Predatory Reef Research Articles

Coral degradation alters predator odour signatures and influences prey learning and survival.

Habitat degradation is a key factor leading to the global loss of biodiversity. This problem is particularly acute in coral reef ecosystems. We investigated whether recognition of predator odours by damselfish was influenced by coral degradation and whether these changes altered survival in the wild. We taught whitespot damselfish to recognize the odour of a predator in the presence of live/healthy coral or dead/degraded coral. Fish were tested for a response to predator odours in environments that matched their conditioning environment or in environments that were mismatched. Next, we taught blue damselfish to recognize the odour of three common reef predators in live and degraded coral environments and then stocked them onto live or degraded patch reefs, where we monitored their subsequent response to predator odour along with their survival. Damselfish learned to recognize predator odours in both coral environments, but the intensity of their antipredator response was much greater when the conditioning and test environments matched. Fish released on degraded coral had about 50% higher survival if they had been trained in the presence of degraded coral rather than live coral. Altering the intensity of antipredator responses could have rather profound consequences on population growth.

Multi-tissue stable isotope analysis reveals resource partitioning and trophic relationships of large reef-associated predators

Defining the role of reef predators is particularly important given the rapid rate at which some species are declining, yet knowledge of trophic relationships is often lacking, particularly for large wide-ranging species that may use coral reefs seasonally or opportunistically. We used a multi-tissue stable isotope approach to investigate the trophic ecology of common reef predators in the central Great Barrier Reef of Australia. Our study revealed significant trophic separation among reef predators, especially when considering isotopic data from muscle, a slower turnover tissue. Based on muscle data, the bull shark Carcharhinus leucas, a large wide-ranging coastal species, occupied a higher trophic position and had a larger isotopic niche breadth (19.12) relative to smaller predators, including resident sharks (4.5 ± 0.72) and large-bodied teleosts (4.4 ± 1.82). Spanish mackerel Scomberomorus commerson and bull sharks had the largest unique total areas of isotopic niche space (expressed as a percentage) that did not overlap with any other species, 95% and 69.4%, respectively, which means they had lower isotopic overlap. In general, faster turnover tissues such as whole blood and plasma showed higher isotopic overlap and smaller niche breadth for all reef predators. These results suggest that bull sharks use similar prey resources to large and small resident predators, at least during short periods. Our findings highlight the importance of investigating dietary changes in faster-turnover tissues of reef predators, particularly large wide-ranging species, which may have key roles in coral reef food webs through direct predation and competition.

Substantial impacts of subsistence fishing on the population status of an Endangered reef predator at a remote coral atoll

Substantial impacts of subsistence fishing on the population status of an Endangered reef predator at a remote coral atoll

Unraveling lionfish invasion: Is Pterois volitans truly a morphologically novel predator in the Caribbean?

The harmful effects of lionfish (Pterois volitans) invasion on ecosystems already affected by overfishing, pollution and climate change in the western Atlantic are widely known. However, despite the detrimental consequences, it is also a unique opportunity to explore differences between invasive and resident species that may have led to the success of the invader. Using a functional morphology approach, we evaluated whether lionfish has novel traits and how they influenced the theoretical ecological space of some of the main small Caribbean reef predators. Additionally, we assessed if the native community generated biological resistance on the density of the invader. Lionfish and 12 native Caribbean small reef predators were used in this study. Thirteen characters were used to produce a morpho-functional space that defined the guild. A correlation was made between the total density of predators and that of lionfish. Morphological analyses indicated that the invasive species presents novel morphological traits, in comparison to native species. Additionally, the invader influences the reduction of the theoretical ecological space, suggesting competition with five Caribbean coral reef meso-predators. On the other hand, our data does not support the biological resistance hypothesis of native predators being the phenomenon that controls lionfish density.

No reef-associated gradient in the infaunal communities of Rapa Nui (Easter Island) – Are oceanic waves more important than reef predators?

Reef-associated predators are thought to influence the distribution of invertebrates of surrounding sediment habitats. In this study, we analyzed the predation pressure and the distributional patterns of macro- and meiofaunal assemblages in soft sediments surrounding two coral reef sites at Rapa Nui (Easter Island), in the central South Pacific. We tested the hypothesis that reef-associated predators negatively affect sediment-dwelling invertebrates, causing macro- and meiofauna to be less abundant and diverse in soft sediments near the reefs. As expected, predation intensity was greater nearer the reef than farther away, but macro- and meiofaunal assemblages did not differ significantly with distance from the reef. Taxon richness of macro- and meiofaunal assemblages were similar irrespective of distance from the reef. Only meiofauna showed significant variation in total abundance with distance from the reef, but this trend was not consistent between the two study sites. No gradient in sediment texture was observed with distance from the reef. Underwater video recordings at one study site also revealed that local hydrodynamics cause frequent disturbance and resuspension of the upper sediment layers. Our results suggest that soft-sediment assemblages are constantly reshuffled by oceanic waves, thereby blurring the potential effects of predation on invertebrate assemblages closer to the reef.

