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The effect of habitat loss on the decline of habitat specialists has been well documented in coral reef fishes, since they have a restricted habitat preference. However, the different competitive advantages of specialists and generalists can impact their performance within varying habitat conditions. The order in which species arrive into a community influences competitive outcomes; these ‘priority effects’ may modify communities within degrading resource scenarios as individuals migrate in search of higher quality resources. In this study, we investigated: how sequence and timing of arrival affects interactions between a habitat generalist and a specialist in healthy and degrading environments, and how prior residency interacts with habitat quality and species identity to affect propensity to migrate. We conducted manipulative field studies using the damselfishes Pomacentrus amboinensis, a habitat generalist, and Pomacentrus moluccensis, a live coral specialist, on live or dead coral habitats, with timing of arrival differing between early and late arrivers (residents and intruders, respectively) by 1, 3 or 24 h. Our results demonstrated that the strength of priority effects (i.e., aggression intensity) increased with increasing timing of arrival when the P. moluccensis arrived after P. amboinensis, suggesting that as the perceived value of the habitat patch increased (owing to increasing ownership duration and defence investment), the tendency to defend it increased. Propensity to migrate from dead to live coral was greater for P. moluccensis compared to P. amboinensis; however, arriving after P. amboinensis significantly reduced willingness to migrate to its preferred live coral habitat, indicating an inhibitory priority effect, directly affecting future persistence. The degree that ecological versatility and priority effects combine to modify competitive outcomes in coral reef fishes has important consequences for the persistence of specialist species in the face of environmental degradation, and has implications for predicting how our changing environment will affect fish communities.

Widespread coral mortality is leading to coral reef degradation worldwide. Many juvenile reef fishes settle on live coral, and their predator-avoidance behaviour is disrupted in seawater exposed to dead corals, ultimately increasing predation risk. Gnathiid isopods are micropredatory fish ectoparasites that occur in higher abundances in dead coral. However, the effect of seawater associated with dead coral on the susceptibility of fish to micropredators has never been investigated. We tested whether the infection rate of cultured gnathiid ectoparasites on individual damselfish, Pomacentrus amboinensis Bleeker 1868, from two different ontogenetic stages (juveniles and adults) was influenced by seawater exposed to three different treatments: dead coral, live coral, or no coral. Seawater treatments were presumed to contain different chemical properties and are meant to represent environmental changes associated with habitat degradation on coral reefs. Gnathiid infection of juvenile fish in seawater exposed to dead coral was twice as high as that of fish in live coral or no coral. Infection rates did not significantly differ between live coral and no coral treatments. In contrast to juveniles, the susceptibility of adults to gnathiids was not affected by seawater treatment. During experiments, juvenile fish mortality was relatively low, but was higher for infected fish (9.7%), compared to fish held without exposure to gnathiids (1.7%). No mortality occurred in adult fish that became infected with gnathiids. Our results suggest that chemical cues released from dead corals and/or dead coral colonisers affect the ability of juvenile, but not adult fish to avoid parasite infection. Considering increased habitat degradation on coral reefs and that gnathiids are more abundant in dead coral substrate, it is possible that wild juvenile fish may experience increased susceptibility to parasitic infection and reduced survival rate. This highlights the importance of including parasitism in ecological studies of global environmental change.

Latitude and body size are generally considered key drivers of swimming performance for larval marine fishes, but evidence suggests that evolutionary relationships and habitat may also be important. We used a comparative phylogenetic framework, data synthesis and case study approach to investigate how swimming performance differs among larvae of fish species across latitude. First, we investigated how swimming performance changed with body length, and we found that temperate reef fishes have the greatest increases in swimming performance with length. Secondly, we compared differences in three swimming performance metrics (critical swimming speed, in situ swimming, and endurance) among post-flexion larvae, whilst considering phylogenetic relationships and morphology, and we found that reef fishes have higher swimming capacity than non-reef (pelagic and non-reef demersal) fishes, which is likely due to larger, more robust body sizes. Thirdly, we compared swimming performance of late-stage larvae of tropical fishes with oceanographic data to better understand the ecological relevance of their high-capacity swimming. We found that reef fishes have high swimming performance and grow larger than non-reef fish larvae, which we suggest is due to the pressures to find a specific, patchily distributed habitat upon which to settle. Given the current bias towards studies on percomorph fishes at low latitudes, we highlight that there is a need for more research on temperate reef fish larvae and other percomorph lineages from high latitudes. Overall, our findings provide valuable context to understand how swimming and morphological traits that are important for dispersal and recruitment processes are selected for among teleost fish larvae.

