11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 25: Predicting Reef Futures in the Context of Climate Change
25-5
Going, Going, Gone? Are 1998 And 2005 Signs Of The Future For Coral Reefs?
C. Mark EAKIN* 1 , Jessica A. MORGAN 2 , Scott F. HERON 2 , Janice M. LOUGH 3 ,
William J. SKIRVING 2 , Gang LIU 2 , Tyler R. L. CHRISTENSEN 2 , Dwight K.
GLEDHILL 2 , Alan E. STRONG 4
1 Coral Reef Watch, National Oceanic and Atmospheric Administration, Silver Spring,
MD, 2 Coral Reef Watch, IMSG at National Oceanic and Atmospheric Administration,
Silver Spring, MD, 3 Australian Institute of Marine Science, Townsville MC, QLD,
Australia, 4 Coral Reef Watch, AJH Environmental at National Oceanic and Atmospheric
Administration, Silver Spring, MD
The 2005 Caribbean coral bleaching event was the most extensive and devastating on
record for this basin. The greatest bleaching and mortality were seen along the Antillean
Arc where the thermal stress exceeded any seen in the Caribbean during the previous 21
years of satellite data and 100 years of gridded, in situ temperature reconstructions. Coral
bleaching exceeded 90% at many sites, and extended across most of the wider-Caribbean
region; mortality exceeded 40% at many sites. The 2005 Caribbean bleaching rivals that
seen in the Indo-Pacific in 1998.
Climate change is rapidly modifying the environmental envelope of coral reefs through
both increased thermal stress and ocean acidification. Both the thermal and chemical
limits that control coral survival and reef growth will likely be passed before 2100
assuming even conservative projections reported in the 4th Assessment Report of the
Intergovernmental Panel on Climate Change. While local stresses currently dominate,
coral reefs are increasingly confronted with global-scale changes due to rising
greenhouse gas concentrations. The 1998 and 2005 bleaching events showed one of the
key problems that climate change poses to coral reefs: warming oceans can kill corals in
even the best-managed or most remote coral reefs. Global action to curb greenhouse gas
emissions is certainly needed. However, because of the time delay between emission
reductions and climate stabilization, emission curbs are not sufficient by themselves.
Steps need to be taken to increase the resilience of coral reefs to survive bleaching, ocean
acidification, and other climate change threats.
25-6
Forecasting Storm-Mediated Changes in Reef Coral Assemblages
Joshua MADIN* 1,2 , Michael O'DONNELL 3 , Sean CONNOLLY 4
1 Department of Biological Sciences, Macquarie University, New South Wales, Australia,
2 National Center for Ecological Analysis and Synthesis, University of California, Santa
Barbara, Santa Barbara, 3 Marine Science Institute, University of California, Santa
Barbara, Santa Barbara, CA, 4 School of Marine and Tropical Biology, James Cook
University, Townsville, Australia
Reef corals build physical structures that provide essential ecosystem services including
substrate for settlement, protection from predators, and shelter from disturbances.
Restricted to shallow-water equatorial regions, corals continually experience moderate
wave forces and intermittent bombardment by severe hydrodynamic disturbances.
Predicted increases in severity of tropical storms and hypothesized weakening of reef
carbonate materials through seawater acidification will necessarily affect the ability of
corals to mechanically withstand hydrodynamic disturbances, but how and to what extent
these will change coral community assemblages remains unclear.
We use field measurements of colony mechanical vulnerability and an existing
mathematical model to forecast changes in coral assemblage structure following tropical
storms under two reef strength scenarios: present-day reef strength measurements and
future estimates assuming a 50% weakening due to acidification. There are dramatic,
morphological-specific differences in the expected numbers of remaining colonies.
Larger disturbances result in dramatic decreases in the median size of the competitively
dominant species. As a consequence, relative cover of the other species increases. At
some point over the continuum of disturbance intensities each species dominates the postdisturbance
assemblage both in relative cover and mean colony size, but absolute
numbers of remaining colonies become sparse for all populations. Hypothetical halving
substrate strength exacerbates these differences: certain populations lose up to 20% more
colonies than present-day conditions and the dominance hierarchy shifts at lower
disturbance intensities.
