The ecological effects of high densities of crown-of-thorns starfish (CoTS, Acanthaster spp.) are driven by their cumulative feeding pressure on coral assemblages, making accurate predictions of feeding impacts essential for management. Despite this, a limited understanding of the spatiotemporal dynamics of feeding behaviour, and the environmental and biological drivers underlying them constrains our capacity to predict feeding impacts. We quantified daily feeding rates for 565 individual Western Pacific CoTS (Acanthaster cf. solaris) across a broad gradient of environmental conditions and population densities on Australia’s Great Barrier Reef (GBR). CoTS body size and local coral cover emerged as the strongest predictors of daily feeding rates, whilst population density, season, and water temperature had no significant effect. Notably, large CoTS (> 40 cm) at high coral cover sites consumed over ten times more coral tissue compared to smaller individuals (15–25 cm) at low coral cover sites, with mean daily consumption rates of 221.99 and 18.86 cm2 (planar area), respectively. These estimates of daily feeding are aggregated across all different coral genera consumed. We present estimates of daily feeding rates for different size classes and coral cover that are directly compatible with existing monitoring methodologies used on the GBR, providing ecologically relevant parameters to improve outbreak impact modelling and enable more accurate forecasting of coral loss for targeted CoTS control on the GBR.

Coral reefs are one of the world's most threatened ecosystems, with transition from coral- to algal-dominated habitats becoming increasingly common. While habitat degradation in other ecosystems can lead to heightened stress among individuals, thereby increasing energetic demands and reducing fitness, the effects of habitat degradation on stress and metabolic performance of coral reef fish is unknown. Therefore, we investigated whether cortisol levels (an indicator of stress), metabolic performance, behaviour, and growth, were influenced by habitat quality in three fish species with varying degrees of reliance on live coral. We reared newly-settled fishes (Pomacentrus amboinensis, P. moluccensis and Dascyllus aruanus) for three weeks in one of three habitat treatments: live coral, dead coral covered in turf algae and cyanobacteria, or a combination of the two. After three weeks we quantified each individuals metabolic performance, cortisol concentration, morphology, and habitat use. Pomacentrus moluccensis had higher cortisol concentrations in the dead coral treatment, compared to the live coral, whereas there was no difference in cortisol levels among habitat treatments for P. amboinensis or D. aruanus. Overall, metabolic performance (aerobic scope, standard and maximum metabolic rate) showed no consistent response to habitat treatments. Regarding morphology, we only found D. aruanus to be impacted, with individuals from the live coral treatment having a significantly higher mass than individuals from the dead coral treatment. Behavioural space-use analysis revealed that D. aruanus and P. moluccensis spent more time away from their habitats in the dead coral treatments, whereas the space-use of P. amboinensis was unaffected by habitat degradation. Understanding how coral loss affects stress levels and fitness of reef fishes is critical to predict future reef fish communities. This study highlights that vulnerability of reef fish to coral reef degradation is species-specific, and related to their reliance on live coral. These changes may provide a mechanistic explanation to observed population declines following coral loss and indicate that remaining individuals have reduced fitness potentially compromising the subsistence of future populations.

The impact of eutrophication on wild fish individuals is rarely reported. We compared physiological and morphological traits of Siganus lineatus chronically exposed to aquaculture-induced eutrophication in the wild with individuals living at a control site. Eutrophication at the impacted site was confirmed by elevated organic matter (up to 150 % higher), phytoplankton (up to 7 times higher), and reduced oxygen (up to 60 % lower). Physiological and morphological traits of S. lineatus differed significantly between the two sites. Fish from the impacted site exhibited elevated hypoxia tolerance, increased gill surface area, shorter oxygen diffusion distances, and altered blood oxygen-carrying capacity. Elevated blood lactate and scope for anaerobic ATP production were observed, suggesting enhanced survival below critical oxygen levels. A significant 8.5 % increase in metabolic costs and altered allometric scaling, related to environmental degradation, were recorded. Our study underscores eutrophication's profound impact at the organism-level and the importance to mitigate it.

