Dr Andrew P. de Wet, EditorKeck Director

Franklin & Marshall College

KECK GEoloGy ConsortiuM

21st KECK rEsEArCh syMPosiuM in GEoloGyshort Contributions

April 2008

2007-2008 ProjECts:

tectonic and Climatic Forcing of the swiss AlpsJohn Garver (Union College), Mark Brandon (Yale University), Alison Anders (University of Illinois),

Jeff Rahl (Washington and Lee University), Devin McPhillips (Yale University)Students: William Barnhart, Kat Compton, Rosalba Queirolo, Lindsay Rathnow,

Scott Reynhout, Libby Ritz, Jessica Stanley, Michael Werner, Elizabeth Wong

Geologic Controls on Viticulture in the Walla Walla Valley, WashingtonKevin Pogue (Whitman College) and Chris Oze (Bryn Mawr College)

Students: Ruth Indrick, Karl Lang, Season Martin, Anna Mazzariello, John Nowinski, Anna Weber

The Árnes central volcano, northwestern icelandBrennan Jordan (University of South Dakota), Bob Wiebe (Franklin & Marshall College), Paul Olin (Washington State U.)

Students: Michael Bernstein, Elizabeth Drewes, Kamilla Fellah, Daniel Hadley, Caitlyn Perlman, Lynne Stewart

origin of big garnets in amphibolites during high-grade metamorphism, Adirondacks, nyKurt Hollocher (Union College)

Students: Denny Alden, Erica Emerson, Kathryn Stack

Carbonate Depositional systems of st. Croix, us Virgin islandsDennis Hubbard and Karla Parsons-Hubbard (Oberlin College), Karl Wirth (Macalester College)Students: Monica Arienzo, Ashley Burkett, Alexander Burpee, Sarah Chamlee, Timmons Erickson

Andrew Estep, Dana Fisco, Matthew Klinman, Caitlin Tems, Selina Tirtajana

sedimentary Environments and Paleoecology of Proterozoic and Cambrian “Avalonian” strata in the united statesMark McMenamin (Mount Holyoke College) and Jack Beuthin (U of Pittsburgh, Johnstown)Students: Evan Anderson, Anna Lavarreda, Ken O’Donnell, Walter Persons, Jessica Williams

Development and Analysis of Millennial-scale tree ring records from Glacier bay national Park and Preserve, Alaska (Glacier bay)

Greg Wiles (The College of Wooster)Students: Erica Erlanger, Alex Trutko, Adam Plourde

The biogeochemistry and Environmental history of bioluminescent bays, Vieques, Puerto rico Tim Ku (Wesleyan University) Suzanne O’Connell (Wesleyan University), Anna Martini (Amherst College)Students: Erin Algeo, Jennifer Bourdeau, Justin Clark, Margaret Selzer, Ulyanna Sorokopoud, Sarah Tracy

Funding provided by:Keck Geology Consortium Member institutions and nsF (nsF-rEu: 0648782)

Keck Geology Consortium Member institutions:Amherst College beloit College Carleton College Colgate university The College of Wooster The Colorado College

Franklin and Marshall College Macalester College Mt. holyoke College oberlin College Pomona College smith College trinity university union College Washington and lee university Wesleyan university Whitman College Williams College

Dr Amy rhodes, symposium organizer

smith College

Keck Geology ConsortiumFranklin & Marshall College

PO Box 3003, Lancaster Pa, 17603

Keck Geology Consortium: Projects 2007-2008

Short Contributions – St Croix

CARBONATE DEPOSITIONAL SYSTEMS: ST. CROIX, U.S. VIRGIN ISLANDS: p151-156 Project Faculty:

DENNIS HUBBARD: Oberlin College KARLA PARSONS-HUBBARD: Oberlin College KARL WIRTH: Macalester College

TEMPORAL AND SPATIAL DISTRIBUTION OF CORALS AT TAGUE BAY REEF AND BUCK ISLAND NATIONAL MONUMENT REEF ST. CROIX, USVI: 157-161

