Reefs at Risk: A Map-Based Indicator of Threats to the Worlds Coral Reefs

This report presents the first-ever detailed, map-based assessment of potential threats to coral reef ecosystems around the world. "Reefs at Risk" draws on 14 data sets (including maps of land cover, ports, settle-ments, and shipping lanes), information on 800 sites known to be degraded by people, and scientific expertise to model areas where reef degradation is predicted to occur, given existing human pressures on these areas. Results are an indicator of potential threat (risk), not a measure of actual condition. In some places, particularly where good management is practiced, reefs may be at risk but remain relatively healthy. In others, this indicator underestimates the degree to which reefs are threatened and degraded.Our results indicate that:Fifty-eight percent of the world's reefs are poten-tially threatened by human activity -- ranging from coastal development and destructive fishing practices to overexploitation of resources, marine pollution, and runoff from inland deforestation and farming.Coral reefs of Asia (Southeastern); the most species-rich on earth, are the most threatened of any region. More than 80 percent are at risk (undermedium and high potential threat), and over half are at high risk, primarily from coastal development and fishing-related pressures.Overexploitation and coastal development pose the greatest potential threat of the four risk categories considered in this study. Each, individually, affects a third of all reefs.The Pacific, which houses more reef area than any other region, is also the least threatened. About 60 percent of reefs here are at low risk.Outside of the Pacific, 70 percent of all reefs are at risk.At least 11 percent of the world's coral reefs contain high levels of reef fish biodiversity and are under high threat from human activities. These "hot spot" areas include almost all Philippine reefs, and coral communities off the coasts of Asia, the Comoros, and the Lesser Antilles in the Caribbean.Almost half a billion people -- 8 percent of the total global population -- live within 100 kilometers of a coral reef.Globally, more than 400 marine parks, sanctuaries, and reserves (marine protected areas) contain coral reefs. Most of these sites are very small -- more than 150 are under one square kilometer in size. At least 40 countries lack any marine protected areas for conserving their coral reef systems

Ecological States and the Resilience of Coral Reefs

We review the evidence for multiple ecological states and the factors that create ecological resilience in coral reef ecosystems. There are natural differences among benthic communities along gradients of water temperature, light, nutrients, and organic matter associated with upwelling-downwelling and onshore-offshore systems. Along gradients from oligotrophy to eutrophy, plant-animal symbioses tend to decrease, and the abundance of algae and heterotrophic suspension feeders and the ratio of organic to inorganic carbon production tend to increase. Human influences such as fishing, increased organic matter and nutrients, sediments, warm water, and transportation of xenobiotics and diseases are common causes of a large number of recently reported ecological shifts. It is often the interaction of persistent and multiple synergistic disturbances that causes permanent ecological transitions, rather than the succession of individual short-term disturbances. For example, fishing can remove top-level predators, resulting in the ecological release of prey such as sea urchins and coral-eating invertebrates. When sea urchins are not common because of unsuitable habitat, recruitment limitations, and diseases, and when overfishing removes herbivorous fish, frondose brown algae can dominate. Terrigenous sediments carried onto reefs as a result of increased soil erosion largely promote the dominance of turf or articulated green algae. Elevated nutrients and organic matter can increase internal eroders of reef substratum and a mixture of filamentous algae. Local conservation actions that attempt to reduce fishing and terrestrial influences promote the high production of inorganic carbon that is necessary for reef growth. However, global climate change threatens to undermine such actions because of increased bleaching and mortality caused by warm-water anomalies, weakened coral skeletons caused by reduced aragonite availability in reef waters, and increased incidence of diseases in coral reef species. Consequently, many coral reefs, including those that are heavily managed, have experienced net losses in accumulated inorganic carbon in recent decades and appear likely to continue this trend in coming decades. Reefs urgently need to be managed with a view to strengthening their resilience to the increased frequency and intensity of these pressures. Ecological targets must include the restoration or maintenance of species diversity, keystone species, spatial heterogeneity, refugia, and connectivity. Achieving these goals will require unprecedented cooperative synergy between human organizations at all political levels, from intergovernmental to local. * [ERRATUM: A longer version of this paper is published as a book chapter in McClanahan, T.R., N.V.C. Polunin and T.J. Done. 2002. Resilience of coral reefs. in L.H. Gunderson and L. Pritchard Jr. (editors). Resilience and the Behavior of Large-Scale Systems. SCOPE and Island Press, Washington. The original version of this paper stated incorrectly that the book chapter was still in press.

Coral reefs in a human-dominated environment : implications of altered disturbance regimes and reduced resilience

Coral reefs are facing an "Anthropocene " era where humans have advanced from a minor species with limited influence on coral reefs to a major source of disturbance. Disturbance arriving from human influences may not only interact with each other, but also with natural disturbance regimes, leading to synergistic effects. Several studies have addressed the influence of natural disturbance regimes on coral reefs. However, experimental studies on disturbance complexity and physiological responses of corals to sublethal stresses, anthropogenic in particular, are surprisingly few. This thesis investigates the effects on corals exposed to single and multiple stress and highlights human influences on the interaction between altered disturbance regimes and ecological resilience. The first three studies have an ecophysiological approach showing that a stressor that do not affect corals when arriving as a single parameter can have a substantial effect when occurring in combination (simultaneously or sequentially) with other stressors. The studies also show that, in the short-term, antagonistic effects may occur.Interacting disturbance regimes can result in ecological surprises, such as phase shifts. A common manifestation of such phase shifts in coral reefs is the shift from coral to algal dominance where overfishing, mass mortality of herbivorous organisms, and eutrophication seem to be some of the major driving forces. This thesis also explores the dual and interactive role of marine protected areas and physical reduction of macroalgae as potential management strategies in reefs that have undergone a phase shift. However, results show that herbivorous fishes are not able to keep algae growth in check after the algae once are removed which might indicate that under prevailing conditions the phase shift might be irreversible.Instead of focusing on recovery of certain species and populations of species within disturbed sites of individual reefs, this thesis also address spatial resilience i.e. the dynamic capacity of a reef matrix to reorganize and maintain ecosystem function following disturbance. The final two papers begin an identification of spatial sources of resilience in dynamic seascapes where the interplay between altered disturbance regimes and ecological resilience is highlighted. Managing for resilience in dynamic seascapes enhances the likelihood of conserving coral reefs and provides insurance to society by sustaining essential ecosystem services. </p