Ecology and culture of the warty sea cucumber (Stichopus cf. horrens) in the Philippines

Stichopus cf. horrens is an exceptional sea cucumber species in its taxonomy, ecology, fisheries, and potential for culture. In the Philippines, it is commonly reported and considered a medium- to high-value commercial species. Phylogenetic analysis of samples collected from various sites throughout the archipelago, using mtDNA cytochrome oxidase I sequences (mtCOI), recovered two monophyletic lineages of S. horrens designated as Clade A and Clade B. Tack-like ossicles previously reported to be diagnostic for S. horrens were found in both clades. Cumulative evidence reveals that each clade exhibits variable body coloration, papillae morphologies, and behaviors that may be influenced by biogeography, habitat, or other intrinsic factors. The species is strictly nocturnal in most sites surveyed throughout the country, although populations in a few sites were observed to be active during the day. They are commonly found in coral reefs and adjacent seagrass beds. Juveniles are more abundant in the latter, but some are also found in macroalgal beds, indicating that these habitats are nursery areas for the species. Stichopus cf. horrens spawns year-round, this being confirmed through detailed observations in situ, spontaneous spawning events in the hatchery, and gonad analysis. Clade A individuals spawn spontaneously in the hatchery a few days before the new moon, while Clade B individuals spawn after the new moon. The species employs various strategies to improve reproductive success, including movement to higher locations, pairing, aggregation, synchronous spawning, and nocturnal and lunar spawning periodicity. This information is now being used to develop culture technology for the species including techniques for broodstock collection and maintenance, larval development, juvenile rearing, and grow-out. The knowledge is also critical in developing management and conservation interventions that will maintain viable spawning populations and sustain the fishery of this commercially valuable species complex for the country.