MONICA ARIENZO: Franklin and Marshall College Research Advisor: Carol de Wet

TAPHONOMY OF MOLLUSC SPECIES FOUND IN LAGOONAL CORES OF SMUGGLER’S COVE, USVI: p162-166

ASHLEY BURKETT: Muskingum College Research Advisors: Karla Parsons-Hubbard and Shelley A. Judge

TROPHIC CASCADES AND SEDIMENT PRODUCTION IN MARINE RESERVES: p167-171

ALEX BURPEE: Washington & Lee University Research Advisors: Lisa Greer and Robert Humston

SEDIMENTARY CONSTITUENTS AS INDICATORS OF CHANGING ENVIRONMENTS: THE EVOLUTION OF SMUGGLER’S COVE, ST. CROIX, USVI: p172-175

SARAH CHAMLEE: Sewanee - The University of the South Research Advisor: Donald B. Potter

DEPTH-RELATED PATTERNS OF INFAUNAL BIOEROSION IN TWO MODERN AND TWO FOSSIL CARRIBEAN REEFS: US VIRGIN ISLANDS AND THE DOMINICAN REPUBLIC: p176-180

TIMMONS ERICKSON: Oberlin College Research Advisor: Dennis K. Hubbard

RATES AND STYLES OF BIOEROSION WITH VARYING SEDIMENTATION: HOLOCENE REEFS IN THE WESERN DOMINICAN REPUBLIC VERSUS MODERN REEFS OFF ST. CROIX, USVI: p181-186

ANDREW J. ESTEP : Oberlin College Research Advisor: Dennis K. Hubbard

POST-HURRICANE DYNAMICS OF CORAL REEFS IN ST. CROIX, USVI: p187-190

DANA FISCO: Colgate University Research Advisor: Connie Soja

SEDIMENTARY CONSTITUENTS AS INDICATORS OF TROPICAL STORM VARIABILITY AND CHANGING HOLOCENE ENVIRONMENTS IN SMUGGLERS’ COVE, ST. CROIX, USVI: p191-196

MATTHEW G. KLINMAN: Bryn Mawr College Research Advisor: Donald Barber

SHELL BED FORMATION IN THE SUB-FOSSIL RECORD: USING MOLLUSCAN ASSEMBLAGES TO DISTINGUISH BIOTURBATION LAGS FROM STORM CONCENTRATIONS: p197-201

CAITLIN TEMS: Colorado College Research Advisor: Chris Schneider

DIATOM STRATIGRAPHY OF SMUGGLER’S COVE, ST. CROIX, USVI: p 202-208

SELINA TIRTAJANA: Wesleyan University Research Advisor: Timothy C. Ku

Funding provided by: Keck Geology Consortium Member Institutions and NSF (NSF-REU: 0648782)

Keck Geology Consortium Franklin & Marshall College PO Box 3003, Lancaster Pa, 17603 Keckgeology.org

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INTRODUCTION

Two major goals of geologists studying reefs has been to understand how these structures are built and how this might have changed over time. Tradi-tional reef-accretion studies have focused on coral growth and have underestimated the importance of bioerosion; construction, destruction (bioerosion), encrustation and cementation are equally important factors in the carbonate budget of a reef. Recently, findings suggest that not only is bioerosion an im-portant part of the accretion equation, but that post-mortem grazing, boring and sediment redistribution might strongly impact depth-related patterns of reef building. A survey of all published reef-accretion data shows that, despite higher carbonate produc-tion in shallow water, accretion stays relatively constant down the forereef (Hubbard, 2008). This suggests that calcification and bioerosion may follow similar patterns, and that higher coral-growth rates are offset by higher rates of post-mortem destruc-tion and downslope sediment transport. However, there have been few studies that define the spatial distribution and abundance of the major bioeroding taxa in a way that can be used to test this idea.

During the past summer, we attempted to quantify bioerosion as it relates to depth across Caribbean reefs. Dead coral samples were collected from two Holocene reefs in the Dominican Republic and two modern reefs in St. Croix (US Virgin Islands). The modern reefs of St. Croix experience high wave energy that helps dissipate sediment and nutrients derived from the adjacent shore. In contrast, the Dominican Republic reefs developed in a protected embayment that experienced low wave energy and high sedimentation rates. Comparing the patterns

of bioerosion in such different settings can identify environmentally-driven shifts within infaunal bor-ing communities, but can also be used to examine spatial trends in bioerosion across individual reef systems.

