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Ocean warming will cause widespread changes in species richness and assemblage composition over coming decades, with important implications for both conservation management and international ocean governance. Anticipating the effect of climate change on biodiversity, in particular on changes in community composition, is crucial for adaptive ecosystem management 1 but remains a critical knowledge gap 2 . Here, we use climate velocity trajectories 3 , together with information on thermal tolerances and habitat preferences, to project changes in global patterns of marine species richness and community composition under IPCC Representative Concentration Pathways 4 (RCPs) 4.5 and 8.5. Our simple, intuitive approach emphasizes climate connectivity, and enables us to model over 12 times as many species as previous studies 5 , 6 . We find that range expansions prevail over contractions for both RCPs up to 2100, producing a net local increase in richness globally, and temporal changes in composition, driven by the redistribution rather than the loss of diversity. Conversely, widespread invasions homogenize present-day communities across multiple regions. High extirpation rates are expected regionally (for example, Indo-Pacific), particularly under RCP8.5, leading to strong decreases in richness and the anticipated formation of no-analogue communities where invasions are common. The spatial congruence of these patterns with contemporary human impacts 7 , 8 highlights potential areas of future conservation concern. These results strongly suggest that the millennial stability of current global marine diversity patterns, against which conservation plans are assessed, will change rapidly over the course of the century in response to ocean warming.

The latitudinal gradient in species richness, with more species in the tropics and richness declining with latitude, is widely known and has been assumed to be stable over recent centuries. We analyzed data on 48,661 marine animal species since 1955, accounting for sampling variation, to assess whether the global latitudinal gradient in species richness is being impacted by climate change.We confirm recent studies that show a slight dip in species richness at the equator. Moreover, richness across latitudinal bands was sensitive to temperature, reaching a plateau or declining above a mean annual sea surface temperature of 20 °C for most taxa. In response, since the 1970s, species richness has declined at the equator relative to an increase at midlatitudes and has shifted north in the northern hemisphere, particularly among pelagic species. This pattern is consistent with the hypothesis that climate change is impacting the latitudinal gradient in marine biodiversity at a global scale. The intensification of the dip in species richness at the equator, especially for pelagic species, suggests that it is already too warm there for some species to survive.

Slower warming in the deep ocean encourages a perception that its biodiversity is less exposed to climate change than that of surface waters. We challenge this notion by analysing climate velocity, which provides expectations for species’ range shifts. We find that contemporary (1955–2005) climate velocities are faster in the deep ocean than at the surface. Moreover, projected climate velocities in the future (2050–2100) are faster for all depth layers, except at the surface, under the most aggressive GHG mitigation pathway considered (representative concentration pathway, RCP 2.6). This suggests that while mitigation could limit climate change threats for surface biodiversity, deep-ocean biodiversity faces an unavoidable escalation in climate velocities, most prominently in the mesopelagic (200–1,000 m). To optimize opportunities for climate adaptation among deep-ocean communities, future open-ocean protected areas must be designed to retain species moving at different speeds at different depths under climate change while managing non-climate threats, such as fishing and mining.Marine biodiversity is at risk as the ocean warms, but currently the focus has been at the surface as the deep ocean has warmed less. Climate velocity—the speed and direction of isotherm displacement—is calculated to be faster in the deep ocean, and projections show this difference will grow.

Climate change is driving changes in the physical and chemical properties of the ocean that have consequences for marine ecosystems. Here, we review evidence for the responses of marine life to recent climate change across ocean regions, from tropical seas to polar oceans. We consider observed changes in calcification rates, demography, abundance, distribution and phenology of marine species. We draw on a database of observed climate change impacts on marine species, supplemented with evidence in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We discuss factors that limit or facilitate species’ responses, such as fishing pressure, the availability of prey, habitat, light and other resources, and dispersal by ocean currents. We find that general trends in species responses are consistent with expectations from climate change, including poleward and deeper distributional shifts, advances in spring phenology, declines in calcification and increases in the abundance of warm-water species. The volume and type of evidence of species responses to climate change is variable across ocean regions and taxonomic groups, with much evidence derived from the heavily-studied north Atlantic Ocean. Most investigations of marine biological impacts of climate change are of the impacts of changing temperature, with few observations of effects of changing oxygen, wave climate, precipitation (coastal waters) or ocean acidification. Observations of species responses that have been linked to anthropogenic climate change are widespread, but are still lacking for some taxonomic groups (e.g., phytoplankton, benthic invertebrates, marine mammals).

