The correct answer is Starfish. Key Points - Keppel Island is located in the Southern Great Barrier Reef. - Coral bleaching occurs when reef-building corals shed their tiny algae to relieve stress and to increase their chances of survival. - A primary cause of coral bleaching on the Great Barrier Reef during summer is heat stress resulting from high sea temperatures and increased UV radiation. - A temperature increase of just one degree Celsius for only four weeks can trigger bleaching. - Deprived of their food source, corals begin to starve once they bleach. - Another major reason for bleaching in Keppel Island is Starfish whose population has grown uncontrollably in this region. - Normally, the starfish contribute to the reef's diversity by eating faster-growing coral species, which allow for slowergrowing species to thrive. - But at outbreak levels, the starfish are able to eat coral, a polyp that builds the limestone reefs on which they communally live, faster than the coral can reproduce. - This causes stress on the corals and leads to bleaching.