Tropical mangroves are known to support fish production, but natural variability in the link between mangrove habitats and fish populations undermines our ability to manage, conserve and restore this ecological relationship. This is largely due to undefined context-dependence in the use of mangroves by fish. We collected a spatially extensive dataset of 494 mangrove fish assemblages using standardised Remote Underwater Video surveys of mangrove edge habitats from five environmentally heterogenous regions in the Indo-Pacific. We used machine learning methods to define contextual limits of the use of mangroves by reportedly mangrove-affiliated fish. We found that tidal range and proximity to coral reefs were the most important contextual predictors of the use of mangroves by most taxa. We established data-driven threshold values for important contextual predictors of the use of mangroves by fish, offering new insights into the variable role played by tropical mangroves in supporting fish life histories. Where mangroves occur as part of reef seascapes in regions with limited tidal range (<1.5 m), they appear to serve an important juvenile habitat function for a wide spectrum of reef fish. In regions with substantially larger tidal ranges, mangroves appear to only support certain reef species with coastal life histories. Coastal and estuary fish were able to use mangroves in a wide variety of non-reef contexts. We demonstrate that key thresholds in environmental context can govern the functional role of mangroves, with strong implications for the role of other habitats in coastal seascapes.

A core challenge in ecology is identifying the factors that determine species distribution and functional diversity of species assemblages. Reef fish are the most diverse group of vertebrates, form taxonomically rich and functionally diverse communities and represent a key source of food for humans. We examine regional distribution patterns of reef fish species richness and functional diversity and investigate how these are determined by historical, biogeographic, energetic, and anthropogenic factors. We compiled data from 3,312 underwater visual censuses performed at 122 locations comprising rocky and coral reefs along the Eastern Tropical Pacific (ETP). We used generalized linear mixed‐effects models (GLMMs) implemented in a Bayesian framework to investigate whether distance from quaternary refugia, distance from mainland, shelf area, primary productivity, sea surface temperature (SST), human population gravity, and conservation status influence reef fish species richness and functional diversity in the ETP. Species richness and functional richness (FRic) peaked towards the center of the ETP and our null model suggests that FRic followed a spatial pattern that would be predicted by species richness. Additionally, functional evenness (FEve) was highest at higher latitudes whereas functional dispersion (FDis) was homogeneous throughout the ETP. Species richness was negatively influenced by shelf area and distance from mainland, but positively influenced by SST and conservation status. FEve was influenced by human population gravity and FDis by shelf area. Reef fish species richness and functional diversity in the ETP exhibited a strong division within the region mainly mediated by SST and human population gravity. Our results also suggest that dominant species within small shelf areas share more common traits than dominant species in large areas. This study uncovers previously unknown regional patterns of reef fish functional diversity and provides new insights into how historical, biogeographic, energetic, and anthropogenic factors influence complementary biodiversity facets.

A core challenge in ecology is identifying the factors that determine species distribution and functional diversity of species assemblages. Reef fish are the most diverse group of vertebrates, form taxonomically rich and functionally diverse communities and represent a key source of food for humans. We examine regional distribution patterns of reef fish species richness and functional diversity and investigate how these are determined by historical, biogeographic, energetic, and anthropogenic factors. We compiled data from 3,312 underwater visual censuses performed at 122 locations comprising rocky and coral reefs along the Eastern Tropical Pacific (ETP). We used generalized linear mixed-effects models (GLMMs) implemented in a Bayesian framework to investigate whether distance from quaternary refugia, distance from mainland, shelf area, primary productivity, sea surface temperature (SST), human population gravity, and conservation status influence reef fish species richness and functional diversity in the ETP. Species richness and functional richness (FRic) peaked towards the center of the ETP and our null model suggests that FRic followed a spatial pattern that would be predicted by species richness. Additionally, functional evenness (FEve) was highest at higher latitudes whereas functional dispersion (FDis) was homogeneous throughout the ETP. Species richness was negatively influenced by shelf area and distance from mainland, but positively influenced by SST and conservation status. FEve was influenced by human population gravity and FDis by shelf area. Reef fish species richness and functional diversity in the ETP exhibited a strong division within the region mainly mediated by SST and human population gravity. Our results also suggest that dominant species within small shelf areas share more common traits than dominant species in large areas. This study uncovers previously unknown regional patterns of reef fish functional diversity and provides new insights into how historical, biogeographic, energetic, and anthropogenic factors influence complementary biodiversity facets.

