The Great Atlantic Sargassum Belt (GASB) first appeared in 2011 and quickly became the largest interconnected floating biome globally. Sargassum spp. requires both phosphorus (P) and nitrogen (N) for growth, yet the sources fueling the GASB are unclear. Here, we use coral–bound nitrogen isotopes from six coral cores to reconstruct N2 fixation, the primary source of bioavailable N to the surface ocean across the wider Caribbean over the past 120 years. Our data indicate that changes in N2 fixation were controlled by multidecadal and interannual changes in the supply of excess P from equatorial upwelling in the Atlantic. We show that the supply of P from equatorial upwelling and N from the N2 fixation response can explain the extent of the GASB since 2011.

The Ross Ice Shelf, Antarctica's largest by surface area, may face increased instability with future warming, posing a significant threat to the stability of the Antarctic Ice Sheet. Understanding the dynamics driving its retreat during past warming events is crucial for predicting future sea-level rise. Here, we present a multi-proxy record that comprehensively reconstructs the paleoenvironmental conditions of the ocean and cryosphere in the Ross Sea during the last 40,000 years. Our results accurately demonstrate the intrusion of warm Circumpolar Deep Water in the JOIDES trough (western Ross Sea) and the embayment of the ancestral ice shelf edge shortly after the end of the Last Glacial Maximum. The oceanic warming documented in the Ross Sea closely aligns with the southward migration of the westerly and easterly winds. This suggests a common, large-scale mechanism driving changes across the Pacific sector of the Southern Ocean, echoing on the continental margin. Our study disentangles the complex interactions between the atmosphere, ocean, and cryosphere that reduced the ice shelf extent since the onset of the last deglaciation, potentially facilitating Marine Ice Sheet Instability.

This study investigates the benthic invertebrate community in the Venice Lagoon using environmental DNA (eDNA) metabarcoding based on superficial water samples. Our objective is to understand if, in a shallow lagoon system, sampling at the surface can provide information on benthic biodiversity, allowing us to establish a baseline for future assessments and to monitor the community's seasonal and spatial variation. eDNA was collected from surface water samples at two sites during nine sampling campaigns from November 2018 to October 2019, and metabarcoding was performed using an available primer pair targeting 16S mitochondrial rDNA of echinoderms, never tested empirically before. Analyses revealed 80 taxonomic units, five not assigned at the species level, belonging not only to the phylum Echinodermata but predominantly assigned to Mollusca, with the majority of the identified species (60 out of 75) representing benthic invertebrates. Several species known to be invasive were detected, some previously recorded in the Venice Lagoon environment and others detected for the first time. Significant spatial differences in species composition were observed between the northern and the southern site of the lagoon. Temporal variation of the benthic community was also observed, mainly due to the distinctiveness of autumn samples, highlighting the dynamic nature of the Venice Lagoon ecosystem. Our results confirm the utility of eDNA for ongoing biodiversity monitoring and management and show that eDNA isolated from superficial water can provide information on the benthic invertebrate community, which might be particularly useful for biodiversity assessment in lagoons, ports, and areas characterized by limited or interdicted access.

Morphometrics of a large dataset of 153 fossil and 226 Recent specimens of abalone (genus Haliotis). All fossil shells are from Europe and range Oligocene-Pleistocene. Recent shells are from the Mediterranean, the eastern Atlantic and the Red Sea. Measures include shell length (L), shell length from apex to L midline (l1), shell width (W), shell width from apex to W midline (w1), shell height (H) and number of tremata, separating total number (NT) from open tremata (OT).

