Black Sea Cucumber, Holothuria (Halodeima) atra

Black Sea Cucumber, Holothuria (Halodeima) atra. Sea Cucumber collected in the Revillagigedo Islands, November 2023. Collection and pPhotographs courtesy of Aaron Woodrow, Juneau, Alaska. Identification courtesy of Dr. Francisco A. Solís Marín, UNAM, Mexico City.

Phylogeny:  The Black Sea Cucumber, Holothuria (Halodeima) atra (Jaeger, 1833), is a member of the Holothuriidae Family of Sea Cucumbers. It is also known as the Lollyfish Sea Cucumber. The Holothuria Genus is one of five genera in the Holothuriidae Family and there are one hundred and sixty species in the Holothuria Genus. The genus name Holothuria comes from the Latinized Greek words meaning “water polyp”.

Morphology: The Black Sea Cucumber has a round tubular elongated body that is slightly larger at one end, with a tapered head. Smaller individuals are short and thick. They are covered with thick skin with tall “tables”. Their mouth is located on the underside of the head and surrounded by a fringe of 20 black, branched tentacles. The Black Sea Cucumber are black in color but normally found camouflaged by a coating of light coral sand held in place by tube feet. They reach a maximum of 60 cm (2 feet 0 inches) in length and 2.0 kg (4 lbs 6 oz) in weight. The Black Sea Cucumber can be easily confused with and often found in close proximity to the Tarzan Sea Cucumber, Holothuria leucospilota (slender; always naked and black, found anchored to the substrate, softer skin with numerous short and squat flat “buttons”, with find protuberances giving it a prickly appearance, maximum length of 25 cm).

Habitat and Distribution: The Black Sea Cucumber is a common, wide-spread abundant, shallow water species that is found on the sea bed at depths up to 30 m (100 feet) found on reef flats and shallow coastal lagoons within sandy-muddy substrate with rubble or coral patches and in seagrass beds that are not fully exposed to wave action. Thy can survive out of the water during low tide events and can tolerate high temperatures. In-shore they are found in denser colonies of smaller individuals; in deeper water they are more scattered and larger in stature. They inhabit depressions and holding onto the relatively smooth reef-flat by means of their tube feet. Holothuria atra is found in the tropical Indo-Pacific region, ranging from the Red Sea and East Africa to Australia. They have a very limited distribution in Mexican waters of the Pacific Ocean being found in the coastal waters of the Revillagigedo Islands.

Diet: The Black Sea Cucumber is an omnivore that sifts through sediment feeding on detritus and other organic materials. At appropriate times they extends their highly mobile and extensible anterior end outward for feeding.

Predators:  The Black Sea Cucumber is not prone to significant predation other than on a limited basis by Sea Gulls. They possess a toxic red fluid in their skin which provides a defense mechanism. Unlike other Sea Cucumbers they do not eject Cuvierian tubules but instead extrude their internal organs through its anus.

Reproduction:  The Black Sea Cucumber has two morphs, that are genetically identical and are gonochoric (male or female for life); the sexes cannot be separated visually. The smaller one is found in coastal waters and reproduces via transversal fission. The larger one is found in deeper or on the outer reefs reproduce sexually via broadcast spawning, with external fertilization. Their gametes form planktonic larvae and after several weeks the larvae settle to the bottom to begin their benthic life.

Ecosystem Interactions: The Black Sea Cucumbers occupy an ecological niche almost devoid of other macroscopic organisms; occasionally small snails occur, but frequently theses sea cucumbers are alone. They are known to associate with the Sea Cucumber Crab, Lissocarcinus orbicularis, the Sea Cucumber Scale Worm, Gastrolepidia clavigeras and a handful of fishes. As they engage in sediment bioturbation they play an important role in the health of coral reefs.

Synonyms:  Halodeima atra, Holothruia amboinensis, Holothuria radackensis and Holothuria sanguinolenta.

Human Interactions: From a conservation perspective the Black Sea Cucumber is currently considered to be of Least Concern with stable, widely distributed populations. In some regions they are fished for human consumption and are prone to overfishing. They are utilized by the aquarium trade on at a nominal level. They are known to possess several chemicals of potential biomedical importance including high concentrations of Atratoxin A, B and B1, which have been shown to possess antimicrobial properties against various yeasts and fungi, lectin, sapogenins and triterpene glycosides.