Temporal environmental variability causes behavioural and physiological responses in organisms that can affect their spatial location in time, and ultimately drive changes in population and community dynamics. Linking ecological changes with underlying environmental drivers is a complex task that can however be facilitated through the integration of physiology. Our overarching aim was to investigate the association between physiological performance and habitat utilisation patterns modulated by short temporal fluctuations in environmental factors. We used in situ monitoring data from a system experiencing extreme environmental fluctuations over a few hours and we selected four fish species with different habitat utilisation patterns across dissolved oxygen (DO) fluctuations: two commonly observed species (Siganus lineatus and Acanthopagrus pacificus), including at low DO (40 and 50% saturation, respectively), and two reef species (Heniochus acuminatus and Chaetodon vagabundus) never recorded below 70% saturation. We hypothesised that these patterns were associated to species' physiological performance in hypoxia. Therefore, we measured different metabolic variables (O2crit, incipient lethal oxygen (ILO), time to ILO, index of cumulative ambient oxygen deficit (O2deficit), maximum oxygen supply capacity (α)) using respirometry. Physiological performance differed among species and was intrinsically associated to habitat use patterns. S. lineatus had a lower O2crit than H. acuminatus, A. pacificus and C. vagabundus (13, 18.7, 20 and 20.2% saturation respectively). Additionally, S. lineatus and A. pacificus displayed better capacity for survival below O2crit than C. vagabundus and H. acuminatus (lower ILO, higher O2deficit and longer time to ILO) and higher α. Field monitoring data revealed that DO temporarily falls below species' O2crit and even ILO on most days, suggesting that short temporal variability in DO likely forces species to temporarily avoid harmful conditions, driving important changes in ecosystem structure over a few hours. Our results support the hypothesis that organismal physiology can provide insights into ecological changes occurring over a few hours as a result of environmental variability. Consequently, integrating physiology with ecological data at relevant temporal scales may help predict temporal shifts in ecosystems structure and functions to account for ecological patterns often overlooked and difficult to identify.

Table S1: Robustness of the random forest model to predict taxonomic richness.The confusion matrix was generated by running the random forest model, built from the training dataset, on the test dataset to identify the percentage of cases when the model was able to predict the exact taxonomic richness observed and the taxonomic richness observed at ± 1 taxon.

Mangrove forests are important habitats for fish. However, their utilisation by fish, and the specific values they confer, are still not fully understood. This study describes how fish use mangrove forests in an Indo-Pacific mangrove-coral reef seascape. Sampling was conducted using underwater video cameras (UVCs) to describe spatial and temporal variations in fish assemblages across a small-scale (~ 2.5 km 2 ) system, and over the tidal and lunar cycle. UVCs were deployed in the two main component habitats of mangrove forests: at the mangrove forest edge, and inside the forest (5 m from the forest edge), to establish patterns of utilisation of fish across the tidal and lunar cycle. Proximity to coral reefs had a strong influence on the mangrove fish community, as most fish recorded were reef-associated. Juveniles of 12 reef species were observed, including two species classified as vulnerable on the IUCN list, and one endemic species. Fish assemblages on the mangrove edge differed significantly from those inside the forest. Most fish utilised the forest edge, with few species making regular use of in-forest habitats, supporting the contention that most fish species remain on the edge and potentially retreat into the forest for opportunistic feeding, or when threatened by larger predators. Species-specific patterns of utilisation varied across the tidal and lunar cycle. Small differences in depth profiles and substrate across the small-scale system had a significant effect on fish assemblages, highlighting the importance of accounting for spatial heterogeneity in these factors. These data provide important information for managers to implement adequate conservation strategies that include broader interconnected habitat mosaics.

