Linear Extension Rates of Massive Corals from the Dry 

Tortugas National Park (DRTO), Florida

By Adis Muslic, Jennifer A. Flannery, Christopher D. Reich, Daniel K. Umberger, Joseph M. Smoak, and 

Richard Z. Poore

Open-File Report 2013–1121

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, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Muslic, Adis, Flannery, J.A., Reich, C.D., Umberger, D.K., Smoak, J.M., and Poore, R.Z., 2013, Linear 

extension rates of massive corals from the Dry Tortugas National Park (DRTO), Florida: U.S. Geological 

Survey Open-File Report 2013–1121, 22 p. (http://pubs.usgs.gov/of/2013/1121/)

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endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

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

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

Study Site ........................................................................................................................................................................... 2

Materials and Methods ....................................................................................................................................................... 3

Coral Collection ...........................................................................................................................................................3

Linear Extension Rates................................................................................................................................................4

Results and Discussion ...................................................................................................................................................... 4

Siderastraea siderea ...................................................................................................................................................6

Diploria strigosa ...........................................................................................................................................................8

Environmental Factors........................................................................................................................................................ 8

Sea-Surface Temperature............................................................................................................................................8

Conclusions...................................................................................................................................................................... 10

Acknowledgments ............................................................................................................................................................ 10

References Cited . 10

Appendix........................................................................................................................................................................... 13

DRTO Montastraea faveolata ....................................................................................................................................13

DRTO Siderastrea siderea.........................................................................................................................................17

DRTO Diploria strigosa..............................................................................................................................................21

Figures

1. Map of the Dry Tortugas National Park (DRTO), Florida. The coral core locations and Coastal Marine Automated 

Networks (C-MAN) stations monitoring SST are denoted on the map by yellow triangles and red circles, respectively. All modern Montastraea faveolata, Siderastrea siderea, and Diploria strigosa coral cores were collected 

from Pulaski Shoal, and one D. strigosa coral core was collected from Middle Key in August 2008.................... 3

2. Average annual linear extension rates (in centimeters) for all DRTO coral cores from 1889 to 2007 with error 

bars (1σ). Y-axis scales were adjusted for each coral to show variability. (A) M. faveolata C2 (B) M. faveolata

B3 Slab 2 (C) M. faveolata B3 Slab 4 (D) M. faveolata B3 Composite (E) S. siderea A1 Slab 2 (F) S. siderea A1 

Slab 1 (G) S. siderea A1 Slab 2 Composite (H) D. strigosa MK (I) D. strigosa C1 ............................................... 5

3. (A) Average annual linear extension rates (in centimeters) comparison for M. faveolata B3 Slab 2 (light blue) 

and B3 Slab 4 (dark blue) from 1960 to 2007 with error bars (1σ). (B) Average annual linear extension rates (in 

centimeters) comparison for M. faveolata B3 Composite (navy blue) and C2 (teal) from 1938 to 2007 with error 

bars (1σ). ............................................................................................................................................................ 6

4. (A) Average annual linear extension rates (in centimeters) comparison for S. siderea A1 Slab 1 (pink) and A1 

Slab 2 (red) from 1944 to 2007 with error bars (1σ). (B) Average annual linear extension rates (in centimeters) 

comparison for S. siderea A1 Composite (red) and M. faveolata B3 Composite (navy blue) from 1889 to 2007 

with error bars (1σ). Y-axis scales were adjusted for each coral to show variability. ......................................... 7

5. (A) Gridded mean annual ICOADS data set centered on 82°W and 24°N from 1889 to 2007 (orange curve) (B) 

Average annual linear extension rates (in centimeters) for S. siderea A1 Composite (red curve) with error bars 

(1s). (C) Mean annual Key West air temperature from 1889 to 2007 (yellow curve). .......................................... 9

Tables

1. Summary of data for cores collected at the Dry Tortugas National Park (DRTO), including collection date, site 

and reef names, location (latitude and longitude), water depth, and core length. ................................................ 3
1

