Cancer remains the primary cause of death worldwide. To develop less toxic anti-cancer drugs to relieve the suffering and improve the survival of cancer patients is the major focus in the anti-cancer field. To this end, marine creatures are being extensively studied for their anti-cancer effects, since extracts from at least 10% of the marine organisms have been shown to possess anti-tumor activities. As a classic Chinese traditional medicine, sea cucumbers and compounds extracted from the sea cucumbers, such as polysaccharides and saponins, have recently been shown to exhibit anti-cancer, anti-inflammatory, and anti-oxidant effects. Holothuria leucospilota (H. leucospilota) is a tropical edible sea cucumber species that has been successfully cultivated and farmed in large scales, providing a readily available source of raw materials to support the development of novel marine anti-cancer drugs. However, very few studies have so far been performed on the biological activities of H. leucospilota. In this study, we first investigated the anti-cancer effect of H. leucospilota protein on three cancer cell lines (i.e., HepG2, A549, Panc02) and three normal cell lines (NIH-3T3, HaCaT, 16HBE). Our data showed that H. leucospilota protein decreased the cell viabilities of HepG2, A549, HaCaT, 16HBE in a concentration-dependent manner, while Panc02 and NIH-3T3 in a time- and concentration-dependent manner. We also found that the inhibitory effect of H. leucospilota protein (≥10 μg/mL) on cell viability is near or even superior to EPI, a clinical chemotherapeutic agent. In addition, our data also demonstrated that H. leucospilota protein significantly affected the cell cycle and induced apoptosis in the three cancer cell lines investigated; in comparison, it showed no effects on the normal cell lines (i.e., NIH-3T3, HaCaT and 16HBE). Finally, our results also showed that H. leucospilota protein exhibited the excellent performance in inhibiting cell immigrations. In conclusion, H. leucospilota protein targeted the cancer cell cycles and induced cancer cell apoptosis; its superiority to inhibit cancer cell migration compared with EPI, shows the potential as a promising anti-cancer drug.

Because most tropical sea cucumbers have been overexploited around the world, the sea cucumber Holothuria leucospilota has become increasingly commercially important in recent years. Restocking and aquaculture of H. leucospilota using hatchery-produced seeds could both enhance declining wild populations and provide sufficient beche-de-mer product to satisfy increasing market demand. Identifying an appropriate diet is important for successful hatchery culture of the H. leucospilota. In this study, we trialed different ratios of microalgae Chaetoceros muelleri ( cells/mL) and yeast (Saccharomyces cerevisiae, cells/mL) in diets for H. leucospilota larvae (6 d after fertilization, referred to as “day 0”) at proportions 4 : 0, 3 : 1, 2 : 2, 1 : 3, and 0 : 4 by volume, in 5 treatments (A, B, C, D, and E, respectively). Larval survival rates in these treatments decreased over time, with the survival highest in treatment B (%) on day 15 (double that of the lowest rate in treatment E (%)). For any sampling event, larval body length in treatment A was always the lowest after day 3, and that for treatment B was always the highest, except on day 15. The maximum percentage of doliolaria larvae occurred in treatment B (23.33%) on day 15, followed by treatments C, D, and E (20.00%, 10.00%, and 6.67%, respectively). No doliolaria larvae occurred in treatment A, and pentactula larvae occurred only in treatment B (3.33%). On day 15 in all treatments, late auricularia larvae had hyaline spheres, but these were not prominent in treatment A. Densities of juveniles attaching to settlement plates varied with treatments, and the values were very low for the larvae only fed microalgae (A, ind per plate) or yeast (E, ind per plate)—only ~5% of the maximum number settling in treatment B ( ind per plate). Increased larval growth, survival and development, and juvenile attachment indicates that diets combining microalgae and yeast are more nutritionally balanced than single diets for hatchery of H. leucospilota. A combined diet of C. muelleri and S. cerevisiae at a 3 : 1 ratio is optimum for the larvae. Based on our results, we propose a larval rearing protocol to facilitate mass production of H. leucospilota.

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.

We conducted a laboratory investigation of the influence of water temperature on the physiological performance—including faecal production, oxygen consumption, and ammonia excretion rates—of the sea cucumber Holothuria moebii. Adult H. moebii (34.39 ± 5.17 g, wet weight) were exposed to four experimental temperatures (15, 20, 25, and 30°C), which represented the temperature range in their natural habitat. Results showed that the maximum faecal production rate was observed at 30°C (71.06 ± 7.21 mg g⁻¹ day⁻¹), which was significantly higher than at other temperatures. This indicated that, at a high temperature, H. moebii could take in more energy than at lower temperatures. The oxygen consumption rate increased with water temperature, and the minimum value observed at 15°C (5.68 ± 0.86 µg O₂ g⁻¹ hr⁻¹) was significantly lower than at other temperatures. The low oxygen consumption rate at 15°C indicated a low level of energy production by H. moebii during winter. The maximum ammonia excretion rate observed at 30°C (0.029 ± 0.007 µmol g⁻¹ hr⁻¹) was significantly higher than at other temperatures, and the positive effect of water temperature on nitrogen catabolism indicated the possibility of H. moebii being in a better nutritional status during the hot season. The minimum value of O/N ratio at 15°C (25.55 ± 4.70) indicated the mixed utilization of protein‐ and carbon‐based substrates during winter, while the high value of O/N ratios in other treatments (all >32) indicated the dominance of carbohydrate and/or lipid metabolism in warm and hot seasons. The results of this study suggest that H. moebii is more suitable for rearing in warm waters (>20°C).