Variation in incidence and severity of injuries among crown-of-thorns starfish (Acanthaster cf. solaris) on Australia's Great Barrier Reef

Despite the presence of numerous sharp poisonous spines, adult crown-of-thorns starfish (CoTS) are vulnerable to predation, though the importance and rates of predation are generally unknown. This study explores variation in the incidence and severity of injuries for Acanthaster cf. solaris from Australia's Great Barrier Reef. The major cause of such injuries is presumed to be sub-lethal predation such that the incidence of injuries may provide a proxy for overall predation and mortality rates. A total of 3846 Acanthaster cf. solaris were sampled across 19 reefs, of which 1955 (50.83%) were injured. Both the incidence and severity of injuries decreased with increasing body size. For small CoTS (60% of individuals had injuries, and a mean 20.7% of arms (±2.9 SE) were affected. By comparison, 450 mm total diameter) CoTS had injuries, and, among those, only 8.3% of arms (±1.7 SE) were injured. The incidence of injuries varied greatly among reefs but was unaffected by the regulations of local fisheries

Size‑specific recolonization success by coral‑dwelling damselfishes moderates resilience to habitat loss

Increasing degradation of coral reef ecosystems and specifically, loss of corals is causing significant and widespread declines in the abundance of coral reef fishes, but the proximate cause(s) of these declines are largely unknown. Here, we examine specific responses to host coral mortality for three species of coral-dwelling damselfishes (Dascyllus aruanus, D. reticulatus, and Pomacentrus moluccensis), explicitly testing whether these fishes can successfully move and recolonize nearby coral hosts. Responses of fishes to localized coral loss was studied during population irruptions of coral feeding crown-of-thorns starfish, where starfish consumed 29 (34%) out of 85 coral colonies, of which 25 (86%) were occupied by coral-dwelling damselfishes. Damselfishes were not tagged or individually recognizable, but changes in the colonization of different coral hosts was assessed by carefully assessing the number and size of fishes on every available coral colony. Most damselfishes (> 90%) vacated dead coral hosts within 5 days, and either disappeared entirely (presumed dead) or relocated to nearby coral hosts. Displaced fishes only ever colonized corals already occupied by other coraldwelling damselfishes (mostly conspecifics) and colonization success was strongly size-dependent. Despite movement of damselfishes to surviving corals, the local abundance of coral-dependent damselfishes declined in approximate accordance with the proportional loss of coral habitat. These results suggest that even if alternative coral hosts are locally abundant, there are significant biological constraints on movement of coral-dwelling damselfishes and recolonization of alternative coral habitats, such that localized persistence of habitat patches during moderate or patchy disturbances do not necessarily provide resilience against overall habitat loss

Modelling growth of juvenile crown-of-thorns starfish on the northern Great Barrier Reef

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

Microsatellites reveal genetic homogeneity among outbreak populations of crown-of-thorns starfish (Acanthaster cf. solaris) on Australia's Great Barrier Reef

Specific patterns in the initiation and spread of reef-wide outbreaks of crown-of-thorns starfish are important, both to understand potential causes (or triggers) of outbreaks and to develop more effective and highly targeted management and containment responses. Using analyses of genetic diversity and structure (based on 17 microsatellite loci), this study attempted to resolve the specific origin for recent outbreaks of crown-of-thorns on Australia's Great Barrier Reef (GBR). We assessed the genetic structure amongst 2705 starfish collected from 13 coral reefs in four regions that spanned -1000 km of the GBR. Our results indicate that populations sampled across the full length of the GBR are genetically homogeneous (G'(ST) = -0.001; p = 0.948) with no apparent genetic structure between regions. Approximate Bayesian computational analyses suggest that all sampled populations had a common origin and that current outbreaking populations of crown-of-thorns starfish (CoTS) in the Swains are not independent of outbreak populations in the northern GBR. Despite hierarchical sampling and large numbers of CoTS genotyped from individual reefs and regions, limited genetic structure meant we were unable to determine a putative source population for the current outbreak of CoTS on the GBR. The very high genetic homogeneity of sampled populations and limited evidence of inbreeding indicate rapid expansion in population size from multiple, undifferentiated latent populations

Movement patterns of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) linked to habitat structure and prey availability

