Crown-of-thorns Starfish

Where Do COTS Live and What Do They Eat?

The species is native to coral reefs in the Indo-Pacific region.The species is most common in Australia, but can appear in the tropical and subtropical latitudes in the Red Sea and the east African coast across the Indian Ocean, and across the Pacific Ocean to the west coast of Central America. It occurs where coral reefs or hard coral communities occur in this region. They are corallivores (coral polyp eaters). Originally the coral-eating starfish played an important role in maintaining the coral reef population. It commonly consumes the fastest growing coral polyps such as staghorns and plate corals, which encouraged other slow coral species to form colonies and increase coral diversity. Even though the starfish tend to have a preference they will eat nearly all types of coral and their feeding preferences and behavior patters vary with population density, water motion and species composition.

The starfish positions itself closely to the surface of the coral by using its tube feet. It then extrudes its stomach out through its mouth over the surface to virtually it own diameter. The stomach then secrets digestive enzymes which absorb the nutrients from the liquefied coral. An individual starfish can consume up to 6 meters of living coral per year.

COTS have only a few predators which include the stripped pufferfish, the titan triggerfish, tritons, and the humphead maori wrasse.

COTS OUTBREAKS

The main concern with these gorgeous creatures is their outbreaks found along many reefs which had made up the Great Barrier Reef. The COT starfish has been one of the leading cause of coral cover loss over the past 27 years along with tropical cyclones.

The outbreaks are encouraged by ocean currents which begin in the north and migrate southward spreading larvae among the reefs. As well as an increase in phytoplankton, which are the main source of nutrients for larvae. Nutrient enrichment from agricultural land run-off may lead to COTS outbreaks because elevated nutrient levels cause phytoplankton blooms which provide a necessary food sources for the larvae. COTS increase in frequency over the last decades, have caused widespread damage to coral reefs in the Indo-Pacific, specifically to the Great Barrier Reef. The aggregation of COTS can strip a reef of 90% of living coral tissue. Outbreaks can last up to 8 years with approximately 1000 starfish per hectare, this leaves 150 reefs devoid of coral and 500 reefs damaged by the species. The exposed skeleton of the coral is diminished by filamentous algae, and is degraded until the coral complete dies.

“Without crown-of-thorns starfish outbreaks over the past 30 years, coral cover on the Great Barrier Reef would have slowly recovered from damage caused by storms and bleaching.”

The COTS can indirectly affect fish populations that depend on the coral reefs for habitat and protection. The affect dramatically decreased several species populations followed by the outbreaks of the starfish.

There have been numerous studies about population outbreaks specifially on the Great Barrier Reef as a means of understanding how the reef was dying and why it is now dead. Hypotheses were formed as to why the outbreaks were so severe, some of them included: over-collection of Trition and other predators of COTS, decline in predator population through habitat destruction and warmer sea temperatures encourage larvae development and survival. Another large hypothesis known as the "aggregation hypothesis" states that the outbreaks are caused by aggregating COTS from other corals, and usually travel in groups to attack coral which is unable to regenerate fast enough and then die.

Link for COT outbreaks:

https://www.youtube.com/watch?v=RBkv_SSvm5U#action=share

CONTROL OF COTSPrograms have been developed to control COTS. Several methods for species control include taking starfish ashore and burying them, injecting them with compressed air, baking them in the sun, injecting them with toxic chemicals such as sodium bisulphate (most effective), vinegar and building underwater fences to control COTS movement. Teams of divers have had kill rates of up to 120 per hour per diver. The latest successful method is injections of thiosulfate-citrate-bile salts-sucrose agar (TCBS), which leaves the species with a contagious disease with ulceration, loss of body turgor, loss of spines, accumulation of mucus and blisters causing sores on their dorsal integument. Even robots have been brought into action which are being tested now as a way of injecting the starfish to protect the divers and make the task less tedious.