Apex predator reintroductions have proliferated across southern Africa, yet their ecological effects and proposed umbrella benefits of associated management lack empirical evaluations. Despite a rich theory on top-down ecosystem regulation via mesopredator (<20kg) suppression, a knowledge gap exists relating to the influence of lions (Panthera leo) over Africa’s diverse mesocarnivore communities. We investigate how geographical variation in mesocarnivore community richness and occupancy across South African reserves is associated with the presence of lions.  An interesting duality emerged: lion reserves held more mesocarnivore-rich communities, yet mesocarnivore occupancy rates and evenness-weighted diversity were lower in the presence of lions. Human population density in the reserve surroundings had a similarly ubiquitous negative effect on mesocarnivore occupancy. The positive association between species richness and lion presence corroborated the umbrella species concept but translated into small differences in community size. Distributional contractions of mesocarnivore species within lion reserves, and potentially corresponding numerical reductions, suggest within-community mesopredator suppression by lions, likely as a result of lethal encounters and responses to a landscape of fear. Our findings offer empirical support for theoretical understanding of processes underpinning carnivore community assembly and are of conservation relevance under current large-predator orientated management and conservation paradigms.

1. The expression of individual behaviour as a function of environmental variation (behavioural plasticity) is recognised as a means for animals to modify their phenotypes in response to changing conditions. Plasticity has been studied extensively in recent years, leading to an accumulation of evidence for behavioural plasticity within natural populations. 2. Despite the recent attention given to studying individual variation in behavioural plasticity, there is still a lack of consensus regarding its causes and constraints. One pressing question related to this is whether individual plasticity carries over across temporal and environmental gradients. That is, are some individuals more plastic (responsive) than others in general? 3. Here, we examined the influence of temporal and environmental gradients on individual behavioural responses in a marine gastropod, Littoraria irrorata. We measured individual boldness repeatedly over time and in response to tidal cycle (high vs low an index of risk) and daily temperature fluctuations (known to affect metabolism), in a controlled field experiment. 4. On average, boldness increased from high to low tide and with increasing temperature but decreased marginally over time. Individuals also differed in their responses to variation in tide and temperature, but not over time. Those that were relatively bold at high tide (when predation risk is greater) were similarly bold at low tide, whereas shy individuals became much more ‘bold’ at low tide. Most notably, individuals that were more responsive to tide (and thus risk) were also more responsive to temperature changes, meaning that plasticity was correlated across contexts (r = 0.57) and that bolder individuals were least plastic overall. 5. This study provides a rare and possibly first example of consistency of individual behavioural plasticity across contexts, suggesting underlying physiology as a common mechanism, and raises the possibility of correlational selection on plasticity.

Recent shifts in the geographic distribution of marine species have been linked to shifts in preferred thermal habitats. These shifts in distribution have already posed challenges for living marine resource management, and there is a strong need for projections of how species might be impacted by future changes in ocean temperatures during the 21st century. We modeled thermal habitat for 686 marine species in the Atlantic and Pacific oceans using long-term ecological survey data from the North American continental shelves. These habitat models were coupled to output from sixteen general circulation models that were run under high (RCP 8.5) and low (RCP 2.6) future greenhouse gas emission scenarios over the 21st century to produce 32 possible future outcomes for each species. The models generally agreed on the magnitude and direction of future shifts for some species (448 or 429 under RCP 8.5 and RCP 2.6, respectively), but strongly disagreed for other species (116 or 120 respectively). This allowed us to identify species with more or less robust predictions. Future shifts in species distributions were generally poleward and followed the coastline, but also varied among regions and species. Species from the U.S. and Canadian west coast including the Gulf of Alaska had the highest projected magnitude shifts in distribution, and many species shifted more than 1000 km under the high greenhouse gas emissions scenario. Following a strong mitigation scenario consistent with the Paris Agreement would likely produce substantially smaller shifts and less disruption to marine management efforts. Our projections offer an important tool for identifying species, fisheries, and management efforts that are particularly vulnerable to climate change impacts.

