Population biology and recruitment of a vulnerable sea cucumber, Stichopus herrmanni, on a protected reef

Abstract

Populations of tropical sea cucumbers, harvested for bêche‐de‐mer, are in a perilous state of conservation, yet there remains a paucity of information on the biology of many harvested species. We examined the population biology of the commercially important curryfish, Stichopus herrmanni, across 2 years on Heron Reef, a protected zone in the Great Barrier Reef (GBR) Marine Park. Stichopus herrmanni, a species recently listed as vulnerable to extinction, is a major target species for the fishery operating in the GBR. The size class distribution and density of S. herrmanni were documented for six sites across Heron Reef. There was distinct spatial variation in the size and density of S. herrmanni across sites, with no significant difference between the 2 years. The smallest individuals found were 10 cm long, some of the only juvenile S. herrmanni documented in nature. Juvenile and sub‐adult populations were found along the leeward reef edge of Heron Reef, a habitat characterized by shallow channels of sand between inter‐tidal coral reef and crustose coralline algae (CCA). Juvenile nurseries of sea cucumbers are rarely observed in nature, making this an important observation for understanding the recruitment and population biology of S. herrmanni. The presence of juveniles in the consolidated CCA habitat each year in autumn following the summer spawning period, and the absence of small individuals several months later in spring, suggests an ontogenetic migration or displacement of these individuals to adult habitat. The distribution of larger S. herrmanni suggests intra‐reef connectivity and migration into deeper lagoon areas. This study contributes to understanding the population dynamics of this vulnerable species, a consideration for fisheries management in light of increasing global harvest.

Gonad development and spawning of the Vulnerable commercial sea cucumber, Stichopus herrmanni, in the southern Great Barrier Reef

“…Gonad maturation is reached by November at OTI and New Caledonia (Conand, 1993a, b), as temperature and day length increase. Summer spawning indicates that the small individuals observed in autumn (four months later) on nearby reefs are likely to be new recruits (Wolfe & Byrne, 2017b).…”

“…At present there are no constraints on fishing throughout the year for S. herrmanni . Importantly, this species exhibits an ontogenetic migration within their recruitment reef (Eriksson et al , 2013; Wolfe & Byrne, 2017b). This connectivity between juvenile recruitment and adult habitats highlights the vulnerability of many marine species to overfishing (Gillanders et al , 2003; Grüss et al , 2011).…”

“…As deposit feeders, they process vast quantities of sediment, and thus play an important role in the mineralization and cycling of nutrients in benthic habitats (Uthicke & Klumpp, 1998; Uthicke, 1999, 2001; Purcell et al , 2016; Lee et al , 2017). The release of nitrogenous waste by aspidochirotids can increase the productivity of benthic microalgae and seagrass systems, a particularly important functional role in oligotrophic coral reef ecosystems (Uthicke & Klumpp, 1998; Uthicke, 2001; Eriksson et al , 2010; Wolkenhauer et al , 2010; Purcell et al , 2016; Wolfe & Byrne, 2017a, b). The digestion and dissolution of carbonate sands by tropical holothuroids can also influence local biogeochemistry by increasing local alkalinity, potentially buffering against ocean acidification and enhancing reef resilience (Hammond, 1981; Schneider et al , 2011, 2013; Wolfe et al , 2018).…”

“…The curryfish, Stichopus herrmanni , is an abundant Indo-Pacific sea cucumber distributed from East Africa to Australia and Indonesia, which inhabits sandy lagoons, seagrass and coral reef habitats between depths of 0–30 m (Conand, 1993a, b; Eriksson et al , 2013; Wolfe & Byrne, 2017a, b). Stichopus herrmanni , a mid- to low-value bêche-de-mer species, has become a major harvest target as populations of higher value species continue to decline (Purcell et al , 2013, 2014; Eriksson & Byrne, 2015).…”

The Effects of Hypoxia and Anthropogenic Disturbance on the Distribution, Abundance and Recruitment of the Sea Cucumber Holothuria leucospilota at the Mouth of a Subtropical Bay, China

“…Wild sea cucumber stocks are easily affected by fisheries, and marine reserves can assist in conserving their declining populations (Uthicke and Benzie, 2000;Anderson et al, 2011;Purcell et al, 2012Purcell et al, , 2013Wolfe and Byrne, 2017;Ramírez-González et al, 2020). In Ngardmau State, Palau, a decline in sea cucumber abundance occurred in one area open to fishing, while recovery occurred within a marine reserve (Rehm et al, 2014).…”