This study focused on macroboring organisms that create voids larger than 1mm. These have been iden-tified as the primary framework-destroying agents that are preserved within the reef substrate (Perry, 2000). Combined with grazing, they can reduce half the carbonate produced by calcifying organisms to sediment (Hubbard et al, 1990; Perry & Bertiling 2000). This paper describes quantitative patterns of boring along a depth gradient in both the modern reefs off St. Croix (d = 3-10m; 3-27m) and their Holocene counterparts in the Dominican Republic (paleodepth = 5-22m).

METHODS

Samples were taken from profiles across two mod-ern reefs and two Holocene Reefs (see Figure 1 in Hubbard et al, this volume). At Cane Bay (17°46’N lat., 64°48’W long.), two linear transects were estab-lished along the modern forereef between depths of 3 and 27m. Eight samples were collected along each transect at depth increments of approximately 3m. Tague Bay Reef (17°46’N lat., 64°36’W long.) was sampled at depths of 3, 6 and 9 meters.

In the Dominican Republic, samples were collected from two Holocene reef outcrops within the En-riquillo Valley reef system (Fig. 1). Lago Enriquillo sits 42 m below sea level, and is the hypersaline remnant of a bay that was cut off from the Carib-bean Sea by rapid sedimentation ca. 4,000 years

DEPTH-RELATED PATTERNS OF INFAUNAL BIOEROSION IN TWO MODERN AND TWO FOSSIL CARRIBEAN REEFS: US

VIRGIN ISLANDS AND THE DOMINICAN REPUBLICTIMMONS ERICKSON: Oberlin CollegeResearch Advisor: Dennis K. Hubbard

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ago (Mann et al., 1984). Most recently, arroyos have cut 5-m sections through the reefs ringing the lake. Within Cañada Honda (18°32’N lat., 71°35’W long.), a storm deposit of Madracis auretenra (Fig. 2) bisects the massive-coral facies of the reef, providing

a timeline that can be followed for up to 130 meters. Coral samples were taken from just below the storm deposit every 10 meters. Each sample was assigned a paleo-depth based on the present elevation of each coral, the 14C age of the storm deposit that buried it and the Caribbean sea level curve developed by Lighty et al. (1982: corrected to CalBP). Ten corals were collected along the entire length of the exposed Madracis layer.

Four additional coral samples were taken from the mixed-coral facies located upslope of the Madracis section. These samples do not have exact paleo-depths but are assumed to have been at shallower depths than those found in the massive zone. An-other set of five samples was collected in an arroyo east of the town of Las Clavellinas (17°46’N lat., 64°48’W long.), presumably from within the mixed-coral facies.

Each sample was slabbed in the field to reveal a complete interior cross section. The corals were re-cut in the lab to create two flat faces that were scanned digitally with Photoshop. Individual mac-roboring galleries were outlined and color coded for over 40 slabs (Fig. 3). Categories of major bioeroders included: molluscs, worms, and three kinds of sponge (“large gallery”, “small gallery” and “meshwork”. Using NIH ImageJ, the total area of bioerosion by each category was calculated for each scanned coral face. The area of the zone in which bioerosion occurred was measured, and the mea-surements of total bioerosion were standardized as percents of the total zone of bioerosion to remove possible biases related to differences in colony size.

RESULTS

The St. Croix reefs are exposed to higher energy and lower sedimentation rates than those in the Domini-can Republic. This is reflected in a difference in the infaunal communities at the two sites that is obvious by even simple visual examination (Fig. 4).

Total bioerosion rates tend to be greater in the DR samples than those from St. Croix. Within the Do-minican Republic corals, bioerosion is dominated

Figure 1. GIS reconstruction of a view looking north across the Enriquillo Valley. The yellow circle shows the location of the sampled reefs. The inset shows the location of the St. Croix and DR sites in the Caribbean. See Figure 1 in Hubbard et al (this volume) for details on St. Croix locations.

