11th ICRS Abstract book - Nova Southeastern University

1.1
Fringing-Reef Geomorphology and Facies controlled by hurricanes at Punta
Maroma, Mexico.
Sócrates IBARRA-FERNÁNDEZ* 1 , Paul BLANCHON 2
1 Oceanographic Research Station of Progreso, Secretary of the Navy, Merida, Mexico,
2 Inst. of Marine Sciences & Limnology, National Autonomous University of Mexico,
Cancun, Mexico
Geological investigation of modern reef tracts using drill-cores has invariably assumed
that coral communities seen on the surface should also be encountered in facies from the
reef interior. Implicit in this fair-weather view of reef development is that storms merely
interrupt community succession and leave little trace in the reef's geological record.
Here we challenge that notion using satellite imagery and a transect of 12 closelyspaced
cores from a fringing reef off Punta Maroma in the northeast Yucatan Peninsula.
We find that the distinct community depth zones across the crest and proximal reef-front
are underlain by a uniform facies type consisting of a medium-cobble coral gravel with
sparse in-place colonies of Acropora palmata. The only variable is the degree of
encrustation by Homotrema rubrum which increases slightly at the crest. Satellite images
show that the reef-crest is located a uniform 300 m distance from a mid-shelf slope break
at 10 m below msl.
These findings support a hurricane control on reef development. Decimetre-sized storm
waves crossing the shelf are tripped by the mid-shelf slope break and spill over shallow
reef-front communities destroying in-place coral thickets and producing a layer of cobble
gravel that culminates in a submerged ridge deposited at mean sea-level. Between storms,
the ridge and rubble sheet are re-colonized by similar coral communities with a similar
depth zonation, thereby completing the cycle.
1.10
Distribution Of Clionid Sponges in The Florida Keys, 2001-2005
Michael CALLAHAN* 1
1 FWC/Florida Fish and Wildlife Research Institute, St. Petersburg, FL
Clionid sponges can be aggressive coral bioeroders and effective spatial competitors. In
2001, the Coral Reef Evaluation and Monitoring Program (CREMP) began monitoring
the abundance and area covered by three clionid sponges (Cliona delitrix, C. lampa,
and C. caribbaea) throughout the Florida Keys National Marine Sanctuary (FKNMS)
and the Dry Tortugas. Three 1-meter wide belt transects, centered on the existing
CREMP video transects, were used to delineate the clionid survey area for an individual
station. For each clionid colony within the 1-meter wide belt transect, the surface area
(m2) and stony-coral species affected was recorded. Surface area was measured using a
40 cm2 quadrat frame divided into 5 cm2 grids. Results are reported for 109 CREMP
stations including offshore shallow (39), offshore deep (34), and patch reef (36) stations.
For all 109 CREMP stations surveyed, mean clionid area (cm2/m2) decreased
significantly from 7.9 cm2/m2in 2001 to 4.9 cm2/m2in 2002 (Wilcoxon rank sum p=
0.04). However, mean clionid area steadily increased between 2002 (4.9 cm2/m2) and
2005 (6.5 cm2/m2). High clionid area (~20 cm2/m2) was recorded consistently only at
Lower Keys patch reef stations during all four years. The back-country patch reef
stations had high mean clionid area, but with high variability between years. Of the three
clionid species, C. delitrix was the most common species, accounting for approximately
80% of the recorded observations. Among the recorded stony coral species,
Montastraea annularis, Montastraea cavernosa, and Siderastrea siderea were
the most frequently and extensively invaded by clionid colonies. However, it is
important to note that the majority of clionid colonies occurred in substrata not associated
with a live coral colony.
Poster Mini-Symposium 1: Lessons from the Past
1.11
Sediment transport pathways on a fringing reef based on taphonomic alteration of larger
benthic foraminifera Baculogypsina sphaerulata
Murray FORD* 1 , Paul KENCH 1
1
School of Geography, Geology and Environmental Science, The University of Auckland,
Auckland, New Zealand
Determining sediment transport pathways on coral reefs is essential in understanding the
delivery of sediment to shorelines considered increasingly vulnerable to the affects of sea-level
rise. Traditional approaches involve the use of tracer grains; grains of sediment identifiable by a
user applied characteristic or by geological/biological origin. Foraminifera have been used
successfully as sediment tracers in the past by following a source to sink methodology where
both the habitat and deposition zones of the target species are determined. Such approaches
generally take a snapshot in time and interpret pathways based on this. Essentially a black box
this methodology offers little detail in terms of the time scale of processes between source and
sink. The key objective of this study was to determine whether the observed patterns of
taphonomic alteration of foraminiferal tests can be used as a proxy for the degree of
transportation. A series of tumbling barrel experiments were used to simulate abrasion as a
result of transportation on the tests of larger benthic foraminifera Baculogypsina
sphaerulata. Image processing and analysis techniques were used to determine shape change
through time. Tests exhibit a predictable non-linear trajectory of shape change based on
exposure to abrading forces. Tumbling barrel results were then compared to observed patterns
of alteration of tests from surfical samples to determine the sediment transport pathways on
Coconut Reef, Great Barrier Reef. This poster presents the approach undertaken using
B.sphaerulata tests and the implication of this on the delivery of sediment to the shoreline
adjacent to Coconut Reef.
1.12
A Comparison of Rates and Styles of Bioerosion With Varying Sedimentation: Holocene
Reefs in the Western Dominican Republic versus Modern Reefs off St. Croix, USVI
Andrew ESTEP* 1 , Timmons ERICKSON 1 , Dennis HUBBARD 1
1 Geology, Oberlin College, Oberlin, OH
While the importance of bioerosion in reef building has been generally accepted, we are just
beginning to appreciate the potential of bioerosion patterns as possible paleo-ecological
indicators. A systematic study of the nature and intensity of infaunal bioerosion was conducted
on two modern reefs off St. Croix and two fossil Holocene reefs exposed in the western
Dominican Republic.
Samples of dead Montastraea spp. were collected at 10-ft depth intervals along three transects
on St. Croix (max = 80 ft). In the Dominican Republic, fossil Siderastrea spp. Montastraea spp.
colonies were recovered at regular intervals along a time surface buried rapidly by storm debris.
These colonies were presumed to have been dead at the time of burial based on surface
taphonomic characteristics. The age and elevation of each coral were used to assign paleo-depth
for comparisons with modern corals. Bioeroded samples were slabbed and scanned at high
resolution. Bioerosion galleries were traced and color-coded using Adobe Photoshop. Area
measurements of each type of gallery were tabulated within the bored coral rim using ImageJ,
and were reported as a percent within the bioeroded rim (i.e., not the entire colony).
Significant differences were identified in both the extent and type of bioerosion within the open
and exposed reefs off St. Croix and the more protected reefs within Bahia Enriquillo. Total
bioerosion off St. Croix ranged consistently between 10 and 20% or less, and was dominated by
sponges that left large galleries or complexes of smaller ones. In the DR reefs, bioerosion was
much greater (20-60%), and was dominated by molluscs (mostly Lithophaga) and large
sponges. Worms were minor players (