for seagrass and macroalgae. Deviations in behaviour of hatchery-reared juveniles under laboratory conditions indicate some degree of acclimation to an artificial environment with minimal threats and a decreased sensitivity to light. The implications of nocturnal feeding, light-induced sheltering, shelter preferences and acclimation to artificial conditions are discussed in relation to juvenile survival in nature and potential restocking of the species.