Linear Extension Rates of Massive Corals from the Dry 

Tortugas National Park (DRTO), Florida 

By Adis Muslic, Jennifer A. Flannery, Christopher D. Reich, Daniel R. Umberger, Joseph M. Smoak, and 

Richard Z. Poore

Abstract

Colonies of three coral species, Montastraea faveolata, Diploria strigosa, and Siderastrea 

siderea, located in the Dry Tortugas National Park (DRTO), Florida, were sampled and analyzed to 

evaluate annual linear extension rates. Montastraea faveolata had the highest average linear extension and variability in (DRTO: C2 = 0.67 centimeters/year (cm yr –1

) ± 0.04, B3 = 0.85 cm yr –1 ± 0.07), 

followed by D. strigosa (DRTO: C1 = 0.73 cm yr –1 ± 0.04; MK = 0.59 cm yr –1 ± 0.06) and S. siderea 

(DRTO: A1 = 0.41 cm yr –1 ± 0.03). Intercolony comparison of M. faveolata from DRTO yielded a significant correlation (r = 0.34, df = 67, P = 0.005) and similar long-term patterns. DRTO S. siderea core 

A1 showed an overall increasing trend (r = 0.61, df = 119, P < 0.0001) in extension rates that correlated 

significantly with International Comprehensive Ocean/Atmosphere Data Set annual sea-surface temperature (r = 0.42, df = 115, P < 0.0001) and an air temperature record from Key West (r = 0.37, df = 111, 

P < 0.0001). In conclusion, annual linear extension rates are species specific and potentially influenced 

by long-term variability in sea-surface temperature.

Introduction

Massive reef-building scleractinian corals have the potential for providing detailed information about past environmental conditions and the response of coral reefs to environmental change. The 

coral skeletons are composed of calcium carbonate in the form of the mineral aragonite. These corals 

are long-lived (multicentury), and their skeletons exhibit distinct annual density banding. A couplet of 

high and low density bands represents 1 year of growth. Some species, such as Montastraea faveolata, 

form their high density bands during the summer months, and lower density bands are deposited during 

the rest of the year (Shinn, 1966; Swart and others, 2002). The annual banding of the skeleton allows 

precise chronology, coral linear extension rates, and guidance of subannually resolved sampling for 

geochemical or isotopic analyses. 

Changes in the width of annual growth bands, or annual extension rates, of coral skeletons represent one measure of coral growth that can be related to coral health. Coral extension rates are species 

specific (Buddemeier and others, 1974; Tomascik, 1990; Logan and others, 1994). Buddemeier and 

others (1974) measured the extension rates of 47 reef-building corals of 15 different species and found 

that coral linear extension rates were more influenced by species than any environmental factor. However, studies measuring linear extension rates within individual species indicate that a variety of factors 

correlate with (and may influence) coral linear extension rates. Correlates of mean annual extension 

rates include season, rainfall (Buddemeier and others, 1974; Alibert and McCulloch, 1997), the El Niño 

Southern Oscillation (ENSO) cycle (Alibert and McCulloch, 1997), light levels (Bak, and others, 2009), 

and location within the reef (Cruz-Pinon and others, 2003).
2

A number of studies suggest that temperature may be an important control on linear extension 

rate variability in corals (Shinn, 1966; Carricart-Ganivet, 2004; De’ath and others, 2009), but the results 

of other studies are conflicting. Some studies indicate that linear extension rates in corals decrease as 

a result of an increase in sea-surface temperature (SST) (Carricart-Ganivet, 2004; Cooper and others, 

2008; De’ath and others, 2009). For example, specimens of genus Porites from the Great Barrier Reef 

(GBR) experienced a 16 percent decline in extension rates (Cooper and others, 2008). Extension rates 

in these Porites specimens decreased 1.02 percent yr –1 from 1988 to 2003 as a result of a rise in SST 

(Cooper and others, 2008). Carricart-Ganivet (2004) determined that decreasing trends in linear extension rates are correlated with increasing SST by measuring linear extension rates from Montastraea 

annularis from six locations across the Gulf of Mexico. 

