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AbstractOcean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed “tropicalization”. A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral‐dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral‐dominated ecosystems. We show that increased herbivory by warm‐water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf‐dominated ecosystems, rather than the complex coral‐dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO2 levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.

The aims of this work are to provide an overview of the current stresses of estuaries in Argentina and to propose adaptation strategies from an ecohydrological approach. Several Argentinian estuaries are impacted by pollutants, derived mainly from sewage discharge and agricultural or industrial activities. Anthropogenic impacts are expected to rise with increasing human population. Climate-driven warmer temperature and hydrological changes will alter stratification, residence time, oxygen content, salinity, pollutant distribution, organism physiology and ecology, and nutrient dynamics. Good water quality is essential in enhancing estuarine ecological resilience to disturbances brought on by global change. The preservation, restoration, and creation of wetlands will help to protect the coast from erosion, increase sediment accretion rates, and improve water quality by removing excess nutrients and pollutants. The capacity of hydrologic basin ecosystems to absorb human and natural impacts can be improved through holistic management, which should consider social vulnerability in complex human-natural systems.

Assessing Biodiversity Declines Understanding human impact on biodiversity depends on sound quantitative projection. Pereira et al. (p. 1496 , published online 26 October) review quantitative scenarios that have been developed for four main areas of concern: species extinctions, species abundances and community structure, habitat loss and degradation, and shifts in the distribution of species and biomes. Declines in biodiversity are projected for the whole of the 21st century in all scenarios, but with a wide range of variation. Hoffmann et al. (p. 1503 , published online 26 October) draw on the results of five decades' worth of data collection, managed by the International Union for Conservation of Nature Species Survival Commission. A comprehensive synthesis of the conservation status of the world's vertebrates, based on an analysis of 25,780 species (approximately half of total vertebrate diversity), is presented: Approximately 20% of all vertebrate species are at risk of extinction in the wild, and 11% of threatened birds and 17% of threatened mammals have moved closer to extinction over time. Despite these trends, overall declines would have been significantly worse in the absence of conservation actions.

The Carnian Pluvial Episode was a phase of global climatic change and biotic turnover that occurred during the early Late Triassic. In marine sedimentary basins, the arrival of huge amounts of siliciclastic sediments, the establishment of anoxic conditions, and a sudden change of the carbonate factory on platforms marked the Carnian Pluvial Episode. The sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as, for example, an extinction among ammonoids and conodonts in the ocean, and a turnover of the vertebrate fauna and the flora on land. Multiple negative carbon-isotope excursions were recorded during the Carnian Pluvial Episode in both organic matter and marine carbonates, suggesting repeated injection of 13C-depleted CO2 into the ocean-atmosphere system, but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood. We here review the existing carbon-isotope records and present new data on the carbon-isotope composition of organic carbon in selected sections of the western Tethys realm that record the entire Carnian Pluvial Episode. New ammonoid, conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections. The results provide biostratigraphically constrained composite organic carbon-isotope curves for the Carnian, which sheds light on the temporal and causal links between the main carbon-isotope perturbations, and the distinct environmental and biotic changes that mark the Carnian Pluvial Episode. The carbon-isotope records suggest that a series of carbon-cycle perturbations, possibly recording multiple phases of volcanic activity during the emplacement of the Wrangellia Large Igneous Province, disrupted Carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years.

Marine space is three dimensional, the turnover of life forms is rapid, defining a fourth dimension: time. The definition of ecologically significant spatial units calls for the spatio-temporal framing of significant ecological connections in terms of extra-specific (biogeochemical cycles), intra-specific (life cycles), and inter-specific (food webs) fluxes. The oceanic volume can be split in sub-systems that can be further divided into smaller sub-units where ecosystem processes are highly integrated. The volumes where oceanographic and ecological processes take place are splittable into hot spots of ecosystem functioning, e.g., upwelling currents triggering plankton blooms, whose products are then distributed by horizontal currents, so defining Cells of Ecosystem Functioning (CEFs), whose identification requires the collaboration of physical and chemical oceanography, biogeochemistry, marine geology, plankton, nekton and benthos ecology and biology, food web dynamics, marine biogeography. CEFs are fuzzy objects that reflect the instability of marine systems.

Antarctic krill (Euphausia superba) is a key species of the Southern Ocean, impacted by climate change and human exploitation. Understanding how these changes affect the distribution and abundance of krill is crucial for generating projections of change for Southern Ocean ecosystems. Krill growth is an important indicator of habitat suitability and a series of models have been developed and used to examine krill growth potential at different spatial and temporal scales. The available models have been developed using a range of empirical and mechanistic approaches, providing alternative perspectives and comparative analyses of the key processes influencing krill growth. Here we undertake an intercomparison of a suite of the available models to understand their sensitivities to major driving variables. This illustrates that the results are strongly determined by the model structure and technical characteristics, and the data on which they were developed and validated. Our results emphasize the importance of assessing the constraints and requirements of individual krill growth models to ensure their appropriate application. The study also demonstrates the value of the development of alternative modelling approaches to identify key processes affecting the dynamics of krill. Of critical importance for modelling the growth of krill is appropriately assessing and accounting for differences in estimates of food availability resulting from alternative methods of observation. We suggest that an intercomparison approach is particularly valuable in the development and application of models for the assessment of krill growth potential at circumpolar scales and for future projections. As another result of the intercomparison, the implementations of the models used in this study are now publicly available for future use and analyses.