Homing behaviour by destructive crown-of-thorns starfish is triggered by local availability of coral prey

Abstract

Corallivorous crown-of-thorns starfishes ( Acanthaster spp.) can decimate coral assemblages on Indo-Pacific coral reefs during population outbreaks. While initial drivers of population irruptions leading to outbreaks remain largely unknown, subsequent dispersal of outbreaks appears coincident with depletion of coral prey. Here, we used in situ time-lapse photography to characterize movement of the Pacific crown-of-thorns starfish ( Acanthaster cf. solaris ) in the northern and southern Great Barrier Reef in 2015, during the fourth recorded population outbreak of the starfish, but prior to widespread coral bleaching. Daily tracking of 58 individuals over a total of 1117 h revealed all starfish to move a minimum of 0.52 m, with around half of all tracked starfish showing negligible daily displacement (less than 1 m day −1 ), ranging up to a maximum of 19 m day −1 . Movement was primarily nocturnal and daily displacement varied spatially with variation in local availability of Acropora spp., which is the preferred coral prey. Two distinct behavioural modes emerged: (i) homing movement, whereby tracked paths (as tested against a random-walk-model) involved short displacement distances following distinct ‘outward' movement to Acropora prey (typically displaying ‘feeding scars') and ‘homebound' movement to nearby shelter; versus (ii) roaming movement, whereby individuals showed directional movement beyond initial tracking positions without return. Logistic modelling revealed more than half of all tracked starfish demonstrated homing when local abundance (percentage cover) of preferred Acropora coral prey was greater than 33%. Our results reveal facultative homing by Acanthaster with the prey-dependent behavioural switch to roaming forays providing a mechanism explaining localized aggregations and diffusion of these population irruptions as prey is locally depleted.

Quantifying shedding and degradation rates of environmental DNA (eDNA) from Pacific crown-of-thorns seastar (Acanthaster cf. solaris)

“…As such, the timing of feeding activities should be considered in the design of eDNA surveys. For example, during evening and nighttime when adult CoTS are more actively feeding (Burn et al 2020;Ling et al 2020), the eDNA concentration in the water column might be higher, introducing bias to the surveillance results.…”

Reef complexity influences distribution and habitat choice of the corallivorous seastar Culcita schmideliana in the Maldives

“…Finally, prey availability has widely been reported to influence corallivorous seastar distribution and movement on coral reefs (Burn et al 2020;Ling et al 2020). In the Maldives, C. schmideliana was observed preying preferentially on small coral colonies (diameter \ 10 cm) of Pocillopora spp.…”

Knowledge Gaps in the Biology, Ecology, and Management of the Pacific Crown-of-Thorns Sea StarAcanthastersp. on Australia’s Great Barrier Reef

“…This is because the feeding ecology of coral-feeding (adult and subadult) COTS is central to understanding their effects on coral assemblages and reef ecosystems (De'ath and Moran, 1998;Pratchett et al, 2009;Baird et al, 2013;Keesing, 2021). Moreover, there are important feedbacks between the availability of coral prey and foraging behavior of COTS (Ling et al, 2020), with potential flow-on effects to the condition and demography of COTS (e.g., Caballes et al, 2016Caballes et al, , 2017a; this, in turn, is likely important for understanding the cyclical nature of population irruptions on the GBR (Antonelli and Kazarinoff, 1984;Babcock et al, 2020). Therefore, there is a recognized need for more resolved information on the feeding ecology of adult COTS to understand whether fluctuations in the availability of coral prey may explain boom-and-bust cycles of COTS populations, as well as reconcile the specific effects of elevated densities of large adult COTS on coral assemblages and on reef ecosystems more generally (Table 1).…”

“…Aside from direct effects of elevated temperatures and other changing environmental conditions (e.g., ocean acidification) on the physiology, replenishment, and persistence of COTS, ongoing environmental change is likely to significantly alter the structure of coral assemblages and reef ecosystems (e.g., Hughes et al, 2018b), as well as environmental and biological (e.g., phytoplankton biomass and composition) conditions in surrounding waters (e.g., Lough et al, 2015). Most notably, severe mass bleaching and mass mortality of corals will alter the availability of coral prey for COTS, raising many questions about how this might affect the feeding behavior (Keesing et al, 2019;Ling et al, 2020), fitness, survival, distribution, and abundance of COTS (Table 7). There is also the potential for fitness, survival, and population dynamics of COTS to be altered by interactions between climate-driven environmental changes Research questions (n 5 38) relevant to the management of crown-of-thorns sea stars (COTS; Acanthaster sp.…”