Marine Ecology Progress Series

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 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.

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

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.

The long-standing misconception that the Galapagos petrel (Pterodroma phaeopygia) and the Hawaiian petrel (Pterodroma sandwichensis) were conspecific masked the severe vulnerability of the Galapagos population. By the time its distinct status was recognized, the Galapagos petrel was already in marked decline, primarily due to invasive predators. Consequently, sustained rodent control programs have been implemented on Santa Cruz Island. An unintentional one-year failure in rodent control provided a rare quasi-experimental opportunity to quantify the demographic consequences of the invasive black rat predator. During this year, hatching success declined by [~]35% and breeding success by [~]40% relative to long-term means (66% and 62%, respectively), representing a substantial reproductive collapse. Fledging success exhibited a comparatively modest decline (from a long-term mean of 94% to 86% in 2017), suggesting stage-specific vulnerability. These results support the hypothesis that invasive black rats primarily affect early reproductive stages through egg predation and predation on small chicks, while older chicks surpass a critical size threshold that reduces susceptibility. Across the remaining managed years, reproductive metrics exhibited great stability, demonstrating the petrels resilience against other environmental or climatic stressors. Our findings provide robust empirical evidence that invasive rodent control is the dominant driver of reproductive success in this endangered seabird. The quasi-experimental failure underscored both the effectiveness and the necessity of continuous predator management, highlighting the severe and immediate consequences of even short-term lapses.

Accurate estimation of post-release survival is fundamental to fisheries stock assessment and effective management. Conventional tag-return studies and acoustic telemetry are commonly used to estimate this probability, yet each approach has limitations when applied independently. Using gag (Mycteroperca microlepis) as a case study, we integrated data from a large-scale conventional tagging program and an acoustic telemetry experiment within a discrete-time statistical modeling framework that links relative recapture risk with telemetry-derived fate. This approach enabled estimation of post-release survival across a broad gradient of capture depths representative of recreational fishing conditions. Estimated survival was high in shallow waters ({approx}97%) but declined with increasing capture depth, consistent with depth-related barotrauma. Applying model predictions to depth distributions from the recreational fishery yielded annual and monthly post-release survival probabilities. Annual estimates were consistent with values assumed in recent stock assessments, while monthly values highlighted seasonal patterns potentially relevant for management. This integrated framework advances post-release survival estimation by combining the extensive sample sizes and environmental coverage characteristic of conventional tagging data with the direct fate observations provided by acoustic telemetry, and offers a transferable approach for other highly targeted fisheries.

Vessel-whale collisions are a growing global concern and remain challenging to quantify. Therefore, the use of proxies, such as Close Encounters (CEs) that comprise Surprise Encounters (SEs) and Near-Miss Events (NMEs), has been proposed and widely employed to assess collision risk. To better understand this risk in the Eastern North Atlantic, where maritime traffic is intensive, this study aimed to redefine and quantify CEs, and to assess detectability-related variables that may affect CE identification. CEs were assessed using a cetacean occurrence dataset collected between 2012 and 2024 on board cargo ships and oceanographic vessels. CEs thresholds were redefined based on Time to Potential Collision (TPC), rather than distance alone (as described in literature), to allow a more dynamic, risk-based, and speed-sensitive approach. In total, 1226 sightings of whales (baleen, sperm, and beaked whales) were recorded, of which 37.4% were classified as SEs and 2.0% as NMEs. The sperm whale, Physeter macrocephalus, was the species most frequently involved in CEs (13.9% of all CEs), followed by the Cuviers beaked whale, Ziphius cavirostris (11.8%). A Generalized Additive Model was used to assess the influence of detectability-related variables (i.e., meteorological conditions, whale taxa, vessel characteristics, and Marine Mammals Observers (MMOs) experience) on TPC. Significantly lower TPC values were observed with beaked whales, cargo ships, poor visibility conditions, and less experienced MMOs. The results of this study provide an CEs assessment in this region and contribute to the ongoing efforts to standardize CE quantification, by using TPC as a metric. This work also highlights the importance of decreased speeds and the presence of experienced MMOs on board to increase detection probability and TPC, thereby potentially minimizing collision risk.

