11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 3: Calcification and Coral Reef - Past and Future
3-9
Are Abiogenic Processes Sufficient To Describe The Formation Of Coral Skeletons?
Michael HOLCOMB* 1 , Anne COHEN 1 , Rinat GABITOV 2 , Jeffrey HUTTER 3
1 Woods Hole Oceanographic Inst., Woods Hole, MA, 2 California Institute of
Technology, Pasadena, CA, 3 The University of Western Ontario, London, ON, Canada
Micronscale analytical and imaging techniques were used to compare morphological
features and chemical signatures of abiogenic aragonites precipitated experimentally
from seawater, and the aragonitic skeleton of scleractinian corals. Morphological features
shared between abiogenic aragonites and coral aragonites include the spherulitic
morphologies of the crystal bundles, the occurrence of granular crystals in nucleation
regions and fibrous crystals in growth regions, and the presence of fine bands, composed
of granular crystals, oriented perpendicular to the direction of fibrous growth. Fusiformshaped
crystals, morphologically similar to those found in corals, were also produced
experimentally. Under experimental conditions, crystal morphology appears linked to
saturation state. Only under highly supersaturated conditions were fusiform crystals
formed (Omega > 25), at slightly lower saturation states, granular crystals with
morphologies similar to those found in the centers of calcification of coral skeletons were
produced. Aragonite fibers with morphologies similar to those found in fiber bundles in
coral skeletons were produced at moderate supersaturation states, while at the lowest
saturation states (Omega 4-5), the aragonite fibers formed were much broader and more
widely separated than those found in coral skeletons. In both abiogenic aragonites and
coral skeletons, the granular nucleation regions are characterized by high Mg/Ca ratios
compared with the fibrous growth regions. Further, abiogenic aragonite and coral
skeletons show similar patterns of fluoresence when stained with acridine orange, with
regions of granular crystals appearing to fluoresce more intensely. These data suggest
that many features of coral skeletons are also characteristic of abiogenic aragonite grown
from seawater. Based on these observations, cycles in the saturation state of the coral’s
calcifying fluid is proposed as a plausible explanation for many of the features observed
in coral skeletons.
3-10
Coral Skeletons: From Calcium Carbonate To Intricate Architecture
Elizabeth GLADFELTER* 1
1 Marine Policy Center, Woods Hole Oceanographic Institution, Woods Hole, MA
A coral skeleton is an intricate architecture of aragonite forming a scaffolding to support
the soft tissues of the animal. Our understanding of the inorganic and organic chemical
processes that result in these beautiful and elaborate structures is still evolving. This is
due partly to the fact that many studies of coral skeletal growth and calcification are
complicated by the role of zooxanthellae in enhancing rates of calcification. Another
important aspect is reconciling the physical (and temporal) scales at which various
studies were conducted. Some recent papers have emphasized the role of an organic
matrix in coral calcification, while others have focused on the essentially inorganic
processes of crystal nucleation and growth that can be produced without organic input. A
model of biomineralization must address the chemistry operative between collections of
inorganic atoms (e.g., nucleation centers; crystal faces) and the multiple arrays of
molecules arranged across organic surfaces (e.g., insoluble proteins, lipid membranes).
We need to understand how molecular-based interactions are integrated into higher levels
of organization and dynamics.
In this work, I examine two key elements of a biomineralization model: (1) the
morphology and site of deposition and growth of the various types of crystals that
compose the skeleton; and (2) the role of organic macromolecules in controlling the
synthesis, construction and organization of the architecture of the skeletal form. The
result is a model of biomineralization of corals that recognizes the production of the
skeleton as an example of “organized-matter chemistry” involving chemical
composition, synthesis and emergence of organized architectures and complex forms.
This model identifies critical areas for further research to better understand this crucial
process, i.e. coral calcification, in coral reefs.
