Collection Methods and Descriptions of Coral Cores 

Extracted from Massive Corals in Dry Tortugas National 

Park, Florida, U.S.A. 

By Michael S. Weinzierl, Christopher D. Reich, T. Don Hickey, Lucy A. Bartlett, and Ilsa B. Kuffner

Open-File Report 2016–1182

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016 

For more information on the USGS—the Federal source for science about the Earth,

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Although this information product, for the most part, is in the public domain, it also may 

contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items 

must be secured from the copyright owner.

Suggested citation: 

Weinzierl, M.S., Reich, C.D., Hickey, T.D., Bartlett, L.A., and Kuffner, I.B., 2016, Collection methods and descriptions 

of coral cores extracted from massive corals in Dry Tortugas National Park, Florida, U.S.A.: U.S. Geological Survey 

Open-File Report 2016–1182, 8 p., https://doi.org/10.3133/ofr20161182.

ISSN 2331-1258 (online)

Cover photograph: A USGS scuba diver prepares to take a core sample from a 3-m tall Orbicella faveolata coral 

colony (“NK1”) in Dry Tortugas National Park, Florida. Photograph by Ilsa Kuffner, U.S. Geological Survey, May 2012.
iii

Acknowledgments

The coral cores described in this study were collected under National Park Service (NPS) Dry Tortugas National 

Park scientific collection permit number DRTO-2012-SCI-0001 and are stored on loan from the NPS under accession number DRTO-00353 at the United States Geological Survey (USGS) St. Petersburg Coastal and Marine 

Science Center (SPCMSC). Additionally, the samples are cataloged in the SPCMSC Core Archive Database 

(http://olga.er.usgs.gov/coreviewer/). The collection expedition was funded by the USGS Coastal Marine Geology 

Program, with additional funding contributed by the USGS Climate and Land Use Research and Development Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by 

the U.S. Government. We thank Kayla Nimmo, Tree Gottshall, and John Spade of the NPS, and Kyle Kelso of the 

USGS for help with locating and collecting the coral cores.
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v

Contents

Acknowledgments ...........................................................................................................................................................................................iii

Abstract ........................................................................................................................................................................................................... 1

Introduction...................................................................................................................................................................................................... 1

Methods........................................................................................................................................................................................................... 3

Results and Summary ..................................................................................................................................................................................... 5

References Cited............................................................................................................................................................................................. 7

Figures

1. Map of the shallow banks of Dry Tortugas National Park, Florida .................................................................................................. 2

2. U.S. Geological Survey scuba diver operating the hand-held hydraulic drill while coring an Orbicella faveolata coral at the 

North Key site ................................................................................................................................................................................. 3

3. Coral LH1 near Loggerhead Key freshly cored with side-plug epoxied in place in May 2012, and after 1 year of healing 

time in May 2013, demonstrating the success of the grafting method............................................................................................ 4

Tables

1. Information for six coral cores from Dry Tortugas National Park, Florida, collected May 10–13, 2012 .......................................... 5

2. Information for six coral cores from Dry Tortugas National Park, Florida, collected May 10–13, 2012 .......................................... 6
vi

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

mile, nautical (nmi) 1.852 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 0.004047 square kilometer (km2

)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2

) 0.09290 square meter (m2)

square inch (in2

) 6.452 square centimeter (cm2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8.

Abbreviations

CE common era

cm centimeter

CT computerized tomography

dpi dots per inch

km kilometer

m meter

mAs milli-Ampere-second

mm millimeter

NPS National Park Service

RNA Research Natural Area

SPCMSC St. Petersburg Coastal and Marine Science Center

USGS United States Geological Survey
1

Collection Methods and Descriptions of Coral Cores 

Extracted from Massive Corals in Dry Tortugas National 

Park, Florida, U.S.A.

By Michael S. Weinzierl, Christopher D. Reich, T. Don Hickey, Lucy A. Bartlett, and Ilsa B. Kuffner

Abstract

Cores from living coral colonies were collected from Dry Tortugas National Park, Florida, 

U.S.A., to obtain skeletal records of past coral growth and allow geochemical reconstruction of environmental variables during the corals’ centuries-long lifespans. The samples were collected as part of the 

U.S. Geological Survey Coral Reef Ecosystems Studies project (http://coastal.er.usgs.gov/crest/) that 

provides science to assist resource managers tasked with the stewardship of coral reef resources. Three 

colonies each of the coral species Orbicella faveolata and Siderastrea siderea were collected in May 

2012 using the methods described herein and as approved under National Park Service scientific collecting permit number DRTO-2012-SCI-0001 and are cataloged under accession number DRTO-353. These 

coral samples can be used to retroactively construct environmental parameters, including sea-surface 

temperature, by measuring the elemental composition of the coral skeleton. The cores described here, 

and others (see http://olga.er.usgs.gov/coreviewer/), can be requested, on loan, for scientific study. Photographic images for each coral in its ocean environment, the coral cores as curated and slabbed, and the 

X-rays of the slabs can be found in an associated U.S. Geological Survey Data Release. 

