Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005shallow reefs bleached first and remained bleached for longer, thus excessively stressing thecoral colonies. The largest decline in coral cover occurred following 1997 and 1998; since thencoral cover has remained low and relatively constant.While there has been relatively little decline in coral cover since 1999, there has been little newcoral recruitment. Thus, it appears that the same environmental and water quality problemsthat contributed as secondary stresses causing the loss of coral have also prevented recovery bynew coral recruits. Another factor was the loss of algal grazing Diadema antillarum in 1983;macro-algae now cover much of the reefs preventing the settlement of new coral recruits, andincreasing competition for space amongst various reef organisms. While there has been somecoral recruitment, it has been insufficient to prevent the reefs from becoming increasinglybarren of living corals.Three hurricanes passed near the Florida Keys in 2005. SSTs (recorded at a SeaKeys C-Man stationon Sombrero Reef) rose to more than 31ºC in July, but the passage of Hurricanes Katrina (K),Rita (R) and Wilma (W) reduced elevated SSTs, alleviating the stressful conditions and resulting inminimal coral bleaching (image from Mark Eakin NOAA/NESDIS).There are more than 9000 patch reefs in the Upper Keys; these have shown the least decline incoral cover and are still the most extensive coral communities. The patch reefs occur in veryturbid, shallow inshore waters of the Keys, through Hawk Channel and to the outer reefs. Theygrow in waters with the highest levels of nutrients in the Sanctuary and are seasonally exposedto the warm waters of the Gulf of Mexico. These waters get very cold in winter and very warm insummer, but the patch reefs have acclimated to the widest range of environmental conditionsin the Florida Keys. There are 200 - 300 year old coral colonies that are unblemished fromdiseases. These are the only reefs that have shown any increase in coral cover during the last10 years.Other reef animals are also disappearing in the Florida Keys; for example, the corallimorph,Ricordea florida, (also known as false coral) was abundant on shallow reefs such as Looe KeyReef in the 1960s and 1970s, but began to disappear from Looe Key Reef in the early 1980s.Most of the populations had vanished from the shallow reefs by the time monitoring startedin 1996. There are anecdotal reports that crinoids have also disappeared from the reefs. These66
Coral Reefs of the U.S. Caribbeanwere frequently seen on shallow reefs like Looe Key Reef in the 1960s and 1970s and werecommon at 20 to 40 m on deep reefs. A survey in September 2001 between 20 and 30 m foundnone during 6 hours in areas where crinoids were previously abundant. However, crinoids arestill seen on the reefs in the Tortugas Ecological Reserve, to the far west of the Sanctuary, inwaters that have been less influenced by elevated SSTs and land-based sources of pollution,indicating that crinoids are another group affected by higher SSTs and pollution.2004-2005: Although elevated SSTs occurred in the Florida Keys in 2004 and 2005, there wasonly minor to patchy coral bleaching. The corals escaped the severe coral bleaching that wasrecorded throughout much of the Wider Caribbean. Both 2004 and 2005 were active hurricaneseasons; each tropical storm reduced SSTs, by mixing the surface waters with deeper, coolerwaters.Co n c l u s i o n sCoral bleaching has been intensifying over the past 25 years at the local scale in the FloridaKeys; this is consistent with other observations at regional and global scales. The pattern andintensity of coral bleaching events has shown a spatial and temporal expansion during thistime, with concurrent increases in secondary impacts, such as coral diseases, loss of livingtissue and low recruitment on the coral reefs of the Florida Keys. The shallow bank-reef habitatshave been most severely affected, probably because they have historically existed in a narrowerrange of environmental conditions. In contrast, patch reefs, which are regularly exposed toelevated nutrient and sediment levels and broad seasonal fluctuations in water temperature,have been least affected and have retained the highest living coral cover. These corals haveprobably survived the bleaching episodes because they are better adapted to a broad range ofphysical conditions, similar to those that occur during doldrum-like weather. The mechanismis unclear; it is possible that natural selection has influenced their genetic composition so thatthey are able to tolerate greater fluctuations of temperature and nutrient levels, and lower lightconditions.Coral reefs of the Florida Keys are affected by the same stresses damaging reefs worldwide:climate change; diseases; land-based sources of pollution; habitat loss and degradation; andover-fishing. There is no longer a debate that coral bleaching is linked to global climate change;and a few people debate the causes of global climate change. Irrespective, coral reef scientistsand managers need to take every possible immediate action to preserve and conserve the coralreef resources of the world. While such scientific debate is healthy and part of the scientificprocess, there comes a time when debate seeking second opinion distracts from the obvious,and provides decision-makers with a no-decision option. The suspected causes for the coralloss in the Florida Keys have varied enormously over the years; now there is recognition thatelevated SSTs are the primary cause of coral bleaching. A minority viewpoint has focused onland-based sources of pollution as the cause of coral decline. Clearly, both have played a majorrole in the decline of coral reefs on a global scale; research should be focused on unraveling thecauses of coral decline at scales from microbial to the ecosystem.Au t h o r Co n ta c tBilly D. Causey, Southeast Regional Director, National Marine Sanctuary Program of USA inKey West, Florida; billy.causey@noaa.gov67
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Dedication: This book is dedicated
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Status of Caribbean Coral Reefs aft
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Status of Caribbean coral reefs after bleaching and hurricanes in 2005

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