Global Climate Change and Coral
Reefs:
A case study in the Phoenix Islands
The
catastrophic mortality of coral reefs in the Phoenix Islands due to global
warming was featured in An
Inconvenient Truth: Coral reefs are an early warning sign for global
warming.
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Global Climate Change and Coral
Reefs:
A case study in the Phoenix Islands
The Planetary Coral Reef Foundation’s (PCRF)
sailing ship visited the remote Phoenix Islands of the
Central Equatorial Pacific Ocean in Nov/Dec 2004. There the crew discovered that
a massive coral mortality event had occurred in Kanton Island between June
2002 and November 2004. There is little or no significant input from any
source of land based pollution on Kanton 2,3,4 and no obvious
populations of coral predators such as Acanthaster planci. The most
plausible explanation for the mass mortality of coral species and coverage is
death due to persistent, excessive water temperatures recorded in the Phoenix
Islands by NOAA/NESDIS (www.osdpd.noaa.gov)
from the months of August 2002 through March 2003. This case study is
extremely important because these corals were devastated by a planetary
phenomena, not a local one.
These islands were considered by Dr. David
Obura, a specialist in coral reefs, to be one of “Earth’s
last pockets of primal ocean…those underwater havens
that have remained unspoiled as long as the ocean can remember”1. Inside
the lagoon of Kanton Island the luxuriant
community of Acropora spp. corals suffered near 100% mortality and
there was an estimated 62% mortality of corals along the reefs outside the
lagoon. The fish populations were not as noticeably affected yet and a total
of 153 species of fish were identified along transects.
In 2004, coralline algae
overgrowing dead corals on the leeward side of Kanton Island were common.
In the Maldivian Islands after the 1998 bleaching event, such overgrowth was
interpreted as an indication of reef regeneration because coralline algae
are suitable substrate for larval recruitment5. It is also
likely that the large population of herbivorous fish helped to limit the
growth of macroalgae which in turn encouraged the growth of the coralline
algae. Coralline algae were observed by the crew at many other reefs in the
South Pacific including Papua New Guinea (Kitava), French Polynesia (Bora
Bora), Cook Islands (Aitutaki), Tokelau (Atafu) and Tuvalu (Nukufetau,
Funafuti). But the team had never before encountered such a high level of
coverage as was seen on the outer reefs of Kanton, Manra and Enderbury
Islands. Curiously, inside the Kanton Atoll lagoon, the dead Acropora
were colonized by algal mat communities, which trap fine sediment. Unlike
the coralline algae, this substrate may slow, or even inhibit, coral
recruitment. Only time and careful studies will reveal if this coral
community in the lagoon will regenerate or travel down the ecological path
to an algal-dominated community.6
For over twenty-five years, scientists have
been discussing the possibility that coral reefs are the indicator of the
health of the oceans and are the “early warning sign” like the canary was for
the coal miners. With the well documented studies by Dr. Greg Stone and
other scientists who were
last at Kanton Atoll as of July 2002 4 and the recent study
by PCRF in 2004, this finding is another example indicating that an abnormal
rise in sea surface temperature can cause massive mortality of reef systems.
With the predictions of accelerated global warming 7, the tragic
example of massive coral mortality in Kanton is both a clear example that
global warming has devastating implications for life as well as a case study
of how this reef and its fish populations will adapt and recover over time.
Support should be given to conduct
repeat studies of the Kanton Atoll in order to closely observe the
progress of the reef's recovery, and to support the Government of Kirabati
with their exemplary efforts over the years to protect their reefs
and fish stocks. Very likely the healthy fish populations are helping
to keep the reef from becoming an algae garden, and this significant vector
will assist the reef to recover.
1. Jokiel, P.L., Maragos, J.E. Reef
corals of Canton atoll: II. local distribution. Atoll Research Bulletin
221 (1978).
2. Stone, G., et al. Marine Biological
Surveys of the Phoenix Islands: Summary of Expedition Conducted from June
24-July 15, 2000 (2001).
3. Stone, G. et al. Summary of Marine
and Terrestrial Assessments Conducted in the Republic of Kiribati, June 5-July
10, 2002 (2002).
4. Stone, G. 2004. Phoenix Islands: a
coral reef wilderness revealed. National Geographic Magazine, 205 (2),
48 – 64 (2004).
5. Loch, K., W. Loch, H.
Schuhmacher, W.R. See. 2004. Coral Recruitment and regeneration on a
Maldivian reef 21 months after the coral bleaching event of 1998. Marine
Ecology, 23 (3), 219-230.
6. Pandolfi, J.M.,
J.B.C. Jackson, N. Baron, et al. 2005. U.S. Coral Reefs on
the Slippery Slope to Slime? Science, 307 (5716), 1725-1726.
7. Kerr, R.A. Climate modelers see
scorching future as a real possibility. Science 307 (2005).
NOAA/NESDIS image showing the pink elevated degree
heating weeks, November 2002. The white star is the approximate location of
the Phoenix Islands.
Alling. A., Doherty, O., Logan,
H., Feldman, L., Dustan, P. 2007. Catastrophic Coral Mortality in the Remote Central Pacific Ocean:
Kirabati Phoenix Islands. Atoll Research Bullentin (in press)
