Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Lévy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators-sharks, bony fishes, sea turtles and penguins-exhibit Lévy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions.

Human activities are releasing gigatonnes of carbon to the Earth's atmosphere annually. Direct consequences of cumulative post-industrial emissions include increasing global temperature, perturbed regional weather patterns, rising sea levels, acidifying oceans, changed nutrient loads and altered ocean circulation. These and other physical consequences are affecting marine biological processes from genes to ecosystems, over scales from rock pools to ocean basins, impacting ecosystem services and threatening human food security. The rates of physical change are unprecedented in some cases. Biological change is likely to be commensurately quick, although the resistance and resilience of organisms and ecosystems is highly variable. Biological changes founded in physiological response manifest as species range-changes, invasions and extinctions, and ecosystem regime shifts. Given the essential roles that oceans play in planetary function and provision of human sustenance, the grand challenge is to intervene before more tipping points are passed and marine ecosystems follow less-buffered terrestrial systems further down a spiral of decline. Although ocean bioengineering may alleviate change, this is not without risk. The principal brake to climate change remains reduced CO(2) emissions that marine scientists and custodians of the marine environment can lobby for and contribute to. This review describes present-day climate change, setting it in context with historical change, considers consequences of climate change for marine biological processes now and in to the future, and discusses contributions that marine systems could play in mitigating the impacts of global climate change.

Summary 11 12The global ocean's near-surface can be partitioned into distinct provinces on the basis of regional 13 primary productivity and oceanography [1]. This ecological geography provides a valuable 14 framework for understanding spatial variability in ecosystem function, but has relevance only part and holds potentially huge fish resources [3][4][5]. It is, however, hidden from satellite observation, and 18 a lack of globally-consistent data has prevented development of a global-scale understanding. 19Acoustic Deep Scattering Layers (DSLs) are prominent features of the mesopelagic. These vertically-20 narrow (tens to hundreds of m) but horizontally-extensive layers (continuous for tens to thousands 21 of km) comprise communities of fish and zooplankton, and are readily detectable using 22 echosounders. We have compiled a database of DSL characteristics globally. We show that DSL and 23 acoustic backscattering intensity (a measure of biomass) can be modelled accurately using just 24 surface primary production, temperature and wind-stress. Spatial variability in these environmental 25 factors leads to a natural partition of the mesopelagic into ten distinct classes. These classes demark 26 a more complex biogeography than the latitudinally-banded schemes that have been proposed 27 before [6,7]. Knowledge of how environmental factors influence the mesopelagic enables future 28 change to be explored: we predict that by 2100 there will be widespread homogenisation of 29 mesopelagic communities, and that mesopelagic biomass could increase by c. 17%. The biomass 30 increase requires increased trophic efficiency, which could arise because of ocean warming and DSL 31shallowing. 32 33

Interannual variability is a characteristic feature of the Southern Ocean ecosystem, yet the relative roles of biological and physical processes in generating these fluctuations are unknown. There is now extensive evidence that there are years when there is a very low abundance of Antarctic krill (Euphausia superba) in the South Georgia area, and that this variation affects much of the ecosystem, with the most obvious impacts on survival and breeding success of some of the major predators on krill. The open nature of the South Georgia ecosystem means this variability has large‐scale relevance, but even though there are unique time series of data available, information on some key processes is limited. Fluctuations in year‐class success in parts, or all, of the krill population across the Scotia Sea can generate large changes in the available biomass. The ocean transport pathways maintain the large‐scale ecosystem structure by moving krill over large distances to areas where they are available to predator colonies. This large‐scale physical system shows strong spatial and temporal coherence in the patterns of the interannual and subdecadal variability. This physical variability affects both the population dynamics of krill and the transport pathways, emphasizing that both the causes and the consequences of events at South Georgia are part of much larger‐scale processes.