11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 25: Predicting Reef Futures in the Context of Climate Change
25-34
Relationship Between Historical Sea-Surface Temperature Variability And Climate
Change-Induced Coral Mortality in The Western Indian Ocean
Mebrahtu ATEWEBERHAN* 1 , Tim MCCLANAHAN 1,2
1 Coral Reef Conservation Project, Wildlife Conservation Society, Mombasa, Kenya,
2 Marine Programs, Wildlife Conservation Society, New York
Coral reefs have become one of the major casualties of climate change. Many of the
world’s coral reefs suffered high coral mortality during the 1998 ENSO, with the highest
mortality in the western Indian Ocean (WIO). We present results of a meta-analysis of
field data on change in coral cover across the 1998 ENSO event for 36 major reef areas in
the WIO. Average coral cover declined by ~40 % across the event with the highest
mortality in the central and northern regions, with the exception of the Red Sea and Gulf
of Aden. Based on multivariate analysis of SST properties, WIO reefs were categorized
into 3 major groups of differing coral mortalities. Basin-wide change was highly variable
and related to historical sea-surface temperature (SST) variability. Mortality was
negatively associated with standard deviation (SD) SST until SD ~2.3, with increasing
flatness of the SST frequency distributions. It increased with further increase in SD as the
SST distributions became strongly bimodal. The predictable environmental patterns
associated with the mortality suggest that future change during a warmer and more
variable climate can be predicted and management priorities directed accordingly.
25-35
Corals Resisting Warming – The Importance Of Experience
Thomas OLIVER* 1 , Stephen PALUMBI 2
1 Hopkins Marine Station, Stanford University, Pacific Grove, CA, 2 Hopkins Marine
Station, Stanford Unveristy, Pacific Grove, CA
Studies have demonstrated that corals hosting certain genotypes of the dinoflagellate
symbiont Symbiodinium sp. better resist the negative effects of temperature increases.
However, the role of these resistant genotypes and the relative importance of other
mechanisms of adaptation are little known. Perfomed on Ofu Island, American Samoa,
this study compared resistance to temperature stress among groups of the coral Acropora
hyacinthus that not only hosted distinct symbionts but also were sampled from two
distinct habitats –a lagoonal pool with extreme swings in its temperature profile and a
more moderate pool. Replicate branches were taken from 32 corals, and housed in either
a tank held at ambient temperature, or a tank held ~2.5 degrees C higher. Sublethal
effects were monitored using a proxy for the photosynthetic health of the symbionts, the
maximum quantum yield (MQY) of PSII, measured before dawn. Visual bleaching was
recorded using a color reference card, and mortality was indicated by coral tissue
sloughing off the skeleton. The experiment ran until ~50% of corals in the elevated tank
experienced mortality (4-6 days), and was repeated 3 times. MQY measurements showed
that there was both a genotype and pool effect: corals fared better either if they hosted a
resistant genotype, or came from the variable pool. However, with regard to both color
loss and mortality, the only discernable effect was higher resistance of the corals from the
variable pool. As the coral populations in our experiment were not genetically distinct,
these results highlight the importance of acclimatization and suggest that bleaching
thresholds can vary considerably depending on a coral’s environmental experience.
25-36
The Effect Of Thermal History On The Susceptibility Of Reef-Building Corals To
Thermal Stress
Rachael MIDDLEBROOK* 1
1 Centre for Marine Studies, University of Queensland, Brisbane, Australia
Thermal stress causes the breakdown of the relationship between corals and their symbionts
(bleaching). This symbiosis may acclimate to changes in the environment, thereby potentially
modifying the environmental threshold at which they bleach. While a few studies have
examined the acclimation capacity of reef-building corals, our understanding of the underlying
mechanism is still in its infancy. This research focuses on the role of recent thermal history in
influencing the response of both corals and symbionts to thermal stress, using the reef-building
corals A.aspera and A.formosa. Symbionts of A.aspera corals that were exposed to 31 ºC for 48
h one or two weeks prior to a six-day simulated bleaching event (when corals were exposed to
34 ºC) were found to have more effective photoprotective mechanisms. These mechanisms
included changes in non-photochemical quenching and xanthophyll cycling. These differences
in photoprotection were correlated with decreased loss of symbionts, with those corals that were
not prestressed performing significantly worse, loosing over 40% of their symbionts and having
a greater reduction in photosynthetic efficiency. Significant differences were also found in the
performance and short-term recovery of A.formosa corals exposed to a rapid and a slow
progressive heating rate. A slow build up in temperature induced acclimation seen through lipid
concentrations, symbiont densities, respiration and photoprotective mechanisms. These results
are important as they show that thermal history, in addition to light history, can influence the
response of reef-building corals to thermal stress and therefore have implications for the
modeling of bleaching events. However, whether acclimation is capable of modifying the
thermal threshold of corals sufficiently to cope as sea temperatures increase in response to
global warming has not been explored fully.
25-37
Bleaching, El Nino, And El Nina: 13 Years Of Seasonal Analysis Of Reef-Building Corals
in Florida, The Bahamas, And The Caribbean
William FITT* 1 , Dusty KEMP 1 , Xavier HERNANDEZ-PECH 2 , Roberto IGLESIAS-
PRIETO 2 , Jennifer MCCABE 1 , Tom SHANNON 1 , Brigitte BRUNS 3 , Gregory SCHMIDT 3
1 Odum School of Ecology, University of Georgia, Athens, GA, 2 Universidad Nacional
Autónoma de México, Puerto Morelos, Mexico, 3 Plant Sciences, University of Georgia, Athens,
GA
Six species of coral were monitored approximately every three months for 13 years in the
Florida Keys, 11 years in the Bahamas, and 4 years in Puerto Morelos , Mexico. Generally all
species exhibited peaks in ash-free dry weight (AFDW) and density of zooxanthellae
(Symbiodinium) during the winter/spring and lowest values in the late summer.
Certain generalities include: shallow water (1-4 m) species showed higher AFDW and densities
of symbionts compared to deep water populations (13 m). Many of the species of corals had one
type of Symbiodinium in shallower colonies, and a different type of Symbiodinium in deeper
colonies. The trends of AFDW of the tissues from corals follow the density of Symbiodiinium,
some three-months later.
Each species of coral appears to have a minimum value of AFDW, below which the coral tends
to die. For instance, the AFDW of 2 mg/cm2 appears to be a minimum for Acropora
cervicornis, with two populations dying when they went below this level in the Bahamas,
compared with one population that is alive and above the minimum AFDW.
During the 1997/8 El Niño the AFDW and symbiont densities were extremely low, but the next
winter (1999) there was a spike in the density of symbionts followed by a slow recovery in
AFDW. There were smaller spikes after the El Niño's of 2002 and 2005. During La Niña the
temperature extremes were less than normal, and the corals showed values for AFDW and
density of Symbiodinium well above the minimum levels. Visible bleaching was only observed
for a few of the coral species, occurring at the end of El Niño events.
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