School is out on noisy reefs: the effect of boat noise on predator learning and survival of juvenile coral reef fishes.

Noise produced by anthropogenic activities is increasing in many marine ecosystems. We investigated the effect of playback of boat noise on fish cognition. We focused on noise from small motorboats, since its occurrence can dominate soundscapes in coastal communities, the number of noise-producing vessels is increasing rapidly and their proximity to marine life has the potential to cause deleterious effects. Cognition-or the ability of individuals to learn and remember information-is crucial, given that most species rely on learning to achieve fitness-promoting tasks, such as finding food, choosing mates and recognizing predators. The caveat with cognition is its latent effect: the individual that fails to learn an important piece of information will live normally until the moment where it needs the information to make a fitness-related decision. Such latent effects can easily be overlooked by traditional risk assessment methods. Here, we conducted three experiments to assess the effect of boat noise playbacks on the ability of fish to learn to recognize predation threats, using a common, conserved learning paradigm. We found that fish that were trained to recognize a novel predator while being exposed to 'reef + boat noise' playbacks failed to subsequently respond to the predator, while their 'reef noise' counterparts responded appropriately. We repeated the training, giving the fish three opportunities to learn three common reef predators, and released the fish in the wild. Those trained in the presence of 'reef + boat noise' playbacks survived 40% less than the 'reef noise' controls over our 72 h monitoring period, a performance equal to that of predator-naive fish. Our last experiment indicated that these results were likely due to failed learning, as opposed to stress effects from the sound exposure. Neither playbacks nor real boat noise affected survival in the absence of predator training. Our results indicate that boat noise has the potential to cause latent effects on learning long after the stressor has gone.

Cascading predator effects in a Fijian coral reef ecosystem

Coral reefs are among Earth’s best-studied ecosystems, yet the degree to which large predators influence the ecology of coral reefs remains an open and contentious question. Recent studies indicate the consumptive effects of large reef predators are too diffuse to elicit trophic cascades. Here, we provide evidence that such predators can produce non-consumptive (fear) effects that flow through herbivores to shape the distribution of seaweed on a coral reef. This trophic cascade emerged because reef topography, tidal oscillations, and shark hunting behaviour interact to create predictable “hot spots” of fear on the reef where herbivores withhold feeding and seaweeds gain a spatial refuge. Thus, in risky habitats, sharks can exert strong ecological impacts even though they are trophic generalists that rarely feed. These findings contextualize the debate over whether predators influence coral reef structure and function and move us to ask not if, but under what specific conditions, they generate trophic cascades.

A large predatory reef fish species moderates feeding and activity patterns in response to seasonal and latitudinal temperature variation

Climate-driven increases in ocean temperatures are expected to affect the metabolic requirements of marine species substantially. To mitigate the impacts of increasing temperatures in the short-term, it may be necessary for ectothermic organisms to alter their foraging behaviour and activity. Herein, we investigate seasonal variation in foraging behaviour and activity of latitudinally distinct populations of a large coral reef predator, the common coral trout, Plectropomus leopardus, from the Great Barrier Reef, Australia. P. leopardus exhibited increased foraging frequency in summer versus winter time, irrespective of latitude, however, foraging frequency substantially declined at water temperatures >30 °C. Foraging frequency also decreased with body size but there was no interaction with temperature. Activity patterns were directly correlated with water temperature; during summer, the low-latitude population of P. leopardus spent up to 62% of their time inactive, compared with 43% for the high-latitude population. The impact of water temperature on activity patterns was greatest for larger individuals. These results show that P. leopardus moderate their foraging behaviour and activity according to changes in ambient temperatures. It seems likely that increasing ocean temperatures may impose significant constraints on the capacity of large-bodied fishes to obtain sufficient prey resources while simultaneously conserving energy.

