Sea cucumbers are a common sight on Hawaii’s reefs. Distinct tubular shape, many times seen lying on sand resembling sausages, sea cucumbers are frequently seen my snorkelers and divers. Closely related to sea stars and sea urchins, their five-part radial symmetry is not as obvious, many of which are due to its internal structure. Tube feet cover the animal’s body are used for locomotion.
Most sea cucumbers feed upon organic matter in the sand. With a sweeping action, they intake sand or sediment with their feeding appendages then digest all organic matter, excreting the remainder in strands and piles of sand. Apart from excreting waste through its anus, it is also a means of respiration. Water is drawn in and expelled, reaching an organ called “respiratory trees” where oxygen is extracted.
Sea cucumbers have a couple of ways to defend themselves. Many have the ability to auto-eviscerate where the sea cucumbers ejects all its internal organs through the anus. It’s believed to sidetrack the predator while the sea cucumber escapes. Depending on species, regeneration can take a few months and during this time it does not have the ability to feed. Another means of protection is by expelling toxic white threads called Cuvierian tubules that can shock and entangle a predator. For an animal that lacks the ability to flee predators rapidly, these defense mechanisms can come in handy.
Sea cucumbers, like most echinoderms, reproduce by releasing sperm and eggs into the water. After a planktonic stage, larval will settle and mature. Many spawning events have been observed on Hawaiian reefs, typically during high tide on a full moon as members of the same species will be seen gathering emitting milky games through a pore near the mouth.
In olden days, some loli or sea cucumbers were eaten and used for medicine. Well represented in the Hawaiian waters, of the 1,200 living sea cucumbers, roughly 50 species inhabit the Islands.
*Due to the constant rotation of animals back to the ocean, the presence of any specific animal cannot be guaranteed.