Coral reef ecosystems are currently under unprecedented stress due to anthropogenic induced climate change. Such stress causes coral habitats to degrade, which has been found to negatively impact the behaviour of some reef fishes. However, it is unknown whether the same chemical stresses from degraded habitats that impacts fish behaviour also impacts energy supporting swimming performance traits of fishes during the pelagic-to-reef life-history bottleneck. Here, we exposed newly settled juvenile Ambon damselfishes (Pomacentrus amboinensis) to either water that had passed over healthy or degraded coral for 24 h. Fishes were then swum at an ecologically relevant swimming speed for 200 min, and oxygen uptake rates were measured periodically. In general, fish swimming in water from degraded coral depressed oxygen uptake rates by 21%, which suggests that degraded habitats can have strong effects on fish physiology during this ecologically-critical time window.

A prerequisite for effective antipredator responses is the ability of a prey to distinguish animals that pose a threat from those that do not. Prey often have efficient learning mechanisms to learn threats but learning to recognize nonpredators may be equally or more important. Moreover, the ability to generalize learned information is of key importance for prey animals. Prey take information they know about one species to make ‘educated guesses’ about the predatory/nonpredatory status of other unknown species. Here, we investigate the ability of Whitetail damselfish Pomacentrus chrysurus to learn the identity of non‐predators and then generalize their responses to other unknown animals. Our work is completed within the context of unprecedented habitat degradation in reef ecosystems. When corals die, the remaining skeleton is colonized by algae, cyanobacteria and sessile invertebrates. These opportunistic colonists change the physical and chemical landscape of the reef and hence the background odour in which predator and non‐predator recognition occurs. Our results indicated that Whitetail damselfish learn to classify Moonwrasse Thalasomma lunare as a non‐predator through the process of latent inhibition, whereby the prey are repeatedly exposed to Moonwrasse odour multiple times in the absence of negative reinforcement. These fish subsequently generalized their nonpredator recognition to other unknown wrasse, but not distantly related fish. Of key importance was our finding that the patterns and extent of non‐predator learning and generalization were dramatically altered in dead coral habitats. As predicted, prey that learned the Moonwrasse as a nonpredator in live coral environments did not subsequently respond to Moonwrasse when we tried to teach them Moonwrasse was a predator in live coral. However, this non‐predator recognition was reduced in dead coral environments. Moreover, generalization completely failed when we changed from live to dead coral environments. Juvenile damselfishes need to rapidly catalogue the identity of unknown animals when they arrive at a reef. Changing background odours, that occur with changing tides and currents, means that prey need to learn non‐predator identities separately in each water source. This cognitive challenge likely has significant survival consequence in a changing environment. A free Plain Language Summary can be found within the Supporting Information of this article.

Coral reefs exhibit consistent patterns in biodiversity across multiple spatial scales, from local to global clines in species richness, abundance and community structure. Knowledge of fundamental processes driving these patterns is largely derived from studies of shallow, emergent and nearshore reefs. Although research efforts are expanding to deeper mesophotic coral reef ecology, distinct and isolated reef morphologies like submerged pinnacles or seamounts have received scant attention. Despite being potentially important for connectivity and as refugia, the extent to which established patterns and processes in coral reef ecology apply to these systems is unknown. Here we examine the fish and benthic communities associated with coral reefs found on submerged pinnacles in Kimbe Bay, Papua New Guinea. Community structure and diversity metrics are compared with emergent reefs at the same depth in both near and offshore settings. We then explicitly test whether benthic complexity variables known to influence reef fish communities exhibit similar patterns at each reef type. Pinnacles were characterised by 3.70 times the mean fish abundance and 1.98 times the species richness recorded at the same depths on emergent reefs. Fish community structure showed distinct separation across reef morphologies, with pinnacles most similar to offshore reefs. Benthic habitat complexity did not vary across reef types while fish assemblages were weakly related to benthic habitat variables, with reef morphology the most consistent predictor of fish community metrics. The pinnacles in our study support high coral reef fish biodiversity despite their small habitat area and relative isolation by depth and offshore setting. Our results suggest that habitat-specific environmental conditions are generated by the distinct geomorphology of pinnacles. As coastal reefs become more increasingly disturbed, understanding ecological patterns on deep patch reef habitats like pinnacles will be useful to provide a more holistic understanding of coral reef seascapes and their resilience.

[Extract:] In their study, Clark et al. suggest that previous studies on the effects of elevated levels of CO2 on the behaviour of coral reef fishes are not repeatable and that ocean acidification does not impair the behaviour of coral reef fishes, even though six significant behavioural effects were detected in their study, each of which was dismissed for a different reason. They then compare the means and variances of six previous ocean acidification studies in fish with a data distribution that is derived from a multi-species compilation of their own data to conclude that the results of previous studies are statistically improbable. However, Clark et al. did not closely repeat previous studies, as they did not replicate key species, used different life stages and ecological histories and changed methods in important ways that reduce the likelihood of detecting the effects of ocean acidification.

