of Southwestern Dominican Republic

lameubiquityMechanics

Feb 21, 2014 (3 years and 5 months ago)

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Evidence of coral reef accretion under
unique environmental conditions: The Mid
-
Holocene fossil reefs of the
Enriquillo

Valley
of Southwestern Dominican Republic

David N. Cuevas Miranda, Ph.D.

US EPA Caribbean Environmental Protection Division, Guaynabo, PR


Clark E. Sherman, Ph.D.

Dept. Marine Sciences, UPR
-
Mayagüez
, PR


Wilson
Ramírez
, Ph.D.

Dept. of Geology, UPR
-
Mayagüez
, PR


Dennis K. Hubbard, Ph.D.

Dept. of Geology, Oberlin College, Oberlin, OH



Geol. Soc. of America Southeastern Section Meeting

March 20
-
22, 2013, San Juan, Puerto Rico

Section T12: Quaternary Caribbean Reef Systems


Statement of the Problem


High sedimentation
rates/resuspension is one of
the primary causes for coral
reef decline in many areas of
the world.



Yet, there is evidence of coral
reefs that thrive in
environments of very high
sedimentation (e.g. inner
reefs within the GBR in
Australia)



Natural vs. Anthropogenic
induced sedimentation:


Is there really a difference?


If there is a difference, are the
effects on coral reefs different
also?

Ikonos Image

Mayag
üez Bay,
Western PR.
(Courtesy of GERS
Lab, Dept. Of
Geology, UPRM)

Inner reefs in Mayag
üez
Bay with no coral and
abundant macroalgae
(Photo by J. Morelock)

Natural vs. anthropogenic


Some limitations:


Earliest coral reef studies date back only to
the 1950’s


Possible changes within the coral reef require
long time


Ecologists are looking at the fossil record.


If fine
-
scale changes documented over the
past decades are shown to be unique, then
human impact comes as a reasonable
explanation

Fossil Approach


Study records of well
-
preserved fossil
reefs in detail



Compare the documented changes with
those occurring in modern reef.



Already been implemented in several
studies (e.g. Pandolfi and Jackson, 2001;
Aronson et al. 1998; 2002)

Previous Studies (Cont.)

Drill Cores (by C. Sherman)

Pleistocene Fossil Coral Reef,

Cura
çao, Netherlands Antilles

Ca
ñada Honda Site

From Cuevas et al. (2009)

Study site

Modified from Mann et al. (2002)

Regional cross section across central Hispaniola (from Draper et al. 1994)


Landsat Image of SW

Dominican Republic

(Front cover of the
9
th

Caribbean
Geological
Conference)

Cordillera Central

Cuenca de San Juan

Sierra de Neiba

Cuenca de Enriquillo

Sierra de Bahoruco

General Geology

Haiti

Haiti

Bahia Enriquillo

Lago Enriquillo

Modified from Hubbard et al. 2008

10,000 CalBP

ca. 3
-
4 kybp
-

Closure

Modified from

Budd et al. 2006

Why these reefs?


Well
-
preserved subaerial
exposures (~10,000
-
4,000
yrs. ago,
Mann et al, 1984;
Taylor et al. 1985
)



The record allows for close
examination of reef changes



Influenced by high
terrigenous sedimentation,
before humans inhabited
Hispaniola

Upstream Las Clavellinas Site

Bed of
Acropora cervicornis

Sand and silt

Vertical Transect


Comparison with
modern reef
community structure
data from
Southwestern Puerto
Rico

Data summarized in Morelock et al. (2001)

Results

Community Structure:



At least 22 species of Scleractinian corals (in
transects)



Siderastrea siderea

most abundant (47.4%)
followed by
Montastraea faveolata

(8.73%)



Two major coral zones:


Branching coral zone


Siderastrea siderea

zone


Mix
-
coral subzone


Massive coral subzone


Platy coral subzone



Coral Species Distribution

Stratigraphy of CH, transect and coral sample
location, and stratigraphy

Coral Morphologies

Coral Morphology


Most morphologies
typical of high
sedimentation
settings

Hubbard, 2005

High sedimentation

Sediment bands

Comparison with SW Puerto Rico

Results (cont.)