Wind has a strong influence on the flight characteristics, movements, energetics, demography, life-history traits and biogeography of flying animals. With climate change affecting atmospheric circulation patterns at different time scales, understanding the links between wind and animal movements is crucial for predicting its impact on flying biodiversity. Most studies on the relationship between wind and seabird movements have, however, focused on local scales, exploring birds perceptive sensitivity to local wind. In this study, we examine low-level wind pattern oscillations in the Southern Indian Ocean at multiple time scales to explain the local- to large-scale movements of the Amsterdam albatross. Adult individuals exhibited smooth trajectories, strongly correlated with seasonal, intra-seasonal or interannual wind oscillations. Conversely, younger individuals displayed more erratic and exploratory movements, often being swept away by eastward moving low-pressure systems at a synoptic time scale. Our results suggest that Amsterdam albatrosses can learn and adapt to the annual and monthly low-level wind climatology and interannual variability of the Southern Indian Ocean. This also highlights the importance of investigating seabird movements in relation to broader-scale wind patterns to support their conservation in a changing climate due to human activities. A robust assessment of regional circulation response to climate change for upcoming decades could help project the impact of climate change on seabird movements and mitigate its effects.

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.

Population density can influence individual predation risk in colonial breeders through shared vigilance and predator deterrence. We investigated how predator-prey interactions are shaped by population density at two Antarctic fur seal (Arctocephalus gazella) breeding colonies at Bird Island, South Georgia, which differ four-fold in seal density. By deploying autonomous time-lapse cameras, we captured high-resolution images at one-minute intervals throughout the breeding season. Using a YOLOv8 neural network, we identified fur seal adult males, females and pups, as well as three predator-scavenger bird species: giant petrels (Macronectes spp.), brown skuas (Stercorarius antarcticus) and snowy sheathbills (Chionis alba). Abundance patterns corresponded to the known foraging and breeding behaviours of these species. Differences in seal density between the colonies were mainly driven by adult females and their pups, but not adult males. The ratios of predatory birds to pups were markedly lower at the high-density colony, while scavenger to pup ratios remained similar. Spatial analyses revealed that predators were largely excluded from areas of high seal density, whereas scavengers overlapped extensively with pups in both colonies. This study demonstrates the value of remote observation in resolving predator-prey interactions and illustrates how density can shape predation risk in a colonial breeder.

Understanding relatedness in sharks is challenging due to uncertainty in distributions, low population densities and difficulties in sampling across life stages. In Fiji, bull sharks (Carcharhinus leucas), with an effective population size estimate of [~]258, aggregate at the Shark Reef Marine Reserve (SRMR), but gravid females disperse at the end of the year to give birth in adjacent rivers. Questions remain regarding reproductive connectivity, female returns across years, and kinship structure. Using population genomics on 296 bull sharks across age classes (neonates, young-of-the-year, juveniles, and adults) collected over a decade at the SRMR and in three adjacent rivers, we assessed familial connections. Direct genetic links, including first- and second-degree relationships, connected SRMR adults with young age classes in the Navua and Rewa rivers, providing evidence of reproductive connectivity. Within rivers, genetic similarities across cohorts revealed reproductive philopatry. Remarkably, several individuals sampled years apart were assigned to the same sire-dam pairs, indicating repeated pairings across breeding seasons. However, the few related links detected between the SRMR and the rivers may reflect incomplete sampling. Altogether, bull shark reproduction in Fiji seems influenced by reproductive philopatry and repeated pairings, suggesting added complexity in their reproductive behaviour.

The north coast of mainland Portugal supports a strong dolphin presence and extensive fishing activity, increasing the likelihood of interactions, such as bycatch. This study provides an initial assessment of potential conflict areas, using automatic identification system (AIS) data from Global Fishing Watch. To this end, sighting data from the ATLANTIDA project (2021-2024) on the common dolphin (Delphinus delphis) were used to describe spatiotemporal patterns of occurrence and encounter rates, and to predict their association with fishing effort to identify and map areas of potential overlap. A generalised additive model (GAM) was then applied, integrating environmental, spatial, temporal, and fisheries-related variables to identify the main predictors of species occurrence. Common dolphins were frequently observed during the summer, with an average encounter rate of 3.662 sightings/km. This high encounter rate may be associated with factors such as sea surface temperature, diet, and purse seine fishing activity. The maps showed a spatial overlap between fishing grounds and areas of common dolphin occurrence. Fishing effort was nearly identical between locations with sightings (2.00 h/km{superscript 2}) and those without (1.62 h/km{superscript 2}), suggesting that dolphins are not actively avoiding fishing areas but may instead frequent them due to shared habitat preferences. The best-fitted GAM indicated that encounters were related to year, latitude, fishing effort, depth, sea surface temperature, and season. There was an increase in occurrence over the years and a decrease with increasing fishing effort and sea surface temperature, possibly linked to changes in prey availability, although broad confidence intervals warrant cautious interpretation. Despite some limitations encountered in this study, we believe our findings provide valuable insights into the relationship between dolphin occurrence, environmental conditions, and fishing activities in the area, establishing an important baseline for future conservation and fisheries management efforts.