1. An increasing number of coral reefs throughout the world have become degraded as a result of climate change. This degradation has resulted in a significant decline in local biodiversity. Studies have shown that some fishes (non‐responders) within these altered habitats are not able to adequately access olfactory cues, specifically chemical alarm cues that are crucial in mediating predation risk. 2. We propose that the inability to access this crucial information is a potential mechanism for increased mortality of these species under natural conditions. However, we posit that the presence of certain key species (responders that are unaffected by degradation) may buffer the handicap of non‐responders by providing an alternate source of information. 3. To explore this hypothesis, we investigated if a high ratio of responders to non‐responders could mitigate the impact of information loss for the affected species. Using mesocosms, we manipulated the ratio of two damselfish species, Pomacentrus chrysurus (responder) and P. moluccensis (non‐responder), to determine if community composition can be predictive of information transfer about predation threats in nearby non‐responder individuals. 4. Our results indicate that, in degraded environments, the magnitude of fear effects seen in P. moluccensis exposed to a predator was proportional to the number of P. chrysurus present and consumed by the predator in the community. This indicates that P. chrysurus became the only functional source of predation‐related information for P. moluccensis in degraded habitats. These results contrasted with those from live coral environments, where all individuals exhibited fear effects, regardless of community composition. 5. Our study provides evidence that the presence of non‐affected species in the community provides a potential mechanism allowing increased resilience by affected species, therefore providing another example of the way biodiversity affects ecological resilience of species in changing ecosystems.

Predators can exert strong ecological effects on their prey either via consumption or by altering their behaviour and morphology. In marine systems, predators and their prey co-occur in a three-dimensional environment, but to date predator-prey studies have largely focussed on behaviours of prey on horizontal (distance from shelter) rather than vertical (height in water column) axes. We used life-size shape-models of a blacktip reef shark Carcharhinus melanopterus (threatening shape-model), a juvenile coral trout Plectropomus leopardus (non-threatening shape-model) and a shape-control to examine the impact of perceived instantaneous (measured by time to first feeding) versus sustained (measured by time to consume the entire bait) predation threats on the feeding behaviour and three-dimensional use of space by mesopredatory reef fishes in a coral reef environment. We found that mesopredatory fishes such as red snapper Lutjanus bohar and spangled emperor Lethrinus nebulosus took longer to begin feeding and to consume predation assays (fish baits) at greater distances from the shelter of a patch reef across both horizontal and vertical axes and that this phenomenon was stronger in the vertical axis than the horizontal. The presence of a life-size shape-model of a shark, which we used to increase the perception of predator threat, magnified the instantaneous effect compared to non-threatening models, but not the sustained effect. We found no evidence for a difference in the level of predation risk posed by the shape-model of the juvenile coral trout (a non-threatening reef fish) and a negative control (no shape-model). Our study suggests that mesopredators modify their behaviours in response to the perceived risk of predation across both horizontal and vertical axes away from shelter, and that this response is most severe on the vertical axis, potentially limiting daytime foraging behaviour to a hemisphere around shelter sites.

Connectivity of coral reef fish populations relies on successful dispersal of a pelagic larval phase. Pelagic larvae must exhibit high swimming abilities to overcome ocean and reef currents, but once settling onto the reef, larvae transition to endure habitats that become hypoxic at night. Therefore, coral reef fish larvae must rapidly and dramatically shift their physiology over a short period of time. Taking an integrative, physiological approach, using swimming respirometry, and examining hypoxia tolerance and transcriptomics, we show that larvae of cinnamon anemonefish (Amphiprion melanopus) rapidly transition between “physiological extremes” at the end of their larval phase. Daily measurements of swimming larval anemonefish over their entire early development show that they initially have very high mass-specific oxygen uptake rates. However, oxygen uptake rates decrease midway through the larval phase. This occurs in conjunction with a switch in haemoglobin gene expression and increased expression of myoglobin, cytoglobin, and neuroglobin, which may all contribute to the observed increase in hypoxia tolerance. Our findings indicate that critical ontogenetic changes in the gene expression of oxygen-binding proteins may underpin the physiological mechanisms needed for successful larval recruitment to reefs.

