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.

Ostreobium, a siphonous green alga capable of living inside of calcium carbonate substrates, including the skeletons of reef-building corals. This study investigates spectral niche preferences and physiological strategies of Ostreobium using community-wide experiments. We exposed natural Ostreobium communities from Porites lutea collected across shallow, mid, and deeper-water sites to three light conditions: far-red, blue, and white light, simulating healthy shallow-water corals, deeper water conditions, and bleached coral skeletons respectively. Using 16S rRNA metabarcoding and chlorophyll analysis, we assessed community changes and physiological responses over 16 weeks. We show significant variation in spectral preferences among Ostreobium OTUs, with clear evidence for both generalist and specialist strategies. Chlorophyll analysis showed photoacclimation responses through changes in pigment compositions. Our work shows that the spectral architecture of the reef plays a role in structuring Ostreobium communities, but the many mismatches between spectral preferences of OTUs and their observed presence in nature, suggests that inter-species competition is likely to be an even stronger contributor to community structure across the reefs microhabitats. We show that physiological heterogeneity within Ostreobium is strongly phylogenetically structured, and our results clearly highlight the importance of considering OTU-level differences when predicting community responses to environmental disturbances such as coral bleaching. While generalist OTUs dominate natural communities, these do poorly in incubations, and we hypothesise that white light specialists may become key players during coral bleaching events. Our work is a substantial advance in our understanding of Ostreobium ecology and provides a framework for interpreting future environmental sequencing data, offering insights into the functional roles of the different OTUs.

Uncontrolled carbon dioxide emissions from human activities contribute to ocean warming and acidification. These alterations in ocean chemistry threaten marine organisms, such as the true giant clam, Tridacna gigas, which is already imperiled due to overharvesting and habitat destruction. To gain an understanding of the physiological and molecular responses of T. gigas and its symbiotic dinoflagellates to ocean warming and acidification, we subjected juvenile individuals to different treatments simulating predicted seawater pH (7.6 and 8.0) and temperature (28{degrees}C, 30{degrees}C, 32{degrees}C and 34{degrees}C) levels for the next century. Juvenile giant clams were able to tolerate sustained exposure to temperatures of up to 32{degrees}C and pH as low as 7.6, while exposure to higher temperature (34{degrees}C), regardless of pH level, resulted in total mortality after a week. However, symbiosis was compromised even in the sublethal treatments, as indicated by the decrease in Symbiodiniaceae density and changes in symbiont gene expression. Symbionts significantly upregulated genes involved in splicing, translation, fatty acid metabolism, and DNA repair, which may constitute an adaptive response, while downregulating genes involved in photosynthesis and transmembrane transport, suggests impaired transfer of photosynthates to the host. These findings demonstrate the vulnerability of the juvenile T. gigas holobiont to heat stress, highlighting the critical importance of continued conservation and management alongside efforts to mitigate global changes in ocean conditions to safeguard this iconic marine bivalve. Summary StatementThis study investigates physiological and molecular responses of Tridacna gigas to seawater warming and acidification, providing insights into the potential future of endangered giant clam populations in a changing ocean.

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.

European tidal flats that host non-native Magallana gigas reefs contribute to several ecosystem functions. Among others, they provide a habitat for a large variety of associated fauna. However, we often lack detailed information about any trophic interactions of the associated macrozoobenthos species with the oysters, and about their role in the carbon and nutrient cycle. Therefore, we performed ex-situ pulse-chase tracer experiments in the Eastern Scheldt (Southwest Dutch Delta, Netherlands) in summer and autumn 2020, where we fed M. gigas and their associated fauna 13C- and 15N-enriched bacterioplankton while the macrozoobenthos was incubated in water containing deuterium oxide (2H2O; enrichment: 1 - 2.5%). The aim was (1) to assess differences in short-term (<12h) processing of bacterioplankton in summer and autumn, and (2) to study differences in 2H incorporation - a proxy for metabolic activity - of M. gigas and its associated fauna in summer and autumn. In summer, all macrozoobenthos species combined consumed significantly less bacterioplankton-derived 13C and 15N than in autumn, while all macrozoobenthos species combined incorporated comparable amounts of 2H into their tissue in both seasons. Most bacterioplankton-derived 13C and 15N was taken up by sponges (Halichondria panicea, Hymeniacidon perlevis), crabs (Carcinus maenas, Eriocheir sinensis, Rhithropanopeus harrisii), and limpets (Crepidula fornicata). Most 2H was taken up by crabs (C. maenas, E. sinensis), sponges (H. perlevis), and snails (Littorina littorea), implying that these species were the most metabolically active ones. Overall, the metabolic activity was linked to feeding activity in summer 2020, whereas in autumn 2020, the link was weaker and the most metabolically active species were not necessarily the species that had incorporated most 13C and/or 15N.

