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Coral-eating crown-of-thorns seastars (CoTS, Acanthaster spp.) are major contributors to the coral reef crises across the Indo-Pacific region. Until recently, CoTS throughout the Indo-Pacific were regarded to be a single species, Acanthaster planci. However, genetic and morphological analyses demonstrated that there are at least four distinct species: Acanthaster benziei in the Red Sea, Acanthaster mauritiensis and A. planci in the Indian Ocean, and Acanthaster cf. solaris in the western Pacific. Acanthaster cf. ellisii in the eastern Pacific needs more taxonomic attention. Here, we review the biological knowledge for each species adapting a pragmatic geographical species definition and using a systematic literature review complemented with more focused searches for individual species. The vast majority of CoTS research (88%) was conducted on A. cf. solaris, with much of this research undertaken on the Great Barrier Reef or in Japan. Many studies of A. cf. solaris are focused on monitoring or documenting incidences of outbreaks, though there is a solid base of knowledge on larval, juvenile and adult ecology derived from field and laboratory experiments. By contrast, most of the published studies on the four remaining species simply document cases of population outbreaks. The major taxonomic bias in CoTS research constitutes a significant limitation for understanding and managing these species for two reasons. First, even for A. cf. solaris, which is the most studied species, limited fundamental knowledge of their biology and ecology constrains understanding of the drivers of outbreaks and hinders corresponding management actions for prevention and control of these events. Second, understanding and management of other species are predicated on the assumption that all CoTS species have similar biology and behaviour, an unsatisfying assumption for ecosystem management. [ABSTRACT FROM AUTHOR]

Indo-Pacific corals predominantly reproduce using synchronous mass spawning events to maximise fertilisation. However, as disturbances continue to thin population densities, the quantities of gametes released declines and colonies become more isolated, reducing the likelihood of cross-fertilisation. Local hydrodynamic conditions can promote or inhibit gamete contact; thus, the interaction between the abiotic environment and sperm density will determine the amount of time gametes interact. In this study, we investigated the sensitivity of reproduction to manipulations of two key limiting factors of fertilisation: sperm concentration and contact time between gametes. We explored fertilisation kinetics of phylogenetically and functionally similar and diverse coral taxa on the Great Barrier Reef and Western Australia (Acropora digitifera, A. tenuis; Coelastrea aspera, Platygyra daedalea). Results indicate that fertilisation is optimised at sperm concentrations > 103 sperm mL−1 and contact times > 30 s, but the extent of these relationships is species-specific. All species showed clear differences in fertilisation success across contact times, although these differences were less distinct for A. tenuis and P. daedalea at very high sperm concentrations. Acropora digitifera and P. daedalea exhibited nonlinear trends with steep slopes of increased fertilisation success once sperm concentration surpassed values of 104 sperm mL−1 and 102 sperm mL−1, respectively, followed by slight declines. Acropora tenuis and A. digitifera had the highest maximum fertilisation success, likely owing to beneficial evolved functional traits like large egg sizes. The present analysis underpins studies of fertilisation kinetics in natural reef populations to help inform management and restoration practices that assist population resilience and recovery. [ABSTRACT FROM AUTHOR]