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.

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.

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 commercially exploited fish stocks have declined over the last few decades. It is therefore essential to identify natural populations and understand local adaptation for sustainable management. Salinity is a key environmental factor shaping local adaptation, and adaptive trait divergence often occurs at the egg and larval stages. The strong salinity gradient in the brackish Baltic Sea has driven rapid adaptation in multiple taxa. The Eastern Baltic cod (Gadus morhua) has adapted to low salinity with buoyant and tolerant eggs and larvae, but the stock has declined both in abundance and geographical range during the last decades. The main reproduction area of this stock is in the Bornholm Basin (ICES subdivision (SD) 25) in the southern Baltic Proper. Cod in this area, however, exhibit stunted growth and small body sizes. In contrast, large and healthy cod in reproductive condition have been observed in the [A]land Sea in the northern Baltic Proper (SD 29), raising the question of whether these fish represent a locally adapted population capable of successful reproduction in the lower salinities (5-10 psu in the northern Baltic Proper (SD 27, 29 and 32). Here, we experimentally assessed egg and yolk-sac larvae survival across salinities, egg size, egg and larval neutral buoyancy and egg survival on sediment, to test whether northern ([A]land) cod show adaptation to low salinity at early life stages as compared to southern cod. Mortality of larvae increased with decreasing salinity in cod from both areas, with the lowest survival at 7 psu. At 9 psu, more than 50% of northern cod larvae survived, suggesting that development could occur in SD29. Egg size and buoyancy were similar between northern and southern cod, and eggs and larvae were negatively buoyant, sinking under local salinity conditions. Nevertheless, the eggs survived and hatched well on sediment, indicating potential for demersal spawning. Our findings show no strong evidence of adaptive divergence to lower salinity in northern cod; however, their ability to tolerate sediment contact at early life stages suggests that Eastern Baltic cod may reproduce outside their historical spawning grounds.

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.

Red Knots (Calidris canutus rufa) rely on Atlantic horseshoe crab (Limulus polyphemus) eggs in the Delaware Bay to refuel during northward migration. Intensive harvest of horseshoe crabs in the 1990s contributed to declines in Red Knot numbers. In 2013, the Atlantic States Marine Fisheries Commission adopted an Adaptive Resource Management (ARM) framework to balance sustainable horseshoe crab harvest with ecosystem integrity and Red Knot recovery, requiring annual stopover population estimates. We estimated the 2025 passage population of Red Knots at Delaware Bay using a Bayesian analysis of a Jolly-Seber mark-resight model which accounts for population turnover and imperfect detection. We also evaluated change in migration timing between 2011 and 2025 with model-derived estimates of arrival at the Delaware Bay each year. The 2025 passage population was 54,043 individuals (95% credible interval: 47,926-61,928), an increase of approximately 17% over 2024 and only the second year since 2011 to exceed 50,000 individuals. Despite the increase, overlapping credible intervals across years indicate a stable stopover population. Migration timing has remained consistent, with 50% of the population typically arriving by 18 May and no evidence of advancement since 2011. These findings provide meaningful input for the ARM framework, supporting sustainable harvest of horseshoe crabs while maintaining adequate foraging opportunities for Red Knots and other shorebirds. Parts of the Introduction, Methods, and Appendices were originally published in Lyons (2024) and are summarized herein.

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.

O_LIPhytoplankton are the major primary producers in the Southern Ocean, participate in the global carbon cycle, nutrient cycles, and are at the base of the food-web. These polar ecosystems are unique in their extended periods of darkness in the winter. C_LIO_LIProlonged darkness has the potential to exert selection that affects the composition of diatom communities if there is differential survival of diatoms in the dark, variation in population growth rates in subsequent light periods, or both. C_LIO_LIWe tested whether prolonged darkness has the potential to exert within-species selection on a model polar diatom species by exposing 5 strains of the polar diatom Porosira glacialis to prolonged darkness at two different temperatures in the laboratory. We measured population survival in the dark, growth rate upon re-illumination, and between strain variability in these traits. C_LIO_LIWe found a pronounced decline in survival and growth rate with time spent in the dark, as well as important intraspecific variation in these. C_LIO_LIHigher temperature exacerbated declines in growth and survival. C_LIO_LIOur results show that the darkness of polar night can exert selection within diatom species, with implications for phytoplankton community composition and subsequent impacts on Southern Ocean biogeochemical cycles. C_LI

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.