Patterns of movement and habitat use by adult crown-of-thorns starfishes (Acanthaster spp.) will have a major bearing on their distribution, reproductive capacity, and impacts on coral assemblages and reef ecosystems. The spatial and temporal scales over which crown-ofthorns starfish move will also have important implications for the scales at which they will be most effectively managed. Movement patterns of crown-of-thorns starfish have been studied previously, though mostly over small distances (metres) and limited timeframes (minutes to hours). This study reports on explicit studies that measured the movement rates and movement patterns of Pacific crown-of-thorns starfish (Acanthaster cf. solaris) at a range of temporal and spatial scales. In the first instance, we measured the instantaneous movement rates of starfish (n = 218) across different substrates; sand, coral rubble and consolidated carbonate pavement. This study was conducted in a large (5m diameter) tank, using video recordings that were then analysed to determine the mean and maximum rates of movement over successive 15-second intervals. To assess movement patterns of A. cf. solaris in the field, short-term tagging and movement studies were undertaken at Rib Reef, in the central GBR. All starfish (n = 357) recorded on semi-permanent transects were individually tagged using numbered pieces of flagging tape. The precise position of each starfish (where detected) was then recorded during successive surveys during day and night for up to 4 days. To further scale-up movement studies for crownof-thorns starfish we tagged 50 crown-of-thorns starfish using V7 (69KHZ) acoustic transmitters, at Lodestone Reef or Big Broadhurst Reef. The position of these starfish relative to acoustic receivers deployed 50-200m along the edge of the reef was recorded (at 3-minute intervals) for up to 8 months. Passive acoustic monitoring was intended to provide greater insights into longer-term (weeks to months) and larger-scale (kilometres) patterns of movement for crown-of-thorns starfish, but provided much less resolution regarding fine-scale movements of individual starfish. Instantaneous measures of movement capacity for A. cf. solaris (in aquaria) showed that these starfish are capable of moving at 20-35 cm per minute, and move fastest over sand. Despite their capacity for movement, field-based studies suggested that crown-of-thorns starfish actually move very little at scales of days to weeks, and even months. For starfish that were tagged with temporary visual markers, the minimum displacement distance recorded for the majority of starfish (88.0%) was <2m throughout the course of the study. Moreover, starfish that did move to feed (mostly at night) often returned to the same resting location between feeding bouts. Similarly, starfish tagged with acoustic transmitters for up to 6 months were only ever detected on adjacent receivers with large overlap in their ranges, suggesting that all starfish remained within 50-100m of where they were initially found and tagged for up to 6- months. The frequency and duration of passive detections varied greatly among individual starfish tagged with transmitters, with detections peaking in early hours of the morning. While this study shows that it is possible to effectively tag crown-of-thorns starfish, both over short and longer time-frames, there were considerable logistical challenges to documenting occasional large-scale, and presumably quite rapid, displacement of individual starfish. It is clear that crown-of-thorns starfish generally move very little and remain within localised areas (even returning to the same sheltering location between successive feeding bouts) of moderate to high coral cover. However, Acanthaster spp. are also capable of moving large distances when necessary, presumably when coral prey are locally depleted. It will be important to understand the nature and scale of both modes of movement to effectively manage population irruptions of crown-of-thorns starfish. Documenting the incidence and rates of movement during these infrequent events remains a priority for future research

Bleaching susceptibility of aquarium corals collected across northern Australia

Abstract There are a wide range of Scleractinian corals that are collected for the global reef aquarium market, often from non-reefal environments. The sustainability of coral harvesting is potentially threatened by increasing anthro- pogenic disturbances and climate change, though it is unknown to what extent many commonly harvested corals are susceptible to environmental change, or actually bleach during marine heatwaves. In this study, we experimentally tested the temperature sensitivity and bleaching suscepti- bility of six coral species (Homophyllia australis, Micro- mussa lordhowensis, Catalaphyllia jardinei, Trachyphyllia geoffroyi, Duncanopsammia axifuga, and Euphyllia glab- rescens), which are important components of the aquarium coral fisheries across northern Australia, in Western Aus- tralia, the Northern Territory, and/or Queensland. Inter- specific differences were evident in the temperature sensitivity and bleaching susceptibility among the study species. Homophyllia australis, and M. lordhowensis were found to be particularly susceptible to elevated temperatures, whereby all corals subjected to elevated temperatures died within the course of the experimental treatment (75 d). Catalaphyllia jardinei and E. glabrescens also exhibited significant increases in mortality when exposed to elevated temperatures, though some of the corals did survive, and C. jardinei mostly died only after exposure to elevated temperatures. The other species (T. geoffroyi and D. axifuga) exhibited marked bleaching when exposed to elevated temperatures, but mortality of these corals was similar to that of conspecifics held at ambient temperatures. This study highlights the potential for envi- ronmental change to impact the sustainability and viability of Australian coral harvest fisheries. More importantly, this study highlights the need for specific and targeted in situ monitoring for important stocks of coral fishery target species, to assess their vulnerability to fishery and fishery- independent effects

Spawning time of Acanthaster cf. solaris on the Great Barrier Reef inferred using qPCR quantification of embryos and larvae: do they know it’s Christmas?