Aquatic prey can gauge predation risk using chemical information, including chemical alarm cues — released when prey are injured, disturbance cues — released when prey are threatened, or the odour of the predator itself. While a lot of work has focused on alarm cues, disturbance cues remained poorly studied in freshwater systems, and has been virtually omitted in marine ones. In the current study, we document the first evidence of disturbance cue use in a marine fish. Juvenile damselfish Pomacentrus nagasakiensis were exposed to cues from undisturbed or disturbed conspecifics, a water control (negative control) and conspecific alarm cues (positive control). Juveniles displayed increased antipredator responses when exposed to alarm cues and disturbed conspecifics, but not when exposed to undisturbed ones. In addition, we demonstrated that disturbance cues, just like alarm cues, could mediate learned predator recognition, a phenomenon undemonstrated in freshwater fishes. Given disturbance cues are thought to be comprised of nitrogenous waste, it has been hypothesised that the constant and dilute release of such products in the hypotonic freshwater environment results in a high level of ‘background chemical’ noise masking subsequent releases. Extending this hypothesis, we propose that in the marine environment, disturbance cues are more easily detected due to low background noise. Prey animals must accurately assess their current predation risk. Aquatic prey rely on chemical cues to gain information on risk. These cues can include odours released when nearby prey are damaged or disturbed, or the odour of a known predator. Prey exposed to a novel odour for the first time must learn if the odour is an indication of risk or benign. This is accomplished when the odour of a known risk (e.g. cues released from a damaged individual) is paired with a novel odour (e.g. a novel predator). In the current paper, we show for the first time that coral reef fishes can use disturbance cues (cues released when prey are chased or otherwise disturbed) as a ‘known risk’ and when paired with a novel odour, are subsequently able to respond to the novel odour when presented alone.

Coral reefs are degrading globally leading to a catastrophic loss of biodiversity. While shifts in the species composition of communities have been well documented associated with habitat change, the mechanisms that underlie change are often poorly understood. Our study experimentally examines the effects of coral degradation on the trait-mediated effects of predators on the morphology, behaviour and performance of a juvenile coral reef fish. Juvenile damselfish were exposed to predators or controls (omnivore or nothing) in seawater that had flowed over either live or dead-degraded coral over a 45d period. No interaction between water source and predator exposure was found. However, fish exposed to degraded water had larger false eyespots relative to the size of their true eyes, and were more active, both of which may lead to a survival advantage. Non-consumptive effects of predators on prey occurred regardless of water source and included longer and deeper bodies, large false eyespots that may distract predator strikes away from the vulnerable head region, and shorter latencies in their response to a simulated predator strike. Research underscores that phenotypic plasticity may assist fishes in coping with habitat degradation and promote greater resilience to habitat change than may otherwise be predicted.

The change in coral reefs from live coral to algal-dominated seascapes prevents some fish species from using chemical alarm cues to gain information about their risk of predation. Field experiments showed that Ambon damselfish, Pomacentrus amboinensis, were able to learn the identity of individual novel predators from a cocktail of odours from three predators derived from digestive products. Learning only occurred when the predators had been fed conspecifics of the prey species in the presence of water that had passed over live hard coral. This allows novel predators to be identified long after the immediate capture and ingestion event. Fish that had the same learning opportunity in degraded water took more risk and died faster on habitat patches in the field. Ambon damselfish respond to chemical alarm cues from closely related Pomacentrus nagasakiensis, in both live and degraded water, yet experiments suggested they cannot use the congeneric diet odours to label predators. However, we did find a modest survival benefit under natural conditions, suggesting some limited learning occurred. Findings suggest that as coral habitats degrade, fishes that are affected by the changing chemistry will have a greatly reduced range of mechanisms for obtaining and updating threat information, altering the resilience of communities.

The fear of predation can have marked effects on an individual's phenotype, and the resulting phenotype is selected to increase an individual's chance of survival during a predator encounter. However, for species with inducible defences, such defensive phenotypes must be costly enough to prevent them from becoming constitutive. While morphological and life-history adaptations have been shown to incur costs, much less research has been done on the costs of behavioural adaptations, which are often thought of as plastic, with limited associated costs. In this study, we document the costs of a high-risk behavioural phenotype. Under high-risk conditions, damselfish are known to exhibit a high-risk phenotype, which among other traits, confer a significant survival advantage during encounters with predators. We exposed juvenile damselfish to a high-risk or low-risk environment for 4 days. We then set up competitive encounters between size-matched pairs of high-risk and low-risk conspecifics. To test for context dependency, we also ran trials when the pair was exposed to a novel predator odour during the competitive encounter. Our results indicate that low-risk fish were the superior competitors in a low-risk environment, but not in a high-risk environment. This result may be explained by an increase in motivation by high-risk individuals to seek shelter from a potential predation threat. Our results highlight (1) the existence of significant costs, even for rapidly induced behavioural phenotypes, and (2) the importance of investigating the adaptive value of phenotypes within the context in which they develop.