Sediment composition
:



The Cañada Honda
fossil reef sediment is
characterized by the
high percentage of
carbonate material.



Carbonate varied from
84% to 96 %.



A significant portion of
CaCO
3

from
allochtonous
(terrigenous) sediment

Model for sediment mineralogy in
CH

Abundance (%) of constituent grains in CH sediment
Echinoid
3.3%
Foraminifera
0.5%
Sponges
0.7%
Barnacles
3.5%
Serpulid worms
1.3%
Quartz/Feldspar
0.5%
Bivalve
15.2%
Gastropods
5.1%
Calcareos algae
0.1%
Red algae/Bryozoa
0.3%
Coral
21.1%
Non-skeletal
48.5%
Discussion


Coral community structure in Cañada
Honda has distinctive features
characteristic of siltation stress:


Remarkable abundance of sediment tolerant
coral species (e.g.
S. siderea, M. faveolata,
Agaricia spp.)


Coral cover dominated mostly by two species


Large colonies, few juveniles


Sediment bands within coral skeleton


Growth morphology (i.e. encrusting domes,
plates, cones).


Discussion (cont.)


A. cervicornis

zone similar to sites in
protected environments with limited wave
action throughout the Caribbean


Unique assemblage in CH


Overwhelming abundances of
Siderastrea
spp.


Absence of important coral genera (
Diploria,
Mycetophyllia, Meandrina
)

Discussion (cont.)


Coral development at
depths of ~10
-
12 m.


In typical reefs under
siltation stress corals do not
grow beyond depths of ~10
m).



High nutrients?:


phytoplankton

turbidity?


High abundance of
macroborers (
Lithophaga
and barnacles)



High carbonate (CaCO
3
)
content of terrigenous and
reef sediment


Unique conditions in Ca
ñada
Honda


Other studies have documented high salinity
fluctuations (
Greer and Swart, 2006
)


Could explain high abundance of
Siderastrea spp.

and the absence of other important genera


High content of CaCO
3

in terrigenous sediment
allowed better light penetration


Sedimentation events probably occurred
sporadic, allowing time for reef corals to “keep
-
up” with rising sea
-
level and high sediment input.

Lessons from Ca
ñada Honda


Yes, coral reefs thrive within natural
conditions of high sedimentation


Substantial evidence for siltation stress


Highly resilient communities over
thousands of years


Storms events


Mid
-
Holocene Thermal Maximum


Greer and Swart 2006; Greer et al. 2009


Conclusions


Although there is evidence for high sediment
influx, the Cañada Honda fossil reef thrived and
accreted for at least 3,000 years.



Unique conditions:


Protected marine setting + semiarid
conditions + high salinity fluctuations + high
terrigenous sediment with high CaCO
3




Development of the CH reef occurred under
conditions of high sedimentation and depths
close to 10
-
12m.




The high content of CaCO
3

of the sediment
allowed more light penetration.



Sedimentation was probably sporadic, allowing
time for reef corals to grow back and “keep
-
up”
with sedimentation and rising sea
-
level.


Acknowledgments


UPR
-
NASA Space Grant Program


AGEP program of UPRM


Southeastern section of the Geological Society of America


Center for Research and Development of UPRM


Sea Grant Program at UPRM.


NSF
-
EPSCoR program of the UPR.


Geology Department at UPRM


Marine Science Department at UPRM


The Faculty of Arts and Sciences

UPRM


Members of the thesis committee


The staff of Hospital San Antonio, Mayag
üez, Puerto Rico


Vanessa Rosario, Viviana D
í
az and Elisa Torres.


Dennis Hubbard, Karla Parsons
-
Hubbard and all the students from Oberlin
College that were involved.


Secretaría de Estado y Ambiente of the Dominican Republic.


The staff of Hotel Iguana in La Descubierta.

Thank you!