Symbiosis with photosynthetic microbes is widespread in marine animals, with various symbiont transmission modes and localisation within the host. Here, we characterise the association between the acoel Convolutriloba macropyga and its photosymbionts, identified as Tetraselmis green algae based on rbcL gene phylogenetic analysis. Symbionts are transmitted vertically to asexual offspring and acquired horizontally by juveniles after sexual reproduction. Embryos develop to aposymbiotic juveniles that ingest Tetraselmis through the mouth. Confocal microscopy shows an increase in algae number within juveniles and in their presence at the body wall. Transmission electron microscopy reveals that symbionts lose flagella and theca. In adults, symbionts are extracellular at the body periphery, but can be intracellular within the parenchyma, in contrast with previously described acoel photosymbionts. This likely reflects different host-symbiont interactions, with algae potentially performing photosynthesis and nutrient exchange at the periphery, while undergoing transport or digestion in the parenchyma. Comparative transcriptomics between symbiotic adults and aposymbiotic juveniles shows an enrichment of amino acid synthesis, lipid metabolism, and osmotic and oxidative stress responses in symbiotic adults. Our data shows that algal symbionts engage with host tissues in distinct ways, inside or outside host cells, highlighting a previously unappreciated spatial complexity in host-algae interactions. HighlightsO_LITetraselmis algae are taken up by Convolutriloba macropyga juveniles C_LIO_LIAlgal symbionts in juveniles lose theca and flagella, proliferate, and move to the body wall C_LIO_LISymbionts are extracellular at the body wall and can be intracellular in the parenchyma C_LIO_LIAmino acid synthesis, lipid metabolism, osmoregulation and stress responses are activated in symbiotic adults C_LI

Climate change is driving species range shifts and population change in density and location globally. Two theories behind these shifts, that species in the ocean are largely tracking climate velocities, and the concept of long-term temporal turnover, have garnered increased attention recently. However, research in marine ecosystems has largely focused on mobile species, namely commercially important fishes. Here we examine changes in sessile invertebrate and algal species on vertical surfaces, subtidal rock walls, in the southern Gulf of Maine (GOM), and to what extent these changes might have been driven by 42 years of warming. In part due to ocean circulation patterns in the GOM, the thermally-sensitive species in this community are unlikely to track climate velocities by moving laterally, and are therefore disappearing, moving into deeper water, or adapting to novel thermal conditions. We find that some species, including one of the previously competitive dominants, Alcyonium siderium, have become exceedingly rare at these sites. Two other competitive dominants, Metridium senile and Aplidiiuam glabrum, have also declined precipitously. Meanwhile, the blue mussel, Mytilus edulis, the non-native tunicate Didemnum vexillum, and a complex of erect bryozoans have become dominant space holders. Over the same period of time, average summer temperatures in the southern GOM increased by more than 3{degrees}C. Using occupancy derived thermal affinities, we find warm-affinity species increasing, while generally, cool and cold-affinity species are decreasing. All species which decreased in abundance normally occupy sites with temperatures below a mean of 17.4{degrees}C maximum summer temperatures. A few species did not change abundance despite the rapidly warming surface waters, indicating their broad tolerances and the importance of other biological processes in mediating community structure in the GOM. Overall, sessile rock wall communities in the southern GOM are transitioning to more thermally-tolerant species, most of which are not native to the Atlantic coast of North America.

Coral white syndromes are among the most prevalent diseases affecting Indo-Pacific reefs, yet their etiology remains poorly understood, particularly in relation to eutrophication and microbial dynamics. Here, we investigated the drivers of Porites cylindrica white syndrome (PCYLWS) across two reef sites in Guam differing in nutrient enrichment and disease pressure. We combined 14 years of long-term disease monitoring with short-term lesion tracking, microbial community profiling of coral tissue and surrounding environments, and measurements of nutrient and environmental conditions. Long-term prevalence of PCYLWS was consistently higher at the oligotrophic site (Luminao) than at the eutrophic site (Tumon Bay), largely due to differences in host size structure and colony abundance. In contrast, lesions at Tumon Bay were larger and rapidly colonized by turf algae, whereas lesions at Luminao progressed faster but stabilized at smaller sizes. Microbial communities were strongly structured by sample type, with distinct assemblages in seawater, sediment, healthy tissue, and diseased tissue. Diseased tissues exhibited high spatial and temporal variability and signatures of microbial dysbiosis, characterized by reduced dominance of Parendozoicomonas and increased relative abundance of opportunistic taxa, including Ruegeria, Muricauda, and Vibrio. Environmental microbial communities and nutrient concentrations varied seasonally, particularly at the eutrophic site, suggesting transient environmental reservoirs of opportunistic bacteria. Together, these findings indicate that PCYLWS is shaped by context-dependent interactions among host population structure, environmental conditions, and dynamic microbial communities, supporting a multi-etiology framework for coral white syndromes. ImportanceCoral white syndromes are among the most common yet least mechanistically resolved coral diseases worldwide. By integrating 14 years of disease monitoring with lesion-scale dynamics, environmental microbiomes, and nutrient data, this study demonstrates that white syndrome expression in Porites cylindrica is shaped by context-dependent interactions among host population structure, eutrophication, and microbial dysbiosis rather than a single causative pathogen. These findings support a multi-etiology framework for coral disease and highlight the importance of environmental microbial reservoirs in modulating disease outcomes. This work provides a long-term, field-based perspective that is rarely available for coral disease systems and is broadly relevant to disease ecology in changing coastal environments.

