Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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Coral Reefs and Climate Change: Susceptibility and Consequences5. Associated Ch a n g e s in UV Radiation In t e n s i t yThe incidence of UV radiation in the tropics is usually very high, particularly in passing throughthe clear waters bathing coral reefs. Most coral reef animals have evolved structural, chemicaland behavioral mechanisms to cope with UV radiation. Thus, no major problems are anticipatedwith predicted thinning of the ozone layer and a likely increase in UV radiation. Shifting oceancurrents and sediment input may cause changes in the clarity of the water column, which willchange visible and UV radiation penetration.6. Weather, Hu r r i ca n e s a n d St o r m sGlobal climate change predictions all emphasize greater variations in weather, such as moreintense periods of rainfall followed by longer periods of drought. Such climate changes overland will affect runoff and sedimentation (which are also affected by land-based humanactivities), and affect water quality on many reefs. More extreme rainfall events, for example,will intensify flooding and river-plume damage to reefs, while a decrease in rainfall shouldlead to improvements in water quality. Tropical cyclonic storms have become more frequentand intense in some regions such as the Caribbean since about 1970, with some evidence thatthis is fuelled by warmer oceans. Climate models predict that cyclones are likely to be moreintense, with more category 4 and 5 storms; but the number of storms may not necessarilyincrease (see Page 14). Strong storms can cause massive damage to coral reefs; for exampleHurricane Andrew in 1992 severely damaged the coral reefs in Florida and other parts of theCaribbean through violent wave impacts. A rise in storm intensity or frequency may put reefsinto a permanent state of recovery, because it takes about 10–15 years for a reef to recover froma major storm. How stronger storms are likely to affect reefs is reviewed in the next chapter.Sy n e r g i e s, Consequences a n d Opportunities f o r Ma n ag e m e n t In t e r v e n t i o nCorals build the framework of coral reefs and therefore support thousands of other species. Manyof these are totally dependent on corals for food, shelter and reproduction, and will disappearwith a loss of coral. Other reef organisms rely only partly on the corals, perhaps needing onlythe complex structure for survival. The loss of coral will result in some local extinctions andreduced diversity of fish species. For example, some fish species are more sensitive than others,with corallivorous (coral eating) species being the most sensitive; herbivores may actuallymultiply because there will be more algae to eat. It is probable that many of the large foodfish and visiting pelagic fish will not be markedly affected, but our knowledge of these systemsis not sufficient to predict which species will or will not show changes with climate change.Several recent estimates suggest that as much as 50% of the fish diversity currently on coralreefs will disappear if coral communities are severely damaged.An understanding of how coral dependent organisms on reefs will change with the loss of coralsis still being developed. However, given the extremely tight relationships between organismsand corals, the loss of corals will almost certainly be accompanied by the loss of many thousandsof species. It is also important to realize that corals may not have to completely disappear tocause big effects on the organisms that use them as habitat. For example, some coral dwellingspecies may require dense coral populations to enable them to live close enough to the oppositesex for reproductive success.27
Status of Coral Reefs in the Caribbean after Bleaching and Hurricanes of 2005Some climate change impacts, particularly in combination with other influences, will likelyreduce the overall resilience of coral reefs. Changes in a coral community (such as reducedbiodiversity) may severely undermine system resilience, resulting in a phase shift to a noncoralreef community. For example, the loss of some fish and invertebrates may leave a coralreef more susceptible to episodic outbreaks of pests or invading species. Effects like this tendto be unpredictable, but such unpredicted changes are likely to increase.Climate change also affects coral reefs in another, fundamental way that is unique to thisecosystem; that is the effects on the geological reef structure itself. Reduced coral cover (e.g.from coral bleaching) coupled with lowered calcification rates and increased dissolution rates(ocean acidification) will reduce the net calcium carbonate production rates on reefs. By theend of this century, the overall balance of carbonate production on many reefs is expected todecline to the point where reef-building may cease or reverse. In addition, any ecosystems thatare influenced by the reef structure and reef sediment production will also be affected. Thesecould include mangroves, seagrass beds, and low-lying coral cays. It might also have significantimplications for human infrastructure on coastlines protected by coral reefs.Against the background of these dire predictions facing coral reefs, implementing managementof local damage may seem irrelevant unless the current growth in greenhouse gas emissionsis constrained. Even with drastic reductions in CO 2concentrations, there will be changesand challenges for coral reefs. However, after the massive coral bleaching in 1998, coral reefsrecovered better and more rapidly where stresses related to poor water quality and overfishingwere well managed. For example, where grazing fish are retained on a reef, corals willrepopulate damaged areas 2–3 times faster than on over-fished reefs; similarly, growth ratesof corals are faster in non-polluted waters. Managing local stresses on reefs may not preventdamage from climate change, however it will enhance recovery.Recent evidence indicates it is imperative that there is strong action on reducing greenhouseemissions to ensure that we don’t exceed much more than 450-500 ppm CO 2in the atmosphere.Any response, however, must include local strategies to increase the effective management oflocal stresses, such as declining water quality and overfishing, damaging coral reefs. Reefs willpersist longer under the stresses of the next 50–100 years if they are given the best chance ofrecovering from the inevitable ecological shocks; this will ‘buy time’. These two approaches,decreasing emissions and increasing protective management, are an integral part of effectivelyaddressing the current coral reef crisis and are discussed in Chapter 10, p. 115.Au t h o r Co n ta c t sJoan Kleypas, National Center for Atmospheric Research Boulder, Colorado, USA, kleypas@ucar.edu; Ove Hoegh-Guldberg, Centre for Marine Studies, University of Queensland, Australia.oveh@uq.edu.auReferencesFine M, Tchernov D (2007). Scleractinian coral species survive and recover fromdecalcification. Science 315:1811.Hoegh-Guldberg O, Mumby PJ, Hooten AJ, Steneck RS, Greenfield P, Gomez E, Harvell DR,Sale PF, Edwards AJ, Caldeira K, Knowlton N, Eakin CM, Iglesias-Prieto R, MuthigaN, Bradbury RH, Dubi A, Hatziolos ME (2007). Coral reefs under rapid climate changeand ocean acidification. Science 318 (5857): 1737-1742.28
Page 1 and 2: Stat u s o fCa r i b b e a nCo r a
Page 3 and 4: Dedication: This book is dedicated
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Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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