Outbreaks of crown-of-thorns seastars (CoTS; Acanthaster spp.) are a major contributor to degradation of Indo-Pacific coral reefs. Understanding the dispersal and fate of planktonic life stages is crucial to understand and manage outbreaks, but visual detection of CoTS larvae is challenging. We apply a quantitative PCR (qPCR) assay to enumerate CoTS larvae in a 3-year time series of plankton samples from two reefs (Agincourt and Moore Reefs) on the Great Barrier Reef. Plankton surveys were complemented with settlement assays, and benthic surveys of juvenile and adult densities over time. Only one out of 109 plankton samples from Agincourt Reef had detectable CoTS mtDNA compared to 41 out of 575 samples from Moore Reef. This may be explained by differences in adult densities, or differences in connectivity and larval retention. Detections of larval CoTS were restricted to summer (November–February), with first detections each year coinciding with water temperatures reaching 28 °C and peak detections late December. A disproportionate number of larval detections occurred in 7 days around full moon. Complementary sampling of settlement and post-settlement life stages confirmed that elevated densities of CoTS larvae at Moore Reef translated to high rates of settlement adding to infestations at this reef. Moreover, there were declines in the detection of larvae, as well densities of juvenile and adult CoTS at Moore Reef, in 2017 and 2018. This study demonstrates that qPCR for genetic identification and quantification of larvae can assist to elucidate life history parameters of nuisance species difficult to obtain with other tools

Age and growth of an outbreaking Acanthaster cf. solaris population within the Great Barrier Reef

Despite having been studied for more than 40 years, much about the basic life history of crown-of-thorns starfish (CoTS; Acanthaster spp.) remains poorly understood. Size at age-a key metric of productivity for any animal population-has yet to be clearly defined, primarily due to difficulties in obtaining validated ages and potentially indeterminate growth due to factors such as starvation; within-population variability is entirely unknown. Here we develop age and growth estimates for an outbreaking CoTS population in Australian waters by integrating prior information with data from CoTS collected from multiple outbreaking reefs. Age estimates were made from un-validated band counts of 2038 individual starfish. Results from our three-parameter von Bertalanffy Bayesian hierarchical model show that, under 2013-2014 outbreak conditions, CoTS on the GBR grew to a 349 ( 326, 380) mm (posterior median (95% uncertainty interval)) total diameter at a 0.54 (0.43, 0.66) intrinsic rate of increase. However, we also found substantial evidence (Delta DIC > 200) for inter-reef variability in both maximum size (SD 38 (19, 76)) and intrinsic rate of increase (SD 0.32 (0.20, 0.49)) within the CoTS outbreak initiation area. These results suggest that CoTS demography can vary widely with reef-scale environmental conditions, supporting location-based mechanisms for CoTS outbreaks generally. These findings should help improve population and metapopulation models of CoTS dynamics and better predict the potential damage they may cause in the future

Rising temperatures may drive fishing-induced selection of low-performance phenotypes

Climate warming is likely to interact with other stressors to challenge the physiological capacities and survival of phenotypes within populations. This may be especially true for the billions of fishes per year that undergo vigorous exercise prior to escaping or being intentionally released from fishing gear. Using adult coral grouper (Plectropomus leopardus), an important fisheries species throughout the Indo-Pacific, we show that population-level survival following vigorous exercise is increasingly compromised as temperatures increase from current-day levels (100-67% survival at 24-30&thinsp;&deg;C) to those projected for the end of the century (42% survival at 33&thinsp;&deg;C). Intriguingly, we demonstrate that high-performance individuals take longer to recover to a resting metabolic state and subsequently have lower survival in warm water compared with conspecifics that exercise less vigorously. Moreover, we show that post-exercise mortality of high-performance phenotypes manifests after 3-13 d at the current summer maximum (30&thinsp;&deg;C), while mortality at 33&thinsp;&deg;C occurs within 1.8-14.9&thinsp;h. We propose that wild populations in a warming climate may become skewed towards low-performance phenotypes with ramifications for predator-prey interactions and community dynamics. Our findings highlight the susceptibility of phenotypic diversity to fishing activities and demonstrate a mechanism that may contribute to fishing-induced evolution in the face of ongoing climate change

Body Size and Substrate Type Modulate Movement by the Western Pacific Crown-Of-Thorns Starfish, Acanthaster solaris

The movement capacity of the crown-of-thorns starfishes (Acanthaster spp.) is a primary determinant of both their distribution and impact on coral assemblages. We quantified individual movement rates for the Pacific crown-of-thorns starfish (Acanthaster solaris) ranging in size from 75–480 mm total diameter, across three different substrates (sand, flat consolidated pavement, and coral rubble) on the northern Great Barrier Reef. The mean (±SE) rate of movement for smaller (diameter) A. solaris was 23.99 ± 1.02 cm/ min and 33.41 ± 1.49 cm/ min for individuals \u3e350 mm total diameter. Mean (±SE) rates of movement varied with substrate type, being much higher on sand (36.53 ± 1.31 cm/ min) compared to consolidated pavement (28.04 ± 1.15 cm/ min) and slowest across coral rubble (17.25 ± 0.63 cm/ min). If average rates of movement measured here can be sustained, in combination with strong directionality, displacement distances of adult A. solaris could range from 250–520 m/ day, depending on the prevailing substrate. Sustained movement of A. solaris is, however, likely to be highly constrained by habitat heterogeneity, energetic constraints, resource availability, and diurnal patterns of activity, thereby limiting their capacity to move between reefs or habitats