Increasing urbanization and climate change pose significant threats to coral reefs, highlighting the need to understand the process underlying coral acclimatization in urban environments. Alterations in the microbiome composition represent a key mechanism by which corals adapt to varying environmental conditions. We compared endosymbionts and bacterial communities associated with Siderastrea siderea from urban and offshore Miami reef tracts across three seasons. We found two distinct genera of endosymbiotic Symbiodiniaceae algae, namely Cladocopium and Breviolum, consistently across sites and seasons, with Cladocopium predominating. The stable presence of these symbionts suggests host specificity in S. siderea and highlights the potential advantage of harboring multiple symbionts to enhance survival in diverse environments. In contrast, bacterial diversity exhibited variation across seasons and locations, with a small subset of microbes identified as a core microbiome demonstrating the remarkable plasticity of bacterial communities in response to environmental changes. Differential analysis revealed an increased abundance of Alteromonas and Synechococcus in urban corals, which may contribute to host nutrient acquisition, antibiotic production, and survival in polluted environments. Predicted functional profiles further demonstrated distinct metabolic reorganization of microbial communities between urban and offshore reefs, with urban corals enriched in pathways associated with stress response, pollutant degradation, and nutrient cycling. Together, these findings indicate that while algal symbionts remain stable, bacterial communities undergo both compositional and functional plasticity that likely supports coral persistence in highly urbanized environments.

Understanding how reef-associated biodiversity responds to seascape features is essential for monitoring and conserving coral reef ecosystems. Environmental DNA (eDNA) from seawater provides access to benthopelagic eukaryotic diversity but its relationship with benthic structure remains poorly understood. We conducted simultaneous assessment of benthopelagic eDNA derived from near-reef seawater and benthic photoquadrat surveys across 12 coral reef sites in the northern Red Sea, spanning three seascape regions: the Gulf of Aqaba, nearshore Northern Red Sea (NRS), and offshore NRS. We examined whether spatial patterns in benthopelagic eDNA communities were structured across regions and whether variation in benthic cover explained differences in eDNA-derived assemblages obtained from water samples. Benthopelagic eDNA revealed fine-scale spatial structuring across regions but showed non-significant whole-community correlation with benthic composition. When examined by major taxonomic groups, taxon-specific relationships emerged, with some taxa (i.e., Micromonas sp.) showing increasing relative abundances in reefs characterized by lower benthic complexity. While traditional photoquadrat surveys captured 72 benthic sessile taxa including dominant benthic groups (e.g. hard corals and algae) across four eukaryotic phyla, benthopelagic eDNA documented a broader range of eukaryotic diversity, including planktonic, cryptic, and low abundant taxa spanning 35 phyla. Notably, eDNA detected cryptic organisms overlooked by visual surveys, such as the giant clam Tridacna sp., even where present but not recorded in photoquadrats. Our results demonstrate that benthopelagic eDNA and visual surveys provide complementary perspectives on reef biodiversity. Rather than serving as a direct proxy for benthic structure, benthopelagic eDNA captures spatial and taxonomic patterns that may be overlooked by visual transects, supporting its use in seascape-scale biodiversity assessments and conservation planning efforts in dynamic and understudied reef systems.

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.