Figure 2. Photograph of the storm layer that defines a timeline within Cañada Honda. The dominant coral, Madracis aureten-ra (the stick coral that runs horizontally across the top half of the photo) is derived from shallow water upslope. All samples were recovered from just beneath this debris layer and are considered to be contemporaneous.

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by Lithophaga sp., a rock-boring bivalve. Mollusc borings made up as much as 80% of the bioerosion within individual corals, and were found within all of the DR samples but two (Fig. 5). In contrast, mollusc boring was seen in only two St. Croix sam-ples, both from Tag Bay, and these constituted less than 6% of the total bioerosion within either sample. Within the DR corals Lithophaga sp. boring appears to generally decrease with depth through the mixed zone, and peak within the upper massive-coral zone at a paleo-depth of ca. 10m. Here Lithophaga sp. is responsible for 80% of the total bioerosion, and has removed 45% of the area within the zone of bioero-sion. Other than this one peak, mulluscan bioero-sion is equal to or lower than that in the mixed-coral zone (Fig. 5).

In contrast, sponges can be responsible for over 90% of the total bioerosion in St Croix, and follows a bi-modal trend (Fig. 5). Large-sponge borings peak at all three sites between 20 and 30%, and then fall off near the shelf break. Below 10m, there is a 10-15% increase in removal with depth down to 27m. In the Dominican Republic, sponge bioerosion follows a similar but less dramatic bimodal trend. Sponge removal rates stay high within the mixed zone, but drop after the upper two massive-facies samples. While boring rates by sponge reach 40% within the mixed- and upper two massive-facies samples, re-moval tends to fall between 10 and 25% throughout the lower part of the outcrop.

The intensity of total infaunal bioerosion on St. Croix is largely bimodal, with maximum rates oc-curring near 6m (20-30%) and dropping abruptly to ~5% near the shelf edge at 10m (Fig. 5). Below the slope break, boring generally increases within the offshore samples, from ~5% at d=10m to ~15% at d=27m. In the Holocene reef of the Dominican Republic, total bioerosion is likewise bimodal, with rates of 40-60% in samples from paleodepths of 5-8m, while between 11 and 22m, total bioerosion generally ranged from 20 to 30 percent.

At both sites, worms exhibit constant but low back-ground levels of removal. In the DR reefs, worm galleries totaled a mean of 0.9% and standard devia-

Figure 3. Coral slab (left) and digitized bioerosion galleries (right).

Figure 4. Typical coral slabs from Cañada Honda (left) and Cane Bay (right). Note the dominance of molluscs (mostly Lithophaga sp.) and large sponges on the left versus meshwork sponges on the right. For a more detailed discussion of differ-ences in the overall borer communities at the two sites, see Estep (this volume).

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tion of 0.6%. The relative percentage of worms only increases near the lower section of the massive facies when bioerosion rates of Lithophaga sp. begin to wane. Within the St Croix reefs, average bioerosion by worms totals only 0.6% (SD = 0.5%).

DISCUSSION

Sommarco & Risk (1990) aptly stated, “such de-structive processes have received little attention compared with their constructive counterparts.” For much of the history of reef research, bioerosion, it’s implications for reef development, and the affects it has on reef morphology have been largely ignored. For those reasons alone, developing a quantitative study of bioerosion and the major biological groups that bore reef substrate was important. Much of the work done on bioerosion has either focused on reef-wide averages, a single reef facies, or as descriptions of bioeroding taxonomic groups (Perry & Hepburn 2008, Hutchings 1986). This study focused on two reef systems that are exposed to very different en-vironmental conditions, and provides a general un-derstanding of the patterns bioerosion both across and between reefs.

