11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 25: Predicting Reef Futures in the Context of Climate Change
25-13
Combined Effects Of Elevated Temperature And Pco2 On The Photo-Physiology Of
symbiodinium Spp. in Two Scleractinian Coral Species
Andrew BAKER 1 , Paul JONES* 1 , Ranjeet BHAGOOLI 2 , Herman WIRSHING 1 , Tom
CAPO 1 , Christopher LANGDON 1
1 Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science,
University of Miami, Miami, FL, 2 Department of Biosciences, University of Mauritius,
Reduit, Mauritius
Few studies have investigated how reef corals respond to the combined effects of thermal
stress and elevated pCO2, yet these conditions are likely to be an environmental reality of
the 21st century. To better understand how these factors interact, we undertook a 14week
pilot experiment using two Caribbean coral species, Porites furcata and
Montastraea faveolata. We exposed replicate nubbins of each species to three pCO2
levels (360, 550 and 800ppm) and three temperatures (28, 30 and 32oC); conditions were
maintained using CO2 bubblers and a computer-controlled heater-chiller system.
Additionally, we used an outdoor system and neutral density screens to expose corals to
ambient or 50% solar irradiance. Prior to the start of the experiment, coral nubbins were
acclimated to different pCO2 levels at ambient temperature (28oC) for four weeks, before
being heated at a rate of 0.3oC per day to the experimental temperatures (30 and 32oC).
Temperatures were maintained (+/- 0.2oC) for nine weeks before being returned to
ambient levels at the same rate. Corals were then monitored for five weeks during a
recovery phase. Elevated pCO2 levels were maintained throughout the acclimation,
exposure and recovery phases. Every 2-4 weeks chlorophyll fluorescence was analyzed
using an Imaging-PAM (Walz, GmbH), and coral tissue samples were taken to determine
algal symbiont densities, pigment concentrations, and Symbiodinium identity. Colorscaled
photographs documented temporal changes in tissue pigmentation and health.
Corals in the highest temperature and light treatments exhibited the most severe
bleaching, regardless of CO2 levels. However, at control temperatures (28oC), elevated
CO2 resulted in healthier corals, as evidenced by symbiont counts, photographs and
fluorescence properties. P. furcata bleached more readily than M. faveolata, although
these species also hosted different Symbiodinium. Together, these results suggest
temperature and CO2 interact in unexpected ways to influence coral health.
25-14
Ocean Acidification Changes The Early Life History Of Scleractinian Corals.
Selina WARD* 1 , Sophie DOVE 2 , david KLINE 2 , kenneth ANTHONY 2 , Ove HOEGH-
GULDBERG 1
1 Centre for Marine Studies, The University of Queensland, Brisbane, Australia, 2 Centre
for Marine Studies, The University of Queensland, brisbane, Australia
Predictions of doubling preindustrial carbon dioxide levels by the middle of this century
create serious concerns for the future state of coral reefs. Reproduction and the early life
history stages of corals have been shown to be particularly sensitive to adverse
conditions. In experiments with four species of acroporid corals, settlement of larvae and
early calcification of the newly settled corals were detrimentally affected by seawater
with reduced pH. Gametes from these species were collected, fertilised and larvae reared
at One Tree Island on the Great Barrier Reef, Australia in spring 2007. Eight thousand
Acropora millepora larvae were placed in ambient seawater or sea water of pH 7.8 or 7.6
with preconditioned terracotta tiles for the settlement period. pH was maintained by
bubbling carbon dioxide in to the seawater. Settlement success was significantly reduced
at pH 7.6 and 7.8 compared to that in ambient seawater. In a separate experiment, larvae
of four species were settled on terracotta tiles in ambient seawater. As soon as most of the
larvae had metamorphosed, the tiles were scored for the number of larvae that had settled,
calcified or were attached but not metamorphosed. Over 16 000 settled corals were used
in the experiment. The tiles were then transferred to 250L chambers of either ambient
seawater, pH of 7.8 or 7.6 for five days. Tiles were then rescored in a similar manner but
stage of calcification was also recorded. Most coral spat in the pH 7.8 and 7.6 treatments
did not calcify past the very early stages of calcification in all four species. These results
represent crucial information for the future of recruitment on coral reefs.