AbstractBeneficial associations between bobtail squids (Cephalopoda: Sepiolidae) and Vibrio bacteria encompass a unique association where symbionts are obtained environmentally from the surrounding environment. Vibrio symbionts are susceptible to a number of ecological pressures such as protozoan grazing whilst in their free-living state. Impacts of grazing have several consequences for symbiosis characteristics such as biofilm formation, a trait crucial for survival both in and outside the squid. Therefore, in order to ascertain how biotic factors such as grazing in the environment effect symbiotic success, two V. fischeri strains, ES114 and ETBB1-C were experimentally evolved in separate biofilm grazing experiments with the amoeba, Acanthamoeba castellanii and ciliate Tetrahymena pyriformis. Both ES114 and ETBB1-C biofilms were evolved up to 50 generations through serial passaging. At 50 generations, ES114 biofilms displayed variability in response to predation by both predators, whereas ETBB1-C biofilms were more stable across generations of grazing. A. castellanii decreased in population numbers when co-inoculated with ETBB1-C, whereas T. pyriformis increased in numbers with biofilm growth. Growth of V. fischeri biofilms in the presence of grazers such as T. pyriformis has an important role in inducing biofilm growth by acting as a chaperone for recycling nutrients back into the environment. Additionally, V. fischeri colonization fitness in the host was dependent on which grazer was used to evolve the biofilms. Such variation in response by V. fischeri to different types of predation demonstrates the versatility of this symbiont in its free living state and has subsequent impacts on the eventual association with squids. ImportanceThis manuscript demonstrates the importance of biotic factors (such as protozoan grazing) in the environment that effect host colonization in a beneficial symbiosis. Using an experimental evolution approach, this work demonstrates how symbiotic biofilms can adapt to pressures such as grazing that subsequently influences the ability to colonize its invertebrate host.

Severe global declines in coral populations have driven growing demand for human intervention and restoration. One goal of restoration is to repopulate reef ecosystems through outplanting, which requires detailed understanding of target systems. However, long term ecological and reproductive data from interventions remain scarce. An exception to this are the critically endangered Caribbean corals, Acropora palmata and A. cervicornis, which have been central to restoration efforts in the region. These species serve as a unique case study due to the abundance of published data spanning ecology, and reproductive biology. In the wild, these species can cross to form an F1 hybrid, A. prolifera, though it is rarely used in restoration. It remains unclear whether A. prolifera is an evolutionary dead-end competing with its parents, or a potential bridge enabling genetic exchange via backcrossing. To evaluate benefits and risks of restoration among Caribbean Acropora, we developed a two-dimensional agent-based simulation using reproductive and ecological data to model realistic reef dynamics. Our model suggests the hybrid can facilitate introgression between parentals without outcompeting them. Yet, such introgression is too limited for large-scale or beneficial ancestry transfer except under ecologically unrealistic conditions or timescales significantly longer than those relevant for management. Thus, our model suggests that the risks of genetic swamping may be overstated, whereas hopes for adaptive introgression are also low, underscoring the value of simulations for generating long-term ecological and evolutionary insights relevant to coral restoration.

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

Seamounts are prominent deep-ocean features that strongly influence geological processes, ocean circulation, and benthic biodiversity. Despite their importance, most seamounts remain unmapped and poorly characterized, particularly in the southeast Pacific Ocean, a region recognized for high marine endemism and ecological isolation. In this study, we present a quantitative habitat characterization of a previously undocumented seamount, informally named Solito Seamount, located between the Nazca-Desventuradas Marine Park and the Juan Fernandez Archipelago. High-resolution multibeam bathymetry and backscatter intensity data were integrated with in situ observations from two remotely operated vehicle (ROV) dives (SO643 and SO645) to investigate how geomorphology and substrate distribution influence benthic community patterns. An automated and hierarchical quantitative mapping framework incorporating objective terrain analysis and multivariate statistical techniques, including principal component analysis and clustering, was applied to delineate five distinct megahabitat types: flat, basal slope, valley, ridge slope, and ridge crest. ROV video transects traversing these megahabitats revealed five associated substrate type forming macrohabitats: bedrock, bedrock with sediment veneer, sediment-rock transition, sediment, and coral rubble. Outputs were used to investigate how environmental heterogeneity structures megafaunal assemblages of Solito Seamount. Multivariate analysis revealed a combined effect of megahabitat type and substrate type on benthic megafaunal assemblages across the depth gradient. These compositional dissimilarities were primarily driven by habitat-forming taxa. In the deeper dive (SO643), a broad suite of taxa contributed to dissimilarities, and assemblages were primarily organised by megahabitat. The ridge crest hosted a distinct reef-building scleractinian community, whereas the ridge slope hosted mixed antipatharian, gorgonian and actiniarian assemblages. In contrast, the shallower dive exhibited simpler patterns with few taxa driving dissimilarities. Substrate effects were most pronounced with coral rubble forming a distinct habitat characterised by sponges (Stelletta sp.). Pronounced biological differences between dives may also represent depth-dependent structuring resulting from differences in oxygen regimes associated with water masses, underscoring the role of oceanographic forcing. This study provides the first quantitative habitat map of this previously undocumented seamount, delivering essential baseline information for this largely unexplored region of the southeast Pacific. The integrated multi-scale geophysical and biological approach presented here offers a robust framework for advancing seamount ecosystem understanding and supporting future biodiversity assessments and conservation planning.