Introduction            

View Map of Bermuda

Abstract

Introduction
Bermuda
Coral Reefs
BBD
Diploria strigosa

Methods
John Smith Bay
Natural Arches

Results
Overview
Chi Square Test
Figure One
Data Table

Conclusion
Observed Mortality
Site Differences
Impacts of BBD
Future Research

Glossary

Bibliography 

Contact Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Abstract

Introduction
Bermuda
Coral Reefs
BBD
Diploria strigosa

Methods
John Smith Bay
Natural Arches

Results
Overview
Chi Square Test
Figure One
Data Table

Conclusion
Observed Mortality
Site Differences
Impacts of BBD
Future Research

Glossary

Bibliography 

Contact Information

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Abstract

Introduction
Bermuda
Coral Reefs
BBD
Diploria strigosa

Methods
John Smith Bay
Natural Arches

Results
Overview
Chi Square Test
Figure One
Data Table

Conclusion
Observed Mortality
Site Differences
Impacts of BBD
Future Research

Glossary

Bibliography 

Contact Information


 

Bermuda
Geological History
          The formation of Bermuda occurred approximately 110 million years ago at the Mid Atlantic Ridge in the Atlantic Ocean (Thomas).  The spreading junction at the European and American tectonic plates pushed the volcanic island 1200km west over 60-80 million years.  During this time another eruption occurred creating the Bermuda Seamount.  Thirty million years later the ridge island had moved another 800km west to its present location (Thomas).
          The Pleistocene epoch was the next important geological marker in Bermuda's formation.  As the climate became cooler, the assembly of ice caps at the poles greatly reduced sea levels and exposed formally submerged substrata, while bringing other geological formations closer to the water's surface.  Marine invertebrates and plants were able to colonize the substrata forming a thin band along the volcano.  As the water levels rose again, peaks of the island were inundated and conducive for marine colonization.  Present day Bermuda is composed of the limestone that early corals and calcareous algae deposited over the entire volcanic region (Thomas).  
Climate
          Bermuda has a sub-tropical climate despite its northern latitude of 32 N due to the Gulf Stream. The Gulf Stream is able to conduct water towards Bermuda because of the Coriolis Effect and unequal heating of the Earth’s surface.  At the equator solar radiation is most intense and warms the air.  The balmy air rises away from the surface, and surrounding air from the north and south move toward the equator to replace the lost atmosphere.  This movement of air north and south of the equator creates Trade Winds.  Northeast Trade Winds move water just north of the equator in a westerly direction restraining it to the Gulf of Mexico.  The Gulf of Mexico displays the confinement of these waters by having a water level 1m higher than areas just outside the Gulf (Thomas). Water transported by Northeast Trade Winds has to cycle out of the Gulf and cannot move east because that is the source of input, therefore north is the only option left as west and south are blocked by the Americas. Tropical waters are moved through the Straits of Florida, marking the beginning of the Gulf Stream, and then north along the western edge of the Atlantic Basin. The volume of water moved is greater than the amount transported by all global rivers and is not effected by wind until reaching Canada (Thomas). The tropical waters although cooled from their original temperature reach Bermuda and prevent the island from having a temperate climate like those of the Canary Islands on the Eastern side of the Atlantic Basin (Thomas).  

Coral Reefs
Threats to Healthy Ecosystems and Biodiversity
          The collapse of a coral reef community does not occur suddenly.  It is hypothesized to be a process that extends over a given period of time marked by two major changes.  For Caribbean reefs the changes would be a decrease in herbivorous fish and a decrease in Diadema as well as other herbivorous invertebrates.  The diagram entitiled, Model for Bermudian Coral Reef Collapse, displays the change of abundance in predators and corals as fishing and other human activities impact a reef (Bertness et al.).  Situation A describes an ideal environment in which there is little or no fishing and nutrient input.  Foraging is shared by a diverse group of herbivorous fish and invertebrates preventing coral overgrowth and creating maximum diversity.  Example B shows an increase in invertebrate grazers due to the loss of herbivorous fish from overfishing.  Since Diadema and other invertebrates compensate for the reduced numbers of fish, coral diversity remains high and algae overgrowth low.  Plane C displays high mortality of the herbivore population allowing algae to out compete corals for space causing the collapse of the coral reef community by reducing diversity and decreasing robustness of surviving coral species.
          Deforestation also impacts the health of coral reefs as well as overfishing and nutrient input.  Increased sediments from erosion, prevents zooanthellae photosynthesis due to murky waters and ultimately kills the corals (Peters 1984).  These human influences coupled with abiotic disturbances such as hurricanes, increasing water temperatures, and global warming may be linked to coral bleaching and infection, which have further promoted macroalgae recruitment and the reduction of corals.  It is important that the diverse and productive coral reef ecosystems are kept healthy for oceanic biodiversity. The study of black band disease (BBD) is one small attempt to solve a menacing problem that inflicts coral reef health in which many persist.  

