Status of Caribbean coral reefs after bleaching and hurricanes in 2005

More documents

Recommendations

Info

Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005Take advantage of resistant coral areasWhen regional sea temperatures become unusually high, the effects on coral reefs are variable.Although many corals will bleach, some will not. What determines the ability of some coralsor reef areas to resist bleaching? How can areas that are resistant be used to increaseoverall resilience of coral reef ecosystems to global climate change?A combination of environmental and intrinsic factors determines whether corals eject theirzooxanthellae or whether they resist bleaching during a regional heat stress event. Localenvironmental conditions can support resistance to bleaching by buffering how corals areexposed to unusually high sea temperatures or to sunlight. Three mechanisms can offerprotection: shading; cooling; and screening. For example, mountains or cliffs on adjacent landoffer shade to some patches of reef, as seen in the high islands of Palau. Some sites may haveconsistently cooler water as a result of upwelling or proximity to deep water. Sediment andorganic matter in turbid waters seems to support coral resistance to bleaching by screeningout sunlight; however, unnaturally turbid conditions can also seriously stress corals, therebyundoing any benefits. An additional environmental mechanism providing bleaching resistanceis flushing. Strong currents may remove toxins that are the physiological trigger for bleaching,thereby helping corals cope with warmer conditions (7).Intrinsic factors that influence resistance to bleaching at the colony level include the individualhistory and genetic composition of the coral and its symbiotic zooxanthellae. This translatesto important differences in the bleaching susceptibility of different coral communities. Forexample, massive, boulder-shaped corals (such as Porites and Favia) tend to be more resistantto bleaching than branching and plate forming corals (such as Acropora and Pocillopora).Corals also have some ability to acclimatize to heat and light stress if they are able to survivestressful conditions. Past exposure of coral colonies or communities to stressful conditionscan lead to an increased resistance to future bleaching events. The ecological significance ofthis mechanism is still being examined, because acclimatization of colonies is often short-livedand acclimatization at the community level is often a result of the less resistant corals beinglost (3).Coral reef areas that are naturally resistant to mass bleaching can be incorporated into the designand placement of management initiatives to enhance the overall resilience of the ecosystem.Some consideration has been given to the feasibility of methods for increasing the resistanceof other reef areas to bleaching. Such strategies are unlikely to be practicable or cost effectiveat sufficiently large spatial scales to provide meaningful protection to ecosystems. However,it may be possible to shade, screen, or cool high-value (small) tourism sites to increase theirbleaching resistance. These strategies are currently experimental and have the potential forunwanted side effects. They are probably best accomplished through partnerships betweenindustry, scientists, and managers.Build coral tolerance to mass bleachingWhen corals lose their zooxanthellae and bleach, they are not dead. Some bleached corals willsurvive the heat stress event and regain their zooxanthellae populations; however, corals thatbleach but survive the event are in a weakened state. They will probably have lower reproductivecapacity, slower growth rates, and greater susceptibility to disease. The ability to survivebleaching events is significant in terms of recovery time. While it may take months or years for118
Managing for Mass Coral Bleaching: Strategies for Supporting Socio–ecological Resiliencecorals to recover from the sub-lethal effects of bleaching, it takes years to decades for reefs torecover after high coral mortality. Therefore, promoting coral survival during bleaching eventsis a particularly efficient focus for management. What allows some corals to be tolerant tomass bleaching? Can management actions be taken to build tolerance and minimize theimpacts of mass bleaching events?Coral health prior to exposure to heat stress may be the most important factor influencingcolony survivorship during bleaching events. Most corals rely heavily on the energy providedby their zooxanthellae, and bleaching effectively robs them of their main energy source. Asa result, corals in a bleached state are beginning to starve, and their ability to endure thishardship is likely to be important in determining whether they survive. Like many animals,corals store surplus energy as lipids (fats); corals in good condition have relatively high lipidlevels, providing a buffer against periods of low energy supply. For this reason, it is thought thatthe condition of a coral at the time it bleaches may play a crucial role in determining whetherit will survive the period of starvation that follows. Conversely, chronic or acute stresses (suchas water pollution or anchor damage) that negatively affect coral condition could increase therisk of corals dying of the additional stress from bleaching (1). Therefore, reducing localizedstressors is an important strategy to help corals survive bleaching events.Some corals, especially species adapted to turbid environments, rely heavily on food particlescaptured from the water column (heterotrophy) to supplement their energy requirements.These corals may be less dependent on the energy provided by their zooxanthellae and thus lessprone to starvation during a bleaching event. A better understanding of coral nutrition couldhelp managers identify tolerant coral communities, allowing them to be incorporated intonetworks of refugia to enhance overall ecosystem resilience.Coral health and heterotrophy help increase coral tolerance to bleaching when the heat stresscausing a bleaching event is moderate. Heat stress above a critical temperature threshold,however, causes direct physiological damage to corals, exceeding any nutritional factors andleading to death. Both environmental and intrinsic factors are important in determining theextent to which this happens. Thus, local environmental factors have an important influenceon the amount of heat stress to which a coral is exposed. Similarly, intrinsic factors, such asgenetics, influence the threshold temperature at which a coral dies; some species are ableto tolerate higher temperatures than others. These factors contribute to patterns of naturaltolerance that can be built into management planning.Promote coral reef recoveryThe rates at which corals can adjust to increases in heat stress are widely considered to be tooslow to keep pace with even conservative climate change projections (Chap. 2). As a result,it is unlikely that coral reefs will continue to exist in their current condition. Instead, theywill increasingly be in a state of recovery. What factors encourage successful ecosystemrecovery after mass bleaching events or when other stresses associated with climate changecause high levels of coral mortality? What management actions can be taken to restore ormaintain these factors?Coral reefs will not necessarily recover to become the same types of reefs they were prior tobeing severely damaged. The goal in managing for resilience is to have a recovery process119
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 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Status of Coral Reefs in the Caribb
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
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
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
5. Stat u s o f t h e Mesoamerican
Page 51 and 52:
Status of the Mesoamerican Reef aft
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
6. Co r a l Reefs o f t h e U.S. Ca
Page 67 and 68:
Coral Reefs of the U.S. Caribbean19
Page 69 and 70: Coral Reefs of the U.S. CaribbeanMe
Page 71 and 72: Coral Reefs of the U.S. Caribbeanwe
Page 73 and 74: Coral Reefs of the U.S. CaribbeanSe
Page 75 and 76: Coral Reefs of the U.S. CaribbeanBl
Page 77 and 78: 7. Th e Effects o f Co r a l Bl e a
Page 79 and 80: The Effects of Coral Bleaching in t
Page 89 and 90: Status of Caribbean Coral Reefs aft
Page 107 and 108: 9. Th e Effects o f Co r a l Bl e a
Page 109 and 110: The Effects of Coral Bleaching in S
Page 117 and 118: 10. Ma n ag i n g f o r Ma s s Co r
Page 119: Managing for Mass Coral Bleaching:
Page 123 and 124: Managing for Mass Coral Bleaching:
show all

Status of Caribbean coral reefs after bleaching and hurricanes in 2005

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?