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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
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Observed
Mortality
Low BBD counts
Despite the reported prevalence of BBD, only two corals were found displaying outward
signs, one at each location. Observations were conducted during the middle
of October when there is a decline of BBD (Rutzler et al.). Although there
is conflicting evidence from Virgin Island reefs about the seasonality and
reinfection of BBD in previously diseased corals, these fall readings may
support previous observations from Bermudian reefs (Kuta et al. & Rutzler et al.). In 1983,
Rutzler reported that Bermudian BBD peaked between the months of July and
September, was uncommon during November, and not found after December.
The low counts of BBD examined in 2002 more than likely reflect the decrease of
disease activity between September and December. However, only replicate
studies in 2003 during the peak season could confirm BBD seasonality as a
continuing trend on Bermudian reefs.
Causal Agents
There
are numerous
reasons for white patches to occur, so initial causes for the observed damage on
D. strigosa can not
be assumed. Possible sources for white patches to develop on corals
include but are not limited to damselfish and parrot fish grazing, coral
bleaching, death due to increasing sediments, and previous microbial
infection (Peters 1984). A closer microscopic look and time lapse photography would help
differentiate between potential origins. Algae overgrowth indicates a
longer duration of death, whereas small patches reveal a recent infection and
large patches without overgrowth show a rapid mortality rate of recent infection (Rutzler et al.). Once again the initial cause of death cannot
be determined, however, algae overgrowth can be related to increased
sedimentation of the area (Peters & Rutzler et al.). As stated
previously in the Introduction, P. corallyticum is hypothesized to be the
causal agent for BBD, but Koch's postulate has not been confirmed, therefore the
mechanism for infection remains unknown. Regardless of the type of
mortality, damage has been done to decrease the robustness of 21 D. strigosa
out of
60, which is 35 percent.
Site
Differences
The number of corals showing no signs of disease or past death was significantly
higher at John Smith Bay than Natural Arches. This outcome may be
influenced by the location of John Smith Bay versus Natural Arches.
Castle Harbour, Bermuda has been influenced by the construction of a landing
strip for the airport and a sewage treatment plant. The harbor is an example of effluents and fishing pressure, shifting
the community structure from healthy corals to a community overgrown with algae
(Bermuda Biological Station for Research). However, researchers in Bermuda
have witnessed a reduction of algae growth with the implementation of fishing
bans. Currently chemicals dumped into Castle Harbour posses the greatest
threat to the full recovery of the reefs (Bermuda Biological Station for
Research). It is important to note that students were able to take a
boating exertion to Natural Arches and observe the reef farther from shore than
the boilers. Unfortunately, data was not taken farther off shore, but D.
strigosa on the reef appeared to be more healthy than the D. strigosa
found on the boilers, which would lead one to believe that the type of reef
rather than location may be a more important role for this experiment.
However, data collecting is needed to confirm these suspicions.
Beside anthropogenic
reasons, coral mortality and disease may have been higher at Natural Arches due
to reef type studied. Boiler reefs look like huge cups that taper at the
base on the ocean floor and are not the best substrata for corals to reside on
(Thomas). Waves are constantly breaking over the boilers and the turbidity
washes sediments on top of the corals. D. strigosa must secrete
mucus to try and slough the sediments off. If unsuccessful enough
sediments could deposit that would encourage algae growth. Due to higher
sedimentation observed at Natural Arches D. strigosa coral heads are
probably more stressed and prone to disease and mortality.
John Smith Bay is on the south shore facing the open ocean and receives little
to none tourist traffic, despite its access right off the main road. The
beach was completely deserted when research was conducted, and only a few locals
were hanging around during a previous visit. Water samples taken by
another student during Clark's visit revealed that there were no contaminants at
John Smith Bay, nor were the levels of any elements such as copper or iron
harmful (Dallaportas). It is hypothesized that due to less anthropogenic
activity and a lagoon-like reef at John Smith Bay there was a higher number of
healthy corals.
Impacts
of BBD
Biodiversity
The impacts of chronic BBD
infection may be extremely detrimental for coral reef ecosystems in Bermuda as
it primarily attacks Scleractinian
corals, although some gorgonians have been seen with the disease (Rutzler et
al.). Scleractinian corals
are reef builders and autogenic engineers, without their presence coral reef
ecosystems would not exist or be able to support the wide variety of organisms
that reside there. If constant infection does not reduce the numbers of
reef builders significantly to eliminate coral reefs, it is creating patches in
a space limited environment (Edmunds). When patches are made it allows for
algae and other primary successional species to overgrow the patch, inhibiting
the re-establishment of coral polyps in that area. If BBD persists a shift
in autogenic engineers may occur and ultimately change the habitat enough to
eliminate other species associated with coral reefs.
Future
Research
Personal
More
monitoring of sites in direct contact
with tourists and water traffic would be interesting to compare with the results
presented, as there may be significant differences and higher mortalities than
exhibited at Natural Arches. Sites of interest would be the Royal Naval
Dockyard, Somerset Island Great Sound shore, and Castle Harbour. It would
also be interesting to survey the North shore of Bermuda at Whalebone Bay,
Tobacco Bay, and Clarence Cove, by hopefully providing differences between North
and South shore sites.
Universal
The continual monitoring
of reefs is needed to understand impact entirety from chronic BBD exposure and
help prevent reef degradation. Further experiments with the microbial mat
need to confirm Koch's postulate, so a causal agent can be identified.
Supplementary etiology studies also need to be conducted as preliminary data
shows that BBD growth is only impeded by the onset of winter, light intensity,
and deficiency of host tissue (Rutzler et al.) Natural transmittance and
P. corallyticum ability to fix nitrogen are still unknown, although
laboratory experiments reveal that stressed or injured corals are more prone to
infection (Ruzler et al.) Still another puzzling factor is that plankton
tows revealed negative presence of P. corallyticum trichomes at locations
with infected corals (Carlton et al.).
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Photographs, drawings, movies, and graphics are under the
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Bermuda Biological Station for Research
Accommodations
provided by BBSR for Clark University. Located St. George, Bermuda.
Photo By D. Robertson, Copyright 2002.
Salt Marsh
A
mangrove community on Nonsuch Island.. Photo By T.
Livdhal, Copyright 2002.
Spittal
Pond
A brackish
pond located
in a natural reserve just south of John Smith Bay, Bermuda. Photo By D.
Robertson, Copyright 2002.
Whalebone
Bay
Located
West of the Bermuda Biological Station for Research.. Photo By
D. Robertson, Copyright 2002.
Church Bay
Located on the south shore
directly below Little Sound., Bermuda. Photo by T. Livdahl, Copyright 2002. |
