Enhancement of larval and juvenile survival and recruitment in Acanthatser planci from the effects of terrestrial runoff: a review

Abstract

A number of authors have hypothesized that outbreaks of the crown-of-thorns starfish (Acanthaster planci) are initiated by increased larval survival. This is then linked to the presence, in the water column, of various components of terrestrial runoff (pesticides, lowered salinity, nutrients, and dissolved and particulate organic matter) during the pelagic larval stage of the starfish. A related hypothesis suggests that recent outbreaks on the Great Barrier Reef (GBR) are initiated by the eutrophic condition of the GBR lagoon. It is claimed that this eutrophication is caused by anthropogenic input of terrestrially derived nutrients. The present paper reviews current knowledge of the possible influence of components of terrestrial runoff on various stages in the life cycle of larval and juvenile A. planci. Processes that could be most influenced by enhanced nutrient conditions are those of planktonic survival, settlement success and juvenile survival. Available data on the state of eutrophication of parts of the GBR lagoon do not support assertions of general eutrophication but do suggest that elevated nutrient conditions exist in localized areas and that this may be caused by terrestrial runoff. The areas affected coincide with areas suggested as the primary initiation areas of two waves of crown-of-thorns outbreaks. Further research required to understand larval survival includes studies on differences in the kinds and amounts of food available to A. planci larvae in low- and high-nutrient conditions, the effects of elevated nutrients on coralline algae and their associated bacteria and hence larval settlement processes, and the offshore effects of river-borne nutrients in coral reef regions.