Coral Reefs

Extreme climatic events are reshaping ecosystems worldwide as individual organisms vary markedly in their ability to withstand these disturbances. Deciphering patterns of persistence on local scales is therefore critical for predicting biodiversity trajectories under intensifying climate extremes. In this study, we examined variation in thermal stress responses among individuals of the coral Stylophora pistillata species complex during a heatwave at Heron Island Reef, Australia. More than half of the focal coral colonies died on the reef, and survival of coral fragments maintained under ex situ common thermal stress conditions was significantly correlated with the survival of their source colony. This demonstrates that survival differences result largely from biological factors rather than differential thermal exposure across reef habitats. Under common garden conditions, we observed striking differences in bleaching severity and survival times among three sympatric cryptic taxa and their highly host-specific symbiont community. Within the most locally common taxon, corals from historically warmer and more seasonally variable reef habitats seem more susceptible to bleaching, contrary to expectations. Together, these results reveal how biological differences among cryptic taxa and among individuals can shape coral responses during a heatwave and advance our understanding of coral vulnerability in a rapidly warming world.

In many polygynous species, males face stronger intrasexual competition, higher energetic demands, and lower survival than females, especially under resource limitation or environmental stress. Such sex-specific vulnerabilities are expected to intensify with climate change. Yet, in sequentially hermaphroditic systems, where individuals change sex during their lifetime, how sex and sex change shape survival remains largely unexplored. We studied sex-specific survival and growth in the haremic protogynous cleaner wrasse Labroides dimidiatus across eight reefs around Lizard Island, Great Barrier Reef. We tracked a total of 731 adult fish (individually recognizable through marking or idiosyncratic color patterns) over two years. This period included the 2024 El Nino-Southern Oscillation (ENSO), which caused a temporary 1-degree increase in water temperature, severe coral bleaching, and coral mortality at Lizard Island. Contrary to expectations from dioecious systems, terminal-phase males exhibited higher survival than initial-phase females under both normal and in particular ENSO conditions. While male mortality was not affected, female mortality more than doubled during the event, indicating greater physiological or energetic vulnerability. A partial explanation for the overall higher female mortality is their generally faster growth rate, which declined in both sexes during the ENSO event. Our findings challenge existing assumptions of male-biased mortality in polygynous species and highlight that sex and sex change fundamentally shape demographic responses to climate extremes.

Many benthic marine invertebrates disperse by releasing microscopic larvae carried by ocean currents to new sites, where they must settle into appropriate habitats and metamorphose to recruit. Species whose larvae settle in response to water-borne chemical cues live in topographically complex habitats. To study whether sinking in response to dissolved cues affects retention of larvae within complex habitats exposed to ambient water flow moving faster than larvae sink, we used the reef-dwelling sea slug, Phestilla sibogae, whose competent larvae stop swimming and sink in response to dissolved cue from their prey coral, Porites compressa. We conducted field experiments where dye-labelled water, neutrally buoyant particles, and larval mimics (particles that sank at the velocity of larvae of P. sibogae) were released together upstream of reefs of branching corals to determine if larval sinking in water above and within a reef affects larval retention within the reef. Wave-driven water flow measured above a reef in the field had instantaneous velocities peaking at 0.3 m s-1, driving slow net advection of water shoreward at [~]0.02 m s-1. Much slower wave-driven flow moved through the interstices within the reef. In this field flow, sinking by larval mimics caused their retention within a reef after dye-labelled water and neutrally buoyant particles had left. Such retention of sinking larvae within topographically complex benthic communities enhances successful recruitment by exposing larvae to high concentrations of cue for long periods, allowing them time to sink to surfaces, adhere, and undergo metamorphosis.

Understanding habitat association of animals and how they change through ontogeny is critical to predict the likely effects of habitat change on populations. We investigated how fine scale habitat associations of three common coral reef damselfish species changed among life-stages on reefs surrounding Lizard Island, northern Great Barrier Reef. All three species showed distinct habitat selection at settlement, however the degree to which these initial associations changed through ontogeny were species specific. Pomacentrus amboinensis associated with sandy areas throughout all life-stages; Pomacentrus chrysurus settled to areas with high cover of sand and rubble, but displayed no clear habitat preferences as juveniles or adults. Pomacentrus moluccensis settled to areas with high cover of fine branching corals before shifting to areas with relatively high cover of soft corals as adults. We also compared two different approaches to estimate habitat selection; one that quantified the benthic composition within the approximate home range of individuals versus a more widely used approach of recording a single point underneath the focal individual when they were first observed. Although results were broadly similar, the benthic composition approach revealed details that was overlooked using the single point method. Decreases in the availability of any of these preferred benthic habitats may adversely affect future populations, therefore understanding habitat associations and their transitions among life stages will be crucial in predicting future reef fish communities under ongoing coral loss and habitat change. This will require to systematically study a broader range of species, integrating relevant spatial and temporal scales.

