News / Species Spotlight / Revisited - Sea Cucumbers (11/10/15)

Revisited - Sea Cucumbers

Taxonomy

  • Class: Holothuroidea
  • Order: Aspidichirotida
  • Family: Holothuriidae
  • Genus: Holothuria
  • Species: Over 90 species
Description

Sea cucumbers are echinoderms that are covered in a thick leathery skin and have an elongated body. These animals have tube feet and the Holothuria spp. have numerous folds and are covered with conical podia, often with pointed tips. Most of the desirable species for the reef aquarium are less than 6 long. H. floridana is a common species from the Western Atlantic and Caribbean that has a variety of color morphs including dark gray, brown, bright yellow and other mottled patterns. H. atra is black and H. edulis is red with black, and both are imported from the Pacific. H. thomasi, also known as the "tiger tail", can reach lengths of 6' but are rarely collected at this size. Sea cucumbers are scavengers, feeding primarily on detritus as they sift through the substratum. When startled or threatened, Holothuria spp. can defend themselves by expelling their cuvierian tubules which may stick to predators. Most species possess toxins that are released when attacked; some are even capable of killing fish in the aquarium. Sea cucumbers are also known to have medicinal properties, and are consumed in some Asian countries as an aphrodisiac. Many mariculture farms now cultivate certain species to supply this demand. Nonetheless, the demand is so great that over-harvesting remains a problem in many regions. Another interesting fact is that many sea cucumbers have commensal relationships with crabs, shrimps, polychaete worms and small fishes.

Natural Habitat

Holothuria spp. are found in benthic zones from inter-tidal to offshore reefs. Primarily tropical and subtropical, sea cucumbers in this genus have a broad distribution range. Most are found in sandy rubble areas, seagrass beds and mangrove forests. They are somewhat cryptic and often cling to the underside of rocks and ledges.

Aquarium Care

As with other aquarium specimens, inspect the animal thoroughly before purchasing. Make sure there are no signs of damage or infection (which may appear as white patches) and that the tentacles are not continually distended. These sea cucumbers are a beneficial addition to the aquarium due to their ability to polish the sand by ingesting large quantities and then cleaning the sand as it passes through their digestive system. This process is critical for aquariums with deep sand beds and may even support the availability of free calcium ions. Most importantly, it keeps organic matter such as detritus from accumulating and the sand surface stays amazingly clean. Care should be given to keep sea cucumbers away from filtration and pump intakes, as they may become damaged and release toxins. Due to their efficient sand sifting, one per 20 gallons is typically suggested. If kept with serpent stars or sand conchs, one per 40 gallons is recommended. Reproduction in Holothuria spp. is commonly through broadcast spawning, while some are capable of asexual transverse fission. Once acclimated to the aquarium, these interesting and beneficial sea cucumbers can live for years and make a nice addition to the balanced reef tank.