The Socotra Cormorant (Phalacrocorax nigrogularis) is a threatened seabird endemic to the coastal areas of the Arabian Gulf and the Arabian Sea, two regions separated by the Strait of Hormuz. Conserving threatened species requires clear delineation of population boundaries and the evaluation of genetic diversity. However, information on population structure and genetic variation, necessary for such an assessment, is lacking for the Socotra Cormorants. In this study, we assessed population structure and genetic diversity of Socotra Cormorants using two contrasting genetic markers: (1) maternally inherited mtDNA cytochrome oxidase 1 (COI) and (2) a nuclear non-coding region, {beta}-fibrinogen intron 7 (FIB7). A total of 279 individuals were sampled from four colonies in the Arabian Gulf and one colony on Hasikiyah Island in the Arabian Sea. Findings based on COI-variation suggest that the Arabian Gulf colonies represent one large population with extensive gene flow between Gulf colonies--except for the most distant pair of colonies--but isolated from Hasikiyah in the Arabian Sea. COI-variation indicated significant differentiation between the colonies inside the Gulf and the Hasikiyah colony. This is consistent with the reported distribution patterns, and may reflect phylogeographic processes of the region. The Gulf population showed substantially lower COI-diversity, with significantly lower nucleotide and haplotype diversity compared to Hasikiyah. In contrast, FIB7 results indicated extensive connectivity among colonies, with no detectable population structure or significant differences between the Gulf population and Hasikiyah. This study presents the first characterization of population structure and genetic diversity of Socotra Cormorants. The low genetic diversity coupled with relative isolation of the Gulf Socotra Cormorants raises conservation concerns regarding their long-term viability by potentially reducing fitness and eroding their evolutionary capacity to adapt to environmental change. LAY SUMMARYO_LIThe Socotra Cormorant is a threatened seabird found in the Arabian Gulf and Arabian Sea, but little was previously known about its population structure and genetic diversity. C_LIO_LIWe analyzed 279 birds from five nesting colonies (4 in the Gulf and 1 in the Arabian Sea), using two genetic markers to assess population connectivity and variation. C_LIO_LIWe found that the Socotra cormorants inside the Gulf appear to form a large, genetically isolated population with relatively low genetic diversity. C_LIO_LIThis is the first study that evaluates population structure and genetic diversity of this endangered seabird. C_LIO_LIThis is important information for the conservation of the Gulf Socotra cormorants because low genetic diversity, coupled with relative isolation, is associated with reduced fitness, and suggests that they may have a lower chance to adapt to environmental changes. C_LI

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

Marine protected areas (MPAs) are increasingly promoted as climate mitigation tools, yet guidance on their placement to maximize resilience against climate stressors like marine heatwaves remains limited. Here, we develop MPA placement guidelines that explicitly consider a mechanistic pathway through which MPAs could enhance kelp forest resilience to heatwaves: protecting fishery-targeted urchin predators to prevent kelp overgrazing. Using a spatially explicit, tri-trophic model of California kelp forests, we evaluate alternative MPA configurations across a hypothetical coastline where half the habitat experiences an increased probability of experiencing heatwaves. We found that effective MPA placement depends on whether MPAs are being newly established or reconfigured within an existing network, and that among-patch connectivity and spillover played vital roles in the relative effectiveness of different MPA configurations. Changes in resilience occurred primarily at the patch scale, with trade-offs between increased within-MPA resilience and decreased resilience in some fished areas, resulting in minimal coastwide population effects. For example, for new MPAs, large single MPAs within heatwave-prone areas maximized within-MPA resilience gains, while multiple small MPAs in heatwave refugia best supported whole-coast resilience. When reconfiguring established networks, expanding existing MPAs in refugia areas was most effective. We also demonstrate the importance of considering MPA recovery timescales: for example, relocating old MPAs to heatwave refugia yielded minimal short-term benefits due to the loss of rebuilt, previously fished, predator biomass. Our findings demonstrate that climate-adaptive marine planning should explicitly consider the spatiotemporal implications of trophic cascades, connectivity, and transient population dynamics to support ecosystem resilience.