Metacommunity theory highlights the potential of β–diversity as a useful link to empirical research, especially in diverse systems where species exhibit a range of stage-dependent dispersal characteristics. To investigate the importance of different components and scales of β–diversity in community assembly we conducted a large-scale disturbance experiment and compared relative recovery across multiple sites and among plots within sites on the rocky shore. Six sites were spread along 80 km of coastline and, at each site, 5 plots were established, matching disturbed and undisturbed quadrats. Recovery was not complete at any of the sites after 1 year for either epibenthos (mostly composed of macroalgae and, locally, mussels) or infauna. Significant differences in recovery among sites were observed for epibenthos but not for infauna suggesting different community assembly processes were operating. This was supported by epibenthos in the recovering plots having higher species turnover than in undisturbed sediment, and recovery well predicted by local diversity, while infaunal recovery was strongly influenced by the epibenthic community’s habitat complexity. However, infaunal community recovery did not simply track formation of habitat by recovering epibenthos, but appeared to be overlain by within-site and among-site aspects of infaunal -diversity. These results suggest that documenting changes in the large plants and animals alone will be a poor surrogate for rocky shore community assembly processes. No role for ecological connectivity (negative effect of among-site β–diversity) in driving recovery was observed, suggesting a low risk of effects from multiple disturbances propagating along the coast, but a limited resilience at the site scale to large-scale disturbances such as landslides or oil spills.

1. Recent technological development has increased our capacity to study the deep sea and the marine benthic realm, particularly with the development of multidisciplinary seafloor observatories. Since 2006, Ocean Networks Canada cabled observatories, has acquired nearly 65 TB and over 90,000 hours of video data from seafloor cameras and Remotely Operated Vehicles (ROVs). Manual processing of these data is time-consuming and highly labour-intensive, and cannot be comprehensively undertaken by individual researchers. These videos contain valuable information for faunal and environmental monitoring, and are a crucial source of information for assessing natural variability and ecosystem responses to increasing human activity in the deep sea. 2. In this study, we compared the performance of three groups of humans and one computer vision algorithm in counting individuals of the commercially important sablefish (or black cod) Anoplopoma fimbria, in recorded video from a cabled camera platform at 900 m depth in a submarine canyon in the Northeast Pacific. The first group of human observers were untrained volunteers recruited via a crowdsourcing platform and the second were experienced university students, who performed the task in the context of an ichthyology class. Results were validated against counts obtained from a scientific expert. 3. All groups produced relatively accurate results in comparison to the expert and all succeeded in detecting patterns and periodicities in fish abundance data. Trained volunteers displayed the highest accuracy and the algorithm the lowest. 4. As seafloor observatories increase in number around the world, this study demonstrates the value of a hybrid combination of crowdsourcing and computer vision techniques, as a tool to help process large volumes of imagery to support basic research and environmental monitoring. Reciprocally, by engaging large numbers of online participants in deep-sea research, this approach can contribute significantly to ocean literacy and informed citizen input to policy development.

Spatial separation within predator communities can arise via territoriality but also from competitive interactions between and within species. However, linking competitive interactions to predator distribution patterns is difficult and theoretical models predict different habitat selection patterns dependent on habitat quality and how competition manifests itself. While models generally consider competitors to be either equal in ability, or for one phenotype to have a fixed advantage over the other, few studies consider that an animal may only have a competitive advantage in specific habitats. We used > 10 years of telemetry data, habitat surveys and behavioral experiments, to show spatial partitioning between and within two species of reef shark (grey reef, Carcharhinus amblyrhinchos, and blacktip reef sharks, C. melanopterus) at an unfished Pacific atoll. Within a species, sharks remained within small ‘sub-habitats’ with very few movements of individuals between sub-habitats, which previous models have suggested could be caused by intra-specific competition. Blacktip reef sharks were more broadly distributed across habitat types but a greater proportion used lagoon and backreef habitats, while grey reef sharks preferred forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef sharks are absent, were distributed more broadly between habitat types than when both species were present. A series of individual-based models predict that habitat separation would only arise if there are competitive interactions between species that are habitat-specific, with grey reefs having a competitive advantage on the forereefs and blacktips in the lagoons and backreef. We provide compelling evidence that competition drives distribution patterns and spatial separation of a marine predator community, and highlight that competitive advantages may not be constant but rather dependent on habitats.