Introduction

Stony corals (Order Scleractinia) are cnidarians that live in shallow, tropical seas around the 

world. These corals are sessile (live attached to the ocean bottom) and precipitate a calcium carbonate 

(aragonite) skeleton, slowly adding a new layer each year. Because stony corals form annual bands composed of high- and low-density band couplets in their skeletons (Knutson and others, 1972), and because 

they are sensitive to environmental factors (Hudson and others, 1976), they are useful for understanding 

shallow-water environmental conditions from the past. Corals provide insight into geological, climatic, 

and geochemical phenomena because their skeletons record local seawater chemistry during deposition 

(Corrège, 2006). Their characteristically large and enduring skeletons can record several centuries of 

change, enabling the reconstruction of environmental conditions during historical periods (Tierney and 

others, 2015) and during past geologic epochs (Flannery and Poore, 2013).

Florida is the only State in the continental United States with extensive shallow reefs near its 

coast. The most extensive living coral reefs occur adjacent to the island chain of the Florida Keys, the 

westernmost of which are the uninhabited and federally protected islands in Dry Tortugas National Park. 

The park includes several small islands, shallow banks, and vast coral reefs. The active reefs around 

the edge of the platform accumulate atop the existing antecedent high of the Key Largo limestone shelf 

(Shinn and others, 1977). The surrounding waters are influenced by the western Florida current—part of 

the loop-current system—which transports warm water from the Caribbean into the Gulf of Mexico and 

out through the Florida Straits (Shinn and others, 1977). This water transport and exchange creates surface waters around the Dry Tortugas that reflect water conditions in the tropical Atlantic, the Caribbean, 

and the Gulf of Mexico. Because of these water conditions and the Dry Tortugas being relatively far 
2

from freshwater influences and human activity, this area is an excellent location for open-ocean proxy 

calibration studies (DeLong and others, 2011; Flannery and Poore, 2013).

The growth records of the coral Orbicella faveolata (formerly part of the Montastraea annularis

species complex) are the most extensively studied in the Atlantic Ocean (Hudson 1981; Hudson and 

others,1994), but recently, growth rates of Siderastrea siderea showed promise as proxies for environmental change (Saenger and others, 2009). Coral growth rates respond to many environmental variables, including water temperature (Shinn, 1966; Jokiel and Coles, 1977), hydrodynamics (Jokiel, 1978; 

Dennison and Barnes, 1988), and solar irradiance (Falkowski and others, 1990). The variables are often 

dynamic in shallow water environments along seasonal and shorter time scales, and growth rates are 

not uniform throughout the year (Kuffner and others, 2013). Therefore, geochemical proxies (Corrège, 

2006) and skeletal growth rates (Lough and Cantin, 2014) can together yield a better understanding of 

past environmental conditions.

The first step in paleoreconstruction of environmental variables is obtaining growth records of 

the coral cores by slabbing, X-raying, and measuring linear extension (growth). After preliminary measurements and preparation, the coral can be analyzed for geochemical composition (elemental and isotopic). This report summarizes coral-core collections made during a May 2012 field expedition within the 

waters of Dry Tortugas National Park (fig. 1). The report provides a description of the collection sites 

and methods, preliminary processing, statistics for the cores and core sites, and preliminary growth rate 

data (linear extension) for six new coral cores.

Figure 1. Map of the shallow banks of Dry Tortugas National Park, Florida. Data-collection sites (red circles) mark the 

locations where six coral cores were collected as part of this study. The inset shows the location of the study area in the 

southern Gulf of Mexico adjacent to the Florida peninsula.
3

Methods

Dry Tortugas National Park, established in 1992, occupies approximately 259 square kilometers 

(km2

) and is located 110 kilometers (km) west of Key West, Fla. In 2007, a 119 km2, no-take “Research 

Natural Area” (RNA) was designated by the National Park Service (NPS) and the Florida Fish and 

Wildlife Conservation Commission in the northwest quadrant of the park (Hallac and Hunt, 2010).

