but Oculina diffusa appears to have declined since the
1978 survey, although Flood et al. (2005) suggest that this
may be an artifact of the different survey methodologies
used.
Factors affecting Bermuda’s reefs
While factors such as coral competitive interactions,
reproductive activity, growth rates, and diseases can affect
the composition of Bermuda’s reefs (Logan, 1992, 1998),
coral bleaching, pollution, and ship groundings are presently regarded as the most important, since they may pose
a threat to the health of Bermuda’s reefs in the long term.
Coral bleaching
Episodes of extensive bleaching in Bermudian corals,
coincident with periods of elevated summer water temperatures, occurred in 1988, 1991, 1997–1998, and 2003,
with minor bleaching in other years, but the long-term
impact of these episodes has been remarkably slight, with
coral mortality low at less than 2%. The most detailed
studies were done on the 1988 and 1991 events by Cook
et al. (1990, 1994) who showed that in both years the species most affected was the hydrozoan Millepora
alcicornis, with lesser effects on Montastrea franksi,
Diploria labyrinthiforms, and Porites astreoides. In
1988 water temperatures were the highest in the previous
38 years (over 28
C offshore), with platform margin rim
reefs the most affected. In contrast, Bermuda’s lagoonal
reefs experienced the most bleaching in the 1997–1998
bleaching event, with Millepora alcicornis again the most
affected species. Cook et al. (1990) suggested that Bermuda’s high latitude corals are thermally sensitive to elevated
temperatures that are within the normal thermal tolerance
range for corals at lower latitudes, indicating that thermal
tolerance in reef corals is inversely related to latitude.
Pollution and ship groundings
Jones (2008) surveyed main terrace coral reefs lying
300 m from a daily discharge of 2.5 million liters of
untreated sewage from the Hungry Bay outfall on the
south shore of Bermuda. He concluded that there is little
or no evidence of adverse environmental effects on the
reefs over the previous decade, in terms of species composition, abundance, and incidence of coral diseases.
The resuspension of sediments by dredging in Castle
Harbour has already been mentioned, but sediment
resuspension by ship propellers is another form of anthropogenic pollution which can have harmful effects on reefs.
Unfortunately, most of this takes place through two shipping channels that cross the central lagoon where otherwise healthy reefs are abundant. Increases in the sizes of
ships have led to a call to redredge and substantially alter
the path of the shipping channels, which is likely to have
a harmful effect on the condition of lagoonal and rim reefs.
A previously serious problem was the effect of ship
groundings, which was studied by Cook et al. (1994).
They listed the major ship groundings from 1940 to
1993 and concluded that damaged sites have been
extremely slow to recover, mainly because of poor recruitment and slow growth of corals, particularly Diploria
(Smith, 1992). They estimated a period of 100–150 years
for coral coverage and species diversity to be restored on
such reefs. Predictably, reef fish populations in these areas
have been reduced and may remain so until sufficient coral
growth has accrued. One further problem is the possible
inhibition of recruitment from biocides in antifouling
paint from the hulls of grounded ships (Jones, 2007). To
prevent any further risks to the Bermuda reefs, the Bermuda government has set up a sophisticated radar surveillance system which has effectively prevented further
grounding since 1993. This system permits the monitoring
of vessel movements to ensure that they keep clear of the
International Maritime Organisation (IMO) and International Association of Marine Aids to Navigation and
Lighthouse Authorities (IALA)-sanctioned Area To Be
Avoided – a 20 nautical mile “no go” zone around the
island to protect Bermuda’s reefs. However, since 2000,
a dramatic increase in marina and nearshore development,
the addition of larger cruise ships, and a new ship pier
appear to be just the start of an increase in large-scale negative impacts on the marine environment, indicating the
need for stronger planning policies and better resource
management.
Summary
Bermuda at 32
N supports the highest latitude coral reefs
in the North Atlantic and one of the highest in the world.
Algal–vermetid cup reefs, particularly well developed
off the south shore of the island, represent an unusual reef
type rarely found elsewhere in the world. While corals,
the main reef builders, show lower diversity than the
Caribbean, presumably in response to cool winter water
temperatures, nevertheless the main physiographic zones
of fore-reef slope, main terrace, rim, and lagoon all support thriving coral reefs which have as yet been little
affected by coral bleaching or anthropogenic influences
such as pollution and ship groundings. Only reefs in the
inshore waters of Castle Harbour have suffered long-term
deleterious effects from extensive dredging for airfield
construction in 1941–1943. However, there is a need for
stronger planning policies and better resource management in the whole area if the Bermuda reefs are to remain
healthy and protected.
Bibliography
Cook, C. B., Logan, A., Ward, J., Luckhurst, B., and Berg, C. J.,
1990. Elevated temperatures and bleaching on a high latitude
coral reef: the 1988 Bermuda event. Coral Reefs, 9, 45–49.
Cook, C. B., Dodge, R. E., and Smith, S. R., 1994. Fifty years of
impacts on coral reefs of Bermuda. In Ginsberg, R. N. (ed.), Proceedings of the Colloquium on Global Aspects of Coral Reefs:
Health, Hazards and History, Rosenstiel School of Marine and
Atmospheric Science, University of Miami, Miami, 1993,
pp. 160–166.