3-11
Large-Scale, In-Situ Measurements Of Coral Reef Community Metabolism Using An
Integrated Control Volume
Cameron MCDONALD* 1 , Robert DUNBAR 2 , Jeffrey KOSEFF 1 , Stephen MONISMITH 1 ,
Ove HOEGH-GULDBERG 3 , Matthew REIDENBACH 4
1 Civil and Environmental Engineering, Stanford University, Stanford, CA, 2 Geological and
Environmental Sciences, Stanford University, Stanford, CA, 3 Center for Marine Studies,
University of Queensland, Brisbane, Australia, 4 Department of Environmental Sciences,
University of Virginia, Charlottesville, VA
In-situ, ecosystem level measurements of inorganic carbon fluxes in a coral reef are critical to
understanding how the reef functions and interacts with the surrounding ocean; furthermore,
ongoing monitoring of this community metabolism will be essential to assess the effects of
ocean acidification on reef health and net community calcification. Traditional methods for
measuring reef metabolism have had some limitations, for example: constraints on location and
flow regime, and lack of spatial or temporal resolution. The method presented here utilizes a
combined Eulerian-Lagrangian control volume approach wherein carbon system parameters are
monitored in place, under natural flow conditions. This enables calculation of inorganic carbon
fluxes on time-scales of minutes to hours in almost any reef sub-environment. A 20m by 40m
Integrated Control Volume was deployed on the fore-reef of Heron Island, Australia (23° 27' S,
151° 55' E) as a test of the ICV concept. Carbon system parameters were measured
continuously by pumping seawater from 6 different depths at each corner of the volume. To
measure seawater fluxes the hydrodynamic field within and adjacent to the ICV was
characterized using 1200 kHz Acoustic Doppler Current Profilers, high frequency (25 Hz)
Acoustic Doppler Velocimeters, and thermistor strings set at different distances down the reef
slope. We measured clear gradients in carbon system parameters, vertically, along the flow, and
also in the cross-shelf direction. The most consistent gradients were in the cross-shelf direction
with total dissolved inorganic carbon (TDIC or ΣCO2) lower inshore during the day and higher
at night. Night sampling showed a strong respiration signal. Periods of both net dissolution, and
net calcification were observed. The ICV method shows promise for in-situ monitoring of reef
metabolism; potentially allowing determination of the relationships between primary
production, carbonate saturation state, and rates of net community calcification.
3-12
Studies Of The Calcfication Rate Of The Coral Reefs in The Bight Of Parguera, Puerto
Rico
Chris LANGDON* 1 , Jorge CORREDOR 2
1 MBF, Uni. of Miami/ RSMAS, Miami, FL, 2 Dept. of Marine Science, Uni. of Puerto Rico,
Mayaguez, Puerto Rico
Little is known about how the calcification of coral reefs in the Caribbean has changed in the
past 30 years. As a result it is not possible to document how this important reef-building and
sustaining process has changed in response to increasing sedimentation, eutrophication,
outbreaks of disease, collapse of Diadema, overfishing, bleaching events and increasing ocean
acidification. With the saturation state of the surface ocean currently declining at a rate of -
0.013 to -0.025 units y -1 we can expect a decrease in calcification of 0.4 to 0.8% y -1 . If a
warming rate of 0.02 to 0.06°C y -1 is factored in based on IPCC’s low emission (B1) and higher
emission (A1F1) scenarios the rate of decline could increase to 0.9 to 2.2% y -1 and these
calculations only consider the direct effect of temperature on calcification. Corals also exhibit a
thermal threshold of 2-3°C above the normal summer ambient temperature at which point
calcification abruptly shuts down. In response to a clear need to establish both a baseline and to
better understand the response to climate change a study of the community calcification of the
coral reefs in the Bight of Parguera, Puerto Rico has been undertaken. Results indicate that in
May 2007 salinity normalized total alkalinity (NTA) decreased from 2278 uEquiv kg -1 offshore
to 2247 at the outer rank of reefs to 2130 at the reefs closest to shore. With a detailed
knowledge of bathometry and the residence time of the waters the spatial distribution of NTA
could be turned into a map of the community calcification of the region. If the average draw
down of NTA relative to offshore source water is taken as 74 uEquiv kg -1 , the mean water depth
as 3 m and the average residence time as 14 days then the average community calcification rate
would be 8 mmol CaCO3 m -2 d -1 or about 30% of the average complete reef-system rate
established by Kinsey (1985).
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