Although individuals within social groups experience reduced predation risk and find food patches more consistently, there can be competition for food among groupmates. Individuals with a higher standard metabolic rate (SMR) may be less social, to prioritize food acquisition over defense, while a greater maximum metabolic rate (MMR) may modulate sociability through increased competitive ability. Therefore, in theory, individuals with a higher SMR may prefer smaller groups and those with greater MMR may prefer larger groups. We examined links among metabolic phenotype, sociability, and choice of group size in the redbelly yellowtail fusilier Caesio cuning. Individuals were exposed to three association tests: (a) a choice between two fish or zero fish; (b) a choice between five fish or zero fish; and (c) a choice between two fish and five fish. The first two tests quantified sociability while the third measured relative group size choice. Although there was no link between SMR and sociability, fish with a higher MMR were more social than those individuals with a lower MMR. While no correlation was found between MMR and group size choice, there was weak evidence that, if anything, individuals with a higher SMR preferred larger groups, contrary to our hypothesis. As C. cuning is an active fish that spends a large proportion of time operating above SMR, this result could suggest that the links between sociability and SMR may shift depending on a species’ routine behavior. Links between sociability and MMR may arise if competitive ability allows individuals to obtain resources within groups. Although metabolic traits had no significant influence on group size choice, variation in food availability or predation risk could alter the effects of metabolism on group size choice.

Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests

The idea that the presence of sharks impacts the behavior of mesopredatory reef fishes is controversial and lacks clear evidence at reef‐wide scales. We compared the abundance and behavior of these reef fishes in response to the presence of reef sharks using Baited Remote Underwater Video System (BRUVS) deployments in two adjacent reef systems where sharks have either been exclusively targeted by fishing or protected by a no‐take marine reserve. For a subset of videos, we also compared the behavior of mesopredatory reef fishes immediately before and after the appearance of sharks in the video. On reefs where sharks were more abundant, mesopredatory fishes spent less time swimming in midwater (i.e., away from shelter) and guarding bait compared to reefs where sharks have been selectively removed. The same responses occurred after the appearance of sharks in the video. Reactions to sharks varied both in strength and type among species of mesopredator and were mediated by the availability of shelter on the reef and, for one species, by the levels of activity of the reef sharks. In contrast, we did not find that the presence of sharks influenced the abundance of mesopredators at either reef system across hour‐long videos or immediately before and after a shark appeared in the video. Collectively, our findings show that the presence of sharks reduces the propensity of mesopredatory fish to engage in potentially risk‐prone behaviors over large spatial scales and that these interactions are mediated by the behavioral characteristics of both predators and prey, and the environment in which they co‐occur. Our results are consistent with the idea that sharks as predators or larger competitors initiate changes in the behavior of mesopredatory reef fishes likely to affect trophic structuring within coral reef ecosystems.

Coral reefs are degrading globally due to increased environmental stressors including warming and elevated levels of pollutants. These stressors affect not only habitat-forming organisms, such as corals, but they may also directly affect the organisms that inhabit these ecosystems. Here, we explore how the dual threat of habitat degradation and microplastic exposure may affect the behaviour and survival of coral reef fish in the field. Fish were caught prior to settlement and pulse-fed polystyrene microplastics six times over 4 days, then placed in the field on live or dead-degraded coral patches. Exposure to microplastics or dead coral led fish to be bolder, more active and stray further from shelter compared to control fish. Effect sizes indicated that plastic exposure had a greater effect on behaviour than degraded habitat, and we found no evidence of synergistic effects. This pattern was also displayed in their survival in the field. Our results highlight that attaining low concentrations of microplastic in the environment will be a useful management strategy, since minimizing microplastic intake by fishes may work concurrently with reef restoration strategies to enhance the resilience of coral reef populations.

Motorboats are a pervasive, growing source of anthropogenic noise in marine environments, with known impacts on fish physiology and behaviour. However, empirical evidence for the disruption of parental care remains scarce and stems predominantly from playback studies. Additionally, there is a paucity of experimental studies examining noise-mitigation strategies. We conducted two field experiments to investigate the effects of noise from real motorboats on the parental-care behaviours of a common coral-reef fish, the Ambon damselfish Pomacentrus amboinensis, which exhibits male-only egg care. When exposed to motorboat noise, we found that males exhibited vigilance behaviour 34% more often and spent 17% more time remaining vigilant, compared to an ambient-sound control. We then investigated nest defence in the presence of an introduced conspecific male intruder, incorporating a third noise treatment of altered motorboat-driving practice that was designed to mitigate noise exposure via speed and distance limitations. The males spent 22% less time interacting with the intruder and 154% more time sheltering during normal motorboat exposure compared to the ambient-sound control, with nest-defence levels in the mitigation treatment equivalent to those in ambient conditions. Our results reveal detrimental impacts of real motorboat noise on some aspects of parental care in fish, and successfully demonstrate the positive effects of an affordable, easily implemented mitigation strategy. We strongly advocate the integration of mitigation strategies into future experiments in this field, and the application of evidence-based policy in our increasingly noisy world.