Displacement effects of heavy human use on coral reef predators within the Molokini Marine Life Conservation District

The impact of marine ecotourism on reef predators is poorly understood and there is growing concern that overcrowding in Marine Protected Areas (MPAs) may disturb the species that these areas were established to protect. To improve our understanding of this issue, we used acoustic telemetry to examine the relationship between human activity at the Molokini Marine Life Conservation District (MLCD) and the habitat use of five reef-associated predators (Caranx melampygus, Caranx ignobilis, Triaenodon obesus, Carcharhinus amblyrhynchos, and Aprion virscens). During peak hours of human use, there was a negative relationship (R2=0.77, P<0.001) between the presence of bluefin trevally (Caranx melampygus) and vessels in subzone A. No other species showed strong evidence of this relationship. However, our results suggest that during this time, the natural ecosystem function that the reserve was established to protect may be compromised and overcrowding should be considered when managing MPAs.

Sponge symbioses between Xestospongia deweerdtae and Plakortis spp. are not motivated by shared chemical defense against predators.

The recently described epizoic sponge-sponge symbioses between Xestospongia deweerdtae and two species of Plakortis present an unusual series of sponge interactions. Sponges from the genus Plakortis are fierce allelopathic competitors, rich in cytotoxic secondary metabolites, and yet X. deweerdtae flourishes as an epizoic encrustation on Plakortis deweerdtaephila and Plakortis symbiotica. Our objective in this study was to evaluate the hypothesis that X. deweerdtae grows epizoic to these two species of Plakortis due to a shared chemical defense against predators. We collected free-living individuals of X. deweerdtae and symbiotic pairs from a wide geographical range to generate crude organic extracts and a series of polarity fractions from sponge extract. We tested the deterrency of these extracts against three common coral reef predators: the bluehead wrasse, Thalassoma bifasciatum, the Caribbean sharpnose puffer, Canthigaster rostrata, and the white spotwrist hermit crab, Pagurus criniticornis. While the chemical defenses of P. deweerdtaephila and P. symbiotica are more potent than those of X. deweerdtae, all of the sponge species we tested significantly deterred feeding in all three generalist predators. The free-living form of X. deweerdtae is mostly defended across the region, with a few exceptions. The associated form of X. deweerdtae is always defended, and both species of Plakortis are very strongly defended, with puffers refusing to consume extract-treated pellets until the extract was diluted to 1/256× concentration. Using diode-array high performance liquid chromatography (HPLC) coupled with high-resolution mass spectrometry (LC-MS/IT-TOF), we found two secondary metabolites from P. deweerdtaephila, probably the cyclic endoperoxides plakinic acid I and plakinic acid K, in low concentrations in the associated—but not the free-living—form of X. deweerdtae, suggesting a possible translocation of defensive chemicals from the basibiont to the epibiont. Comparing the immense deterrency of Plakortis spp. extracts to the extracts of X. deweerdtae gives the impression that there may be some sharing of chemical defenses: one partner in the symbiosis is clearly more defended than the other and a small amount of its defensive chemistry may translocate to the partner. However, X. deweerdtae effectively deters predators with its own defensive chemistry. Multiple lines of evidence provide no support for the shared chemical defense hypothesis. Given the diversity of other potential food resources available to predators on coral reefs, it is improbable that the evolution of these specialized sponge-sponge symbioses has been driven by predation pressure.

Size structuring and allometric scaling relationships in coral reef fishes.

Temperate marine fish communities are often size-structured, with predators consuming increasingly larger prey and feeding at higher trophic levels as they grow. Gape limitation and ontogenetic diet shifts are key mechanisms by which size structuring arises in these communities. Little is known, however, about size structuring in coral reef fishes. Here, we aimed to advance understanding of size structuring in coral reef food webs by examining the evidence for these mechanisms in two groups of reef predators. Given the diversity of feeding modes amongst coral reef fishes, we also compared gape size-body size allometric relationships across functional groups to determine whether they are reliable indicators of size structuring. We used gut content analysis and quantile regressions of predator size-prey size relationships to test for evidence of gape limitation and ontogenetic niche shifts in reef piscivores (n=13 species) and benthic invertivores (n=3 species). We then estimated gape size-body size allometric scaling coefficients for 21 different species from four functional groups, including herbivores/detritivores, which are not expected to be gape-limited. We found evidence of both mechanisms for size structuring in coral reef piscivores, with maximum prey size scaling positively with predator body size, and ontogenetic diet shifts including prey type and expansion of prey size. There was, however, little evidence of size structuring in benthic invertivores. Across species and functional groups, absolute and relative gape sizes were largest in piscivores as expected, but gape size-body size scaling relationships were not indicative of size structuring. Instead, relative gape sizes and mouth morphologies may be better indicators. Our results provide evidence that coral reef piscivores are size-structured and that gape limitation and ontogenetic niche shifts are the mechanisms from which this structure arises. Although gape allometry was not indicative of size structuring, it may have implications for ecosystem function: positively allometric gape size-body size scaling relationships in herbivores/detritivores suggests that loss of large-bodied individuals of these species will have a disproportionately negative impact on reef grazing pressure.

