42672-B8
Holocene Coral-Reef Development of the SW Dominican Republic: Views Forward and Back in Time
This project examined unique exposures of Holocene reefs in the Dominican Republic. The research provided the first quantitative documentation of the relationship between carbonate production and sea-level rise as they relate to transgression/regression. We also quantified the effectiveness of coring in characterizing the three-dimensional structure of reef deposits. Finally, we identified high diversity (26 coral species), despite elevated and variable sedimentation - a result that is contrary to dogma. Specific conclusions include:
1) Modern-Ancient Comparisons: All the reef zones found on modern reefs were preserved in the outcrops. The depth-related distribution of 26 coral and 52 mollusc species was similar to what we see on modern reefs.
2) Carbonate Production and Sea-Level Change: Annual growth bands from 30 colonies of mostly Siderastrea spp and Montastraea spp. showed that corals were growing at rates below those for the same species at the same depth today, probably the result of high sediment stress – perhaps following an ENSO cycle. Facies patterns showed early transgression, followed by regression as sea level slowed. This allows us to project future rates of rise that might be problematic for the world's coral reefs.
3) Sedimentation and Wave Energy: Patterns of species change and coral-colony shape between outcrops allowed us to characterize differences in sedimentation and wave energy around the Enriquillo Valley between 11,000 and 4,000 CalBP.
4) Comparing Interpretations Based on Cores vs Outcrops: Comparisons between detailed quadrat measurements and "virtual cores" created on the outcrop face showed that 3-4 cores can accurately characterize the general facies patterns. However, the number of species found by carefully examining the outcrop (26) far exceeded what we typically saw in cores (<10).
5) Quantitative Modern/Ancient Comparisons: Modern reef surveys quantify live corals present at one place or along a spatial gradient. In contrast, these same methods used in outcrop examine coral distributions over time. Detailed measurements of live versus dead corals on a time line imply that data from outcrops inflate live cover at a ratio of ca. 2:1.
Student Support: 11 undergraduate students during five field visits; 3 Honors Theses; 5 Senior Projects; 1 PhD student (logistical support only – no PRF funds); 4 visiting faculty (no PRF funds). 22 abstracts (14 senior-authored by students – in boldface ) and two peer-reviewed publications have resulted from this project. Selected examples include:
- Brewer and Hubbard 2006, Molluscs as storm-deposition indicators in a Madracis mirabilis layer, Cañada Honda, Dominican Republic, NC-GSA
- Cuevas et al 2006, Species distribution, coral growth and sedimentation in a Mid-Holocene coral reef: Cañada Honda, Dominican Republic: GSA
- Hubbard 2006, Holocene reef development in the Caribbean, geologic perspectives revisited, NE-GSA
- Hubbard and Ramirez 2006, Coral growth versus reef accretion: problems of scale, taphonomy and perception, NC-GSA
- Mead et al 2006, Coral morphology as a control of bioerosion and encrustation in Holocene reef corals of the western Dominican Republic, NC-GSA
- Stein et al 2006, Effects of chronic high sedimentation on facies patterns, coral abundance, diversity and morphology – Las Clavillinas, Dominican Republic, NC-GSA
- Cuevas et al 2007, Reef development and coral growth rates in a high-sedimentation, mid-Holocene fossil coral reef, Southwestern Dominican Republic: Simposio de Flora y Fauna del Caribe
- Cuevas et al 2007, Species distribution, coral growth and sedimentation in a Mid-Holocene coral reef: Cañada Honda, Dominican Republic: PR Interdisciplinary Scientific Meeting
- Hubbard 2008, Depth and species-related patterns of Holocene reef accretion: a critical Assessment of existing models, in: Swart, P. K., Eberli, G. P. & McKenzie, J. (eds.) IAS Special Publication.
- Hubbard et al 2008, Coral-reef geology: Puerto Rico and the U.S. Virgin Islands, in: Coral Reefs of the USA, Springer-Verlag.
Cuevas et al 2008, The Mid-Holocene Cañada Honda fossil reef of the Enriquillo Basin, Southwestern Dominican - Republic: Evidence for coral growth and reef accretion at great depth and high siltation prior to anthropogenic disturbance, Caribbean Geological Conference
- Cuevas et al 2008, Environmental factors controlling community structure, morphology and linear extension of Mid-Holocene reef corals from Cañada Honda, Southwestern, Dominican Republic, International Coral Reef Symposium (ICRS)
- Davis et al 2008, Coral morphology as an indicator of sedimentation rate in two exposed Holocene reefs, western Dominican Republic, (ICRS)
- Erickson et al 2008, Depth-related patterns of infaunal bioerosion in two modern and two fossil Caribbean reefs: US Virgin Islands and the Dominican Republic, (ICRS)
- Estep et al 2008, 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, (ICRS)
- Hubbard 2008 Sedimentation, sea level and facies geometry: Enriquillo Valley reefs, western Dominican Republic, Caribbean Geological Conference
- Hubbard 2008, Holocene reef accretion along the north side of Bahia Enriquillo (western Dominican Republic): unique insights into patterns of reef development in response to paleoceanography and sea-level rise, (ICRS)
- Lescinsky et al (2 students) 2008, Estimating live coral cover in fossil reefs: a microboring approach, (ICRS)