AimsSponge microbiomes have been extensively studied, in part due to their potential as sources of novel antimicrobials and other biologics, with most research focusing on Demosponges. Here, we investigate the Hexactinellid sponge Pheronema carpenteri, previously identified as a promising source of antibiotic-producing bacteria. MethodsUsing next-generation sequencing of bacterial 16S rRNA genes and a single sponge metagenome, we examined the composition of bacterial communities of P. carpenteri sponges recovered from the Porcupine Seabight, along with local water and sediment samples. ResultsOur results show that P. carpenteri harbours a microbiome abundant in Proteobacteria (47.1-59.4%) and Actinobacteria (11.5-27.5%), with consistent intra-aggregation similarities and structured intra-sponge communities. A metagenomic analysis revealed the presence of several nitrogen cycling genes (nirK, nosZ, nirS homologues of proteobacterial origin), supporting a suggestion that these sponges may play a role in nitrogen cycling, while biosynthetic gene clusters (BGCs) were limited (4 complete clusters). Notably, bacterial community structures within P. carpenteri aggregations resemble those observed in both low and high microbial abundance (LMA/HMA) sponges. ConclusionsHexactinellids are traditionally considered LMA sponges, so identifying species that deviate from this dichotomy provides new insights into sponge microbiome ecology. Integrating Hexactinellids into both culture-dependent and culture-independent studies will advance our broader understanding of sponge-associated microbial diversity and could inform biodiscovery programmes in marine environments. Impact StatementOur findings support the suggestion that a combination of culture-based and molecular analyses is required to generate a comprehensive picture of the biosynthetic potential of P. carpenteri sponges. We also reveal insights into the ecosystem services that sponge microbiomes may contribute towards. These observations could facilitate a deeper understanding of the biotechnological and environmental value of key marine resources.

Probiotics can enhance coral thermal tolerance, yet their ecosystem-level effects remain unknown. Here, we present the first long-term in-situ test of whether coral-targeted probiotics influence adjacent cryptobenthic reef communities during a record marine heatwave. Probiotics were applied to Pocillopora favosa and Acropora spp. coral colonies for 18 months, spanning the fourth global bleaching event. Cryptobenthic communities were assessed using biomimetic monitoring structures integrating biodiversity surveys, molecular profiling, microbial network analyses, and metabolic assays. Before the heatwave, probiotic and control patches were comparable across structural, microbial, and functional metrics. Following thermal stress, control patches exhibited pronounced losses of cryptobenthic invertebrate abundance and taxonomic breadth, microbial network fragmentation, and net carbonate dissolution. In contrast, probiotic-treated patches retained higher biodiversity, cohesive microbial interaction architectures, and positive calcification. These findings demonstrate that coral-targeted probiotics can scale from host-level intervention to buffer adjacent ecosystem-level responses to extreme marine heatwaves under accelerating climate change. TeaserA coral-targeted probiotic strategy enhances multi-trophic resilience under heat stress.

Animals must continually balance foraging with the risk of predation. In complex natural environments, this means quickly distinguishing between threats and harmless situations. We investigated how site-associated coral reef fishes decide to escape in response to visual cues mimicking predator attacks, using controlled underwater presentations of looming stimuli at varying speeds. We measured escape responses across species and social contexts, comparing them to predator attack speeds observed in the same habitat. Escape responses were highly sensitive to the speed of the looming stimulus, with no responses occurring at low speeds. The speeds triggering escape matched those of predator attacks, whereas cruising swim speeds never triggered a response. Species employed distinct antipredator strategies: Brown Chromis foraged away from shelter with high responsiveness, whereas Bicolor Damselfish remained shelter-dependent with lower escape propensities. Contrary to expectations, the social factors did not affect responses in this study. These findings demonstrate that reef fish are highly sensitive to the approach speed of objects, with species-specific strategies further shaping behaviors. By combining realistic visual threats with natural predator attack data, this study offers insight into how animals make escape decisions in complex, real-world environments.