Movement patterns of reef predators in a small isolated marine protected area with implications for resource management

Reef predators play a critical role in maintaining the balance of marine ecosystems and are an important component of Hawaii’s recreational and commercial fisheries. In response to the increasing anthropogenic demands on these populations across the main Hawaiian Islands, the study of predator movements in marine protected areas has become a research priority. To this aim, we used passive acoustic telemetry to investigate the spatial and temporal movement patterns of five reef predator species: bluefin trevally (Caranx melampygus), giant trevally (Caranx ignobilis), green jobfish (Aprion virescens), whitetip reef sharks (Triaenodon obesus) and gray reef sharks (Carcharhinus amblyrhynchos) at the 31 ha Molokini Marine Life Conservation District (MLCD) off Maui, Hawaii (Lat: 20°37′56.70″N, Lon: 156°29′44.52″W) from November 13, 2013 to August 28, 2015. Our results indicate that the predator assemblage in the MLCD was dominated by teleost fishes during the day and sharks at night. Residency was variable across species, with bluefin trevally exhibiting the highest residency in the MLCD, green jobfish the lowest, and long-distance movements between the Molokini MLCD and the other islands of the Maui Nui Complex were common for gray reef sharks and giant trevally. These results indicate that despite its small size, the Molokini MLCD provides a high level of protection to resident species such as bluefin trevally. However, this MLCD is less effective at protecting more mobile predators such as green jobfish, gray reef sharks and giant trevally.

Acoustic telemetry and network analysis reveal the space use of multiple reef predators and enhance marine protected area design.

Marine protected areas (MPAs) are commonly employed to protect ecosystems from threats like overfishing. Ideally, MPA design should incorporate movement data from multiple target species to ensure sufficient habitat is protected. We used long-term acoustic telemetry and network analysis to determine the fine-scale space use of five shark and one turtle species at a remote atoll in the Seychelles, Indian Ocean, and evaluate the efficacy of a proposed MPA. Results revealed strong, species-specific habitat use in both sharks and turtles, with corresponding variation in MPA use. Defining the MPA's boundary from the edge of the reef flat at low tide instead of the beach at high tide (the current best in Seychelles) significantly increased the MPA's coverage of predator movements by an average of 34%. Informed by these results, the larger MPA was adopted by the Seychelles government, demonstrating how telemetry data can improve shark spatial conservation by affecting policy directly.

Seeing is believing: metabolism provides insight into threat perception for a prey species of coral reef fish

Responding appropriately to predator threat is a critical survival skill for all organisms. Under-responding can result in death, while continually over-responding can waste precious energy reserves and compromise important life history attributes such as growth and reproduction. This trade-off becomes particularly pertinent in predator-rich environments such as coral reefs, yet almost nothing is known of the sublethal physiological responses that coral reef predators elicit in their prey. To address this knowledge gap, we designed equipment and protocols to measure the metabolic responses of a common coral reef fish (juvenile ambon damsel, Pomacentrus amboinensis ) to chemosensory and visual stimuli of a common predator (adult yellow dottyback, Pseudochromis fuscus) . Pomacentrus amboinensis did not exhibit a metabolic response to the chemosensory predator stimulus, yet there was a consistent and significant metabolic response to the visual stimulus that endured for at least 24 h if the predator remained visible. A complete lack of metabolic response of P. amboinensis to the visual stimulus of a nonpredatory wrasse, Halichoeres argus , revealed an impressive ability of juvenile P. amboinensis to rapidly discriminate between similar-sized predatory and nonpredatory fishes. These divergent metabolic responses of P. amboinensis were not explained by measureable differences in their swimming behaviour in the predator versus nonpredator treatments, yet prey that were exposed to repeat predation attempts (predatory strikes) had the strongest metabolic response to the predator. Our findings demonstrate the capacity of coral reef fishes to interpret predator cues and prioritize threats and actions. Moreover, this study is the first to demonstrate that high predator densities on coral reefs could result in repetitive short-term or even chronic long-term elevations in energy expenditure of prey communities.