Other studies concluded that linear extension rates increased with increasing SST (Shinn, 1966; 

Dodge and Lang, 1983). Dodge and Lang (1983) found that extension rates in M. annularis from the 

Gulf of Mexico increased with increasing SST. Additionally, some other studies concluded that SST

had no significant correlation with coral extension rates (Gladfelter and others, 1978; Bak and others, 

2009; Helmle and others, 2011). 

A study was conducted by the U.S. Geological Survey (USGS) to report linear extension rate 

measurements for several common massive reef building corals in the Dry Tortugas National Park 

(DRTO), Florida. The study included three species (Siderastraea siderea, Montastraea faveolata, and 

Diploria Strigosa) of coral collected from the DRTO.

Study Site

The DRTO (fig. 1) is located 112.9 kilometers (km) west of Key West, Florida (http://www.

nps.gov/drto/index.htm), the closest inihabited area to the park. The DRTO forms an elliptical atolllike structure that is 27 km along the major axis (southwest-northeast) and 12 km along the minor axis 

(Davis, 1982). The three major banks—Pulaski Shoal (northeast), Long Key (south), and Loggerhead 

Key (west)—are separated by 10–20 meter (m) deep channels. The average water depth of the banks 

is 2–3 m, and the banks are surrounded by 12–23 m deep lagoons. The Holocene reefs composing the 

DRTO are situated on the South Florida margin and occupy a transitional zone between the south- and 

east-facing rimmed margin and the west-facing ramp margin (Mallinson and others, 2003). The reefs 

are situated on the Key Largo Limestone platform composed mainly of older (~125 thousand years old) 

massive coral heads (Hickey and others, 2012). 
3

A

A

A

B

Montastraea faveolata

DRYF1

PLSF1

Long Key

82.95W 82.9W 82.85W 82.8W 82.75W

24.7N

24.65N

24.6N

24.7N

24.65N

24.6N

Legend

Coral core site

SST buoy stations 

0 0.8 1.6 2.4 3.2

Kilometers

Garden Key/Fort Jefferson

Loggerhead Key

Dry Tortugas

Pulaski Shoal

Pulaski Reef

F l o r i d a

Dry Tortugas

Diploria strigosa

Middle Key

Diploria strigosa

Siderastrea siderea

82.95W 82.9W 82.85W 82.8W 82.75W

Figure 1. Map of the Dry Tortugas National Park (DRTO), Florida. The coral core locations and Coastal Marine 

Automated Networks (C-MAN) stations monitoring SST are denoted on the map by yellow triangles and red circles, 

respectively. All modern Montastraea faveolata, Siderastrea siderea, and Diploria strigosa coral cores were collected from Pulaski Shoal, and one D. strigosa coral core was collected from Middle Key in August 2008.

Materials and Methods

Coral Collection

The DRTO coral cores were collected from Pulaski Shoal and Middle Key, Florida, in 

August 2008. The cores were collected from live coral heads at water depths ranging from 3.4 to 4.3 m 

(table 1), using the USGS rotary hydraulic coring system. 

Table 1. Summary of data for cores collected at the Dry Tortugas National Park (DRTO), including collection date, 

site and reef names, location (latitude and longitude), water depth, and core length. 

Core Date Location Coral Species Latitude (N) Longitude (W) Water Depth (m) Core Length (cm)

B3 8/7/2008 Pulaski Shoal Montastraea faveolata 24.699 82.799 3.4 142

C2 8/8/2008 Pulaski Shoal Montastraea faveolata 24.695 82.795 3.7 156

C1 8/7/2008 Pulaski Shoal Diploria strigosa 24.699 82.798 3.4 60

MK 8/6/2008 Middle Key Diploria strigosa 24.645 82.832 3.4 23

A1 8/6/2008 Pulaski Shoal Siderastrea siderea 24.699 82.798 4.3 113
4

The equipment used for drilling included a hydraulic-powered submersible drill, a 10-centimeter 