Black band disease (BBD)
Description
         
In 1975 black band disease was first surveyed in Bermuda by Garrett and Ducklow seperate from Antonius' experiments in Belize and the Florida Keys (Rutzler et al.).  Since the intial discovery, BBD has been studied and included the documentation of a new species, Phormidium corallyticum, by Rutzler & Santavy in 1983.  The black microbial mat includes P. corallyticum, Beggiatoa spp., Desulfovibrio spp., nonphyotosynthetic bacteria, and marine fungi (Carlton et al., Peters 1984, & Rutzler et al.).  Color morphology is dark brown to black due to phycoerythrin (Carlton et al.). 
          P. corallyticum is a filatmentous cyanobacterium, which creates a flim hovering over and through the microbial mat layers (Rutzler et al.).  Light intensity and oygen demands are high for optimal growth as well as warm temperatures, 28ēC-32ēC (Ruzler et al.).  The cyanobacterium is also effectively resistance to high salinity changes (Rutzler et al.).  Beggiatoa spp. oxidize sulfur and are found in the lower layers of the microbial mat near the corallum above lysed polyp cells (Rutzler et al.).  Desulfovibrio spp. are sulrur-reducing bacteria (Peters 1984).  The distinguishing characteristic of BBD from other microbial mats is its ability to maintain sulfur and oxygen gradients, while migrating over the coral's surface, which creates a stable anoxic envrionment (Carlton et al.).  This anoxic environment ultimately kills poylps since they are obligate aerobes.     
Mode of infection
         
The transmittance of BBD and infection mechanism in natural environments is unknown, but many conjectures have been made (Kuta et al.).  Labratory experiments performed by Antonius, Ruzler, and Santavy have oberseverd BBD spreading from diseased to healthy coral heads when distance is less than 2 mm.  The bacteria found in the microbial mat have also been isolated from sediments stuck to the mucus covering coral heads (Carlton et al.).  Peters suggested that herbivorous fish feeding on the corals may be transmitting and initiating innoculation by damage sustained through grazing.  Innoculation experiments done in 1983 by Rutzler and Santavy found that only the injection of P. corallyticum below the ectoderm resulted in the onset of BBD.  No other microbes within the mat initiated BBD when injected.  However, Kuta pointed out that Koch's postulate was not fullfilled because reisolation and reinnocluation from the isolation was not performed.  Therefore the virulity of P. corallyticum as the infecting microbe has not been established (Kuta et al.).    
Rate of mortality in Diploria strigosa
         
In 1983, Ruzler reported BBD's minimum spreading rate at 2.4 mm -1day, an average of 3.2 mm -1day, and a maximum of 4 mm -1day on D. strigosa found at Carrie Bow reef, Belize.  In May a maximum destruction radius of 20 mm was observed, while December exhibited 370 mm of maximum radius destruction.  These numbers gave Rutzler reason to believe that there was a seasonal element to BBD activity, peaking during summer months and almost disappearing during the winter.  Other studies with the exception of Kuta have also observed the seasonal trend (Edmunds et al. & Peters).  Edmunds reported that overall 3.9 percent of D. strigosa tissue was killed by BBD annually at Greater Lameshur Bay, Virgin Islands.

Diploria strigosa
Description
         
Diploria strigosa is commonly referred to as the common brain coral.  The genus, Diploria, lacks paliform lobes and displays color morphs in hues ranging from yellow to a light muddy brown with a green tint (Sterrer).  Taxonomical marks on D. strigosa are un-grooved collines, which distinguish the species from D. labyrinthiformis.  The width of D. strigosa valleys are approximately 6 mm, with coralla reaching diameters of 200 cm.  Three major forms of coralla may be found: hemispherical, spheroidal, and encrusting.  At the sites studied only hemispherical coral heads were found and observed.  Distribution of D. strigosa include inner reefs, outer reefs, and muddy bays within depths of 1-8 m (Sterrer).      
Feeding Habits
         
Polyps are suspension feeding invertebrates.  Mesenterial filaments and tentacles containing nematocysts filter zooplankton, juvenile fish, minute crustaceans, jellyfish, etc. out of the water column (Sterrer).  Nematocysts are a type of cnidae, more commonly referred to as stinging cells, and are able to immobilize and adhere to prey (Brusca et al.).  Detritus containing bacteria can also be trapped and ingested due to mucus and cilia assisting in the suspension feeding process, which may explain why some corals are found to contain disease causing bacteria without displaying outward signs of any disease (Carlton et al. & Peters).
Anthozoan Reproduction
         
