11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 3: Calcification and Coral Reefs - Past and Future
3.45
Physiological Vs. Environmental Factors Triggering Skeletal Mineralogy And
Geochemistry in Scleractinian Corals
Jaroslaw STOLARSKI* 1 , Anders MEIBOM 2
1 Institute of Paleobiology, Polish Academy of Sciences, Warsaw, Poland, 2 Muséum
National d'Histoire Naturelle, Paris, Paris, France
Environmental influence on biomineralization processes of scleractinian corals is widely
acknowledged, and it is interpreted from the various skeletal geochemical and isotopic
proxies. However, it is still a matter of debate whether those skeletal geochemical
signatures reflect mainly polyp’s physiological response to the changed environment
(biologically controlled calcification) or represent direct migration of the ions from the
ambient seawater to the mineralization sites (physicochemical model of calcification). By
analogy with chemical CaCO3 precipitation, it has been proposed that the Mg/Ca ratio of
seawater may also directly control the mineralogy of hypercalcifying organisms such as
corals, favoring those with aragonitic mineralogy in seas with high Mg/Ca ratio or those
with calcite mineralogy in seas with low Mg/Ca ratio. The Mg/Ca ratio of seawater
changed dramatically through the scleractianian evolutionary history and was probably
the lowest during the Cretaceous. Exactly from the same period (ca. 70 milions years
ago) we have evidence that some solitary scleractinian corals produced pristine calcite
skeleton. However, from the same sediments and other Late Cretaceous sediments we
have also abundant examples of clearly aragonitic scleractinians. It seems therefore that
the Mg/Ca ratio of seawater does not control the scleractinian skeleton mineralogy
directly, however, it may influence biomineralization physiology of some groups of
corals.
3.46
Computational Modelling Of Calcification in Zooxanthellate Scleractinian Corals
Jiangjun CUI 1 , Marten POSTMA 1 , Jaap KAANDORP* 1 , Denis ALLEMAND 2
1 Section Computational Science, University of Amsterdam, Amsterdam, Netherlands,
2 Centre scientifique de Monaco, Monaco, Monaco
Zooxanthellate scleractinian corals take up large amounts of CO2 and Ca 2+ during the
formation of the calcareous skeleton. This process requires active transport of ions
through several layers of tissue, which consumes high amounts of energy. The main
source of energy comes from symbiotic algae, the Zooxanthellae, which live in the
corals’ cells and produce nutrients through photosynthesis. Both calcification and
photosynthesis require inorganic carbon. The carbon from photosynthesis in the form of
sugars is released during respiration in mitochondria, producing CO2 and ATP that is
further used in the calcification process to form CaCO3.
To study the complex interplay between the different physiological processes and
environmental conditions, we have developed a multi-compartmental model. The
compartments represent the different layers in the coral tissue. The production,
consumption and fluxes between layers of the relevant compounds are described by a set
of coupled transport equations. To develop realistic models we have used detailed
experimental data where available.
The light dependent CO2 assimilation during photosynthesis was approximated by an
experimental curve for C3 plant cells. Respiration in the layers with mitochondria was
modelled by a CO2 and ATP production term. The transport processes in each layer for
Ca 2+ , H + and HCO3 - was modelled by diffusion, channels and transporters. The action of
carbonic anhydrase was modelled explicitly. The precipitation rate in the extracellular
calcifying fluid was modelled by a rate equation adopted from a model for deep-sea coral
calcification.
The numerical modelling allows us to extract the most important factors that determine
calcification rate. More specifically, it allows us to validate various mechanisms
proposed for light-enhanced calcification. Furthermore the model can predict how
calcification rate dependents on several other environmental factors e.g. pCO2, pH, Ca 2+
and temperature.
3.47
Temporal Variations in Coral Growth And Microskeletal Development in Nearshore
Terrigenoclastic-Dominated Reef Environments.
Ronan ROCHE* 1 , Ken JOHNSON 2 , Christopher PERRY 1 , Scott SMITHERS 3
1 Manchester Metropolitan University, Manchester, United Kingdom, 2 Natural History Museum,
London, United Kingdom, 3 James Cook University, Townsville, Australia
Recent published data from the central Great Barrier Reef lagoon suggests that sediment
loading has increased five to ten fold, total nitrogen discharge has increased by a factor of four, and
nitrate and total phosphorus by a factor of ten since the period of European settlement and subsequent
land clearance (since ~ 1850 AD) 1 . Whilst such inputs have intuitively been regarded as
exerting a negative affect on nearshore coral communities, recent studies have shown high live
coral cover on many of these reefs and stratigraphic data suggests that these reefs have been
growing steadily over the late Holocene period with relatively stable community structures.
This raises interesting questions about whether these coral communities have been able to
produce reefs in areas of high terrigenous sediment accumulation because of high calcification
rates?
The objective of this study is therefore to quantify temporal and spatial variations in coral
growth and microskeletal characteristics within coral reefs that are, and which have been
through their growth history, strongly influenced by terrigenoclastic sediment inputs.
Specifically the research is utilising coral samples obtained from reef cores recovered from a
range of nearshore sites along the central and northern sections of the Great Barrier Reef (GBR)
shelf at Magnetic Island, Paluma Shoals, Lugger Bay and King Reef. Evidence for changes in
coral community structure, calcification rates and skeletal microarchitectural development over
time are being obtained using novel (and non-destructive) Computerised Tomography (CT)
scanner and X-ray diffraction (XRD) approaches, as well as existing Scanning Electron
Microscopy (SEM) techniques. The detailed examination of coral skeletal characteristics in this
study will shed light on the long-term development of turbid-zone, nearshore coral reefs and
inform the on-going debate over the effects of the land-use changes on coral health in the
central GBR region.
1) McCulloch M., Fallon S., Wyndham T., Hendy E., Lough J. & Barnes D. (2003) Coral
record of increased sediment flux to the inner Great Barrier Reef since European settlement.
Nature 421, 727-730.
3.48
A geochemical model for coral reef formation based on organic and inorganic carbon
productions of reef communities
TAKASHI NAKAMURA* 1 , TORU NAKAMORI 1
1 Institute of Geology and Paleontology, Graduate school of Science, Tohoku University,
Sendai, Japan
The conspicuous growth of a reef crest and the resulting differentiation of reef topography into
a moat (shallow lagoon), crest and slope have long attracted the interest of scientists studying
coral reefs. A geochemical model is here proposed for reef formation, taking into account
diffusion-limited and light-enhanced calcification. First, to obtain data on net photosynthesis
and calcification rates in the field, a typical coral communities were cultured in situ on a reef.
Using these data, equations including parameters for calcification were then developed and
applied in computer simulations to model the development over time of reef profiles and the
diffusion of carbon species. The reef topography simulated by the model was in general
agreement with reef topography observed in nature.
The process of reef growth as shown by the modeling was as follows. Increases in the shore-tooffshore
gradients of the concentrations of carbonate species result from calcification by reef
biota, giving a lower rate of growth on near-shore parts of the reef than on those further
offshore. As a result, original topography is diversified into moat and reef crest for the first
time. Reef growth on the reef crest is more rapid than in the inshore moat area, because more
light is available at the crest. Reef growth on the near-shore side of the reef is further inhibited
by damming of carbon-rich seawater on the seaward side of the reef by the reef crest. Over
time, the topographic expression of the reef crest and moat becomes progressively more clearly
defined by these geochemical processes.
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