(cm) diameter by 61-cm long core barrel with a surface set diamond bit and a hydraulic power unit operated from the boat. Corals were drilled along their vertical growth. Following drilling, cores were taken 

to the USGS Coastal and Marine Science Center in St. Petersburg, Florida, where they were cut into 

5 millimeter (mm) thick slabs along their maximum growth axis (Reich and others, 2009; Hickey and others, 2012). The DRTO slabs were x-rayed at Louisiana State University by an AGFA CR 35-X machine 

at 55 kiloVolts (kV) for 2.5 milliAmp seconds (mAs). The x-ray images were converted into Adobe 

Photoshop files with 100 pixel cm–1 resolution. 

Linear Extension Rates

Extension rate measurements were made on coral x-ray images using the ruler tool in Adobe 

Photoshop. Measurements were made along the thecal wall, a part of the skeleton where calcium carbonate is deposited continuously and high and low density bands are distinguished. Linear distance between the tops of successive high density bands was measured. Since the high density bands are formed 

during the late summer and early fall (Swart and others, 2002), a coral year does not correspond to a 

calendar year. For consistency, in comparisons to other parameters, it is assumed that each coral year 

starts on the 1st day of September. 

Eight flat coral slabs from five different DRTO cores from three different species (M. faveolata, 

S. siderea, and D. strigosa) were analyzed from the DRTO (nomenclature for cores and slabs used in 

this text is found in table 1). Intracolony replication was performed on two slabs of M. faveolata and 

S. siderea, and intercolony comparison was done on two different M. faveolata and D. strigosa colonies. 

In an effort to reduce measuring errors, paths with clear, distinguished high and low density bands were 

chosen over those with less clear banding. At least three linear extension transects for each year were 

measured from each DRTO coral slab. 

Siderastrea siderea deposits calcium carbonate more evenly throughout the year, causing high 

and low density bands to be less distinctive than the other two species, proving more difficult to designate a starting and ending point of each density band. Montastraea faveolata polyps tend to have meandering paths that grow at an angle, which appear shorter or longer on the x-ray than they actually are, 

leading to incorrect measurements. To avoid this discrepancy, paths were measured until meandering 

started, then another path was chosen for measuring. 

The coral density bands on the x-rays were counted backward from 2008 down core for DRTO 

corals, excluding year 2008 because data for this year were incomplete and lacked high density band 

formation. In cases where multiple slabs were analyzed for the same core, the results were averaged 

to form a composite record. Statistical calculations were made using Microsoft Office Excel 2010 by 

applying standard statistical procedures for average and standard deviation. Correlations between coral 

linear extension rates and environmental parameters (including SST) were made using standard linear 

regression with 95 percent confidence interval (α=0.05).

Results and Discussion

Montastraea faveolata had the highest average extension rate and variability of all three species from DRTO. The average linear extension rates of M. faveolata cores (fig. 2A–D; C2 = 0.67 cm 

yr –1

 ± 0.04 (n = 69 (number of years)); B3 = 0.85 cm yr –1 ± 0.07 (n = 119)) were within the range (0.38 

to 0.98 yr –1

) for this species for studies throughout the Caribbean (Carricart-Ganivet and others, 2000; 

Helmle and others, 2011). For example, average linear extension rates for M. faveolata varied from 
5

0.38 cm yr –1 in Discovery Bay, Jamaica (Dustan, 1975), to 0.87 cm yr –1 in the Mexican Caribbean 

Carricart-Ganivet and others, 2000), and 0.91 cm yr –1 to 0.98 cm yr –1 in St. Croix, U.S. Virgin Islands 

(Baker and Weber, 1975; Dodge and Brass, 1984, respectively). 

