Movement dynamics, sediment turnover and sheltering behaviours of the nocturnal coral reef sea cucumber, Stichopus cf. monotuberculatus

Abstract

Animal movement and feeding studies shed light on ecological roles and can inform management strategies for fished species. However, the feeding and movement of nocturnal sea cucumbers have been rarely studied. We determined the movement dynamics, feeding ecology and sheltering behaviour of the nocturnal Stichopus cf. monotuberculatus (dragonfish) at One Tree Reef and Heron Island Reef on the southern Great Barrier Reef. The short-term movement of individual sea cucumbers were tracked, and sediment defecation rates were measured. Displacement rates averaged 3–33 cm h−1 across the four sites, with the sea cucumbers moving more slowly approaching sunrise and within patches of organically rich sediment. The movement paths were moderately tortuous, with larger sea cucumbers moving along straighter paths. Rates of sediment turnover averaged 7.8 g h−1 and were greatest for larger individuals. The faecal casts were organically richer and composed of finer grains than the ambient surface sediments, implying that S. cf. monotuberculatus avoids consuming coarse sediments and feeds on nutritionally rich particles. The sea cucumbers sheltered under hard reef substrata and moved non-directionally on the seascape, with a few individuals homing back to their original refuges. The affinity to reef substrata and short nightly net displacements of S. cf. monotuberculatus have implications for the spatial management of this and other similar species. Larger individuals occupied deeper refuges, implying that projected declines in substratum rugosity on coral reefs due to climate change could impact the size structure of sea cucumber populations, with implications for fisheries.

Community structure of sea cucumber (Echinodermata: Holothuroidea) resources in the Kepulauan Seribu National Park, Indonesia

“…Fishermen and the community rarely take this type of sea cucumber so that its existence is easily found and very abundant compared to the type of sea cucumber that has high economic value. The people of the Kepulauan Seribu National Park search for sea cucumbers with a time ratio of every day, the search is carried out every day at the start of the evening, because they believe that it is easier to find sea cucumbers at night, this fact is reinforced by research that sea cucumbers are nocturnal animals (Purcell et al 2023), in addition to their nocturnal nature, sea cucumbers can also be found in the light of day, but the percentage is small and tends to be difficult, because sea cucumbers take refuge in coral reef ecosystems (Purcell et al 2023) in (Gray et al 2023). Remote locations in Indonesia have been used as used as fishing grounds because cucumber because cucumber fishermen have to scour the places to find the target species that the market wants.…”

“…Because they believe that sea cucumbers are more easily found at night, this is supported by research that shows sea cucumbers are nocturnal animals (Purcell et al 2023). Although sea cucumbers can also be found during the day, the percentage is small and they tend to be difficult to find because they hide in coral reef ecosystems (Purcell et al 2023) according to (Gray et al 2023). Many fishermen prefer to catch sea cucumbers with high economic value.…”