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.

Mesopredators contribute to food web stability and as such, understanding their trophic ecology can help to predict potential consequences of ongoing ecosystem modification. Here, multi-tissue carbon and nitrogen stable isotope analysis ({delta}13C and {delta}15N) and biochemical blood parameters ({beta}-hydroxybutyrate, glucose, lactate, and osmolality) were used to assess sex, size, spatial and seasonal differences in trophic ecology and condition of southern stingrays, Hypanus americanus, in Bimini, The Bahamas. Stingrays exhibited a dietary preference for molluscs and annelids, with an ontogenetic shift towards lower {delta}13C with increasing body size indicating a shift towards more mangrove associated prey. Nitrogen isotope values showed minimal seasonal changes, but higher {delta}15N values in males indicated foraging at a higher trophic level than females. Blood {beta}-hydroxybutyrate concentrations and osmolality revealed a similar energetic state and condition between sex, size, location and season. Our results advance our understanding of the seasonal trophic ecology of a benthic, marine mesopredator and identify the southern stingray as an important trophic link in seagrass and mangrove habitats in Bimini.

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.

Predation is a strong environmental and selective pressure that can favour rapid and plastic shifts in behaviour and escape ability to increase an organisms immediate survival. However, maintaining antipredator responses under repeated predation stress can induce physiological costs to an organism from long-term exposure to elevated cortisol. We know little about how individuals balance this trade-off between short-term survival and longevity, including whether males and females balance this trade-off differently based on life history differences in reproduction, survival, and risk adversity. To assess sex differences in long-term behavioural responses and physiological costs to predation risk, we exposed threespine stickleback (Gasterosteus aculeatus) to visual cues of a live rainbow trout (Oncorhynchus mykiss) predator twice a week for 14 weeks, then measured stickleback antipredator behaviour and swimming performance 5 months later. To quantify potential long-term costs of behavioural adaptation, we measured relative telomere length as a proxy for long-term oxidative damage. We found strong sex specific effects in behaviour and swim endurance: males, but not females, altered their hiding behaviour and had shorter swim endurance in the first trial, suggesting overall lower activity. Surprisingly, we found no evidence for chronic predation shortening telomere length or hindering growth in body length. Overall, these results suggest that plastic responses can be dictated by the different life-history strategies for males and females, and suggest that individuals can maintain long-term changes in antipredator behaviour without costs to their physiological state. HighlightsO_LIChronic predator exposure produced persistent sex differences in space use and swim performance. C_LIO_LIPredator-exposed males altered their hiding strategy and showed reduced swim performance, while females showed no behavioural or performance differences. C_LIO_LIDifferences in swim times were restricted to the first trial and all individuals were exhausted by trial 3. C_LIO_LIRelative telomere length and growth in length did not differ between exposed and unexposed individuals. C_LI

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.

Benthic remineralization of organic matter is key to carbon and nutrient cycling, influencing both long-term carbon storage in the sediments and the release of nutrients that support primary production in the water column. With its multiple forms and ages of sea ice, Nares Strait in the Canadian Arctic offers a unique opportunity to address the knowledge gap of variability of benthic remineralization rates along a natural sea ice gradient. Here, we incubated sediment cores in different locations in Nares Strait characterised by different sea ice conditions ranging from first-year ice to multi-year ice, to measure oxygen and nutrient fluxes. To identify potential drivers, we measured environmental variables, identified macrofauna and calculated a suite of taxonomic and functional diversity indices. Our analyses showed that benthic fluxes varied significantly between the northern and southern regions of Nares Strait. The presence of deposit feeders and sea ice cover (number of days since ice-free) were the main drivers in benthic fluxes, explaining 22.6% and 13.9% of the benthic flux variation, respectively. Overall, functional diversity was a better predictor of benthic fluxes than taxonomic diversity, indicating its primary importance in controlling benthic ecosystems functioning. Our results reveal that, from a benthic biogeochemical point of view, Nares Strait seems to be dissected into two main sub-regions: (i) a permanently and highly sea ice-covered area north of Kennedy Channel, resembling deeper regions of the Arctic Ocean and (ii) a seasonally ice-covered area between the North Water Polynya and Kane Basin, where benthic fluxes values are equivalent to those reported in similar continental Arctic shelves. Consequently, the rapid functional shifts resulting from the ongoing decline in sea ice could enhance benthic remineralisation rates if deposit feeder were to become dominant in certain areas, reducing the role of the region and by extension, the Arctic, as a carbon sink.

