Modelling Growth of Juvenile Crown-of-Thorns Starfish on the Northern Great Barrier Reef

Abstract

Abstract:The corallivorous crown-of-thorns starfish (Acanthaster spp.) is a major cause of coral mortality on Indo-Pacific reefs. Despite considerable research into the biology of crown-of-thorns starfish, our understanding of the early post-settlement life stage has been hindered by the small size and cryptic nature of recently settled individuals. Most growth rates are derived from either laboratory studies or field studies conducted in Fiji and Japan. The Great Barrier Reef (GBR) is currently experiencing its fourth recorded outbreak and population models to inform the progression of outbreaks lack critical growth rates of early life history stages. High numbers of 0+ year juveniles (n = 3532) were measured during extensive surveys of 64 reefs on the northern GBR between May and December 2015. An exponential growth model was fitted to the size measurement data to estimate monthly ranges of growth rates for 0+ year juveniles. Estimated growth rates varied considerably and increased with age (e.g., 0.028-0.041 mm·day −1 for one-month-old juveniles versus 0.108-0.216 mm·day −1 for twelve-month-old juveniles). This pioneering study of 0+ year juveniles on the GBR will inform population models and form the basis for more rigorous ongoing research to understand the fate of newly settled Acanthaster spp.

30 Years of Research on Crown-of-thorns Starfish (1986-2016): Scientific Advances and Emerging Opportunities

“…Observations of newly settled A. cf. solaris in the field (Yokochi and Ogura 1987;Zann et al 1987;Wilmes et al 2016), have revealed a strong and consistent association with CCA, which is expected given that newly settled starfish feed almost exclusively on coralline algae (Yamaguchi 1973;Lucas 1984;Zann et al 1987).Settlement experiments conducted under laboratory conditions (Yamaguchi 1973;Johnson et al 1991;Uthicke et al 2015b;Wolfe et al 2015a;Kamya et al 2016;Pratchett et al 2017b) reaffirm that CCA is important for inducing CoTS settlement. When examined microscopically, the surface of CCA is roughly textured -this finescale topographic complexity can provide a tactile stimulus for larvae to settle (Lucas 1974).…”

“…However, collections were mainly intended to inform growth models (see section 2.16) and so limited information was collected regarding the specific habitat conditions and exact densities. Despite limited success in the past (Doherty and Davidson 1988;Johnson et al 1992), current work by Wilmes et al (2016) demonstrates that 0+ year juveniles can be effectively sampled in the field, and much more sampling is required to establish variation in rates of settlement across different reef areas, depths and habitats. There are also methods available for measuring settlement rates of Acanthaster spp., using settlement collectors constructed from high surface area plastic biospheres (Keesing et al 1993), which will be important to differentiate where larvae settle versus where they survive and are actually recorded several months after settlement (sections 2.9-2.11).…”

“…This special issue (Biology, Ecology and Management of Crown-of-Thorns Starfish) reflects the latest resurgence in scientific interest and research on Acanthaster spp., unequivocally focused on better understanding the initiation and spread of outbreaks, as well as refining the capability and capacity for effective management. In all, the papers presented in this special issue address: i) environmental drivers of fertilization and early development (Allen et al 2017;Caballes et al 2017b); ii) larval nutrition, larval development and implications for the 'nutrient enrichment hypothesis ' (Nakajima et al 2016;Brodie et al 2017;Caballes et al 2017a;Mellin et al 2017;Pratchett et al 2017b); iii) predation and implications for the 'predator removal hypothesis ' (Cowan et al 2016a' (Cowan et al , 2017Messmer et al 2017); iv) factors influencing settlement (Cowan et al 2016a;Pratchett et al 2017b); v) dispersal and genetics ; vi) longevity, growth, and size-and-age relationship (Wilmes et al 2016;MacNeil et al 2017); vii) movement (Sigl and Laforsch 2016); and viii) control and management (Buck et al 2016;Nakamura et al 2016).Aside from ongoing research to address critical issues related to the effective management of CoTS outbreaks, there have also been some fundamentally new directions for CoTS research in the last decade, enabled by advances in research methods and analytical capabilities. Therefore, this review also considers some of the foremost new directions for CoTS research, related to i) systematics and biogeography, ii) genetic and genomic sampling, iii) ecological modelling and iv) projected effects of environmental change.…”

“…However, the inability to quantify larval supply, settlement, and recruitment has so far prevented explicit testing of such assumptions. New methods aimed at measuring these processes are being developed and tested (Uthicke et al 2015a;Wilmes et al 2016) and will not only provide new opportunities to test questions pertaining to recruitment limitation, but may also provide an early warning system for detecting new and renewed outbreaks.The relationship between adult densities of Acanthaster spp. and their corresponding reproductive output versus local densities of larvae or juveniles (stock-recruitment relationships) is important for understanding the role of adult biology and behavior in initiating outbreaks, as well as informing the effectiveness of population regulation based on culling of adult starfish.…”

“…Importantly, these demographic processes have already been quantified for A. cf. solaris (Caballes and Pratchett Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 22 August 2017 doi:10.20944/preprints201708.0076.v1Peer-reviewed version available at Diversity 2017, 9, 41; doi:10.3390/d904004133 of 50 2014; Babcock et al 2016b;Wilmes et al 2016;MacNeil et al 2017;Pratchett et al 2017b) and are key to understanding population dynamics. …”