Abstract
Despite the commercial importance of the sea cucumberHolothuria leucospilotaincreasing in recent years, little is known of its spatial distribution and ecology in the South China Sea. We investigate the distribution, abundance, and recruitment ofH. leucospilotafrom 2017 to 2020 at two sites (S1 and S2) in Daya Bay, a typical subtropical bay which is strongly influenced by human activities in the South China Sea. We report hypoxia to driveH. leucospilotafrom deeper into shallower waters with higher DO concentrations at the mouth of Dapeng Cove in Daya Bay (S1), particularly during summer. Population size at S1 decreased by 90% from 2017 levels, before this area was opened to the public in 2018; recruitment was not observed by August (summer) of 2020. In contrast, in summers of 2017 and 2020,H. leucospilotaabundance at S2, a protected open-water area, increased by 84%, and the proportion of small-sized (recently recruited) sea cucumber in the population increased by 20%. Severe summer hypoxia at S1 could negatively influenceH. leucospilotaspawning and larval settlement, which combined with depletion of broodstock because of fishing pressure and/or hypoxia-induced mortality, could inhibit recruitment. In contrast, higher DO concentrations and abundant broodstock during summer (the breeding season) favoured recruitment ofH. leucospilotaat S2. Overall, hypoxia and anthropogenic disturbance impede recovery ofH. leucospilotaat S1, while at the protected S2, larvae may be released to settle in nearby areas. It is imperative to develop a better understanding of the biology, ecology and conservation of tropical sea cucumbers in China.
Highlights
Throughout Asia this species is fished in China, Malaysia, Thailand, Indonesia, the Philippines, and Viet Nam, and where it is fished there are few or no regulations pertaining to its harvesting (Purcell et al, 2012)
Site S2 might function as a nursery ground for sea cucumbers, and provide planktonic larvae for recruitment into nearby areas, it is unknown if these larvae will disperse to areas that are fished
Our results demonstrated that the summer hypoxia at the mouth of a subtropical bay (S1) could force sea cucumber H. leucospilota to aggregate in shallower waters, where they were captured by fishermen and tourists after this area was opened to the public
Summary
The sea cucumber Holothuria leucospilota occurs widely in shallow tropical and subtropical Indo-Pacific Ocean waters, where it is usually found on seagrass beds, and sandy and muddy substrata with rubble or coral reefs (Bonham and Held, 1963; Liao, 1997; Purcell et al, 2012; Yu et al, 2013). Holothuria leucospilota plays an important ecological role in nearshore marine systems by moving large amounts of sand, selectively feeding on organically rich components within the sediment, increasing nutrient and dissolved oxygen exchange between water and sediments, and altering sediment biota and carbonate dynamics (Bonham and Held, 1963; Sloan, 1979; Che, 1990; Zamani et al, 2018) It is a proposed bioremediator of organic polluted environments; its coculture in aquaculture systems mitigates organic pollution and improves environmental quality, rendering it a good candidate for integrated multi-trophic aquaculture (IMTA) systems (Yu et al, 2012, 2013). Overfishing and a lack of fishing regulations in Malaysia could put H. leucospilota at risk of local extinction (Harith et al, 2018)
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