Abstract
The Great Barrier Reef (GBR) is currently experiencing widespread crown of thorns starfish (CoTS) outbreaks, as part of the fourth wave of outbreaks since 1962. It is believed that these outbreaks have become more frequent on the GBR and elsewhere in the Indo-Pacific and are associated with anthropogenic causes. The two widely accepted potential causes are (1) anthropogenic nutrient enrichment leading to the increased biomass of phytoplankton, the food of the planktonic stage of larval CoTS; and (2) the overfishing of predators in the juvenile to adult stages of CoTS, for example, commercially fished species such as coral trout. In this study, we show that the evidence for the nutrient enrichment causation hypothesis is strongly based on a large number of recent studies in the GBR. We also hypothesise that secondary outbreaks in the region between Cairns and Townsville can also be enhanced by nutrient enriched conditions associated with the annual nutrient discharge from Wet Tropics rivers.
Highlights
The crown of thorns starfish (Acanthaster sp—CoTS) is a specialized coral-feeder and is found across the Indo-Pacific
The range of phytoplankton biomass, as measured via the chlorophyll a concentration, for the favorable development of CoTS, is 0.6–1 μg·L−1. It appears that well-nourished [73] larvae may be able to reach competency at a lower phytoplankton biomass, this has not been demonstrated. This may correspond to the low chlorophyll results of Wolfe et al [72], where larvae were able to reach competency at chlorophyll a concentrations in the range of 0.1 to
0.4 μg·L−1 ; in this study, the CoTS larvae were fed the microalga Proteomonas, an algae with hardly any chlorophyll, and so the results are hard to interpret compared to other phytoplankton food
Summary
The crown of thorns starfish (Acanthaster sp—CoTS) is a specialized coral-feeder and is found across the Indo-Pacific. Following the initiation of a primary outbreak, massive larval production [18] leads to secondary outbreaks to the north and south of the initiation area, with a wave of secondary outbreaks occurring to the south of the initiation area from Cairns towards Townsville, over approximately eight to nine years after the primary outbreak and offshore from Mackay (12 years after primary outbreak), after which the outbreaks appear to diminish [5] This contribution examines the latest research on the nutrient enrichment hypothesis for CoTS outbreaks, with a specific focus on the GBR, north-eastern Australia. We reinterpret recent works on the potential causes of CoTS outbreaks in the southern GBR
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