Understanding how fish navigate complex natural environments requires bridging fine-scale biomechanics with ecological behavior. We investigated the volitional movement and energetics of wild red drum (Sciaenops ocellatus) across laboratory, mesocosm, and field settings. Using flow-respirometry, we quantified metabolic costs and swimming kinematics under ecologically relevant flow conditions shaped by bluff bodies mimicking mangrove roots and oyster mounds. Fish swimming in turbulent wakes exhibited reduced oxygen consumption and altered tailbeat dynamics, especially at high flow speeds. In a large outdoor mesocosm, dual accelerometers revealed a rich behavioral repertoire, including maneuvering and rest, which is not easily observable in confined lab settings. Spectral analysis and clustering identified eight distinct locomotory states, highlighting the limitations of summed acceleration metrics. Field telemetry tracked wild red drum across a 54 km estuarine corridor for a three-year period through an array of 36 acoustic receivers, revealing movement patterns shaped by tidal flow and physical habitats. Hydrodynamic modeling revealed that while laboratory trials demonstrated substantial energetic savings at high flows (approaching 100 cm/s), wild fish were detected predominantly in low-velocity microhabitats (<30 cm/s) near structurally complex features. This mismatch suggests that habitat selection is an adaptive strategy driven by ecological factors such as foraging opportunities, predation refuge, and site fidelity, rather than hydrodynamic efficiency alone. Our multi-scalar approach demonstrates that while flow-structure interactions can reduce locomotor costs for fish, habitat use in the wild reflects broader ecological constraints, offering a framework for integrating biomechanics, physiology, and ecology in conservation-relevant contexts.

Using linear inverse ecosystem modeling as a data assimilation tool, we compare spawning grounds of Atlantic and Southern Bluefin Tuna (ABT and SBT, respectively) based on results from field campaigns in the Gulf of Mexico (GoM) and eastern Indian Ocean off northwest Australia (Argo Basin). Both regions are warm, stratified, low-nutrient waters dominated by cyanobacteria (Prochlorococcus). Despite these similarities, the Argo Basin is more productive, with [~]1.5X higher net primary production and nearly 2X higher production of top trophic levels in the model (tuna larvae, planktivorous fish, and predatory gelatinous zooplankton). Higher primary production in the Argo Basin is mainly driven by higher N2 fixation and storm mixing of new nutrients in the upper and lower euphotic zone, respectively. Increased ecosystem efficiency (secondary production of top trophic levels / primary production) results from differences in plankton food web organization. In the GoM, protistan zooplankton are the direct consumers of nearly all phytoplankton production. In contrast, higher rates of herbivory by crustaceans feeding on nanophytoplankton combines with a higher impact of appendicularians on cyanobacteria to convert plankton production into larval tuna prey more efficiently in the Argo Basin. Despite similarities in the proportions of phytoplankton production mediated by cyanobacteria and other picoplankton in both systems, food web pathways to larval tuna and other planktivorous fish are substantially shorter in the Argo Basin. Our results highlight the impact of distinct zooplankton ecological niches on ecosystem efficiency and suggest a need for better inclusion of plankton food-web structure in models simulating climate impacts on fisheries production. HIGHLIGHTSO_LIDeveloped food web models of tuna spawning habitat (Indian Ocean & Gulf of Mexico) C_LIO_LISpawning habitats in the Argo Basin and Gulf of Mexico (GoM) are both oligotrophic C_LIO_LIArgo Basin had higher net primary production in part as a result of nitrogen fixation C_LIO_LIArgo Basin had higher rates of direct herbivory by metazoan zooplankton C_LIO_LIThis resulted in greater ecosystem efficiency in the Argo Basin. C_LI

Theory suggests that pairs of mutualist species will often co-disperse and share the same dispersal patterns, though the extent to which this happens remains unclear. Photosynthetic corals constitute an example of this dynamic, as they rely on algal symbionts to meet their energetic needs, yet many acquire their symbionts environmentally after their larval dispersal phase. Consequently, corals and their symbionts may exhibit similar or contrasting patterns of genetic variation across the seascape, with implications for their evolutionary and ecological processes. Here, we densely sample corals of the key reef-building taxon Acropora cf. tenuis and their algal symbionts across a reefscape in the central Philippines to examine genetic variation across space. Four distinct coral taxa show genetic evidence of long distance dispersal, including weak or absent isolation by distance signals and parent-offspring pairs at widely spaced sites. These coral taxa all host a single group of algal symbionts from the genus Cladocopium, which shows landscape genetic structure independent from its coral hosts. In fact, Cladocopium genetics vary with both latitude and depth, potentially indicating genome-wide local adaptation at a finer spatial scale than that seen in their hosts. Genetic variation at markedly different spatial scales between host and symbiont may be beneficial for hosts if these differences enable them to acquire symbionts adapted to their settlement environments.