After obtaining scientific research permit # DRTO-2012-SCI-0001 from the NPS, corals were 

collected during a field expedition in May 2012. Coral colonies were selected by searching areas known 

to have large colonies that represent centuries of growth. Two corals were chosen inside the borders of 

the RNA near Loggerhead Key (fig. 1; designated as LH1 and LH2), two corals were collected from 

north of North Key Harbor (NK1 and NK2), and two corals were collected from the “Coral Gardens” 

area of Pulaski Shoal (CG1 and CG2).

Previously established coral-coring methods (Reich and others, 2009; Hickey and others, 2013) 

were followed, including the use of a DL07652 Stanley hydraulic drill and drill head with a 4-inchdiameter core barrel, 24 inches in length, attached to a drill operated from the surface supply boat. A 

pilot hole was drilled into the coral surface with a 1⁄4-inch starting bit to prevent the 4-inch bit from slipping sideways across the top of the coral head. To collect full coral cores, extension pieces were added 

after the primary core section was collected from the diamond-studded core barrel. The core barrel was 

reinserted into the drill hole several times to collect the full length of the core (fig. 2). For Orbicella 

faveolata, a plug of live coral was taken with the drill from the side of the colony to patch the main 

Figure 2. U.S. Geological Survey scuba diver operating the hand-held hydraulic drill while coring an Orbicella faveolata

coral (NK1) at the North Key site. Photograph credit: Ilsa B. Kuffner, U.S. Geological Survey
4

upward-facing hole (Hudson, 1983). This technique was successful for O. faveolata (fig. 3) but not for 

Siderastrea siderea because of the dense skeleton of the species. Instead, a precast concrete plug was 

inserted into the 4-inch holes remaining in the S. siderea heads, providing a suitably compatible substratum that can be overgrown by the coral. Following extraction, cores were placed on a table to dry before 

being wrapped in plastic and secured for travel.

Coral cores were sectioned along the primary growth axis into 4-millimeter-thick slabs using a 

lapidary saw with a carbide-tipped blade. Multiple (~3 to 4) slabs were taken from each coral-core section because corallite walls meander over time, and replicate slabs increase the chance of obtaining a 

continuous path for geochemical sampling. When necessary, the cores were angularly slabbed to follow 

the main axis of growth. The resulting slabs were cleaned in milli-Q water using a Branson Sonifer 450 

sonication device and air dried before storage. None of the slabs were treated with bleach or oxidizing 

chemicals.

X-radiographs (X-rays) of each coral slab were taken at the U.S. Geological Survey (USGS) 

St. Petersburg Coastal and Marine Science Center (SPCMSC) in St. Petersburg, Fla. The coral slabs 

were placed on a phosphor plate and X-rayed at 55 kilovolts and 2.5 milli-Ampere-seconds (mAs). The 

distance between the plate and the X-ray source was 79 centimeters (cm). The plate was scanned on an 

iCR3600+ scanner at 254 dots per inch (dpi) resolution (10 pixels per millimeter (mm)), processed on 

iCRco, Inc., software, and adjusted for contrast with Adobe Photoshop.

Linear extension (mm per annual density-band couplet) was estimated by two separate observers using iSolution Capture version 3.1 image analysis software (IMTi-Solution, Inc., Vancouver, 

British Columbia, Canada) and averaged for each slab. The mean-growth rate reported for each coralcore section is an average of the mean estimates for each replicate slab (the number of slabs varying 

from 1 to 4), and the standard error is based on the corresponding number of slabs for each section.

Figure 3. Coral LH1 (Orbicella faveolata) near Loggerhead Key (A) freshly cored with side-plug epoxied in place in May 

2012, and (B) after 1 year of healing time in May 2013, demonstrating the success of the grafting method (note the fusion of live 

tissue between the transplanted plug and the surrounding hole). Photograph credits: Ilsa B. Kuffner, U.S. Geological Survey.
5

Results and Summary

The objective was to sample living coral colonies and obtain material to use in understanding 

recent (<200 years) changes in environmental and oceanographic conditions in the Dry Tortugas area. 

Three specimens each of Orbicella faveolata and Siderastrea siderea (table 1) were obtained. Several of 

the corals are estimated to be older than 100 years, dating back to the late 1800s. Photographs of individual coral colonies, resulting cores and slabs, and X-rays of slabs can be found in an associated USGS 

Data Release (Kuffner and others, 2016).