The pelagic larval stage is a critical component of the life cycle of most coral reef fishes, but the adaptive significance of this stage remains controversial. One hypothesis is that migrating through the pelagic environment reduces the risk a larval fish has of being parasitised. Most organisms interact with parasites, often with significant, detrimental consequences for the hosts. However, little is known about the parasites that larval fish have upon settlement, and the factors that affect the levels of parasitism. At settlement, coral reef fishes vary greatly in size and age (pelagic larval duration), which may influence the degree of parasitism. We identified and quantified the parasites of pre-settlement larvae from 44 species of coral reef fishes from the Great Barrier Reef and explored their relationship with host size and age at settlement, and phylogeny. Overall, less than 50% of the larval fishes were infected with parasites, and over 99% of these were endoparasites. A Bayesian phylogenetic regression was used to analyse host-parasite (presence and intensity) associations. The analysis showed parasite presence was not significantly related to fish size, and parasite intensity was not significantly related to fish age. A phylogenetic signal was detected for both parasite presence and intensity, indicating that, overall, closely related fish species were likely to have more similar susceptibility to parasites and similar levels of parasitism when compared to more distantly related species. The low prevalence of infection with any parasite type and the striking rarity of ectoparasites is consistent with the ‘parasite avoidance hypothesis’, which proposes that the pelagic phase of coral reef fishes results in reduced levels of parasitism.

Roving herbivorous fishes play an important role in coral reef communities by removing turf-algae, which can facilitate the settlement of coral larvae. Territorial damselfishes can influence the foraging patterns of roving herbivores by excluding them from their territories, altering the benthic assemblage. However, the impacts depend on the intensity of aggression and which taxonomic groups of roving herbivores are being excluded. Here we document the foraging activity of roving herbivores (Acanthuridae, Scaridae, Siganidae) and the extent to which they are subject to aggression by Pomacentrus adelus, the most abundant territorial damselfish in Kimbe Bay, Papua New Guinea. We then conducted experimental removals (220 m2 plots on the reef flat) of P. adelus to examine its impact on roving herbivores and the benthic community structure. We hypothesized that the removal of P. adelus would lead to an increase in roving herbivore abundance and foraging activity and a decline in algal cover. The relative abundance (MaxN) and foraging activity (bite rate) of each taxa were examined pre and post-removal using video quadrats. The overall relative abundance of roving herbivores was not influenced by the removal of P. adelus. No changes in foraging patterns were observed for parrotfish, the family that received the highest rate of agonistic interactions, and rabbitfish. The removal of P. adelus resulted in a significant decrease in surgeonfish feeding, suggesting P. adelus alters foraging patterns indirectly through territorial maintenance and not aggression. The only measurable benthic impact of the P. adelus removal was an increase in sediment, while all other substratum types remained constant. These results indicate that P. adelus does not have a negative impact on all roving herbivores and instead may contribute to surgeonfish foraging indirectly through the removal of sediment. The generalisation that territorial damselfish reduce foraging rates of roving herbivores may not be applicable in all systems or for all species.

Human noise pollution has increased markedly since the start of industrialization and there is international concern about how this may impact wildlife. Here we determined whether real motorboat noise affected the behavior, space use and escape response of a juvenile damselfish (Pomacentrus wardi) in the wild, and explored whether fish respond effectively to chemical and visual threats in the presence of two common types of motorboat noise. Noise from 30 hp 2-stroke outboard motors reduced boldness and activity of fish on habitat patches compared to ambient reef-sound controls. Fish also no longer responded to alarm odours with an antipredator response, instead increasing activity and space use, and fewer fish responded appropriately to a looming threat. In contrast, while there was a minor influence of noise from a 30 hp 4-stroke outboard on space use, there was no influence on their ability to respond to alarm odours, and no impact on their escape response. Evidence suggests that anthropogenic noise impacts the way juvenile fish assess risk, which will reduce individual fitness and survival, however, not all engine types cause major effects. This finding may give managers options by which they can reduce the impact of motorboat noise on inshore fish communities.

