The coral reefs in various areas of Nogas Island are now threatened due to the outbreak of COTS (crown-of-thorns starfish) observed in January 2008.
Crown-of-Thorns Starfish (Acanthaster planci) has thorn-like venomous spines sprouting all over its body. It could grow to more than 1 m in diameter and could have at least 12 arms up to 21 arms. It is considered the second largest starfish in the world after the giant sunstar.
COTS is a coral reef predator or a corallivor. It preys on the coral climbing onto them, extruding its stomach over them, and releasing digestive enzymes to then absorb the liquefied tissue. It is said that COTS can consume about 5-6 square meter of coral tissue per year.
According to the initial result of a study being conducted by UP Visayas Institute of Marine Fisheries and Oceanology and COASTHAVEN, Inc., if densities above 100 individuals per hectare are considered outbreaks, then the COTS densities counted at the island indicate an outbreak.
In their survey of the island, an estimated total of 297 COTS were counted and the occurrence of COTS around the island ranges between 1 and 122 individuals. High densities of 11-30 and 31-122 individuals were observed at the Northern and Southwestern part of the island, respectively.
Crown-of-Thorns Starfish (Acanthaster planci) has thorn-like venomous spines sprouting all over its body. It could grow to more than 1 m in diameter and could have at least 12 arms up to 21 arms. It is considered the second largest starfish in the world after the giant sunstar.
COTS is a coral reef predator or a corallivor. It preys on the coral climbing onto them, extruding its stomach over them, and releasing digestive enzymes to then absorb the liquefied tissue. It is said that COTS can consume about 5-6 square meter of coral tissue per year.
According to the initial result of a study being conducted by UP Visayas Institute of Marine Fisheries and Oceanology and COASTHAVEN, Inc., if densities above 100 individuals per hectare are considered outbreaks, then the COTS densities counted at the island indicate an outbreak.
In their survey of the island, an estimated total of 297 COTS were counted and the occurrence of COTS around the island ranges between 1 and 122 individuals. High densities of 11-30 and 31-122 individuals were observed at the Northern and Southwestern part of the island, respectively.
This outbreak could be due to natural fluctuations in temperature, salinity and availability of planktonic food that are favorable to high survival rates of COTS larvae. It could also likely be due to the decline of COTS natural predators through overharvesting and pollution. Another factor could be an increase of agricultural runoff which causes increase algal blooms. The more algal bloom there is for the coral polyps, which eat the eggs of the COTS, predation on the starfish's eggs are reduced.
As of now, cause of the outbreak is unknown.
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Thank you to Dr. Marielle C. van Riel of COASTHAVEN, Inc., San Jose, Antique for the information and data.
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