Reefs in peril
 
  Reefs in peril
 
 
Proximal causes of decline in health of coral reefs
hot buttons for peril part of BIOLOGY OF CARIBBEAN CORAL REEFS eutrophication of Caribbean coral reefs pollution on Caribbean coral reefs future of Caribbean coral reefs SCUBA/snorkeling recreation on Caribbean coral reefs disease on Caribbean coral reefs overfishing/reef collecting on Caribbean coral reefs
There are several major proximal causes for reef decline. The topic of disease is dealt with here, while other topics are accessible via the "hot" buttons.
hot button for bleaching part of Biology of Caribbean Coral Reefs
 
 
subtitle button for disease section of BIOLOGY OF CARIBBEAN CORAL REEFS Disease
 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a diseased boulder coral Montastrea sp.

"Hmmm! Some sort of disease on this boulder coral. This is becoming an all too familiar sight on coral reefs...not just in the Caribbean, but the world over."
- Turks & Caicos 2006

NOTE Montastrea sp.

 
 

boulder coral Montastrea sp. with algal and sponge infestationCoral diseases are becoming more prevalent throughout the Caribbean region.  Certain coral-killing filamentous red algae were not seen a few decades ago, and other disease-conditions are on the rise.  In the examples shown below it is not clear whether the red algae are doing the killing, or are just taking advantage of a weakened place on an organism to grow. Antonius 1999 Coral Reefs 18: 301.

 

 

 

 

Boulder coral colonized by boring sponge Siphonodictyon
coralliphagum
, and at least 2 types of red algae

  Some diseases involving red alga:
 


red-algal diseases of coral reefs

 
 

photograph of diseased brain coral Diploria labyrinthiformisBlack-band, white-band, and other diseases are increasingly prevalent in Caribbean corals.  Mortality from yellow-band disease, especially in boulder corals, has noticeably increased from 1997 in the southern Caribbean area.  While diseases of corals are most obvious owing to their visibility, newly emerging diseases are also affecting other reef organisms such as gorgonians, sponges, and echinoderms. 

 

 

 

Diseased brain coral Diploria
labyrinthiformis
in Bonaire 0.3X

 

photograph of elkhorn coral Acropora palmata infested with white-pox diseaseWhite-pox disease is common in many areas of the Caribbean, such as in the Florida Keys and U.S. Virgin Islands. It is caused by a bacterium Serratia marcescens. The disease is not always fatal, as some lesions heal with time. Rogers et al. 2005 Coral Reefs 24: 194; photograph courtesy the author.

NOTE white-pox is characterised by irregular white patches or blotches. The patches distinguish it from white-band disease, which produces a distinctive white band as it advances over the coral surface

 

 

White-pox disease in elkhorn coral Acropora
palmata
in St. John, US Virgin Islands

 

photograph of dead encrusted elkhorn coral Acropora palmata in Carrie Bow Cay, BelizeOnce a defining element of healthy Caribbean reefs, elkhorn coral Acropora palmata has been so decimated by white-pox disease that it was designated a threatened species in 2006 under the Endangered Species Act. It is therefore heartening to see any sort of comeback for the species, as evidenced in Carrie Bow Cay, Belize where bored and photograph of new growth of elkhorn coral Acropora palmata in Carrie Bow Cay, Belizeencrusted dead branches are being overgrown by healthy colonies. Macintyre & Toscano 2007 Coral Reefs 26: 757;photographs courtesy the authors.

Dead Acropora palmata,
encrusted and bored



New, healthy colonies of
Acropora palmata
with no
sign of white-pox disease

 

 

  From the mid-1970s onwards both elkhorn and staghorn corals Acropora palmata and A. cervicornis in Florida, Bahamas, and other Caribbean areas have been serverely affected by White Band Disease, often with accompanying depredations by coral-eating snails and bristle-worms. In some areas losses of more than 95% have been recorded. Loss of critical habitat provided by both species for fishes and other organisms is accompanied by increased dominance of macroalgae and reduced rates of reef accretion. Precht et al. 2002 Coral Reefs 21: 41; photographs courtesy the authors.
 
photograph of elkhhorn coral Acropora palmata showiing poxy necrosis or "white pox" disease photograph of elkhhorn coral Acropora palmata showiing White Band Disease photograph of elkhorn coral Acropora palmata not diseased but bleached owing to high temperatures photograph of staghorn coral A. ecrvicornis showing White Band Disease 0.1X
Elkhorn coral Acropora palmata showing poxy necrosis or "white pox" disease 0.1X Elkhorn coral A. palmata showing White Band disease 0.6X Elkhorn coral A. palmata not diseased but bleached owing to high temperatures 0.05X Staghorn coral A. palmata showing White Band disease 0.5X
 