0.6 

0.8 

1.0 

1.2 

1885 

1895 

1905 

1915 

1925 

1935 

1945 

1955 

1965 

1975 

1985 

1995 

2005 

0.4 

0.6 

0.8 

0.4 

0.6 

0.8 

1.0 

0.4 

0.6 

0.8 

1.0 

1.2 

0.3 

0.4 

0.5 

0.6 

0.3 

0.4 

0.5 

0.6 

0.6 

0.7 

0.8

0.9 

0.7 

0.8

0.5 

0.6 

Years

C1

MK A1 Slab 1

A1 Slab 2

B3 Slab 2

B3 Slab 4

B3 Composite

C2

Linear Extension (cm)

Linear Extension (cm)

M. faveolata

S. siderea

D. strigosa

(A)

(B)

(H)

(G)

(F)

(E)

(D)

(C)

0.3 

0.4 

0.5 

0.6 

A1 Composite

(I)

Figure 2. Average annual linear extension rates (in centimeters) for all DRTO coral cores from 1889 to 2007 with 

error bars (1σ). Y-axis scales were adjusted for each coral to show variability. (A) M. faveolata C2 (B) M. faveolata

B3 Slab 2 (C) M. faveolata B3 Slab 4 (D) M. faveolata B3 Composite (E) S. siderea A1 Slab 2 (F) S. siderea A1 

Slab 1 (G) S. siderea A1 Slab 2 Composite (H) D. strigosa MK (I) D. strigosa C1.
6

 Intracolony correlation between different slabs from the same species (slabs 2 and 4) was high 

in M. faveolata B3 (fig. 3A, r = 0.82, df = 44, P < 0.0001), most likely resulting from a combination of 

genetics (because they are from the same colony; (Oliver, 1968)) and picking paths with similar coral 

polyp orientation. 

0.6 

0.8 

1.0 

1.2 

1935 

1945 

1955 

1965 

1975 

1985 

1995 

2005 

0.4 

Years

B3 Composite

Linear Extension (cm)

C2 0.6 

0.8 

1.0 

1.2 B3 Slab 4

B3 Slab 2

Linear Extension (cm)

r = 0.82

r = 0.34

(A)

(B)

Figure 3. (A) Average annual linear extension rates (in centimeters) comparison for M. faveolata B3 Slab 2 (light

blue) and B3 Slab 4 (dark blue) from 1960 to 2007 with error bars (1σ). (B) Average annual linear extension rates 

(in centimeters) comparison for M. faveolata B3 Composite (navy blue) and C2 (teal) from 1938 to 2007 with error 

bars (1σ). 

Intracolony M. faveolata slabs had a higher correlation than intercolony M. faveolata slabs. 

Montastaea faveolata cores B3 and C2 had a significant positive correlation with each other (fig. 3, 

r = 0.34, df = 67, P = 0.0043), although M. faveolata core B3 had a 25.4 percent higher average extension rate than M. faveolata C2. Both M. faveolata cores B3 and C2 showed a slight negative trend until 

the late1960s (fig. 3B). It is likely that both M. faveolata colonies experienced similar environmental 

conditions because they were collected from the same reef patch from similar water depths (~3.5 m; 

table 1). 

Siderastraea siderea 

Of the three DRTO species, Siderastrea siderea A1 had the lowest extension rates (0.41 cm 

yr –1 ± 0.03 (n = 119), fig. 2D,E), approximately 0.3 cm yr –1 less than those determined from S. siderea

specimens from Panama (Guzman and Tudhope, 1998) but similar to S. siderea specimens from Puerto 
7

Rico (0.35 to 0.43 cm yr –1; Torres and Morelock, 2002). Like M. faveolata, two intracolony slabs from 

S. siderea A1 were highly correlated with one another (fig. 3A, r = 0.95, df = 62, P < 0.0001). Intracolony comparison of S. siderea reveals a higher correlation (r = 0.95) than that of M. faveolata (r = 0.82).

