Full Citation (click to download full paper):
Haines, Leon (2015) The dietary preferences, depth range and size of the Crown of Thorns Starfish (Acanthaster spp.) on the coral reefs of Koh Tao, Thailand. Thesis paper. Van Hall Larenstein University of Applied Science, Netherlands, 38pp.
Acanthaster is a specialized coral-feeder and feeds nearly solely, 90-95%, on sleractinia (reef building corals) preferably Acroporidae and Pocilloporidae families. The Acanthaster is common in small numbers on reefs; in these abundances the starfish do not threaten the overall reef health. However when densities increase, large-scale coral predation can cause wide spread coral mortality and destroy the living habitat provided to reef fishes and invertebrates.
These large increases of Acanthaster densities are referred to as ‘outbreaks’. This increase is likely caused by anthropogenic influences such as; overfishing of predators and nutrient runoff causing phytoplankton blooms, which provide abundant food sources for Acanthaster larvae. The threat of the Acanthaster outbreaks may have significant implications for the island of Koh Tao compounding other environmental threats.
Acanthaster poses a great biological threat to the coral reefs on which the islands environment and economy rely. Understanding the biology of this population is important in creating effective management techniques for controlling Acanthaster population outbreaks on Koh Tao. In this study the dietary preferences, size and depth of Acanthaster on Koh Tao were researched.
On Koh Tao the preferred prey genera for Acanthaster is Fungia, which was found to be the prey of 17% of Acanthaster found during this study. After Fungia, Pavona was found as most preferred with 15%, Porites 14%, Acropora & Favia 9% and Favites 8%.
Acanthaster individuals located during the study ranged in size from 12 cm in diameter to 52 cm in diameter. The average size was found to be 35 cm in diameter. The life stage of individuals over 35 cm in diameter is categorized as senile adults, aged 5 years and over.
The majority of Acanthaster was found in the size classes 29-36 cm (41%) and 37-44 cm (33%). This means the majority of Acanthaster found can be classed in either the life stage; coral feeding adults or senile adults.
The average depth of Acanthaster on Koh Tao was found at 9.8 meters deep. The majority of Acanthaster was found in the depth classes 6-9 meters (32%) and 9-12 meters (29%) deep. The minimum depth Acanthaster was found on was 2.1 meters and the maximum depth was 18.5 meters deep.