Australostichopus is a genus of sea cucumbers in the family Stichopodidae. It is monotypic, being represented by the single species Australostichopus mollis,[2] commonly known as the brown sea cucumber or Australasian sea cucumber.[3] This species has stimulated interest for its fishery potential in the Southern Hemisphere,[4] and for its capability to reduce waste produced by aquaculture. Despite its ecological role and abundance in New Zealand coastal waters, the scarcity of knowledge regarding A. mollis biology and ecology has hindered the development of a stable fishery industry. Importantly, A. mollis represents promising business potential within an important Asian market.[5] Recently its potential as a functional food has been evaluated, highlighting the nutritious components [6]
In New Zealand, A. mollis is found around the entire coast line of the country, sometimes co-existing with reef structures;[7] and from New South Wales to south Western Australia. The species principally inhabits the littoral at low tide level on sand, as well as in mud in protected areas. Their vertical range goes from shallows waters on the coast to around 200 metres of depth.[8][9]
Adult size is typically from 13 to 25 cm.[10] Body is soft, and colour varies from light mottled brown to black. A tube foot is present ventrally or extending up the whole body. Tentacles (20) with disc shaped tips surround the slit-like mouth. Retractor muscles are absent. Dorsally, A. mollis has pointed papillae which can be reduced on preservation.[7]
Described as detritivores, A. mollis mainly capture particles of organic matter from the substrata, which is highly nutritious.[7][11][12][13][14]
Via sexual reproduction, and sexes are generally separate, however some hermaphrodites have been found. Population sex ratio is 1:1.[10] Reproductive season is from October to February,[15] and periodicity of spawning is regulated by lunar cycles, specifically following a full moon.[16] Morphologic changes in reproductive periods include females changes in gonad colour and oocyte numbers, while in males there is an increase in the amount of spermatozoa in particular zones described as "wet mounts of 'mashed' gonad tissue".[16] Furthermore, there is an increase in spermatozoa in the lumen of histological sections. Studies suggest that spawning may occur repeatedly during a single reproductive season.[16]
Like other holothurians, A. mollis has the ability to regenerate its internal organs after undergoing a phenomenon called auto-evisceration. This process, which is thought to be induced by external stimuli, is characterized by violent and rapid expulsion of organs, followed by regeneration, which occurs at a slower rate than in other genera.[9] Nevertheless, a more recent study reports no spontaneous evisceration or seasonal atrophy of the viscera, highlighting that handling these organisms does not trigger such reactions and even suggesting than during predation it would not occur easily.[10][17]