A1 Slab 2 S. siderea

Linear Extension (cm)

B3 All Slabs M. faveolata

A1 Slab 1

A1 Slab 2

0.6 

0.8 

1.0 

1.2 

0.3 

0.4 

0.5 

0.6 

B3 Composite

Linear Extension (cm)

0.3 

0.4 

0.5 

0.6 

A1 Composite

1885 

1895 

1905 

1915 

1925 

1935 

1945 

1955 

1965 

1975 

1985 

1995 

2005 

Years

0.4 

1.4 

S. siderea

(A)

(B)

r = 0.95

r = -0.20

Figure 4. (A) Average annual linear extension rates (in centimeters) comparison for S. siderea A1 Slab 1 (pink) and 

A1 Slab 2 (red) from 1944 to 2007 with error bars (1σ). (B) Average annual linear extension rates (in centimeters) 

comparison for S. siderea A1 Composite (red) and M. faveolata B3 Composite (navy blue) from 1889 to 2007 with 

error bars (1σ). Y-axis scales were adjusted for each coral to show variability. 

Montastraea faveolata B3 had a significant negative correlation with S. siderea A1 (fig. 4B, 

r = –0.20, df = 117, P = 0.0292). Siderastrea siderea A1 had a significant overall positive trend 

(r = 0.61, df = 119, P < 0.0001) in linear extension rates from 1889 to 2007, while M. faveolata B3 had 

a signifcant negative trend for the same time interval (r = –0.22, df = 119, P = 0.0153). This suggests 

that fast-growing M. faveolata reacts differently to similar environmental conditions compared to slowgrowing S. siderea.

Differences in growth strategies among these species may have contributed to their different responses to environmental challenges. For example, a S. siderea from Puerto Rico was found to 

be tolerant to sedimentation while Montastraea annularis was sensitive to sedimentation (Torres and 

Morelock, 2002). This implies that coral species respond differently to similar localized environmental 

conditions. Although the aforementioned study focused on sedimentation, it is conceivable that different coral species may respond differently to other environmental conditions as well, such as SST. Local 
8

environmental factors may cause extension rates to vary, even in corals that live in close proximity to 

each other (Heiss, 1996). 

Diploria strigosa

The average extension rates (C2: 0.73 cm yr –1 ± 0.04 (n = 54), MK: 0.59 cm yr –1 ± 0.06 (n = 35)) 

and variability in Diploria strigosa were lower than those of M. faveolata but higher than that of S. 

siderea (fig. 2). D. strigosa C1 had extension rates on average 19.6 percent higher than D. strigosa MK, 

and no similar trends or correlations were observed between the two D. strigosa cores. X-rays of D. strigosa C1 revealed that the coral had a hyperplasia tumor, typically known to increase coral cell growth 

leading to abnormally high extension rates (Gateño and others, 2003), as observed in this core. Diploria 

strigosa MK extension rates were closer to those found elsewhere in the Caribbean Sea and the Gulf of 

Mexico, suggesting normal growth (0.25 cm yr –1 to 0.42 cm yr –1, Logan and others, 1994). Other D. strigosa linear extension rates measured in various locations across the West Atlantic included 0.46–0.59 

cm yr –1

 in Panama (Guzman and Cortes, 1989), 0.43–0.46 cm yr –1 in Aruba (Harriot, 1992), 0.35–1.00 

cm yr –1 in Bahamas (Hubbard and Scaturo, 1985), 0.5 cm yr –1 in East Flower Banks (Hudson and others, 

1994), and 0.33 cm yr –1

 in Bermuda (Johannes and others, 1983). The average extension rate of 0.59 cm 

yr –1 in D. strigosa MK is above regional average but still within the range for the species collected near 

the Gulf of Mexico.

Environmental Factors

Sea-Surface Temperature

Several studies proposed that SST is a leading cause of extension rate variability in corals 

(Shinn, 1966; Carricart-Ganivet, 2004; De’ath and others, 2009). Three temperature data sets were 

available in proximity to the coral coring locations: local buoy SST (DRYF1 and PLSF1), Key West air 

temperature, and the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) SST. Local buoy data sets were collected from Coastal Marine Automated Network (C-MAN) stations PLSF1 

(fig. 1; 24.69°N, 82.77°W) and C-MAN DRYF1 (fig. 1; 24.64°N, 82.86°W). Both stations are located 

within the boundaries of DRTO (PLSF1 was located at Pulaski Shoal near the locations of the corals). 

