Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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Coral Reefs and Climate Change: Susceptibility and Consequencesparticularly between major organism groups. This will depend on where calcification occurs(e.g. intracellular versus extracellular), and the biological mechanisms of calcification. Apuzzling aspect of biological calcification is that corals and other calcifying organisms have theability to isolate calcifying fluids and strongly control the chemistry of those fluids. Why willthe chemistry of the external seawater strongly affect the calcification rates? There are severalhypotheses on the coupled nature of calcification and photosynthesis, but no hypothesis hasbeen fully accepted by the science community.Coral calcification is not only determined by seawater carbonate chemistry, but also by otherfactors such as temperature, light and nutrients. Evidence that coral calcification rates aredeclining is now appearing in the scientific literature although some studies up until the early1980s recorded a rise in calcification over the majority of the 20th century. The increase isprobably a result of global warming, because many coral species calcify faster in warmer waters.Coral calcification rates increase with rising temperatures to some optimal temperature,which is near the summer maximum. Calcification then declines when temperatures exceedthis maximum. This appears to have been happening over the past 15 years, during which timecalcification rates have started to decline, most probably because of the combined impacts ofincreasing thermal stress and the reduced availability of carbonate ions.Our understanding of how rises in atmospheric CO 2will affect seawater chemistry has greatlyimproved over the last decade. There is little doubt that the carbonate system in seawateris changing according to predictions, and evidence is mounting that calcification rates willdecrease, and carbonate dissolution rates will increase. The main area of uncertainty relatesto how changes in calcification and dissolution will affect an organism’s fitness and survival.Several functions of CaCO 3precipitation have been proposed, but there have been few studiesto test how they affect the organism or the community. Some coral species grown underextremely high CO 2levels completely lost their ability to secrete skeletons; but regained theirskeleton-building ability when conditions returned to normal. This is hopeful news that somecoral species can survive without their skeletons, but even if ‘naked’ corals survive they will notretain their original ecological functions and roles within coral reef communities.Coral reef ecosystems are unique because the excess production of calcium carbonate resultsin building the reef; the very basis of a coral reef habitat. As calcification rates decline anddissolution rates rise, the balance between reef growth and reef destruction will also change.Reefs that already have a low surplus of carbonate production, e.g. those at high latitudes,may shift from net reef building to net reef loss, and lowered calcification rates will reduce theability to keep up with rising sea levels.3. Sea Level RiseThe 2007 4th IPCC Report suggests that there will be a rather modest sea level rise of 20–60cm by 2100, principally caused by thermal expansion of the oceans but including some meltingof glaciers and ice caps. However, the authors of this report acknowledge that the modelsdid not include processes related to increased ice flow. It is also important to realize that theinherently conservative consensus opinion of the fourth assessment report of the IPCC doesnot include some of the perspectives of the expert committee on sea level. When these opinionsare included, the prospect of much higher sea level rise over the 21st century becomes a greaterreality. For example, continued melting of the Greenland ice sheet could cause an additional25
Status of Coral Reefs in the Caribbean after Bleaching and Hurricanes of 2005The list below details some of the functions of Calcium Carbonate skeletons in reef-buildingorganisms.FunctionProtectionEnhances photosynthesisLight modificationReproductionAnchoring to substrateExtension above the bottomCompetition for space, light andother resourcesDescriptionSkeleton protects organism from predators, stronghydrodynamic conditions, sedimentation, etc.In photosynthetic calcifiers, calcification releases protonsthat converts bicarbonate to CO 2CaCO 3skeleton enhances light field for photosynthesis byfocusing and reflecting lightColony size sometimes determines fecundity or age ofreproductive maturity; rates of fragmentation may beaffected by skeletal densitySecures the organism to the substrate, may also affectinitial settlement of recruitsUpward growth limits time that an organism is subjectedto bottom sedimentation or scourMany reef-builders compete for space and light by growingfaster than their competitorsrise of a meter or more this century, and with complete melting, an additional 6–7 m rise insea level over the next few centuries. Such rises would not normally pose problems for mostcoral reefs; indeed sea level rise provides more space for corals to grow upwards without beingexposed to the air.There will, however, be major problems for islands and low lying coastlines. Coral cays developvia a combination of winds and waves concentrating carbonate sediments; seeds and vegetationcarried in by winds and birds help to consolidate these sediments. The combination of sea levelrise and possibly more tropical storms will counteract any accretion. A reduction in carbonateproduction because of ocean acidification will add another negative factor. Many of these coralislands and atolls in the Pacific and Indian Oceans, and in the wider Caribbean will becomeuninhabitable as seawater washes over the islands during storm surges, penetrates into thefresh groundwater and disrupts food crops. There are no predicted mechanisms for the sand onthese islands to build up sufficiently rapidly to keep up with expected sea level rise; thereforehuman populations will be displaced and parts of some countries including the Bahamas andColombia, and whole Indo-Pacific states such as Tuvalu, Kiribati, the Marshall Islands and theMaldives may cease to exist.4. Possible Sh i f t i n g o f Oc e a n Cu r r e n t sWe have a good understanding of how coral reef ecosystems will be affected by ocean warming,acidification, and sea level rise; however, we know less about other factors associated withclimate change. Changing climate conditions may cause oceanic currents to slow or evenchange direction; and large scale events such as the El Niño Southern Oscillation may changein frequency and/or intensity. Given that currents connect coral reefs to other coral reefs andrelated marine ecosystems, these changes could have profound effects on the sustainability andmanagement of coral reef ecosystems.26
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
Page 5 and 6: Status of Caribbean Coral Reefs aft
Page 25 and 26: Status of Coral Reefs in the Caribb
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Page 35 and 36: 3. Hu r r i ca n e s a n d t h e i
Page 37 and 38: Hurricanes and their Effect on Cora
Page 39 and 40: Hurricanes and their Effect on Cora
Page 41 and 42: 4. Th e 2005 Bl e a c h i n g Ev e
Page 43 and 44: The 2005 Bleaching Event: Coral-Lis
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The Effects of Coral Bleaching in t
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10. Ma n ag i n g f o r Ma s s Co r
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Managing for Mass Coral Bleaching:
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Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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