Female octopuses are known to store sperm from multiple males they encounter throughout a breeding season, before laying a single clutch with mixed paternity. Although octopuses display a broad range of precopulatory behaviours, and both sperm competition and cryptic female choice have been hypothesized to occur, the current understanding of how these processes influence resulting paternity remains limited. This study aimed to identify behavioural factors associated with paternity patterns and the capacity of females to bias paternity postcopulation to specific males in the southern blue-ringed octopus, Hapalochlaena maculosa. Genetic markers and controlled, sequential, laboratory pairings of genotyped individuals were used to examine paternity patterns and compare them to relative signatures of male sperm remaining in female oviducal glands after egg laying. Multiple paternity was discovered in all 12 laboratory-reared clutches. There was no indication that the relative time spent in copulation affected the resulting paternity. Males that waited for females to terminate the copulation had greater paternity when they were the first candidate male, but this was not the case among second candidate males. The relative quantities of candidate male alleles detected in female oviducal glands after egg laying were consistent with relative paternity of the candidate males in all but three cases. In one of these, sibship analysis revealed that the male that obtained less paternity than expected was in fact the female's full-sibling brother. Although this study found no evidence for female postcopulatory selection of male sperm, anecdotal evidence suggests that female H. maculosa might benefit from polyandry if chemical processes can favour clutch fertilization by unrelated males. Future studies, investigating paternity bias among genotyped males of varying, but known relatedness to the female, might help to validate this pattern.

A major goal of ecology is to explain the mechanisms that drive species distributions and ecological partitioning along gradients in the natural environment. The distributions of ecologically similar animals may depend on the degree of habitat specialization and behavioural interactions within and among species. The extent of ecological partitioning in guilds of coral reef fishes has been a matter of debate, but the roles of habitat selectivity and agonistic interactions have received little attention. Here these effects were examined by investigating fine-scale species distributions, microhabitat use, and aggression in a guild of 7 territorial damselfish species in Kimbe Bay, Papua New Guinea. We documented patterns of habitat partitioning across the 3 reef zones—reef flat, reef crest, and reef slope—with distinct patterns of distribution within these zones at extremely fine scales (1-2 m). Distinct differences between neighbouring species in the substrata selected were also observed. We hypothesized that fine-scale differences in distribution and microhabitat use could be maintained by aggressive interactions. To test this, we employed a ‘bottle’ experiment, where stimulus fish were introduced into a resident’s territory, and aggression was recorded. Aggression elicited by neighbouring species was significantly higher for all species, compared with non-adjacent species. Levels of aggression differed among species, with the most aggressive species dominating the reef crest where the most distributional overlap occurred. This study revealed a fine level of spatial partitioning among reef zones and microhabitats in this guild of damselfish, which is likely to be maintained by agonistic interactions among neighbouring species. We demonstrate that when exploring coexistence in reef fish communities, the more traditional niche mechanisms operate alongside competitive dynamics, and within highly diverse systems these ecological processes are magnified.

Mortality through predation is often selective, particularly at life-history bottlenecks. While many studies have looked at the importance for survival of specific prey characteristics in isolation, few have looked at a broad array of attributes and how they relate to survival in a realistic context. Our study measures 18 morphological, performance and behavioural traits of a juvenile damselfish that have been hypothesized as important for prey survival, and examines how they relate to survival in the field immediately after settlement. These attributes included size, relative false eye-spot size, fast-start escape response kinematics, thigmotaxis, laterality, and space use and activity in the field. Using conditional inference trees, we identify the most important drivers out of a reduced suite of 13 characters. Fast-start response latency, boldness, feeding rates and two measures of activity were found to significantly contribute to survival. Morphological variables and most laboratory measures of performance appeared to contribute little to survival. Results suggest selection works on a suite of characters associated with boldness. Bold and active fish are those that will be best able to learn using public information, but because of the relative naivete of newly metamorphosed fishes, speed to react to a strike from an unknown predator is of critical importance. Findings substantiate the ecomorphological paradigm by suggesting that selection on behaviour modifies the correlations of morphological and performance variables with survival probabilities, since behaviour modifies performance capabilities by making them specific to context.

The southern blue‐ringed octopus, Hapalochlaena maculosa (Hoyle, 1883) lacks a planktonic dispersal phase, yet ranges across Australia's southern coastline. This species’ brief and holobenthic life history suggests gene flow might be limited, leaving distant populations prone to strong genetic divergence. This study used 17,523 genome‐wide SNP loci to investigate genetic structuring and local adaptation patterns of H. maculosa among eight sampling sites along its reported range. Within sites, interrelatedness was very high, consistent with the limited dispersal of this taxon. However, inbreeding coefficients were proportionally lower among sites where substructuring was not detected, suggesting H. maculosa might possess a mechanism for inbreeding avoidance. Genetic divergence was extremely high among all sites, with the greatest divergence observed between both ends of the distribution, Fremantle, WA, and Stanley, TAS. Genetic distances closely followed an isolation by geographic distance pattern. Outlier analyses revealed distinct selection signatures at all sites, with the strongest divergence reported between Fremantle and the other Western Australian sites. Phylogenetic reconstructions using the described sister taxon H. fasciata (Hoyle, 1886) further supported that the genetic divergence between distal H. maculosa sites in this study was equivalent to that of between established heterospecifics within this genus. However, it is advocated that taxonomic delineations within this species should be made with caution. These data indicate that H. maculosa forms a clinal species pattern across its geographic range, with gene flow present through allele sharing between adjacent populations. Morphological investigations are recommended for a robust resolution of the taxonomic identity and ecotype boundaries of this species.