Both colony size and proportion cover have consequences for recovery following
disturbances. For example, larger colonies tend to be more resistant physical abrasion and
disease, have greater competitive and reproductive potential, and command greater
proportions of limited substrate space. The number of associated species supported by a
colony scales with both colony size and morphological complexity. Therefore, the
forecasted dominance of mechanically robust, morphologically simple coral species in
future reef environments will lead to decreases in whole-reef biodiversity.
25-7
Seasonal To Decadal Changes in The Carbonate System Of The North Pacific Ocean
Richard FEELY* 1 , Chris SABINE 2 , Kathryn FAGAN 3
1 OCRD, PMEL/NOAA, Seattle, WA, 2 PMEL/NOAA, Seattle, WA, 3 University of Washington,
Seattle, WA
The addition of fossil fuel carbon dioxide to the atmosphere is rapidly changing seawater
chemistry and the calcium carbonate saturation state of the world’s oceans as a result of the
acidifying effects of CO2 on seawater. This acidification makes it more difficult for corals to
build their skeletons. Repeat hydrographic and coastal cruises in the North Pacific show direct
evidence for ocean acidification. The dissolved inorganic carbon increases, of about 10-15 µmol
kg-1 in surface and intermediate waters over the past 15 years, are consistent with
corresponding pH decreases of approximately 0.025 units over large sections of the northeastern
Pacific. These dramatic changes can be attributed, in most part, to anthropogenic CO2 uptake
by the ocean over the past decade. These data verify earlier model projections that the oceans
are undergoing ocean acidification as a result of the uptake of carbon dioxide released as a
result of the burning of fossil fuels. From these results we have estimated an average upward
migration of the aragonite saturation horizon of approximately 1 m yr-1 in the North Pacific.
Such shoaling is due to the effects of anthropogenic CO2, ventilation and biological respiration
processes in the surface and intermediate waters. We have also instrumented a Coral Reef
Instrumented Monitoring and CO2 Platform (CRIMP-CO2) in southern Kaneohe Bay in
December 2005 and have been collecting data almost continuously since that time. The CO2
mooring collects air pCO2 and pO2 and surface water pCO2, pO2, temperature, and salinity
data every three hours. The results show a seasonal trend in the pCO2 data with higher levels
occurring during the summer months and lower levels occurring during the winter. Changes in
water temperature had a small effect on surface water pCO2 levels and seasonal changes in
pCO2 are driven mainly by changes in calcification.
25-8
Marine Biocalcifiers Exhibit Mixed Responses To Co2-Induced Ocean Acidification
Justin RIES* 1 , Anne COHEN 1 , Daniel MCCORKLE 1
1 Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA
We have conducted 6-month laboratory experiments to investigate the effect of CO2-induced
reductions in seawater CaCO3 saturation state on biocalcification by 21 aragonitic and calcitic
(low-high Mg) taxa representing eight of the major marine calcifying groups: Chlorophyta;
Rhodophyta; Crustacea; Bivalvia; Gastropoda; Annelida; Cnidaria; and Echinodermata. The
CaCO3 saturation states of the experimental seawaters, constrained by intercalibrated
determinations of pH, alkalinity, and DIC, were attained with bubbled air-CO2 mixtures of 380
(ambient), 560, 840, 2240 ppm CO2, yielding Ωarag of 3.2 (ambient), 2.4, 1.8, 0.8, respectively.
Net calcification/dissolution rates obtained from buoyant weighing reveal that nearly half of the
species exhibited reduced calcification, and even dissolution, in the elevated-CO2 seawaters.
However, each of the major taxonomic groups that we investigated contained at least one
species (9 species in total) that exhibited increased calcification in the moderately (560 ppm) or
extremely (840 or 2240 ppm) elevated CO2 conditions. This surprising observation runs
counter to the conventional belief that CO2-induced ocean acidification necessarily reduces
calcification rates in marine organisms. Rather, some calcifying organisms appear to benefit
from the elevated DIC, either directly through photosynthesis or indirectly through
calcification, which requires conversion of HCO3 - to CO3 = via proton-pumping from the
organism’s internal calcifying medium. No single trait governed the pattern of responses
amongst the organisms. A confluence of factors, including skeletal mineral polymorph
solubility, proton-pumping efficiency, and the utilization of photosynthesis, appears
determinant of each organism’s response.
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