Dietary shift in juvenile coral trout (Plectropomus maculatus) following coral reef degradation from a flood plume disturbance

Acute environmental disturbances impact on habitat quality and resource availability, which can reverberate through trophic levels and become apparent in species' dietary composition. In this study, we observed a distinct dietary shift of newly settled and juvenile coral trout (Plectropomus maculatus) following severe coral reef habitat degradation after a river flood plume affected the Keppel Islands, Australia. Hard coral cover declined by similar to 28 % in the 2 yr following the 2010-2011 floods, as did the abundance of young coral trout. Gut contents analysis revealed that diets had shifted from largely crustacean-based to non-preferred prey fishes following the disturbances. These results suggest that newly settled and juvenile coral trout modify their diet and foraging strategy in response to coral habitat degradation. This bottom-up effect of habitat degradation on the diet of a top coral reef predator may incur a metabolic cost, with subsequent effects on growth and survival.

Contrasting movements and connectivity of reef-associated sharks using acoustic telemetry: implications for management.

Understanding the efficacy of marine protected areas (MPAs) for wide-ranging predators is essential to designing effective management and conservation approaches. The use of acoustic monitoring and network analysis can improve our understanding of the spatial ecology and functional connectivity of reef-associated species, providing a useful approach for reef-based conservation planning. This study compared and contrasted the movement and connectivity of sharks with different degrees of reef association. We examined the residency, dispersal, degree of reef connectivity, and MPA use of grey reef (Carcharhinus amblyrhynchos), silvertip (C. albimarginatus), and bull (C. leucas) sharks monitored in the central Great Barrier Reef (GBR). An array of 56 acoustic receivers was used to monitor shark movements on 17 semi-isolated reefs. Carcharhinus amblyrhynchos and C. albimarginatus were detected most days at or near their tagging reef. However, while C. amblyrhynchos spent 80% of monitoring days in the array, C. albimarginatus was only detected 50% of the time. Despite both species moving similar distances (< 50 km), a large portion of the population of C. albimarginatus (71%) was detected on multiple reefs and moved more frequently between reefs and management zones than C. amblyrhynchos. Carcharhinus leucas was detected less than 20% of the time within the tagging array, and 42% of the population undertook long-range migrations to other arrays in the GBR. Networks derived for C. leucas were larger and more complex than those for C. amblyrhynchos and C. albimarginatus. Our findings suggest that protecting specific reefs based on prior knowledge (e.g., healthier reefs with high fish biomass) and increasing the level of protection to include nearby, closely spaced reef habitats (< 20 km) may perform better for species like C. albimarginatus than having either a single or a network of isolated MPAs. This design would also provide protection for larger male C. amblyrhynchos, which tend to disperse more and use larger areas than females. For wide-ranging sharks like C. leucas, a combination of spatial planning and other alternative measures is critical. Our findings demonstrate that acoustic monitoring can serve as a useful platform for designing more effective MPA networks for reef predators displaying a range of movement patterns.

Habitat Selectivity and Reliance on Live Corals for Indo-Pacific Hawkfishes (Family: Cirrhitidae).

Hawkfishes (family: Cirrhitidae) are small conspicuous reef predators that commonly perch on, or shelter within, the branches of coral colonies. This study examined habitat associations of hawkfishes, and explicitly tested whether hawkfishes associate with specific types of live coral. Live coral use and habitat selectivity of hawkfishes was explored at six locations from Chagos in the central Indian Ocean extending east to Fiji in the Pacific Ocean. A total of 529 hawkfishes from seven species were recorded across all locations with 63% of individuals observed perching on, or sheltering within, live coral colonies. Five species (all except Cirrhitus pinnulatus and Cirrhitichthys oxycephalus) associated with live coral habitats. Cirrhitichthys falco selected for species of Pocillopora while Paracirrhites arcatus and P. forsteri selected for both Pocillopora and Acropora, revealing that these habitats are used disproportionately more than expected based on the local cover of these coral genera. Habitat selection was consistent across geographic locations, and species of Pocillopora were the most frequently used and most consistently selected even though this coral genus never comprised more than 6% of the total coral cover at any of the locations. Across locations, Paracirrhites arcatus and P. forsteri were the most abundant species and variation in their abundance corresponded with local patterns of live coral cover and abundance of Pocilloporid corals, respectively. These findings demonstrate the link between small predatory fishes and live coral habitats adding to the growing body of literature highlighting that live corals (especially erect branching corals) are critically important for sustaining high abundance and diversity of fishes on coral reefs.