Coral restoration is recognised as a critical tool to mitigate pantropical degradation of reef ecosystems. Robust monitoring of restoration progress is crucial for projects to evaluate their success, improve practice, and share knowledge. However, traditional visual surveys often fail to capture the full impact of coral restoration on reef function. Therefore, we employed Passive Acoustic Monitoring (PAM) to assess whether the soundscape of a coral restoration site in the Seychelles differs from adjacent healthy and degraded reference reefs. We applied two methods of soundscape analysis: manual detection of unidentified fish sounds; and machine learning-based Uniform Manifold Approximation and Projection analysis. Results were approach-specific: the manual approach highlighted similarities in fish calls between the restoration site and the healthy reference reef, while the machine learning approach extracted broader soundscape patterns, clustering the restoration site alongside the degraded reference reef. Although this is a single-site study, these findings suggest that a) coral restoration alters reef soundscapes, though recovery time may be taxon-specific, and b) multiple metrics are needed to bridge single-taxon and broad soundscape scales. This study contributes to the evolving field of soundscape ecology in coral reef ecosystems, highlighting the utility of PAM in monitoring changes to reef function through coral restoration.

Protogynous sex change, where individuals first function as females and later as males, is a key life-history strategy among polygynous reef fishes. In haremic systems, sex change is typically socially regulated, with dominants suppressing subordinates sex change through aggression. Females within a harem form a size-based hierarchy that can remain stable in most species through the threat of eviction. We studied a different situation in the cleaner wrasse Labroides dimidiatus, where larger females have incomplete control, as they spend most of their time alone at their own cleaning territory. We tracked over 400 individuals for 12 months, recording growth, behavior, social organization, and sex change. We confirmed earlier reports that both sexes direct aggression primarily at those ranked immediately below them. However, we observed 30 cases where smaller females outgrew larger ones, revealing hierarchy instability. Of 42 sex change events, 43% occurred in presence of the male, and half of these early sex changers were not the largest female, but individuals overlooked by the male. Fast growth relative to harem-mates and harem switching increased the likelihood of sex change. Local population densities also influenced growth and sex change, with individuals in high-density demes growing faster and changing sex at larger sizes. Our findings reveal flexible sex change dynamics in a system with incomplete social dominance. Such incomplete control and observations that becoming male confers both higher reproductive success and survival highlight the need to expand game-theoretical and life-history frameworks to encompass such strategic flexibility. Lay summaryDominant cleaner wrasse cannot fully control subordinates as individuals occupy distinct core areas. Tracking 400 fish for a year, we found that smaller females could outgrow initially larger ones, and early sex change despite a larger male. Fast growth and harem switching increased the chances of becoming male. Population density also shaped these strategies. Our findings reveal flexible sex change dynamics in a system where becoming male confers both higher reproductive success and survival.

O_LIAquatic algae are key primary producers in the Arctic and Antarctic, yet how cold-water species respond to environmental change is poorly understood. The Polar Regions are increasingly exposed to frequent heat waves, leading to declining ice cover, increased light availability, and decreasing salinity in polar waters. We compared three phylogenetically related but geographically distant polar Chlamydomonas species to test how habitat history shapes algal responses to light, salinity, and temperature stress. C_LIO_LIWe assessed the growth, morphology, and photochemistry of psychrophilic Chlamydomonas acclimated to native-like (lower light, higher salinity) and climate-shifted conditions (higher light, lower salinity). Next, we exposed acclimated cultures to a lethal heat shock and observed how acclimation affects algal temperature stress resilience. C_LIO_LIAll three species acclimated to climate-shifted conditions grew rapidly but showed the greatest sensitivity to temperature stress, with rapid loss of viability and photosynthetic efficiency. In contrast, slow-growing cultures acclimated to native-like conditions exhibited significantly greater resilience to temperature stress. C_LIO_LIOur work is the first to directly link light and salinity acclimation with temperature resilience in psychrophilic algae, suggesting that fast-growing polar green algae may be particularly vulnerable to increasingly frequent heat waves, with major implications for primary productivity in polar environments. C_LI