The 4-inch-diameter coral cores were slabbed along their major growth axes to obtain slabs for 

growth and geochemical analysis. The cores were not consumed by the slabbing process; vertical portions appropriate for computerized tomography (CT) scanning and other uses remained. The quality 

of the cores, with respect to their growth-axis angles, varied by species and core section. Table 2 summarizes the sections (designated by letter) for each core and the number of slabs per core section. The 

Siderastrea siderea cores (LH2, CG1, and CG2) had much straighter, consistent growth axes, resulting 

in high-quality slabs for geochemical and growth analysis. Growth rates (linear extension) for select sections of each core are also presented in table 2. Using the linear extension measurements and counting 

from the year of collection (2012), LH2 dates to approximately 1877 CE (common era); CG1 to 1900 

CE; and CG2 to 1806 CE. Of note for core LH2 is a >20 cm length of subfossil Orbicella faveolata in 

core-section B, upon which the S. siderea colony grew.

The three O. faveolata (LH1, NK1, and NK2) cores did not produce easy-to-use slabs for geochemical or growth analysis. LH1 shows meandering of the main growth axes (see X-rays in Kuffner 

and others, 2016), but the use of multiple slabs per section enabled linear extension measurements, and 

analysis determined that this coral dates to approximately 1877 CE. The coral cores from NK1 and NK2 

show extreme meandering of the main growth axis, necessitating slabbing on the bias, starting with the 

second section (B) down the core. This type of slabbing results in high numbers of slabs per core section 

(table 2) with considerable overlap in time for each slab. Sampling these cores for geochemistry would 

require advanced skill and resources, but based on the successful capture of the main growth axis by 

slabbing on the bias, it is possible.

Studies using these cores to discern paleoceanographic and paleoclimate conditions through elemental analysis of coral powders subsampled along the thecal walls of the growth axis of each coral are 

underway (for example, Flannery and others, in press). The cores belong to the NPS and are on loan to the 

USGS at the SPCMSC in St. Petersburg, Fla., under NPS accession number DRTO-00353. Permission to 

borrow the samples for scientific investigation can be requested from the NPS and facilitated by the USGS.

Table 1. Information for six coral cores from Dry Tortugas National Park, Florida, collected May 10–13, 2012. Water 

depth reported is the ocean floor. To calculate depth at colony surface, subtract the length of the core.

Core 

Name Location Coral Species Date Collected Latitude (N°)

Longitude 

(W°)

Water 

Depth 

(m)

Core 

Length 

(cm)

LH1 Near Loggerhead Key Orbicella faveolata 5/10/2012 24.640 -82.919 3 149

LH2 Near Loggerhead Key Siderastrea siderea 5/11/2012 24.637 -82.924 3.6 85

CG1 Near Pulaski Shoal Siderastrea siderea 5/11/2012 24.695 -82.795 4.2 58

CG2 Near Pulaski Shoal Siderastrea siderea 5/13/2012 24.699 -82.799 3 93

NK1 Near North Key Harbor Orbicella favealata 5/12/2012 24.703 -82.848 3.9 302

NK2 Near North Key Harbor Orbicella faveolata 5/13/2012 24.703 -82.844 4.5 274
6

Table 2. Information for six coral cores from Dry Tortugas National Park, Florida, collected May 10–13, 2012. 

Sections are the contents of each core-barrel extracted from the colony; the topmost section is labeled “A,” the 

section beneath it is labeled “B,” and the labeling process continues in alphabetical order. The number of slabs 

shows how many replicate slabs were cut from each core section. Linear extension estimates were made from 

X-ray images of the slabs (see the Methods section for details). N/A = not applicable.

Coral Core Section Total Slabs Core-section

 Length (cm)

No. of Slabs

X-rayed

Linear Extension 

(mean mm year –1 ± SE)

LH1 A 4 52 4 8.2 ± 0.2

B 4 55 4 9.4 ± 0.2

C 4 42 4 10.9 ± 0.3

LH2 A 4 56 4 4.2 ± 0.1

B 0 29 N/A N/A

CG1 A 4 52 4 4.4 ± 0.1

B 0 6 N/A N/A

CG2 A 3 53 2 4.3

B 3 40 1 N/A

NK1 A 4 28 1 11.0

B 4 53 0 N/A

C 25 56 0 N/A

D 12 45 0 N/A

E 10 34 0 N/A

F 0 13 N/A N/A

G 1 17 0 N/A

H 12 56 0 N/A

NK2 A 4 55 1 8.4

B 4 48 0 N/A

C 3 50 0 N/A

D 0 55 N/A N/A

E 0 39 N/A N/A

F 0 27 N/A N/A
7

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Weinzierl and others—Collection Methods and Descriptions of Coral Cores Extracted from Massive Corals in Dry Tortugas National Park, Florida, U.S.A.—

Open-File Report 2016–1182

ISSN 2331-1258 (online)

https://doi.org/10.3133/ofr20161182