Crown of thorns (Acanthaster) are a vicious looking ‘starfish’ with a spiny circular body and more than 20 short arms covered in short spines. They tend to have red or green colouration and are unmistakable. Juveniles feed on coralline algae but adults feed voraciously on living coral. For this reason they are considered a pest and threat to coral reef health. Sudden increases in populations can be responsible for large areas of coral death; such population outbreaks are possible when natural predators such as triggerfish, wrasses and the giant triton shell are removed from an area. With the reduction in coral cover, biodiversity and abundance of fish species is impacted heavily, with families such as Butterfly fish who feed directly on live coral tissues disappearing from these areas.
Recently, on GVI Kenya’s snorkel surveys we have spotted three Crown of Thorns; two were found on transect 13 which is an area reef near Sii Island, still under pressure from fishing methods such as seine and ring nets which are dragged along the sea floor, and one on Transect 3, a reef inside the Mpunguti Marine Reserve where only traditional line and trap fishing is permitted. Corresponding closely with this was the number of sea urchins also located on these particular transects with 350 and 480 respectively.