Sea cucumbers, giant clams, and sea urchins are just some of the indicator species that are recorded around Koh Tao.
Sea cucumbers detritus feeders removing organic material from the substrate They are usually found in abundance in sandy areas but some species can live on bio-film on rocks.
Crown of Thorns Starfish
A voracious predator of coral that has few natural predators. If unchecked, as happened on the Great Barrier Reef these can cause massive destruction of coral reefs in a relatively short space of time. The crown of thorns starfish is covered in venemous thorns, hence the name meaning that it has few natural predators. The Titon Trumpet, some large reef fish and the harlequin shrimp are some of the species that will eat the crown of thorns starfish. In small numbers they can help increase biodiversity by eating coral allowing that space to be occupied by new coral growth.
Giant clams filter sea water to extract plankton for food. They are sensitive to water quality and are therefore a good indication of water quality.
Diadema Sea Urchins
Diadema Sea Urchins consume periphyton. Periphyton is a mixture of algae and other nutrients. Periphyton is also an important indicator of water quality because it is extremly sensitive to ambient nutrient concentration. A high or low population of urchins indicate water quaility without expensive testing.
Trumpet Tritons are important as a control of on coral predation such as Crown of Thorn Starfish. Unfortunately their shells are often over collected in some areas. It was the over collection of these in the Great Barrier Reef that caused the Crown of Thorn population to grow to epidemic proportions. This in turn caused massive damage to coral on the reef.
Ascidians or sea squirts are exceedingly important to the coral reef ecosystem. They are divided into colonial or solitary species. Colonial species are inflated with water and the siphon action filters water for nutrients. Reportedly, a 3cm sea squirt siphon 4-5 quartz of water an hour. As filter feeders they do not do well in water with fluctuating salinity and therefore are a vital indicator water quality.
Drupella snails are a small mucirid gastropod found throughout the indo-pacific ocean which feed on living coral tissue (coralivore). The outbreaks, or overpopulations, have led to dramatic loss in living coral tissue, reduced reef resilience and recovery, from diseases. A stable ecosystem would see their numbers reduced as larvae when eaten by reef fish, however over fishing allows masses to survive to adulthood where they have few natural predators.