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BERMUDA
1978 survey, although Flood et al. (2005) suggest that this
may be an artifact of the different survey methodologies
used.
Factors affecting Bermuda’s reefs
While factors such as coral competitive interactions,
reproductive activity, growth rates, and diseases can affect
the composition of Bermuda’s reefs (Logan, 1992, 1998),
coral bleaching, pollution, and ship groundings are presently regarded as the most important, since they may pose
a threat to the health of Bermuda’s reefs in the long term.
Coral bleaching
Episodes of extensive bleaching in Bermudian corals,
coincident with periods of elevated summer water temperatures, occurred in 1988, 1991, 1997–1998, and 2003,
with minor bleaching in other years, but the long-term
impact of these episodes has been remarkably slight, with
coral mortality low at less than 2%. The most detailed
studies were done on the 1988 and 1991 events by Cook
et al. (1990, 1994) who showed that in both years the species most affected was the hydrozoan Millepora
alcicornis, with lesser effects on Montastrea franksi,
Diploria labyrinthiforms, and Porites astreoides. In
1988 water temperatures were the highest in the previous
38 years (over 28
C offshore), with platform margin rim
reefs the most affected. In contrast, Bermuda’s lagoonal
reefs experienced the most bleaching in the 1997–1998
bleaching event, with Millepora alcicornis again the most
affected species. Cook et al. (1990) suggested that Bermuda’s high latitude corals are thermally sensitive to elevated
temperatures that are within the normal thermal tolerance
range for corals at lower latitudes, indicating that thermal
tolerance in reef corals is inversely related to latitude.
Pollution and ship groundings
Jones (2008) surveyed main terrace coral reefs lying
300 m from a daily discharge of 2.5 million liters of
untreated sewage from the Hungry Bay outfall on the
south shore of Bermuda. He concluded that there is little
or no evidence of adverse environmental effects on the
reefs over the previous decade, in terms of species composition, abundance, and incidence of coral diseases.
The resuspension of sediments by dredging in Castle
Harbour has already been mentioned, but sediment
resuspension by ship propellers is another form of anthropogenic pollution which can have harmful effects on reefs.
Unfortunately, most of this takes place through two shipping channels that cross the central lagoon where otherwise healthy reefs are abundant. Increases in the sizes of
ships have led to a call to redredge and substantially alter
the path of the shipping channels, which is likely to have
a harmful effect on the condition of lagoonal and rim reefs.
A previously serious problem was the effect of ship
groundings, which was studied by Cook et al. (1994).
They listed the major ship groundings from 1940 to
1993 and concluded that damaged sites have been
extremely slow to recover, mainly because of poor recruitment and slow growth of corals, particularly Diploria
(Smith, 1992). They estimated a period of 100–150 years
for coral coverage and species diversity to be restored on
such reefs. Predictably, reef fish populations in these areas
have been reduced and may remain so until sufficient coral
growth has accrued. One further problem is the possible
inhibition of recruitment from biocides in antifouling
paint from the hulls of grounded ships (Jones, 2007). To
prevent any further risks to the Bermuda reefs, the Bermuda government has set up a sophisticated radar surveillance system which has effectively prevented further
grounding since 1993. This system permits the monitoring
of vessel movements to ensure that they keep clear of the
International Maritime Organisation (IMO) and International Association of Marine Aids to Navigation and
Lighthouse Authorities (IALA)-sanctioned Area To Be
Avoided – a 20 nautical mile “no go” zone around the
island to protect Bermuda’s reefs. However, since 2000,
a dramatic increase in marina and nearshore development,
the addition of larger cruise ships, and a new ship pier
appear to be just the start of an increase in large-scale negative impacts on the marine environment, indicating the
need for stronger planning policies and better resource
management.
Summary
Bermuda at 32
N supports the highest latitude coral reefs
in the North Atlantic and one of the highest in the world.
Algal–vermetid cup reefs, particularly well developed
off the south shore of the island, represent an unusual reef
type rarely found elsewhere in the world. While corals,
the main reef builders, show lower diversity than the
Caribbean, presumably in response to cool winter water
temperatures, nevertheless the main physiographic zones
of fore-reef slope, main terrace, rim, and lagoon all support thriving coral reefs which have as yet been little
affected by coral bleaching or anthropogenic influences
such as pollution and ship groundings. Only reefs in the
inshore waters of Castle Harbour have suffered long-term
deleterious effects from extensive dredging for airfield
construction in 1941–1943. However, there is a need for
stronger planning policies and better resource management in the whole area if the Bermuda reefs are to remain
healthy and protected.
Bibliography
Cook, C. B., Logan, A., Ward, J., Luckhurst, B., and Berg, C. J.,
1990. Elevated temperatures and bleaching on a high latitude
coral reef: the 1988 Bermuda event. Coral Reefs, 9, 45–49.
Cook, C. B., Dodge, R. E., and Smith, S. R., 1994. Fifty years of
impacts on coral reefs of Bermuda. In Ginsberg, R. N. (ed.), Proceedings of the Colloquium on Global Aspects of Coral Reefs:
Health, Hazards and History, Rosenstiel School of Marine and
Atmospheric Science, University of Miami, Miami, 1993,
pp. 160–166.
122
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