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The corallivorous crown-of-thorns starfish (Acanthaster planci) is perhaps one of most well known echinoderms on coral reefs, notorious for episodic population explosions and coral consumption on such unprecedented scales with major consequences to community structure. Outbreaks of A. planci, represent one of the most significant biological disturbances on coral reefs and remain one of the principal causes of widespread decline in live coral cover in Indo-Pacific reefs. At several locations, the effects of severe outbreaks on reef-building corals have been far greater than combined effects of all other major disturbances, including climate-induced coral bleaching. Increasing frequency and intensity of outbreak episodes have resulted in progressively slower recovery, which consequently degrades the integrity of reef ecosystems. Despite previous and ongoing efforts to control A. planci populations, outbreaks continue to pose serious reef management challenges. Long-term or permanent solutions depend on understanding the different biological and ecological aspects of the life history of A. planci to establish key limitations in recruitment and population replenishment. Outbreaks are manifestations of inherent instability within certain systems, attributed to either unique life-history features (e.g., high fecundity, short generation times, high mortality during their early life-history, and generalised patterns of prey and habitat use) which predispose A. planci to major fluctuations in population size, or major changes in the physical and biological environment that release populations from usual regulating factors. The three most prominent hypotheses put forward to explain outbreaks of A. planci all involve natural variation and constraints on the reproductive biology and early life history. The 'natural causes hypothesis' is based on the assumption that population sizes of highly fecund organisms with planktotrophic larvae, such as A. planci, are inherently unstable. The 'predator removal hypothesis' suggests that A. planci populations are normally regulated by high rates of predation on post-settlement juvenile starfish and that outbreaks arise as a consequence of the release from predation pressure due to overharvesting of predators. The 'larval starvation hypothesis' suggests that terrestrial runoff due to heavy rainfall causes elevated nutrient levels and lead to phytoplankton blooms, which provides nutrition for otherwise starved A. planci larvae. These hypotheses are not always mutually exclusive and will most likely vary spatially and temporally. This chapter reviews the unique features of A. planci reproductive biology and early life history that make it predisposed to population fluctuations and discuss factors that regulate gametogenesis, fecundity, spawning, fertilization, larval development, and post-settlement survival. These stages of the life cycle of A. planci are subject to stochastic processes involving food availability, predation, disease, settlement and spawning cues, dispersal, and environmental factors. Understanding the collective response of A. planci to this array of factors is essential in developing strategies to manage A. planci populations and reverse sustained declines in coral cover.

Item ID: 34189
Item Type: Book Chapter (Research - B1)
ISBN: 978-1-63321-191-9
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A version of this publication was included as Chapter 3 of the following PhD thesis: Caballes, Ciemon Frank (2017) Environmental influences on the reproductive biology and early life history of the crown-of-thorns starfish. PhD thesis, James Cook University, which is available Open Access in ResearchOnline@JCU. Please see the Related URLs for access.

Date Deposited: 24 Nov 2014 02:27
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