11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 15: Progress in Understanding the Hydrodynamics of Coral Reef Systems
15.515
Influence Of Florida Current Frontal Eddies On Circulation And Fish Recruitment
Around The Florida Keys Reef Tract
HEESOOK KANG* 1 , Vassiliki KOURAFALOU 1 , Claire PARIS 2
1 MPO, RSMAS/Univ. of Miami, Miami, FL, 2 MBF, RSMAS/Univ. of Miami, Miami, FL
The coastal seas around the Florida Keys Reef Tract exhibit complex dynamics resulting
from the interaction with offshore flows, namely the Loop Current/Florida Current
system and the frontal eddies that interact with the complex reef topography. A nested
modeling approach has been employed to ensure the proper representation of such
interactions. A high resolution (~900m) application of the HYbrid Coordinate Ocean
Model has been developed focusing on the Florida Keys (FKEYS-HYCOM model).
Nesting to a succession of coarser, regional models (South Florida SoFLA-HYCOM and
Gulf of Mexico GoM-HYCOM) and finally to basin-wide and global models allows the
downscaling of large scale flows to scales appropriate for the study of reef related
processes.
Eddies that travel along the Loop Current/Florida Current front are known to be an
important mechanism for the interaction of nearshore and offshore flows. They enable
upwelling in the vicinity of the Reef Tract and they influence transport and recruitment
pathways, as they carry waters of different properties (such as river-borne lowsalinity/nutrient-rich
waters from as far as the Mississippi River) and waters containing
larvae from upstream source, or entrained from nearby spawning grounds. As such, they
play an important role in the circulation around the Reef Tract and connectivity pathways
with the Gulf of Mexico and the Caribbean at large. FKEYS-HYCOM is able to simulate
both mescoscale and sub-mesoscale eddy passages during a targeted 2-year simulation
period (2004-2005), forced with high resolution/high frequency atmospheric forcing.
Coupling with the ecological population connectivity BOLTS model (BiOphysical Larval
Tracking System) allows simulations of larval transport, taking into account not only the
dispersion of active physical larvae, but also the interaction of factors influencing larval
survival, habitat selection and condition at settlement.
15.516
Wave Transformation And Wave-Induced Currents On A Submerged Barrier Reef:
Field Observations And Boussinesq-Type Modelling
Philippe BONNETON* 1 , Rodrigo CIENFUEGOS 2 , Sylvain OUILLON 3 , Patrice
BRETEL 1 , Jean-Pierre LEFEBVRE 3 , Natalie BONNETON 1
1 UMR EPOC, CNRS - Bordeaux 1 University, Talence, France, 2 Pontifica Universidad
Catolica de Chile, Santiago de Chile, Chile, 3 IRD Nouméa, Nouméa, France
As waves break on a reef, they create a radiation stress gradient that drives wave-setup
and wave-induced currents (e.g. Symonds et al. (1995), Hearn (1999) or Gourlay and
Colleter (2005)). These phenomena exert a major influence on the hydrodynamics and
biological variability of shallow submerged coral reefs and have a significant impact on
the circulation and flushing of lagoons. Wave-induced circulation is mainly controlled by
wave dissipation due to wave breaking and bottom friction. When waves propagate over
a submerged barrier reef they may decompose into shorter components referred to as
secondary waves. This process can strongly affect wave dissipation and then the waveinduced
circulation. To improve our understanding of these phenomena, a 3-week field
experiment was conducted on the Aboré coral reef (southwest lagoon of New Caledonia)
in October 2005 (Bonneton et al. (2007)). In this area the tides are semidiurnal (Douillet
(1998)), with a tidal range on the reef between 0.6 and 1.4 m at neap and spring tides. At
low water spring, the reef-top is located just below the sea surface. During the
experiment, the significant offshore wave height ranged between 0.3 and 1.8m. Pressure
and current were synchronously measured along a cross-reef transect at a 8 Hz sampling
rate. In this communication, we analyse the tidal modulation of wave-setup and waveinduced
currents on the reef and interpret our results using analytical models by Symonds
et al. (1995) and Hearn (1999). Then, we present “high frequency” observations, showing
that turbulent bores propagating over the Aboré reef flat frequently evolve into nonbreaking
oscillating bores. Classical time-averaged models do not account for the
generation of secondary waves. To analyse the impact of this phenomenon on waveinduced
circulation, time-dependent numerical simulations based on a Boussinesq-type
model (Cienfuegos et al. (2006, 2007)) are compared to the Aboré reef data set.
15.517
Numerical Modelling Of A Coastal Reef–lagoon System
Ryan LOWE* 1 , James FALTER 2 , Stephen MONISMITH 3 , Marlin ATKINSON 2
1 School of Environmental Systems Engineering, University of Western Australia, Perth,
Australia, 2 Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI, 3 Civil and
Environmental Engineering, Stanford University, Stanford, HI
The response of the circulation of a coral reef system in Kaneohe Bay, Oahu, Hawaii to varying
environmental forcing conditions is investigated using the numerical circulation model
DELFT3D, coupled with the wave model SWAN. To validate the model, field data was
obtained during a two-month experiment in winter 2006, in which current and wave conditions
were measured continuously at several locations on the fore reef, reef flat and lagoon. The
model was forced for the observation period with the known tidal constituents for the NE coast
of Oahu, the offshore wave conditions measured by a directional wave buoy, and hourly wind
data measured in the southern end of the Bay. Modeled and observed wave heights are in good
agreement throughout the system, and indicate that the dominant source of wave energy
dissipation in Kaneohe Bay is bottom friction (and not wave breaking), due to the large physical
roughness of the reef. The modeled wave setup peaks just shoreward of the surf zone (on the
reef flat), however setup within the lagoon is found to be a surprisingly large fraction (40-70%)
of the peak reef value, and clearly not zero as assumed in many one-dimensional reef
hydrodynamic models. A comparison between the observed and modelled current time-series at
the various sites reveals that the model accurately predicts the dominant circulation in Kaneohe
Bay. We can use model output of bottom friction and near-bottom flow speeds to drive masstransfer
models of phosphate uptake across the entire Kaneohe Bay Barrier revealing spatial
zonation of uptake and release which are ultimately responsible for driving ecosystem net
primary production.
15.518
A Multi-Scale, Large-Area Analysis Of Coral Reef Roughness
David G. ZAWADA* 1 , John C. BROCK 1
1 Center for Coastal and Watershed Studies, U.S. Geological Survey, St. Petersburg, FL
Coral reefs represent one of the roughest structures in the marine environment. This roughness
or topographic complexity is a significant component of the high degree of habitat complexity
associated with reefs and may vary over a range of spatial scales. In this study, we present a
synoptic view of reef roughness for a 5-km x 5-km portion of Biscayne National Park, FL,
extending from patch-reef to forereef zones. A 1-m spatial-resolution digital-elevation model of
the study area was constructed from lidar data (NASA’s Experimental Advanced Airborne
Research Lidar or “EAARL”). A number of different biological, chemical, and physical
processes, acting on different spatial scales, affect the surface of the reef. In this context, the
fractal dimension (D) is an appropriate metric for quantifying reef roughness and potentially
represents an effective means for designating different zones within a reefscape. Values of D
are bounded between 2 for a flat plane and 3 for a cube. A difference in D of 0.1 corresponds to
a significant and visually apparent change in roughness. Fractal dimensions were computed
over spatial scales ranging from 3 m to 1 km. The results reveal how roughness varies as a
function of reef zone. In general, roughness increased with distance from shore as relatively
smooth patch reefs (D = ~2.3) gave way to more complex fore reefs (D = ~2.6).
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