Sea cucumber culture, farming and sea ranching in the tropics: progress, problems and opportunities

Tropical sea cucumber mariculture has potential to become a profitable industry and contribute towards natural population replenishment. Here, we synthesise the fields of progress, current impediments and research opportunities in tropical sea cucumber aquaculture arising from recent studies and an Indo-Pacific symposium. We present novel comparisons of data from hatcheries, earthen ponds and sea pens from published and unpublished studies in various countries. Of the few tropical species to have been cultured, only the sandfish Holothuria scabra has been bred extensively. While risks from hatchery-produced sea cucumbers are recognised, more genetic research is needed in farming and sea-ranching programmes. Advances have been made in the culture and nursery rearing of tropical sea cucumber juveniles but few have been published. Sandfish larvae have now been grown successfully on just one microalga species, but experimental studies to optimise culture conditions are needed urgently. Disease of tropical sea cucumbers in culture is infrequent but the treatment of disease and parasites is understudied. Earthen ponds are currently most effective for nursery rearing of juvenile sandfish to a size for stocking. Growth rates and survival of sandfish in ponds to market size are also favourable, and should improve via studies on stocking density, feeding regimes and pond management. Sea pens confer ownership of released stock and can provide a means of limiting predation in natural habitats but the costs of materials, maintenance and surveillance against poaching can diminish profitability. Sea ranching has minimal material costs but needs a large leased area and may require juveniles to be marked prior to release. Retail prices of sandfish in Hong Kong increased exponentially with body size. A cost-benefit analysis illustrated that labour and utility costs in pond farming will preclude profitability of monoculture in some cases, forcing proponents to look towards co-culture or gamble with uncertain survival in sea ranching. Better governance and consultation regarding the stocking of sea cucumbers have been advocated. We conclude that well-designed experiments and meta-analyses are needed to fill critical knowledge gaps if sea cucumber mariculture is to expand in the tropics as it has in temperate Asia. Co-culture remains a burgeoning frontier despite poor success of initial studies. Sea cucumbers have superb potential to diversify mariculture industries in the tropics and potentially ameliorate the detrimental effects of mariculture on coastal ecosystems.