Introduction to the special issue: The global state of the ocean; interactions between stresses, impacts and some potential solutions. Synthesis papers from the International Programme on the State of the Ocean 2011 and 2012 workshops

This Special Issue publishes papers on ocean stresses, impacts and solutions that underpinned the findings of workshops hosted by The International Programme on the State of the Ocean (IPSO; http://www.stateoftheocean.org) in partnership with the International Union for the Conservation of Nature (IUCN: http://http:// www.iucn.org/). IPSO was founded to investigate anthropogenic stressors and impacts on the global ocean and to define workable solutions to reduce or eliminate these problems. The distinguishing feature of this programme is that it treats the effects of such stressors collectively, taking a holistic view of marine ecosystems and impacts on them. Recent research has emphasised that to assess the totality of human impacts on the oceans, and the biodiversity it contains, and the resultant negative effects on the goods and services provided by marine ecosystems, the interactions between stresses must be resolved. This is critical because many direct and indirect human stressors act in a cumulative or synergistic fashion. A well-known example of this is the over exploitation of algivorous fish species on coral reefs leading to a decrease in reef resilience, with respect to shocks such as mass coral bleaching, and promoting the phase shift from coral-dominated to algal dominated systems (e.g. Hughes, 1994; Mumby et al., 2006; Hoegh-Guldberg et al., 2007; Hughes et al., 2007). Another example is the increasing recognition of interactions between overfishing and nutrient pollution (eutrophication) in causing cascading changes in marine ecosystems via food-web interactions (e.g. Daskalov, 2002; Daskalov et al., 2007). Climate-change effects, including ocean warming, acidification and hypoxia all potentially interact with each other and with other human impacts including overfishing, pollution and the establishment of invasive species (e.g. Cheung et al., 2010; Johnson et al., 2011; Doney et al., 2012). Addressing the direct and indirect human impacts on the ocean requires a holistic approach to develop viable and practical approaches to reduce or eliminate current degradation of marine ecosystems. Such approaches must be joined up, for example, the effectiveness of local action to reduce direct human stresses on coral reefs must come with global-level actions to reduce CO2 emissions. Efforts to reduce fishing mortality to a point where fishing should become sustainable (i.e. below MSY) is of little use if essential fish habitat is eliminated by destructive fishing methods and the resilience of the ecosystem eroded through bycatch of nontarget species. Such an approach, which aims to maintain ecosystem health whilst enabling the provision of the goods and services humankind requires, forms the basis for ecosystem-based management (Thrush and Dayton, 2010). It is important to also bear in