Tropical coral reef ecosystems worldwide are being impacted by combined pressures of climate change and human activities that introduce large quantities of nutrients and sediments into coastal areas. In this context, phytoplankton represent a critical link between dissolved inorganic nutrients and coral reef food webs, yet their role in these ecosystems remains understudied. We investigated ecological responses of the summer phytoplankton community of Shiraho Reef (Ishigaki Island, Okinawa, Japan) to nutrient enrichment using field-based microcosm experiments under natural light and temperature conditions in September 2022 and 2023. Treatments included single and combined additions of nitrogen, phosphorus, and silicon. Chlorophyll a (Chl a) concentrations increased after three days under combined nutrient conditions, whereas single-nutrient additions produced limited responses, indicating a strong co-limitation by nitrogen and phosphorus in the reef. Analysis of size-fractionated Chl a revealed shifts from picophytoplankton that typically dominate tropical oligotrophic ecosystems toward larger groups supported by enhanced nutrient availability. Our results show short-term impacts of nutrient enrichment events on phytoplankton size structure and biogeochemical cycling in coral reefs, and highlight the importance of pelagic processes in coral reef carbon dynamics under nutrient-enrichment.

Climate change and anthropogenic pressures are reshaping marine food webs, altering prey availability and affecting top predators. The European Shag (Gulosus aristotelis), a coastal demersal seabird, provides a valuable model for examining environmentally mediated dietary variation, given its trophic plasticity and capacity to adjust prey use according to local availability, while also allowing assessment of potential demographic consequences. This study investigated spatial and temporal variation in diet at two Portuguese colonies (Berlengas and Arrabida) between 2016 and 2024 and assessed long-term reproductive productivity at Berlengas. A total of 468 regurgitated pellets were analysed, and diet composition was quantified using the Index of Relative Importance (IRI). Generalised additive models were applied to assess environmental, spatial, and period-specific effects on diet composition, while reproductive productivity was modelled in relation to prey biomass. Diet variation was primarily explained by environmental predictors, including sea surface temperature, chlorophyll-a concentration, and zooplankton, whereas year per se had no significant effect, indicating environmentally mediated bottom-up effects. Spatial differences between colonies reflected contrasting prey field structures, and period-specific patterns suggested increased specialisation during breeding. Higher biomass of sandeels (Ammodytidae) was positively associated with reproductive output, whereas shifts toward lower-energy prey were associated with reduced productivity. These findings demonstrate that environmentally driven dietary change has measurable demographic consequences, underscoring the importance of bottom-up processes in shaping seabird population dynamics and informing conservation strategies under ongoing climate change.

Understanding behavioral differences between non-native and closely related endangered species could be important to aid conservation management. In volume 169 of Zoology, Bels et al. (2025) reported on their comparison of display-action-patterns (DAP) between native Iguana delicatissima and non-native iguanas present on islands of the Guadeloupe Archipelago in the Caribbean Lesser Antilles. Here, we address conceptual and methodological concerns about their work and reanalyze their data given our proposed corrections, primarily a literature-informed adjustment of their "species" category. We additionally utilize online videos from South American mainland I. iguana populations, from where the non-native iguanas in the Guadeloupe Archipelago originate, to better understand the different DAPs between native and non-native iguanas in the Guadeloupe Archipelago. Significant differences in DAP characteristics among "species" categories (native I. delicatissima, non-native iguanas, and hybrids) show that Bels et al. (2025) oversimplified their data analyses by merging all non-native populations into one group. This result indicates the presence of behavioral variation among subpopulations within widely hybridizing iguanid populations, which has been poorly studied. Additionally, videos from mainland populations across two major mitochondrial clades of Iguana iguana show that non-native iguanas on Guadeloupe retained DAP characteristics of those populations from which they originate. We discuss these findings in light of the proposed hypotheses put forward by Bels et al. (2025), of which two can be excluded. Overall, our reanalysis shows that studies focusing on characteristics within settings of complex hybridization in diverse species should acknowledge this complexity.

Coral reefs face widespread declines under global change, yet the status of their genetic diversity remains largely unknown. Here, we compiled genome-wide DNA sequencing data for 2,520 individuals from 18 reef taxa--including corals, fish, sharks, oysters, shrimp, sea anemones, and manta rays. These data were used to assess spatiotemporal patterns of genetic distances across 173 reefs worldwide between 1998-2018. While we did not observe an overall temporal decline in genetic distances, within-reef distances showed negative temporal trends, potentially reflecting population-level diversity loss. These effects varied across species but did not show clear distinctions between taxa. We then used satellite-derived seascape variables to predict local effects on genetic distances across reefs globally. Negative effects were predicted for the Red Sea, Northern Caribbean, and Coral Triangle, while positive effects were found across the South Pacific. Key predictors included declining oxygen levels, increasing nitrate concentrations, and rising water temperatures--variables that can be tracked in real time via Earth observation (EO), enabling early warning for coral reef genetic diversity loss.

