Evidence of coral reef accretion under Evidence of coral reef accretion under unique environmental conditions: The Mid-unique environmental conditions: The Mid-

Holocene fossil reefs of the Enriquillo Valley Holocene fossil reefs of the Enriquillo Valley of Southwestern Dominican Republicof 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 MeetingMarch 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 Mayagüez Bay, Western PR. (Courtesy of GERS Lab, Dept. Of Geology, UPRM)

Inner reefs in Mayagüez 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, Curaçao, Netherlands Antilles

Cañada 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 9th 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 fromBudd 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 CaCO3 from allochtonous (terrigenous) sediment

Model for sediment mineralogy in CH

Abundance (%) of constituent grains in CH sediment

Echinoid3.3%

Foraminifera0.5%

Sponges0.7%

Barnacles3.5%

Serpulid worms1.3%

Quartz/Feldspar0.5%

Bivalve15.2%

Gastropods5.1%

Calcareos algae0.1%

Red algae/Bryozoa0.3%

Coral21.1%

Non-skeletal48.5%

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?:– phytoplanktonturbidity?– High abundance of

macroborers (Lithophaga and barnacles)

• High carbonate (CaCO3) content of terrigenous and reef sediment

Unique conditions in Cañada 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 CaCO3 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 Cañada 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 CaCO3

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

• The high content of CaCO3 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, Mayagüez, Puerto Rico• Vanessa Rosario, Viviana Díaz 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!