Spatial management tools, such as marine spatial planning and marine protected areas, are playing an increasingly important role in attempts to improve marine management and accommodate conflicting needs. Robust data are needed to inform decisions among different planning options, and early inclusion of stakeholder involvement is widely regarded as vital for success. One of the biggest stakeholder groups, and the most likely to be adversely impacted by spatial restrictions, is the fishing community. In order to take their priorities into account, planners need to understand spatial variation in their perceived value of the sea. Here a readily accessible, novel method for quantitatively mapping fishers' spatial access priorities is presented. Spatial access priority mapping, or SAPM, uses only basic functions of standard spreadsheet and GIS software. Unlike the use of remote-sensing data, SAPM actively engages fishers in participatory mapping, documenting rather than inferring their priorities. By so doing, SAPM also facilitates the gathering of other useful data, such as local ecological knowledge. The method was tested and validated in Northern Ireland, where over 100 fishers participated in a semi-structured questionnaire and mapping exercise. The response rate was excellent, 97%, demonstrating fishers' willingness to be involved. The resultant maps are easily accessible and instantly informative, providing a very clear visual indication of which areas are most important for the fishers. The maps also provide quantitative data, which can be used to analyse the relative impact of different management options on the fishing industry and can be incorporated into planning software, such as MARXAN, to ensure that conservation goals can be met at minimum negative impact to the industry. This research shows how spatial access priority mapping can facilitate the early engagement of fishers and the ready incorporation of their priorities into the decision-making process in a transparent, quantitative way.

As ocean temperatures rise, species distributions are tracking towards historically cooler regions in line with their thermal affinity1,2. However, different responses of species to warming and changed species interactions make predicting biodiversity redistribution and relative abundance a challenge3,4. Here, we use three decades of fish and plankton survey data to assess how warming changes the relative dominance of warm-affinity and cold-affinity species5,6. Regions with stable temperatures (for example, the Northeast Pacific and Gulf of Mexico) show little change in dominance structure, while areas with warming (for example, the North Atlantic) see strong shifts towards warm-water species dominance. Importantly, communities whose species pools had diverse thermal affinities and a narrower range of thermal tolerance showed greater sensitivity, as anticipated from simulations. The composition of fish communities changed less than expected in regions with strong temperature depth gradients. There, species track temperatures by moving deeper2,7, rather than horizontally, analogous to elevation shifts in land plants8. Temperature thus emerges as a fundamental driver for change in marine systems, with predictable restructuring of communities in the most rapidly warming areas using metrics based on species thermal affinities. The ready and predictable dominance shifts suggest a strong prognosis of resilience to climate change for these communities.

Research that combines all available studies of biological responses to regional and global climate change shows that 81–83% of all observations were consistent with the expected impacts of climate change. These findings were replicated across taxa and oceanic basins. Past meta-analyses of the response of marine organisms to climate change have examined a limited range of locations 1 , 2 , taxonomic groups 2 , 3 , 4 and/or biological responses 5 , 6 . This has precluded a robust overview of the effect of climate change in the global ocean. Here, we synthesized all available studies of the consistency of marine ecological observations with expectations under climate change. This yielded a meta-database of 1,735 marine biological responses for which either regional or global climate change was considered as a driver. Included were instances of marine taxa responding as expected, in a manner inconsistent with expectations, and taxa demonstrating no response. From this database, 81–83% of all observations for distribution, phenology, community composition, abundance, demography and calcification across taxa and ocean basins were consistent with the expected impacts of climate change. Of the species responding to climate change, rates of distribution shifts were, on average, consistent with those required to track ocean surface temperature changes. Conversely, we did not find a relationship between regional shifts in spring phenology and the seasonality of temperature. Rates of observed shifts in species’ distributions and phenology are comparable to, or greater, than those for terrestrial systems.