25-15
Effects Of Climate Change On Coral Reef Algae: Will Algae Be The Winners?
Guillermo DIAZ-PULIDO* 1 , Kenneth R.N. ANTHONY 2 , David I. KLINE 2 , Laurence
MCCOOK 3 , Selina WARD 2 , Ove HOEGH-GULDBERG 2 , Sophie DOVE 2
1 Centre for Marine Studies and ARC Centre of Excellence for Coral Reef Studies, University of
Queensland, Brisbane, St Lucia, Australia, 2 Centre for Marine Studies and ARC Centre of
Excellence for Coral Reef Studies, University of Queensland, St Lucia, Brisbane, Australia,
3 Great Barrier Reef Marine Park Authority, Townsville, Australia
Climate change predictions imply that intensified levels of thermal bleaching and ocean
acidification will lead to increasing rates of coral mortality. A general perception is that such
coral reef degradation will result in a phase shift from coral to macroalgal dominance. However,
the effects of ocean acidification and warming on tropical coral reef algae have rarely been
studied and the vulnerabilities of this key group of organisms to climate change are poorly
known. Here we explore the impacts of warming and ocean acidification due to rising
atmospheric carbon dioxide emissions on a range of coral reef macroalgae, including crustose
coralline algae (CCA) and fleshy macroalgae. We used controlled experimental conditions to
simulate acidification and warming scenarios for the Great Barrier Reef, Australia (GBR) in the
years 2050 and 2100. Preliminary results from the southern GBR indicate that both groups of
benthic algae (calcareous and fleshy) are highly sensitive to climate change. Rates of
calcification, photosynthesis, survivorship and recruitment of the CCA Porolithon onkodes
were severely reduced with increasing CO2 levels and temperature. Similarly, the fleshy
macroalga Lobophora variegata showed a 50% growth reduction under high levels of CO2
and temperature representative of levels predicted for 2100. Further experiments performed on
Lizard Island (northern GBR), confirmed that other species of coral reef macroalgae have
relatively low temperature thresholds for physiological stress. Our results suggest that the coral
reef macroalgae studied are at least as vulnerable to ocean acidification and global warming as
are corals. The high vulnerability of CCA is likely to lower the reef’s recovery and cementation
capacity, while a reduction in fleshy macroalgae may affect primary productivity with
consequences for trophic relations and ecosystem function.
25-16
Climate Change Thresholds And Coral Reef Degradation
Kenneth ANTHONY* 1 , Guillermo DIAZ-PULIDO 1
1 Centre for Marine Studies, University of Queensland, St Lucia, Australia
The healthy functioning of coral reefs is underpinned by processes operating at organism,
population, community and ecosystem levels. Current reef-resilience models provide excellent
insight into the role of coral-algae-herbivore interactions. However, predictions of how coral
reefs will behave under unprecedented climate conditions require information about stress
responses across all organizational levels. Here, we explore coral community responses along
gradients of ocean acidification and thermal stress using a new dynamic coral community model
parameterized by organism and population responses to climate-change variables from
experimental studies. Model runs for years 2050 and 2100 indicate that key framework builders
such as crustose coralline algae and Acroporid corals will gradually diminish in reef
communities on the Great Barrier Reef. Contrary to general assumptions, transitions from
healthy to degraded reefs are not triggered by the exceedence of distinct threshold values, but
show a gradual decline to depauperate states. Whether corals will be replaced by macroalgae
depends on the physiological responses of the algal species, and model runs based on recent
data suggest that shifts to barren rather than algal-dominated reefs are likely outcomes.
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