The Humboldt upwelling ecosystem has been intensively harvested by people since the early Holocene. Understanding past and present human choices under climatic variability in these productive environments may hold key insights for its future sustainability by unraveling different adaptive pathways. To this end, we studied shellfish exploitation and climate patterns in the Taltal region of the Atacama desert coast (25{whitebullet}S) from the early Holocene until today using a compilation of archaeological, and modern benthic fisheries data together with direct ecological surveys. In addition we obtained satellite sea surface temperature (SST) and published{delta} 18O SST for the study region. The archaeological record and the modern rocky shore assemblage were dominated by herbivorous gastropods -Fissurella spp., Enoplochiton spp., Tegula spp.-and the carnivorous whelk Concholepas concholepas. Functional composition from the early Holocene to the present was remarkably stable. Using SST as a latent variable, we examined changes in functional composition across the Holocene and in a 16-year series of artisanal fisheries landings using bayesian ordination. The analysis identified functional groups characteristic of kelp ecosystems in association with cooler SST conditions during the Holocene and the present. Changes in functional composition during warm and cold periods of the Holocene broadly mirrored effects of interannual SST variability in the modern fisheries. The archaeological record suggests two cross-Holocene transitions social-ecological transitions. The generalized shoreline harvesting strategy that prevailed during the cold early Holocene shifted to a specialized maritime economy towards the warmer mid-Holocene. The maritime technological and cultural adaptions remained, but were part of more diversified lifestyles in the cooler and more variable late Holocene. The latter emerged at the same time as the modern El Nino climate pattern. Our insights from the direct analysis of human choices and SST variability highlight the role of flexibility and agency under a changing environment. The broad range of human decisions in the past, inform current regulatory frameworks for benthic artisanal fisheries. Marine resources and the livelihoods that depend on them are integrated into coupled coastal socioecological systems; their future sustainability hinges on fostering the different dimension of their adaptive capacity.

Ocean Alkalinity Enhancement (OAE) is a marine carbon dioxide removal (mCDR) strategy that involves adding alkaline substances to surface waters to enhance CO2 uptake and storage. The dispersal of alkaline materials such as sodium hydroxide (NaOH) into seawater can cause rapid increases in pH and total alkalinity (TA) that substantially exceeds natural variability in marine environments. Such fluctuations may negatively affect marine life, especially small animals like copepods who cannot avoid OAE plumes and whose physiological processes could be disrupted by large and rapid shifts in seawater pH. To address knowledge gaps regarding potential biological impacts of OAE, we studied these effects in Calanus finmarchicus, a keystone copepod species in the Northwest Atlantic Ocean. We exposed C. finmarchicus from the late juvenile copepodite stages and adult females to NaOH-dosed seawater at pH 10.5 ([~]5,000 {micro}mol kg-1 TA) and pH 9.0 ([~]3,150 {micro}mol kg-1 TA) for durations that reflect expected short-term exposure times during field OAE deployments (pH 10.5: 1, 5, 10 minutes; pH 9.0: 1, 15, 30 minutes). None of the treatment combinations resulted in mortality immediately after the initial exposure. Individuals were monitored for survival for 72 hours post-exposure (hpe), and only one treatment group (juveniles exposed to pH 10.5 for 10 minutes) showed a significant reduction in final survival; no other pH-duration combination showed increased mortality. Effects on the ability to initiate an escape response were more substantial. Adult females treated with pH 10.5 for 5 or 10 minutes showed a significant reduction in escape response immediately after exposure. In contrast, juveniles showed no immediate change in escape response following exposure to pH 10.5 or pH 9.0, although juveniles exposed to pH 10.5 for 10 minutes exhibited reduced escape response at 24 hpe. Using microrespirometry, we measured oxygen consumption following a 10-minute exposure to pH 10.5 and detected no effect on routine metabolic rate immediately post-exposure or at 12 hpe. Overall, our results suggest that C. finmarchicus is relatively tolerant to short-term exposures to very high pH and alkalinity. Future work should prioritize longer-term exposure under more moderate ocean OAE conditions.

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.