Global maps constructed using climate-change velocities to derive spatial trajectories for climatic niches between 1960 and 2100 show past and future shifts in ecological climate niches; properties of these trajectories are used to infer changes in species distributions, and thus identify areas that will act as climate sources and sinks, and geographical barriers to species migrations. Species mobility in a changing climate To survive in a changing climate, a species may need to move in order to stay in an area with a constant average temperature. Such mobility would depend on an ability to keep pace with a moving climate — and on the absence of physical barriers to migration. These authors use the velocity of climate change to construct a global map of how ecological climate niches have shifted in recent decades and go on to predict changes in species distribution to the end of this century. The map indicates areas that will act as climate sources and sinks, and geographical barriers likely to impede species migration. The data show that geographical connections and physical barriers — mostly coasts — have profound effects on the expected ability of organisms to track their preferred climate. This work underlines the importance of migration corridors linking warmer and cooler areas as a means of maintaining biodiversity. The reorganization of patterns of species diversity driven by anthropogenic climate change, and the consequences for humans 1 , are not yet fully understood or appreciated 2 , 3 . Nevertheless, changes in climate conditions are useful for predicting shifts in species distributions at global 4 and local scales 5 . Here we use the velocity of climate change 6 , 7 to derive spatial trajectories for climatic niches from 1960 to 2009 (ref. 7 ) and from 2006 to 2100, and use the properties of these trajectories to infer changes in species distributions. Coastlines act as barriers and locally cooler areas act as attractors for trajectories, creating source and sink areas for local climatic conditions. Climate source areas indicate where locally novel conditions are not connected to areas where similar climates previously occurred, and are thereby inaccessible to climate migrants tracking isotherms: 16% of global surface area for 1960 to 2009, and 34% of ocean for the ‘business as usual’ climate scenario (representative concentration pathway (RCP) 8.5) 8 representing continued use of fossil fuels without mitigation. Climate sink areas are where climate conditions locally disappear, potentially blocking the movement of climate migrants. Sink areas comprise 1.0% of ocean area and 3.6% of land and are prevalent on coasts and high ground. Using this approach to infer shifts in species distributions gives global and regional maps of the expected direction and rate of shifts of climate migrants, and suggests areas of potential loss of species richness.

It is now widely accepted that global warming is occurring, yet its effects on the world's largest ecosystem, the marine pelagic realm, are largely unknown. We show that sea surface warming in the Northeast Atlantic is accompanied by increasing phytoplankton abundance in cooler regions and decreasing phytoplankton abundance in warmer regions. This impact propagates up the food web (bottom-up control) through copepod herbivores to zooplankton carnivores because of tight trophic coupling. Future warming is therefore likely to alter the spatial distribution of primary and secondary pelagic production, affecting ecosystem services and placing additional stress on already-depleted fish and mammal populations.

Climate change challenges organisms to adapt or move to track changes in environments in space and time. We used two measures of thermal shifts from analyses of global temperatures over the past 50 years to describe the pace of climate change that species should track: the velocity of climate change (geographic shifts of isotherms over time) and the shift in seasonal timing of temperatures. Both measures are higher in the ocean than on land at some latitudes, despite slower ocean warming. These indices give a complex mosaic of predicted range shifts and phenology changes that deviate from simple poleward migration and earlier springs or later falls. They also emphasize potential conservation concerns, because areas of high marine biodiversity often have greater velocities of climate change and seasonal shifts.