All buoy values were obtained hourly and were computed into average monthly and mean annual SST

values. Five complete years of data were available for annual comparisons, making this record the shortest of all three records available. The local buoys likely produced the most comparable SST records, but 

the records do not cover the necessary time interval. ICOADS SST data contain observations by ships 

and buoys and are considered by the National Oceanic and Atmospheric Administration (NOAA) to 

be one of the most complete and heterogeneous collections of SST (http://icoads.noaa.gov/). ICOADS 

contains the SST for the past 300 years and is arranged in 2° latitude by 2° longitude boxes prior to 1959 

and 1° by 1° since 1960. The grids used in this study were centered on 82°W and 24°N. Gridded SST 

data sets such as ICOADS are widely used in coral studies (Payet and Agricole, 2006; Vargas-Angel and 

others, 2006; Guzman and others, 2008). Lastly, Key West air temperature was recorded daily and sensors were maintained by the National Weather Service (Menne and others, 2011). Air temperature was 

measured 1.22 m above sea level at the Key West International Airport (station 084570) from 1895 to 

2007. The mean annual Key West air temperature record was compared to the linear extension rates to 

potentially compensate for the increased ICOADS grid size prior to 1960.
9

Mean annual ICOADS SST correlated significantly with S. siderea A1 linear extension rates 

(fig. 5A,B; r = 0.42, df = 115, P < 0.0001) but not with the extension rates of the other corals. The mean 

annual Key West air temperature data also correlated significantly with the A1 linear extension rates 

(fig. 5B,C; r = 0.37, df = 111, P < 0.0001). Slow-growing S. siderea produces short yet steady extension 

rates. The extension rates of the fast-growing M. faveolata and D. strigosa had no significant correlation with annual SST. The DRTO results agree with Helmle and others (2011) who found no correlation between M. faveolata extension rates and SST from Florida Keys. In agreement with other studies, 

the linear extension rates were species specific (fig. 2; Buddemeier and others, 1974; Tomascik, 1990; 

Logan and others, 1994).

1885 

1895 

1905 

1915 

1925 

1935 

1945 

1955 

1965 

1975 

1985 

1995 

2005 

25.0 

25.5 

26.0 

26.5 

27.0 

24.0 

24.5 

25.0 

25.5 

26.0 

26.5 

A1 Composite Linear Extension (cm)

ICOADS SST (°C) Key West Air Temperature (°C)

Years

0.25 

0.30 

0.35 

0.40 

0.45 

0.50 

0.55 

0.60 

y = 0.0011x - 1.6937 

R = 0.41 

y = 0.0099x + 5.7166 

 = 0.39

r = 0.42

(A)

(B)

(C)

r = 0.37

R

R

y = 0.0091x + 8.5305 

 = 0.41 

2

2

2

Figure 5. (A) Gridded mean annual ICOADS data set centered on 82°W and 24°N from 1889 to 2007 (orange 

curve). (B) Average annual linear extension rates (in centimeters) for S. siderea A1 Composite (red curve) with error bars (1s). (C) Mean annual Key West air temperature from 1889 to 2007 (yellow curve). 
10

Conclusions

The current study documents linear extension rates for three massive coral species (Montastraea 

faveolata, Siderastrea siderea, and Diploria strigosa). It can be concluded that extension rates in the 

Dry Tortugas National Park are species specific as well as colony specific. Montastraea faveolata had 

the highest linear extension rates (fastest growth) of all three species in DRTO, and S. siderea had the 

lowest (slowest growth). Intracolony comparisons of both M. faveolata and S. siderea demonstrate that 

environmental factors influence each polyp within the colony in a similar way. Intercolony comparisons 

in M. faveolata from DRTO had a significant positive correlation. 