Longitudinal fission, pedal laceration, transverse fission, and budding are methods of asexual reproduction in Anthozoans (Brusca et al. & Sterrer).  Budding is a typical mode of asexual reproduction for colonial polyps like D. strigosa.  Three types of budding can occur for Anthozoans:  intratentacular, extratentacular, or parricidal (Sterrer).  Intratentacular budding happens when the clone polyp is created within the original tentacular ring, while extratentacular budding takes place outside.  Usually the primary polyp remains intact, however this is not true for parricidal budding.  The initial polyp is destroyed and gives rise to many daughter polyps.  The Faviidae family does not utilize parricidal budding (Sterrer).  Asexual reproduction can create entire colonies consisting of millions of polyps, which originated from one founder polyp.    
          Founder polyps are products of sexual reproduction, which can be produced through
dioecious or hermaphroditic means.   Gonads are located and restricted to particular mesenteries, and internal or external fertilization can take place.  Unfortunately, little is known concerning periods of sexual activity for the majority of Anthozoan species (Sterrer).
       
Autogenic Engineers
         
T
he common brain coral, belongs to the order Scleractinia, more generally referred to as true or stony corals.  Scleractinian corals are major contributors to reef building in the areas where they persist (Bertness et al.).  Mounding corals that dominate the landscape of a reef are important biological engineers, which determine the actual physical structure of a community and available resources to other organisms.  Brain corals are abundant in Bermuda's shallow and deep reef communities and without Diploria spp. presence,  Bermuda reefs would collapse and be altered from the elimination of such an important foundation species (Bermuda Biological Station for Research).
Calcium Deposition and  Zooanthellae Symbiosis
         
Hermatypic corals are defined as possessing zooanthellae in their tissues, specifically the gastrodermis or epidermis (Brusca et al.).  Host tissue concentrations of zooanthellae have been measured up to 30,000 cells per cubic cm.  All reef building corals are included within the hermatypic group and are light dependent due to the symbiosis, preventing colonization of depths greater than 90 m (Brusca et al.).  Zooanthellae are responsible for coral color morphology, rate of calcification, removal of metabolic wastes, and in some instances provide nutritional value through the photosynthetic production of glycerol, glucose, and alanine (Brusca et al.).  In return the zooanthellae are offered protection, nitrogen, and phosphorous, which are needed for photosynthesis.  The drawing, Zooanthellae and Calcium Deposition, shows possible calcium and carbonate pathways in the coral tissue (Brusca et al.).  Precipitate is always added to the previous top layer in the corallum, so growth is upward.  The enzyme catalyst for the reactions occurring in the calicoblastic epidermis is carbonic anhydrase (C.A.).

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Homotrema rubrum on a piece of coral 
Commonly called the sea strawberry, this foraminiferan protozoan gives Bermuda beaches a pink hue when its eroded skeleton becomes part of the sand (Thomas).  Found at Natural Arches beach, Bermuda.  Photo By T. Livdahl, Copyright 2002.
 


Major Currents of the Atlantic Basin
Drawing by Melinda Hewitt, Copyright 2002 (Robertson)


Satelite Imagery of Gulf Stream Water Temperature
(Robertson)


Unequal Heating of the Earth's surface at the Equator
 Drawing by Melinda Hewitt, Copyright 2002 (Robertson).


Wind Patterns due to Unequal Heating and Coriolis Effect
 Drawing by Melinda Hewitt, Copyright 2002 (Robertson)


Diagram One:  Model for Bermudian Coral Reef Collapse
Drawing by Melinda Hewitt, Copyright 2002 (Bertness et al.)

 

Phylum:  Cyanophyta
 
Order:  Hormogonales

Family:   Oscillatoriaceae

Genus:  Phormidium

Species:
corallyticum
Classification of Phormidium corallyticum
(Rutzler)

450x292 photo of black-band disease
BBD on brain coral
Photo By E.C. Peters.  Copyright 2000, used with permission.

450x300 close-up photo of black-band disease
Close-up of microbial mat of BBD on M. cavernosa
Photo By H. McCarty.  Copyright 2000, used with permission.

Kingdom:  Animalia

Subkingdom:  Metazoa
 
Phylum:  Cnidaria
 
Class: Anthozoa

Order: Scleractinia

Suborder:  Faviina

Family:  Faviidae
 
Genus:  Diploria

Species:
strigosa
Classification of Diploria strigosa
(Brusca & Sterrer)


Life Cycle of Anthozoans by means of Sexual Reproduction
Drawing By Melinda Hewitt, Copyright 2002 (Brusca).


Distribution of Reef Building Corals in the Pacific and Atlantic Basins
 Drawing by Melinda Hewitt, Copyright 2002 (Robertson)
.


Distribution of Reef Building Corals in the Pacific and Indian Basins
 Drawing by Melinda Hewitt, Copyright 2002 (Robertson)
.


Zooanthellae and Calcium Deposition
Drawing By Melinda Hewitt, Copyright 2002 (Brusca).


Skeleton of Polyp
Drawing By Melinda Hewitt, Copyright 2002 (Brusca).