Development of nocturnal feeding and photosensitivity in early juveniles of the warty sea cucumber Stichopus cf. horrens

Abstract

Behavioral responses to light of early life stages provide insights on the development of photosensitivity in nocturnal species such as Stichopus cf. horrens. In this study, the onset of nocturnal feeding behavior, growth, and survival during early juvenile development (0.56 ± 0.16 cm; 47 days post-settlement) of the species were investigated for 30 days, in the presence (S) or absence (W) of artificial shelters and under three light regimes: constant light (24 L), constant dark (24D), and a 12 -h light, 12 -h dark period (12 L:12D). Juveniles in all treatments fed initially during daytime hours but eventually exhibited a shift to nocturnal feeding by day 11. This behavioral shift to nocturnality was delayed among individuals under constant dark conditions. Continuous light exposure without shelter resulted in low juvenile survival and mass mortality in some replicates of the treatment. In contrast, growth and survival were highest for juveniles in constant dark. This study showed the endogenous control of feeding in this species. It also demonstrated that growth increases significantly when early juveniles are reared with shelters or in constant dark. Optimizing the light regime and type of shelter can improve food accessibility and juvenile growth without hindering the development of photosensitivity in early juveniles. Further studies are needed to enhance the nursery culture of this species.