Although rates of bioerosion are dominated by Lithophaga sp. in the Dominican Republic and by sponges in St. Croix, there are similar trends within each system. Across the Dominican Republic and St. Croix reefs, bioerosion rates appear to trend

in a bimodal pattern. Both show peak bioerosion rates at depths between 6 and 10 meters, followed by lower bioerosion rates further offshore and away from sources of high nutrients. The steady rise be-low a depth of 10 m at Cane Bay is associated with a sudden increase in slope, which is absent in the DR

examples. Due to limitations on sampling at depths greater than 27m at Cane Bay and ca. 15m in Cañada Honda, it is unknown how far downslope the rise in bioerosion contin-ues. Sponges, when consid-ered separately are the most similar bioeroding taxa across both reefs. Within St. Croix and the Dominican Repub-lic sponge not only follow a common rate, but are also the group responsible for the peak in bioerosion around 6 meters followed by a sudden drop

and an eventual resurgence. The significance of this trend is not clear.

The rates for worm bioerosion were different from those found by other researchers. In a Jamaican reef system with high sponge and low Lithophaga sp. boring rates, Perry (1998) observed a higher rate of worm boring within the mixed facies than is reported here. It is not clear whether these differ-ences are real or due to different interpretations of the smallest galleries. This study is also incomplete in its scope as an assessment of total bioerosion; the effects of grazing fish and echinoderms are ignored. To complete the picture, other studies addressing rates of bioerosion by both grazers and infaunal borers will be needed. Sampling could also be extended to greater depths along reefs with differ-ent environmental controls, such as wave energy and light. Nevertheless, this study does show that higher rates of bioerosion correlate with the region of highest calcification along the reef (see Hubbard et al., 1990 for Cane Bay), and that increased levels of nutrient availability either between sites or along a depth gradient exerts a primary control on bioero-sion communities.

Figure 5. Bioerosion versus water depth at Cane Bay and Cañada Honda.

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REFERENCES

Lighty R.G., Macintyre I.G., Stuckenrath R., 1982, Acropora palmata reef framework: a reliable indicator of sea-level in the western Atlantic for the past 10,000 years. Coral Reefs v. 1 p. 125–130

Hubbard, D.K., 2008, in: Gischler, E., Swart, P. K. & Lomando, A. J. Perspectives in Carbonate Geology: A Tribute to the Career of Robert Nathan Ginsburg, IAS Special Publication 41, eds. Swart, P. K., Eberli, G. P. & McKenzie, J. (Blackwell, Oxford).

Hubbard, D.K., Miller, A.I. and Scaturo, D., 1990, Production and cycling of calcium carbonate in a shelf-edge reef system (St. Croix, U.S. Virgin Islands): applications to the nature of reef sys-tems in the fossil record: Journal of Sedimen-tary Petrology, v. 60, p. 335-360

Hutchings, P. A., 1986, Biological Destruction of Coral Reefs. Coral Reefs v. 4, p. 239-252

Mann, P., Taylor, F.W., Burk,e K., and Kulstad, R., 1984b, Subaerially exposed Holocene coral reef, Enriquillo Valley, Dominican Republic: GSA Bulletin v. 95, p. 1084-92

Perry, C. T., 1998, Macroborers within Coral Frame-work at Discovery Bay, north Jamiaca: Species Distribution and Abundance, and Effects on Coral Preservation. Coral Reefs v. 17, p. 277-287

Perry, C. T., 2000, Macroboring of Pleistocene Coral Communities, Falmouth Formation, Jamaica. Palaios, v. 15, p. 483-491

Perry, C. T. & Bertling, 2000, Spatial and Temporal Patterns of Macroboring within Mesozoic and Cenozoic Coral Reef Systems. In: Invaslaco, E., Skelton, P.W., & Palmer, T. J. (eds) Carbonate Platform Systems: Components and interac-tions. Geological Society of London, London.

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Perry, C. T., & Hepburn, L. J., 2008, Syn-Depositional alteration of coral reef framework through bioerosion, encrustation and cementation: Ta-phonomic signatures of reef accretion and reef depositional events. Earth Science Reviews v. 86, p. 106-144

Sommarco, P. W., & Risk, M. J., 1990, Large-Scale patterns in internal bioerosion of Porities: cross continteal shelf trends on the Great Barrier Reef. Marine Ecology Progress Series v. 59, p. 145-156