The response of prey to predation threats is often plastic and can vary with the individual's perceived level of threat. To determine whether prey escape responses can be modulated by background levels of risk or short-term acute risk, we maintained juvenile damselfish, Acanthochromis polyacanthus, under high- or low-risk background conditions for several days and then exposed them to an acute risk (high-risk alarm cues or a low-risk saltwater control) minutes prior to startling them with a mechanical disturbance. Fish responded in one of two ways: they either made a C-start escape response or backed away from the threat. While exposure to either background high risk or acute high risk increased the proportion of C-starters, surprisingly the frequency of C-starters decreased when background high risk and acute risk types were combined. Exposure to an acute high-risk cue increased the escape performance for both types of escape responses. However, when the acute high-risk cue occurred within high-risk background conditions, this only increased the performance of C-start escape responses. Non-C-starters reacted similarly in both background risk conditions. Background risk and acute risk acted in a simple additive manner, as seen by the lack of interaction between the two factors. Results showed that escape responses are amplified as the level of perceived risk increases.

Anthropogenic noise pollution is rapidly increasing in the marine environment. Anthropogenic noise can mask biotic sounds, disrupting the successful transmission between caller and receiver, and can cause physical, physiological and behavioural changes in some species. The effect of noise pollution produced by small motorboats is of particular interest in shallow, coastal habitats where vessel numbers are steadily increasing. The present field study examined the effect of small motorboat noise on the behaviour of the juvenile common damselfish, Pomacentrus amboinensis, and their potential to perform typical behaviours when presented with increased noise over a short time period. Behavioural observations in the field (before, 1, 10 and 20 min after the start of boat noise) found there was an immediate decrease in the boldness and relative distance moved by P. amboinensis in response to the noise produced by a boat with a 30 hp 2-stroke engine travelling 30–80 m away. However, fish appeared to return to pre-boat noise exposure behaviours within 20 min. The immediate change in behaviour may alter mortality rates in the short-term, but the potential for de-sensitization to boat noise may allow long-term persistence in noisy environments if they survive the initial disruption.

Many animals respond differentially to stimuli on one side of their body compared to the other. This is a reflection of being lateralized, and is a feature common in vertebrates. Given that any particular stimulus that an animal encounters, be it food, a predator or a competitor, has an equal probability of coming from either side of the body, there may be negative selection for lateralization. However, the costs of lateralization may be offset if being lateralized confers a considerable advantage in other contexts, including cognition. Here, we showed that learned responses of juvenile ambon damselfish, Pomacentrus amboinensis, to a novel predator was strongly influenced by the degree of lateralization. While both lateralized and nonlateralized fish were able to learn the predator, lateralized fish showed much stronger responses to the learned predator than nonlateralized fish. When we paired lateralized and nonlateralized fish and allowed them to interact over a shelter resource, we observed that lateralized fish were poorer competitors. They attacked less often, showed fewer displays and exhibited greater avoidance of their competitor. For many gregarious species, the expression of lateralization likely reflects a fine balance of competing selection pressures. Our work highlights the need for integrative studies.

Elevated CO2 levels associated with ocean acidification (OA) have been shown to alter behavioural responses in coral reef fishes. However, all studies to date have used stable pCO2 treatments, not considering the substantial diel pCO2 variation that occurs in shallow reef habitats. Here, we reared juvenile damselfish, Acanthochromis polyacanthus, and clownfish, Amphiprion percula, at stable and diel cycling pCO2 treatments in two experiments. As expected, absolute lateralization of A. polyacanthus and response to predator cue of Am. percula were negatively affected in fish reared at stable, elevated pCO2 in both experiments. However, diel pCO2 fluctuations reduced the negative effects of OA on behaviour. Importantly, in experiment two, behavioural abnormalities that were present in fish reared at stable 750 µatm CO2 were largely absent in fish reared at 750 ± 300 µatm CO2. Overall, we show that diel pCO2 cycles can substantially reduce the severity of behavioural abnormalities caused by elevated CO2. Thus, past studies may have over-estimated the impacts of OA on the behavioural performance of coral reef fishes. Furthermore, our results suggest that diel pCO2 cycles will delay the onset of behavioural abnormalities in natural populations.