Methodology used in study of causes of decline of elkhorn corals Acropora palmata in the Florida KeysExplanation for the massive decline in elkhorn-coral Acropora palmata populations throughout the Caribbean, but especially in the Florida Keys, has been long in coming. However, after a detailed 7yr study on several reefs in the Keys during which a number of possible stressors were periodically monitored on 15 reefs, several strong possibilities have emerged. In order of importance these include fragmentation, disease, and snail predation, together accounting for a 50% decline in the study population from 2004-2010. Most of the fragmentation occurred during a catastrophic hurricane season of 2005, and this may have been a catalyst for ensuing losses. Fragmentation itself can be evolutionarily advantageous as it is a means for colonies to replicate themselves asexually when conditions for growth are good. But, if conditions are not good, fragmentation is just another kind of tissue loss. The snail predator referred to is the corallivorous Coralliophila abbreviata, which daily may daily consume up to 20 sq cm of coral surface. The snails’ grazing creates open wounds that may in turn be succeptible to colonisation by other invasive organisms such as bacteria, fungi, and various algae. Williams & Miller 2012 Coral Reefs 31: 369; photographs courtesy the authors.

NOTE top- and side-view photographs are used to follow individual colonies, such as the one featured above. From the photos the authors determine total skeletal structure-area (black outlines above), recent mortality area (blue outlines), and total dead area (orange outlines), and from these calculate total live area. For the specimen above this last is calculated as 65%. Each surveyed colony was assessed in this way at least once per year. In this specimen, all “recent mortality” was attributable to “white disease” (white-band + white-pox). As for corallivorous snails, with a “typical” density of 12 per sq m surface area, this particular colony would be expected to host 4-5 snails. More on the predatory activity of these snails can be found at carnCora.php

NOTE these include white-band disease, white-pox, and rapid-tissue loss, the last being a more recent affliction and as yet not well characterised

 
 

photograph of coralline alga Neogoniolithon accretum afflicted with Coralline White Band SyndromeAlthough not uncommon on tropical reefs in the Pacific, a disease of coralline algae known as Coralline White Band Syndrome has been identified in the coralline alga Neogoniolithon accretum on Caribbean reefs, in southwestern Puerto Rico. Ballantine et al. 2005 Coral Reefs 24: 117; photograph courtesy the authors.

 

 

Diseased coralline alga Neogoniolithon accretum growing on coral
Porites astreoides. The affected coralline dies, loses its pigmentation, and
becomes colonised by green alga. Note that the coral appears unaffected 0.5X

 

Studies on black-band disease in boulder and brain corals in the Virgin Islands show that many colonies are chronically infected, but at low levels.  The disease is caused by blue-green algae in association with bacteria and can apparently be spread by contact.  During daylight hours the disease may photograph of diseased brain coral Diploria labyrinthiformisadvance up to 1 cm per day.  An interesting ecological note for brain corals is that by killing off the living coral, the disease can annually convert about 4% of coral area to free space, thus creating new substrata for successional processes. Antonius 1981 Proc 4th Int Coral Reef Symp 2: 7; see also Edmunds 1991 Coral Reefs 10: 161. 

NOTE series of more-or-less predictable stages in types of colonising organisms, one following after the other, starting usually from bare substratum

Diseased brain coral Diploria labyrinthiformis in Little Cayman Island.
The white area is dead coral, below which is the diseased part. The
remaining healthy part of the coral is below the black area, out of view 1X

 

fan gorgonian infected with fungus disease apergillosisStudies on diseases of mound corals and fan gorgonians on a fore-reef in Akumal, Mexico show that severity of photograph of mound coral Montastrea sp. with diseaseyellow-band and aspergillosis-fungus diseases is markedly increased after experimental enrichment with nitrogen and phosphorus nutrients. Such nutrients are commonly present in agriculture- and sewage-enriched run-off waters, and the results may help to explain the greater frequency and severity of such diseases seen throughout the Caribbean region over the past 2 decades correlative with increased urban and agricultural development. Bruno et al. 2003 Ecology Letters 6: 1056.

Fan gorgonian Gorgonia ventalina infected with
fungal disease Aspergillus sydowii 0.2X

 

Mound coral Montastrea sp. with
possible yellow-band disease 0.3X

 
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