11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 15: Progress in Understanding the Hydrodynamics of Coral Reef Systems
15-5
Experimental Characterization Of The Oceanic Water Fluxes in A Macro-Tidal
Intermittently Open Lagoon Bounded By Semi-Submerged Coral Reef
Cristele CHEVALIER* 1 , Jean-Luc DEVENON 2 , Gilles ROUGIER 3
1 Cyroco, IRD, Marseille, cedex 09, France, Metropolitan, 2 Laboratoire d'Océanologie et
de Biogéochimie, Université de la Méditerranée, Marseille, cedex 09, France,
3 Laboratoire d'Oceanographie et Biogeochimie, Université de la Méditerranée, Marseille
cedex 9, France, Metropolitan
In the macro-tidal lagoons, of the Indian Ocean, coral reefs can be momentarily
submerged by water at high tide and partially emerged at low tide. This process
contributes to lagoon and open sea exchanges, although the reefs are often considered as
impervious and the water fluxes assumed to occur only through the passes. We study the
influence of this reef hydrodynamic control, by developing an original experimental
approach combining small ship side mounted ADCP measurement following transects
thru passes and near reefs, with more classical high resolution ADCP moorings. The aim
is to gain insight in spatial variability of fluxes at a reasonable cost that moorings alone
cannot be able to provide. This new strategy of measurement is exemplified at the
occasion of an experimental campaign on the Mayotte lagoon and the results of this
experiment are presented. Particularly, it is shown how the mounted ADCP data are
validated. A specific tidal analysis methodology is then proposed to get the spatial
variability of the tidal component of the current thru the passes and above the reef. This
variability is identified by least square fitting of spatial distribution of the tidal
amplitudes owing the availability of repeated transects associated with fixed point
temporal sequences of current issued from moored ADCP currentmeters. This method
has been validated against a priori known theoretical spatial distribution as well as in-situ
already available data. All these analysis allow us to estimate the tidal induced fluxes thru
the passes and above the reefs and to evaluate their respective part in water lagoon
renewal.
15-6
Morpho-Space Exploration Of Simulated Coral Morphologies And Three-
Dimensional Images Of Scleractinian Corals
Maxim FILATOV* 1 , Chris KRUSZYÑSKI 2 , Jaap KAANDORP 1 , Robert VAN LIERE 2 ,
Mark VERMEIJ 3 , Rolf BAK 4
1 Section Computational Science, University of Amsterdam, Amsterdam, Netherlands,
2 Center for Mathematics and Computer Science, Amsterdam, Netherlands, 3 University of
Hawaii at Manoa, Maui fieldstation, Lahaina, HI, 4 Netherlands Institute of Sea Research
(Nioz), Den Burg, Nepal
We developed a method for the quantitative analysis of three-dimensional images of
complex-shaped scleractinian corals obtained with X-ray Computed Tomography
scanning techniques. The analysis is based on a number of morphometric quantities, i.e.
branching rate, branch thickness, branch spacing etc. We use this method for the
quantitative comparison of morphological variation in closely related species in the
Caribbean coral genus Madracis: M. decactis, M. carmabi, M. Formosa and M. mirabilis.
We compare the Madracis morphologies with a range of simulated morphologies. In the
simulations the morphologies were obtained in an accretive growth process where layers
of materials are deposited on top of previous ones. The local thickness of new layers is
controlled by the simulated physical environment (local availability of light and nutrient)
and the amount of translocation of nutrient over the surface of the object. With the
simulation model, varying a model parameter representing the amount of local
translocation of nutrient over the surface of the object, we simulate a range of
morphologies where branching forms gradually transform into more spherical shapes. By
varying a parameter controlling the contribution of local light intensity we can change the
overall branching pattern. Some of the simulated morphologies are almost
indistinguishable from three-dimensional images of actual M. mirabilis and M. decactis
colonies; some three-dimensional images (M. formosa) cannot be completely captured by
our model. Our aim now is to find missing model parameters and to detect which actual
morphologies can be predicted by our model using a systematic comparison of actual and
simulated morpho-spaces.
15-7
Use Of The Coral-Sel Technique in Water Flow Research
Carolyn MARGOLIN* 1
1 Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL
When flow experiments are carried out in open flow-through systems, several non-targeted
variables also change with changing flow rate. These may include temperature, oxygen level,
and food availability. In order to keep these factors constant across flow treatments, it is
necessary to place all corals into a single water system while still exposing them all to different
water flow rates. In order to accomplish this, a rotating “coral-sel” was constructed in an
outdoor tank at the University of Miami’s Aplysia Resource Center on Virginia Key. The
coral-sel allows corals to be placed at three set distances from the center of rotation of the
apparatus. This allows the corals to experience one of three set water flow rates while
simultaneously being immersed in water with identical characteristics other than flow rate.
These rates can be adjusted using a gear system on the external component of the coral-sel.
Clod card techniques were used in order to test differences in flow rates at each of the specified
distances prior to attachment of coral to each site. Fragments of Montastraea faveolata were
attached to plates at each of the tested positions. Each fragment was monitored for survival,
change in weight, change in surface area, and zooxanthellar activity. These data were used to
determine the effects of water flow on the coral holobiont in terms of growth, calcification, and
zooxanthellar activity. Statistical analysis showed that changes in fragment surface area were
inversely related to water flow speed. However, the greatest increases in weight occurred at
mid-flow rates (15.7 cm/s). Area and weight data were used to determine calcification rates.
Apparent calcification rates were greatest for fragments exposed to mid-speed flow rates
(15.7cm/s).
15-8
Importance of the infragravity band in the wave energy budget of a fringing reef
Anne-Christine PEQUIGNET* 1
1 Oceanography, University of Hawaii, Honolulu, HI
In an effort to understand and quantify wave energy at the shoreline of fringing reefs, a series of
pressure sensors and current meters were deployed across fringing reefs on Guam and Oahu,
Hawaii as part of the PILOT (Pacific Island Land-Ocean Typhoon) experiment. Spectral
transformation of waves from the forereef to the shoreline is analyzed in terms of energy flux
along the cross shore transects. Reflection, dissipation and non linear interactions are estimated
during various offshore wave conditions and phases of the tide.
The wave transformation across the reef is strongly dependent on wave frequency and the wave
energy spectrum on the reef flat is dominated by infragravity waves. This results from the
combined effects of strong dissipation of sea and swell through breaking and friction, weaker
dissipation of infragravity energy through friction and the generation of infragravity energy as
the waves cross the forereef and the reef crest. Infragravity waves are reflected both at the
forereef and the shoreline, whereas sea and swell waves are not reflected despite the steep reef
face.
The wave energy in the sea and swell band at the shoreline of a fringing reef depends
predominantly on the reef platform water depth, whereas the infragravity energy appears to
depend more strongly on the offshore wave energy.
Although general trends in wave transformation may be observed on fringing reefs of different
bathymetries, the presence of morphological features (such as porous reef face, longshore
variation due to spurs and groove...) significantly affects wave transformation and makes each
reef a unique breakwater system.
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