Apostichopus japonicus

Background

The Japanese sea cucumber has a cylindrical leathery body with blunt, thorny protuberances. At the anterior end is a mouth surrounded by a ring of short feeding tentacles, and at the posterior end is the anus. Three different colour morphs exist: red, green, and black.

The red morphs are found on gravel beds offshore at depths of 40 metres or deeper, while the other two colours are found intermingled on muddy and sandy bottoms at shallower depths. Although the red morph may breed red offspring due to reproductive isolation in a different microhabitat, DNA studies show limited genetic difference between it and the other morphs, with no significant difference between the black and green forms. In lagoons in southern Sakhalin, Russia, they are found on solid substrates among growth of the red alga Ahnfeltia tobuchiensis and in oyster beds (Crassostrea gigas).

The Japanese sea cucumber sifts through sediment with its tentacles, feeding on detritus and organic matter including plant and animal remains, bacteria, protozoa, diatoms, and faeces. The sexes are separate; males and females release gametes into the sea for fertilization. In the laboratory, spawning can be induced by varying temperature or using the neuropeptide cubifrin. Planktonic larvae develop through several stages before settling on hard surfaces, undergoing metamorphosis, and becoming juveniles.

In locations where water heats up excessively in summer, it undergoes aestivation—a state of dormancy where feeding stops, the gut degenerates, metabolism slows, and weight is lost. The threshold temperature is about 25 °C, higher for smaller individuals and those from the southern part of the range. This sea cucumber has been known to continue aestivation in some areas of China for four years.