Intertidal mangrove forests are harsh environments that can naturally experience hypoxia in association with low tide. However, we know relatively little about dissolved oxygen (DO) fluctuations and DO-induced responses by fish, although DO is a fundamental water quality parameter. This study examines DO as a potential factor regulating the utilisation of intertidal mangrove forests by fish and consequently their widely recognised feeding, refuge and nursery values. We deployed underwater video cameras, coupled with DO and depth loggers, in a mangrove forest to record changes in fish assemblages in response to tidal variations in DO and other associated environmental parameters. Our results indicate that DO underwent extreme tidal fluctuations, reaching levels as low as 14 % saturation. As DO was identified as a significant factor for explaining variability in fish assemblage composition, we further investigated fish responses to DO fluctuations. Higher taxonomic richness and frequencies of occurrence were observed once DO reached 70 %–80 % saturation. More detailed examination revealed species-specific responses. Three distinct patterns of mangrove utilisation in response to DO were identified, driven by apparent taxa's behavioural DO avoidance thresholds. Most taxa did not display any behavioural avoidance, including presence at the lowest DO levels, while other taxa were not observed either below 50 %–60 % saturation or below 70 %–80 % saturation. This implies that tidal migrations, often observed in intertidal environments, could be the result of differential DO tolerances and are not simply initiated by changes in water depth. Taxa remaining in the mangrove forest even at low DO were on average more frequently observed than the other taxa and were mostly species commonly associated with mangrove habitats. This suggests that being adapted to withstand low DO might be an important condition for using mangrove habitats extensively. The need of being tolerant to low DO could constrain fish utilisation and explain the relatively low species richness often observed in other intertidal mangrove forests.

Little is known about levels of dissolved oxygen fish are exposed to daily in typical urbanised tropical wetlands found along the Great Barrier Reef coastline. This study investigates diet dissolved oxygen (DO) dynamics in one of these typical urbanised wetlands, in tropical North Queensland, Australia. High frequency data loggers (DO, temperature, depth) were deployed for several days over the summer months in different tidal pools and channels that fish use as temporal or permanent refuges. DO was extremely variable over a 24 h cycle, and across the small-scale wetland. The high spatial and temporal DO variability measured was affected by time of day and tidal factors, namely water depth, tidal range and tidal direction (flood vs ebb). For the duration of the logging time, DO was mainly above the adopted threshold for hypoxia (50% saturation), however, for around 11% of the time, and on almost every logging day, DO values fell below the threshold, including a severe hypoxic event (<5% saturation) that continued for several hours. Fish still use this wetland intensively, so must be able to cope with low DO periods. Despite the ability of fish to tolerate extreme conditions, continuing urban expansion is likely to lead to further water quality degradation and so potential loss of nursery ground value. There is a substantial discontinuity between the recommended DO values in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality and the values observed in this wetland, highlighting the limited value of these guidelines for management purposes. Local and regional high frequency data monitoring programs, in conjunction with local exposure risk studies are needed to underpin the development of the management that will ensure the sustainability of coastal wetlands. (C) 2017 Elsevier Ltd. All rights reserved.

Ocean warming, eutrophication and the consequent decrease in oxygen lead to smaller average fish size. Although such responses are well known in an evolutionary context, involving multiple generations, this appears to be incompatible with current rapid environmental change. Instead, phenotypic plasticity could provide a means for marine fish to cope with rapid environmental changes. However, little is known about the mechanisms underlying plastic responses to environmental conditions that favour small phenotypes. Our aim was to investigate how and why European sea bass that had experienced a short episode of moderate hypoxia during their larval stage subsequently exhibited a growth depression at the juvenile stage compared with the control group. We examined whether energy was used to cover higher costs for maintenance, digestion or activity metabolisms, as a result of differing metabolic rate. The lower growth was not a consequence of lower food intake. We measured several respirometry parameters and we only found a higher specific dynamic action (SDA) duration and lower SDA amplitude in a fish phenotype with lower growth; this phenotype was also associated with a lower protein digestive capacity in the intestine. Our results contribute to the understanding of the observed decrease in growth in response to climate change. They demonstrate that the reduced growth of juvenile fishes as a consequence of an early life hypoxia event was not due to a change of fish aerobic scope but to a specific change in the efficiency of protein digestive functions. The question remains of whether this effect is epigenetic and could be reversible in the offspring.