xvi C\IUBU. MAR. STUD., SPECIAL EDITION, 2007 has been lost in the past 20 years. This unprecedented rate of degradation has seen some reefs change lrom 50% cover with live coral organisms, to just I 0%•. It has been estimated that the continued decline of coral reefs could cost the region between U.S. S350 million and U.S. $870 million per year by 2050. A number of factors, each interacting with the other, arc causing the degradation of coral reefs. They include increased sedimentation lrom rivers discharging into the Caribbean; excess nutrients due to pollution lrom fannland runolT and sewage, including from cruise ships; overtishing; diseases atlccting creatures such as sea fans and sea urchins critical to the ecological balance of the reef; physical damage through dynamiting and dredging: and "bleaching" of corals, in which rising sea temperatures upset the symbiotic balance between coral polyps and the algae on which they teed. The decline of coral reels has reduced their ability to act as a protective barrier, and this may be one reason for increased levels of beach erosion. It has recently been estimated thtll 70% of Caribbean beaches arc eroding at rates of between 0.25 and 9 metres per year. The cost of artificially replacing this sand, in a process known as beach nourishment, can run into millions of dollars. Scagrass beds and mangrove forests have each seen widespread declines through direct removal to make way for vurious types of coastal development: seagrass is oficn cleared to "improve" bathing benches, while mangroves have made way lor commercial and housing construction, and lor shrimp-tanning ponds. Fish stocks under pressure In common with ocean regions across the world, the Caribbean has seen drmnatic chungc over the past 30 years in the elliciency and intensity with which !ish stocks have been targeted. Greatly increased demand, combined with the usc of new types of catching gear, have helped to exert unprecedented pressure on this key resource of the ecosystem. A number of !actors set the Caribbean apart and present particular problems in protecting !ish stocks lor future generations. One is the sheer variety of fish and invertebrates involved in commercial fishing. It has been estimated that 680 species of bony !ish, including 49 types of shark, arc targeted in the region. This makes it extremely difficult to monitor the stale of particular stocks, and to manage them sustainably. For example, of the 197 fish stocks falling under the jurisdiction of the Caribbean Fisheries Management Council (CFMC), the status of 175 (88%) was unknown or undefined. Another problem arises from the luck of a unified political authority with responsibility for the resources of the Caribbean. Fish arc no respecters of national boundaries, und the failure to regulate adequately those stocks shared by ditlerent states has led to damaging disputes between Caribbean countries in competition lor shared resources. In addition, existing arrangements enable fishing !1ects !rom throughout the world to engage in a "tree lor all," placing added pressure on the marine lilc of the Sea. It is the tragedy of the commons. Lack of reliable data makes it di!licult to give a complete picttirc of the condition of this particular service of the Caribbean Sea ecosystem. Some trends, however, give cause for concern. All the major commercially important species and groups of species in the region arc reported to be fully developed or over-exploited. In the case of one valuable stock, the conch, the pressure has been serious enough to put it on the list of threatened species held by the Convention on International Tmdc in Endangered Species (CITES). New analysis of historical trends carried out lor this assessment suggests that !ish landings in the Caribbean rose to unprecedented levels during the 1990s, reaching a peak of nearly 500,000 tonncs in 1998, but subsequently went into sharp decline. The reasons tor variations in the size of catches arc complex, involving both human and environmentallactors, but some indicators do point to the impacts of ovcrlishing. A recent study of fishing data lor four of the Windward Islands, lor example, found that while overall catches increased in the period from !980 to 1999, the increase in the eflort used to catch those !ish was very much greater. The ratio of tlsh caught for each "unit of etlorl" is estimated to have declined by up to 70% over these two decades, an indication that lish arc becoming more difficult to tlnd. There arc also signs that Caribbean !ish stocks arc sulTcring from the phenomenon known as "fishing down the lood web," in which longer-lived, predatory fish become more scarce, and stocks become dominated by shorter-lived, plankton-eating species. This reduction in the average trophic level, as it is tcnned, may not a!lect catches in the short tern1, but signals long-tenn trouble lor the ecosystem. D.-ivers of Change It is a central part of the assessment of any ecosystem to identity the key factors leading to changes which can aiTcct the services provided by the natural systems of a region or locality. Known as drivers, these can either be direct - 18-