Sea cucumbers what actually are they? There similar shape to the salad ingredient is the only similarity they have with cucumbers. They are actually distant relatives to starfish and urchins, as they are all part of the phylum echinoderms (a grouping together of related animals) which is from the Greek literally meaning “spiny skin. There are no land or freshwater dwellers, all echinoderms can only be found in our oceans. Sea cucumbers live on the sea floor worldwide and there is over 1700 different species. The Asia pacific region actually has the greatest numbers of sea cucumbers. On average they live for 5-10 years and range in size from less than a cm to one of the larger species (Synapta maculata) reaching up to a few meters.
Their diet consist mostly of decaying organic matter on the sea floor and sifting through the sediment and plankton in the water. They feed using tube feet (bit like tentacles) located around the mouth anything from 8-30 of them. They filter through sediment or use them to catch plankton, and one at a time wipe the food off in their mouth bit like sucking your fingers. They play an important role of cleansing their environment in multiple ways. One of which is they digest sediment and rubble and then poop out high levels of calcium carbonate. Which in turn increases the levels of calcium carbonate in the water by up to 50%. Good news for coral which uses this calcium carbonate for growth. They also eat large amounts of decaying Organic materials which are then redistributed from the marine sediments back into the water column.
Another few interesting facts, when they come under attack they do something called self-evisceration which involves expelling some of its internal organs. When threatened this t may actually satisfy the predator appetite or even scare it off. Good news its not the end of the world for the cucumber, they can regrow their organs in a few weeks. Not such a useful defense tactic against humans who harvest them for food. They are considered a delicately especially in Asia such as China. Population numbers seem to be steady, with none of the species being endangered or numbers declining as of yet. This could have something to do with their ability to reproduce completely by themselves however most sea cucumbers prefer or do reproduce by releasing sperm and eggs into the water to become fertilized.
Koh Tao’s sea cucumbers
Marbled sea cucumber– Pearsonothuria graeffei
This cucumber grows to about 30cm. Its mouth at one end as up to 24 paddle shaped tentacles which have black stalks and black on top with a white underneath. The body tends to be a pale brown and white, with black speckles. The juveniles however can easily be mistaken for the varicosa wartslug a type of nudibranch which mimics the marbled sea cucumber. These cucumbers are very interesting to watch feeding they are nocturnal so best to be on a night dive! as part of your Advanced open water or try the night Diving specialty. They also play an important role on the reefs of Koh Tao clearing substrate of algae, helping with new coral settlement.
Black sea cucumber or Lollyfish– Holothuria atra
The Lollyfish is an entirely black sausage shapedsea cucumber which tends to have sand stuck to it. When fully grown most commonly around 20cm but can reach up to 60cm. one of its defence mechanism against predators, is to emit a toxic red fluid when its skin is rubbed or damaged. They feed by filtering through the sand making it an important contributor to controlling nutrient levels.
Edible sea cucumber–Holothuria edulis
The Edible sea cucumber as the name suggests is edible it is most commonly dried first and then sold as “bêche-de-mer” or “trepang” most commonly in China and Indonesia. It is most active at night and during the day can be fond hiding under rocks or coral. Similar to the Lolly fish it feeds on the seabed by ingesting sand and other organic matter
Other species that can be found include