Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef-associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled-up management intervention and decisive action on global emissions are required if the loss of coral-dominated ecosystems is to be avoided.

w ww ww w. .f fr ro on nt ti ie er rs si in ne ec co ol lo og gy y. .o or rg g C oastal ecosystems and the services they provide are under global siege. Climate change, nutrient loading, habitat degradation, food web alteration, and pollution all threaten their existence (Silliman et al. 2005;Orth et al. 2006;Halpern et al. 2008). Quantifying the economic values of services provided and incorporating these values into socioeconomic analyses is key to conserving these benefitgenerating ecosystems (NRC 2005;Hein et al. 2006). Currently, with few exceptions (eg Farnsworth 1998;Gaston 2000;Petersen et al. 2003;Dobson et al. 2006;Aburto-Oropeza et al. 2008), a major underlying assumption of the valuation process is that the quantity of an ecosystem function varies linearly with independent characteristics and forcing variables, such as ecosystem size, seasonality, disturbance, and species interactions (Barbier et al. 2008a). However, the responses these independent variables generate in ecosystem functions are highly dynamic and non-linear across both space and time (Farnsworth 1998). For example, the function of wave attenuation by some seagrasses may be at its maximum during summer, when plants are reproducing (Chen et al. 2007), at medium levels in spring and fall, and non-existent during winter, when density and biomass are low. Furthermore, many ecological functions are likely to be characterized by a tendency to level off (ie asymptotic relationship) or change dramatically (ie ecological thresholds) over time and space, as is the case with certain ecological processes, such as population growth, predator functional responses, and species-area relationships (Cain et al. 2008). However, such non-linear relationships between ecological traits and ecosystem function, and ecosystem function and service delivery, have not been explored in depth, quantitatively or conceptually (except see Aburto-Oropeza et al. 2008).Improvements in the understanding and quantification of non-linearities in ecosystem functions are likely to provide more realistic ecosystem service values and also to improve ecosystem-based management (EBM) practices (Barbier et al. 2008a). Current conservation decision making often takes into account only the qualitative benefits of ecosystems (eg whether or not a habitat is a fish nursery, rather than the value of the fisheries it maintains), as quantitative measures are generally unavailable.

Sustainably managing ecosystems is challenging, especially for complex systems such as coral reefs. This study develops critical reference points for sustainable management by using a large empirical dataset on the coral reefs of the western Indian Ocean to investigate associations between levels of target fish biomass (as an indicator of fishing intensity) and eight metrics of ecosystem state. These eight ecological metrics each exhibited specific thresholds along a continuum of fishable biomass ranging from heavily fished sites to old fisheries closures. Three thresholds lay above and five below a hypothesized window of fishable biomass expected to produce a maximum multispecies sustainable yield (B MMSY ). Evaluating three management systems in nine countries, we found that unregulated fisheries often operate below the B MMSY , whereas fisheries closures and, less frequently, gear-restricted fisheries were within or above this window. These findings provide tangible management targets for multispecies coral reef fisheries and highlight key tradeoffs required to achieve different fisheries and conservation goals.human-environment interactions | sustainable fisheries | marine protected areas | resilience | social-ecological systems C oral reefs have proven difficult to manage sustainably, in part because the multispecies nature of reef fisheries, the complexity of trophic interactions, and the times scales on which processes manifest may allow coral reefs to appear healthy long after serious degradation has occurred (1, 2). This also means that signs of degradation may not be readily apparent in the information that many managers use to evaluate the condition of reef systems [metrics such as catch data or coral cover (2)]. In addition, most reefs are located in developing countries (3) where food security concerns often take priority over conservation. In the absence of reference points that signal when further exploitation may have serious consequences for reef ecosystems, managers are often unlikely to make the socially and politically difficult decisions to restrict fishing activities. A question of critical relevance to scientists, managers, and resource users alike is whether meaningful limits or reference points can provide effective warning of conditions beyond which coral reef social-ecological systems incur a risk of serious degradation and lost value (4, 5).Here we examine where major changes in coral reef systems occur along a gradient of fishable biomass, a readily measured and managed variable, and explore how this can be used to define key reference points that can help inform management decisions (4, 6). We compiled information from more than 300 surveys of shallow coral reefs from nine countries across the Indian Ocean (Table S1 ). Survey sites spanned some 35°of latitude and 52°of longitude and were evenly distributed among unregulated, restricted, and fisheries closure management areas (details in SI Methods). We used a suite of four statistical models (null, linear, switch-point, and piecewis...

A 194-year annual record of skeletal delta(18)O from a coral growing at Malindi, Kenya, preserves a history of sea surface temperature (SST) change that is coherent with instrumental and proxy records of tropical Pacific climate variability over interannual to decadal periods. This variability is superimposed on a warming of as much as 1.3 degrees C since the early 1800s. These results suggest that the tropical Pacific imparts substantial decadal climate variability to the western Indian Ocean and, by implication, may force decadal variability in other regions with strong El Nino-Southern Oscillation teleconnections.

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Ecosystem-based management is logistically and politically challenging because ecosystems are inherently complex and management decisions affect a multitude of groups. Coastal ecosystems, which lie at the interface between marine and terrestrial ecosystems and provide an array of ecosystem services to different groups, aptly illustrate these challenges. Successful ecosystem-based management of coastal ecosystems requires incorporating scientific information and the knowledge and views of interested parties into the decision-making process. Estimating the provision of ecosystem services under alternative management schemes offers a systematic way to incorporate biogeophysical and socioeconomic information and the views of individuals and groups in the policy and management process. Employing ecosystem services as a common language to improve the process of ecosystem-based management presents both benefits and difficulties. Benefits include a transparent method for assessing trade-offs associated with management alternatives, a common set of facts and common currency on which to base negotiations, and improved communication among groups with competing interests or differing worldviews. Yet challenges to this approach remain, including predicting how human interventions will affect ecosystems, how such changes will affect the provision of ecosystem services, and how changes in service provision will affect the welfare of different groups in society. In a case study from Puget Sound, Washington, we illustrate the potential of applying ecosystem services as a common language for ecosystem-based management.