UNSTRUCTURED ABSTRACTIn several species, vaccine-like approaches, where hosts are primed through controlled pathogen exposure, have proven effective in enhancing responses to subsequent infections. This principle remains unexplored in corals. Here, we demonstrate that chronic exposure to non-lethal concentrations of live or inactivated Vibrio coralliilyticus primes the coral holobiont to counter subsequent infections under heat stress. Non-primed corals experienced greater heat stress pathogen-driven bleaching and a significant decline in their photosynthetic efficiency compared to primed samples. These results were linked to microbiome conditioning and host gene expression modulation, including a layered, fine-tuned immune and cellular response to microbial invasion. This proof-of-concept challenges strictly innate immune responses in corals and positions immune priming and microbiome conditioning as integrated mechanisms of coral holobiont resilience. Together, these findings can contribute to redefine coral immunity concepts and lay the groundwork for developing new microbiome-based strategies to enhance coral health for reef conservation under climate change. LAY SUMMARYCoral reefs are increasingly threatened by rising seawater temperatures and disease. Unlike vertebrates, corals do not possess a classical adaptive immune system, so they have been thought to rely only on innate defenses. However, our study shows that corals may be more capable than previously believed. We demonstrate that exposing corals to non-lethal doses of a widespread bacterial pathogen can train them to better withstand subsequent infections under heat stress. Corals that were not pre-exposed suffered more pathogen caused bleaching and showed a stronger decline in physiological performance, while those that were primed were more resilient. This improved resistance appears to come from two coordinated processes. First, the corals associated bacterial community shifted in a way that seems to help protect the host. Second, the coral itself adjusted its gene expression, mounting a more effective and controlled response to infection. These findings suggest that corals may be able to remember past exposures and respond more effectively to future infections, even without a traditional adaptive immune system, providing a foundation for developing new strategies to support coral resilience.

Mesophotic coral ecosystems have been proposed as climate refugia for shallow reefs, yet the capacity of mesophotic corals to persist across depth gradients remains unresolved. We conducted a long-term reciprocal transplantation of the Caribbean coral Porites astreoides between shallow (10 m) and mesophotic (40 m) reefs to assess physiological, skeletal, and transcriptomic plasticity. Depth, rather than season, was the primary driver of coral performance. Shallow colonies exhibited higher metabolic activity and calcification, whereas mesophotic colonies showed reduced protein content, slower skeletal extension, and elevated expression of skeletal organic matrix genes. Transplant responses were asymmetric: shallow-to-deep corals acclimated through coordinated physiological and transcriptional adjustments, while deep-to-shallow transplants experienced mortality and limited transcriptional reprogramming. Moderate genetic connectivity across depths suggests that performance differences arise primarily from phenotypic plasticity rather than fixed genetic divergence. Our findings indicate that shallow populations harbor greater acclimatory capacity, whereas mesophotic corals show constrained upward resilience, challenging the generality of deep reefs as refugia under rapid environmental change. TeaserAsymmetric plasticity limits the capacity of mesophotic corals to rejuvenate shallow reefs under climate change.

Although predation is a major driver of group living across taxa and the antipredator benefits of grouping are well established, the energetic costs experienced by groups under predation remain largely unexplored. In the current study, we use wild, white mullet (Mugil curema, Valenciennes 1836), to provide the first real-time quantification of the energetic cost of escape in schooling fish using intermittent, closed-loop respirometry. We found that small groups exposed to predators showed a 53.8% increase in their organismal metabolic rate (MO2) as compared to groups without predator exposure. When we evaluated antipredator behaviors such as escape response, group cohesion, and displacement of the group centroid, we found a positive correlation to energetic costs. We then investigated whether escape responses are socially modulated by comparing the energetic costs of escape across solitary individuals, solitary individuals with visual access to a group, and groups. We found that escape frequency and energetic costs to predation were comparable across social contexts, indicating that escape may be an intrinsic survival response independent of cues from group members. Furthermore, we found that fish exposed to predators showed markedly reduced feeding, suggesting that predation constrains energy acquisition in addition to imposing direct energetic costs. Our results provide the first direct quantification of the energetic costs of escape in a schooling fish, offering new insights into the physiological trade-offs underlying collective antipredator defenses.