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.

We developed an agent-based model (ABM) to assess how area-based controls on fishing methods can reduce fishing mortality and population declines. The model incorporates the behavior and distributions of dolphins and fishing vessels, and realistic displacement of fishing effort when protection is extended. Our case study is New Zealand dolphin - Hectors and Maui dolphins. The model was designed and calibrated using pattern-oriented modeling. Our results show that mortality due to entanglement in fishing gears has been reduced thanks to a gradual increase in dolphin protection. However, current protection is not as effective as previously thought, and scarce populations are negatively affected by Allee effects. Neither national nor international goals for reducing bycatch are met by current dolphin protection. The IUCN has recommended banning gillnet and trawl fisheries in New Zealand waters < 100m deep. For most New Zealand dolphin populations, this would be effective in achieving national and international goals for reducing bycatch. Only two populations would require additional protection. This modelling approach is also suitable for assessing impacts of bycatch and ship strikes for other marine species, making it suitable for informing management decisions in many regions.

Catch inequality--the disproportionate distribution of catch across anglers-- is a fundamental but overlooked driver of recreational fisheries dynamics. Here, we use 11 years (2012-2022) of compulsory angler report cards to characterize long-term catch dynamics in the specialized recreational steelhead (Oncorhynchus mykiss) fishery in California, U.S.A. Spatialized catch data reveal the fishery is principally supported by wild fish, despite evidence of widespread hatchery straying. California steelhead appear to represent the most catch-unequal recreational fishery studied yet, exhibiting a statewide Gini coefficient of 0.81. Across basins, inequality varies substantially but remains relatively stable over time and flow conditions; high inequality is primarily driven by significant proportions of zero-catch anglers. We find the relationship between sample size and inequality measures is especially influential in fisheries data. Hence, we develop a three-prong approach for identifying minimal sample sizes required for robust Gini estimation. Across basins and years, an average minimum of 77 report cards were required for the present fishery. Collectively, these findings demonstrate the necessity of considering catch inequality in fisheries management, particularly when utilizing angler data. Graphical AbstractN.a.

The yellownose skate (Dipturus chilensis) is an endangered skate with a narrow distribution in the southeastern Pacific, facing intense fishing pressure and potential climate threats. Using a species distribution model, we projected the current and future distribution of D. chilensis under contrasting climate change scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) for mid-century (2050) and end-of-century (2100). Our models, which demonstrated robust predictive performance significantly better than random expectations, identified maximum temperature and minimum oxygen as the primary environmental drivers of habitat suitability. Projections revealed a consistent poleward range shift towards the Channels and Fjords of Southern Chile ecoregion across all scenarios. While localized habitat loss was projected in Central Chile and Araucanian ecoregions, particularly under high emissions (SSP5-8.5), these losses were outweighed by southern expansions, leading to a net increase in total suitable habitat by 2100. These findings underscore the critical need for climate-adaptive management strategies, including the protection of emerging southern refugia and dynamic fisheries regulations, to ensure the long-term persistence of D. chilensis.

Theory suggests that different components of environmental fluctuations, from daily and seasonal cycles to multidecadal trends, can have distinct and even opposing effects on species abundances and community dynamics, depending on their specific adaptations. But empirical research that deconstructs the influence of these different cycles on communities is lacking. Here, we used long-term biological monitoring data together with flow records of rivers across New Zealand to (i) investigate the role of fast, slow, and seasonal river-flow fluctuations in structuring macroinvertebrate communities; and (ii) to assess whether life-history and mobility traits mediate the response. Using joint species distribution models, we found striking differences in taxon and community responses to the different components of river flow variation. Responses to slow fluctuations were generally stronger and better predicted by traits, while responses to seasonal fluctuations were highly heterogeneous. Fast increases in flow, typical of flooding events, had pervasive negative effects on species abundances, but the severity of impact partly depended on mobility traits. Our results suggest that different ecological mechanisms underpin the response to distinct environmental fluctuations, highlighting the value of jointly considering multiple temporal scales of variation and species functional traits to understand and predict how communities reorganise under fluctuating environmental regimes.