The effects of background risk on behavioural lateralization in a coral reef fish

Summary Behavioural lateralization – the preferential use of one side of the body or either of the bilateral organs or limbs – has been well documented in many species, in a number of contexts. While the benefits reported are numerous, existing latent variability in the degree of lateralization within and across populations, species and taxa indicates that existing costs may modulate its expression. Few studies have reported changes in the degree of lateralization at the individual level, in response to long‐term changes in environmental conditions, but not in response to short‐term changes in environmental conditions. Predation is highly variable both temporally and spatially and hence is a good candidate for testing lateralization effects based on short‐term changes in environmental conditions. Here, we tested the hypothesis that the degree of behavioural lateralization changes following short‐term exposure to different levels of risk. We tested whether wild‐caught juvenile damselfish exposed to a high or low background level of risk for 4 days would subsequently differ in their turning bias, a trait that has been linked to predator escape behaviour in fishes. We found that 4 days is enough to induce a difference in the absolute lateralization scores of the fish, with high‐risk fish being more strongly lateralized than low‐risk fish. Practically, this difference stemmed from decreasing lateralization scores for newly recruiting coral reef fishes that were kept in low‐risk environments, with the concurrent maintenance of higher lateralization scores for fish maintained under high‐risk conditions. Fish from the high‐risk background had higher survival than those from the low‐risk background upon release into mesocosms containing reef predators. Our study highlights how early exposure to differential predation risk affects the degree of behavioural lateralization. Given the profound effects of lateralization on many aspects of an animal's life from its ability to discriminate conspecifics to how it forages and interacts during agonistic interactions, predation risk may be a key driver of animal development.

Long-term movement patterns of a coral reef predator

Long-term monitoring is required to fully define periodicity and patterns in animal movement. This is particularly relevant for defining what factors are driving the presence, location, and movements of individuals. The long-term movement and space use patterns of grey reef sharks, Carcharhinus amblyrhynchos, were examined on a whole of reef scale in the southern Great Barrier Reef to define whether movement and activity space varied through time. Twenty-nine C. amblyrhynchos were tracked for over 2 years to define movement patterns. All individuals showed high residency within the study site, but also had high roaming indices. This indicated that individuals remained in the region and used all of the monitored habitat (i.e., the entire reef perimeter). Use of space was consistent through time with high reuse of areas most of the year. Therefore, individuals maintained discrete home ranges, but undertook broader movements around the reef at times. Mature males showed greatest variation in movement with larger activity spaces and movement into new regions during the mating season (August–September). Depth use patterns also differed, suggesting behaviour or resource requirements varied between sexes. Examination of the long-term, reef-scale movements of C. amblyrhynchos has revealed that reproductive activity may play a key role in space use and activity patterns. It was unclear whether mating behaviour or an increased need for food to sustain reproductive activity and development played a greater role in these patterns. Reef shark movement patterns are becoming more clearly defined, but research is still required to fully understand the biological drivers for the observed patterns.

Temporal links in daily activity patterns between coral reef predators and their prey.

Few studies have documented the activity patterns of both predators and their common prey over 24 h diel cycles. This study documents the temporal periodicity of two common resident predators of juvenile reef fishes, Cephalopholis cyanostigma (rockcod) and Pseudochromis fuscus (dottyback) and compares these to the activity and foraging pattern of a common prey species, juvenile Pomacentrus moluccensis (lemon damselfish). Detailed observations of activity in the field and using 24 h infrared video in the laboratory revealed that the two predators had very different activity patterns. C. cyanostigma was active over the whole 24 h period, with a peak in feeding strikes at dusk and increased activity at both dawn and dusk, while P. fuscus was not active at night and had its highest strike rates at midday. The activity and foraging pattern of P. moluccensis directly opposes that of C. cyanostigma with individuals reducing strike rate and intraspecific aggression at both dawn and dusk, and reducing distance from shelter and boldness at dusk only. Juveniles examined were just outside the size-selection window of P. fuscus. We suggest that the relatively predictable diel behaviour of coral reef predators results from physiological factors such as visual sensory abilities, circadian rhythmicity, variation in hunting profitability, and predation risk at different times of the day. Our study suggests that the diel periodicity of P. moluccensis behaviour may represent a response to increased predation risk at times when both the ability to efficiently capture food and visually detect predators is reduced.