11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 15: Progress in Understanding the Hydrodynamics of Coral Reef Systems
15.519
Defining the Reefal Bay System Hydrodynamically
Ava MAXAM* 1,2 , Dale WEBBER 2
1 Mona Geoinformatics Institute, University of the West Indies, Kingston, Jamaica, 2 Life
Sciences Department, University of the West Indies, Kingston, Jamaica
Investigations into the hydrodynamics of a partially enclosed reefal bay, Wreck Bay,
showed that inner bay waters re-circled the reef constantly. This circulation formed
permanent gyres, the extents of which were utilized to delineate a boundary for the reefal
bay system. Results from in-situ, long-term current meter and drogue measurements
depicted the spatial and temporal variability in circulation, revealing that inner bay water
diverged on to the fore-reef, then either re-entered the back-reef to close the circum-reef
circulation, or continued along the fore-reef as open circum-reef circulation. Multiple
regression values confirmed that back-reef currents played a major role in driving
channel flow, accounting for 47% of the variability in the channel currents. Open circumreef
circulation was found to be the larger gyre of the system and facilitated greater
extension of the inner bay, while closed circulation gave smaller but more retentive
gyres. Gyres expanded or abated around the same reef location, demonstrating that the
presence of subtending reef with channels offered stability in the location of circum-reef
systems. Reef parabola, fringing and partially enclosing bays, are generally accepted as
the boundary of the reef-bay system. However, the dynamics displayed at Wreck Bay
showed the reef as the heart - not the limit - of main circulation and therefore the centre
of the hydrodynamic bay.
15.520
Patterns in Benthic Communities At A Remote Subtropical Atoll Along A Wave
Exposure Gradient
Kimberly PAGE-ALBINS* 1 , Peter VROOM 2 , Mark ALBINS 1 , Ronald HOEKE 2 , Celia
SMITH 3
1 Department of Zoology, Oregon State University, Corvallis, OR, 2 Joint Institute for
Marine and Atmospheric Research, Honolulu, HI, 3 Department of Botany, University of
Hawaii at Manoa, Honolulu, HI
In coral reef ecosystems, wave exposure and its associated bed shear stresses can be both
essential and detrimental to organisms; therefore, a morphological tradeoff may exist
favoring some species over others depending upon the wave exposure regime. In this
study, we examined whether wave exposure is responsible for variations in benthic
community composition at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands.
Our expectation was that sites with similar levels of wave exposure would exhibit similar
benthic community composition. Additionally, species richness of coral and macroalgae
were compared to predictions from Connell’s intermediate disturbance hypothesis (IDH)
with the expectation that sites with intermediate levels of wave exposure would have the
highest species richness. To test each of the above hypotheses, percent cover of benthic
organisms was observed at 34 sites from 4 wave exposure categories: high, intermediatehigh,
intermediate-low, and low. Multivariate statistical analyses revealed variation
among sites both within and between all wave exposure categories with the exception of
low. Despite such variation, a nonmetric multidimensional scaling ordination (nMDS)
and cluster diagram grouped sites from low, high, and intermediate-high wave
disturbance areas into three relatively discrete clusters. Sites with low wave exposure
exhibited highly homogenous community assemblages. Sites experiencing intermediatelow
wave exposure did not group together in the nMDS ordination or cluster diagram,
suggesting greater variability in benthic compositions among these sites. In accordance
with expectations based on the IDH, coral and macroalgal species richness was
significantly higher at sites with intermediate-high and intermediate-low levels of wave
exposure than at sites with low wave exposure, although not significantly higher than
sites with high wave exposure. Our results support IDH and suggest that the absence of a
disturbing force is a strong homogenizing mechanism in communities.
15.521
The Particle Tracking Model: Method To Quantify External Sediment Loading To Coral
Reef Regions
Zeki DEMIRBILEK* 1 , Tahirih LACKEY 1 , Joseph GAILANI 1 , Jarrell SMITH 1
1 US Army Corps of Engineers, Engineer R&D Center (ERDC-CHL), Vicksburg, MS
Coral reefs can be adversely impacted by anthropogenic, intermittent sediment sources
introduced, for example, by dredging operations, placement of dredged material, ship passage,
construction, etc. PTM is a Lagrangian particle tracking model specifically designed to monitor
the pathway and fate of sediment sources generated by human activity. The USACE has
developed methods for quantifying sediment sources released to the water body by dredging
and placement operations as well as ship passage. These source terms are used as input to PTM,
which then tracks the sediment pathway and fate. The model is often used to predict quantity of
sediment (loading) introduced to sensitive habitat. Diagnostic tools such as PTM are applied
prior to dredging operations to quantify sediment pathways and assess environmental impact.
PTM is also used to compare various scenarios that may minimize impacts. PTM simulates
sediment transport by applying hydrodynamics and wave data as forcings to user defined
sediment sources. The model contains algorithms designed to represent relevant transport
processes such as advection, diffusion, settling, and particle bed interactions. Regions of coral
reefs are represented by variations in roughness. The PTM interface is the Surface-water
Modeling System (SMS) which provides data analysis tools for concentration, exposure,
deposition, and accumulation mapping. PTM is applied to a hypothetical dredging operation
near a sensitive habitat (coral reef) to demonstrate model utility and applicability to assess
sediment loadings to these habitats. Multiple scenarios are analyzed to determine variability in
loadings due to variations in dredging operations.
15.522
Water Quality And Movement Over The Forereef At Carrie Bow Cay, Belize: A Wind-
Driven System?
Karen KOLTES* 1 , Tom OPISHINSKY 2
1 Office of Insular Affairs, U.S. Department of the Interior, Washington, DC, 2 Interactive
Oceanographics, East Greenwich, RI
Meteorological and oceanographic conditions have been monitored at the Smithsonian
Institution’s Field Station at Carrie Bow Cay (CBC), Belize, since 1993 through the
CARICOMP monitoring program and since 1997 through an automated monitoring system.
Qualitative and quantitative observations indicate that turbidity has increased since monitoring
began and that the frequency and degree of “turbidity events” are related to several factors
including rainfall and tidal stage. To better characterize water quality, light meters were
installed on the forereef at the CARICOMP site (13.5 m). Light intensity (L/sf) has been
recorded there intermittently since 2002. Temperature has been recorded continuously at this
site since 1993 as well as in the seagrass beds at Twin Cays (1.4 m) and in the lagoon behind
CBC (2.0 m).
Comparisons of meteorological and oceanographic data from the weather station and
CARICOMP revealed significant correlations between certain weather conditions, both episodic
and seasonal, and water properties. Wind direction has emerged as a strong driving force of
water movement. Observations demonstrate that shoreward (coastal) water and ocean water
flow into and mix in the survey area. Strong signatures of different water masses are most
evident following major weather events, however strong correlations are also apparent during
less prominent changes in weather and particularly wind direction.
We suggest that the prevailing northeasterly winds normally hold turbid coastal water
shoreward of the barrier reef. Under decreased or westerly winds, turbid coastal water drifts or
is pushed out onto the reef from the lagoon. We also note that only about 36% of incident light
reaches the reef in December compared to about 65% of incident light in June, suggesting that
increased turbidity, lower sun angle and/or higher sea states are causing the attenuation of
incident solar radiation to nearly double during the winter months.
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