Siderastrea siderea and M. faveolata produced long linear extension rate records. DRTO S. 

siderea A1 had an overall positive trend that correlated significantly with ICOADS SST (centered on 

24°N and 82°W) and an air temperature record from Key West, Fla. Both species merit the attention of 

future studies in the field of climatology for subtropical and tropical oceans.

Acknowledgments

The authors thank Don Hickey, B.J. Reynolds, Jordan Sanford, David Zawada, Ilsa Kuffner, and 

Christopher Smith of the USGS. The authors also thank the M/V Fort Jefferson crew, Dry Tortugas National Park personnel, and Kristine DeLong of LSU for discussions that improved the manuscript. We thank 

CMG for funding. We thank Bayfront Medical Plaza Radiology Department for x-radiograph assistance. 

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13

Appendix

DRTO Montastraea faveolata

Year B3 Composite B3 Composite 

Error (1σ)

B3 Composite 

n n

B3 Slab 2 B3 Slab 2 

Error (1σ)

B3Slab 

2 n

B3 Slab 4 B3 Slab 4 

Error (1σ)

B3Slab 

4 n

C2 C2 Error 

(1σ)

C2 n 

2007 0.763 0.110 6 0.757 0.056 3 0.77 0.164 3 0.78 0.056 3

2006 0.843 0.138 6 0.796 0.017 3 0.89 0.259 3 0.733 0.071 3

2005 0.756 0.111 6 0.818 0.137 3 0.693 0.084 3 0.797 0.064 3

2004 0.879 0.050 6 0.958 0.031 3 0.8 0.069 3 0.74 0.094 4

2003 0.823 0.093 6 0.896 0.126 3 0.75 0.06 3 0.62 0.049 5

2002 0.756 0.082 6 0.819 0.069 3 0.693 0.095 3 0.676 0.048 5

2001 0.982 0.080 6 0.993 0.058 3 0.97 0.102 3 0.69 0.029 4

2000 0.920 0.062 7 0.917 0.043 3 0.923 0.082 4 0.793 0.054 4

1999 0.933 0.129 7 0.881 0.048 3 0.985 0.209 4 0.773 0.041 4

1998 0.756 0.057 6 0.859 0.002 3 0.653 0.112 3 0.607 0.038 3

1997 0.869 0.064 7 0.952 0.024 3 0.785 0.104 4 0.528 0.023 5

1996 0.758 0.046 6 0.807 0.032 3 0.71 0.06 3 0.617 0.032 3

1995 0.964 0.042 6 1.004 0.014 3 0.923 0.070 3 0.713 0.006 3

1994 0.827 0.053 6 0.808 0.026 3 0.847 0.080 3 0.643 0.026 4

1993 1.002 0.076 6 1.083 0.047 3 0.92 0.104 3 0.72 0.039 4

1992 0.964 0.111 6 1.002 0.015 3 0.927 0.206 3 0.753 0.022 4

1991 0.778 0.093 7 0.838 0.112 3 0.718 0.074 4 0.817 0.029 3

1990 0.859 0.074 7 0.906 0.035 3 0.813 0.114 4 0.653 0.035 3

1989 1.07 0.146 6 1.017 0.041 3 1.123 0.251 3 0.7 0.036 3

1988 0.781 0.031 6 0.811 0.021 3 0.75 0.04 3 0.643 0.049 3

1987 0.923 0.039 6 0.936 0.034 3 0.91 0.044 3 0.763 0.104 3

1986 0.839 0.036 7 0.848 0.027 4 0.83 0.046 3 0.6 0.035 3

1985 0.608 0.099 8 0.607 0.117 4 0.61 0.081 4 0.653 0.006 3

1984 0.687 0.069 7 0.7 0.083 4 0.673 0.055 3 0.663 0.099 3

1983 0.801 0.075 7 0.782 0.085 4 0.82 0.066 3 0.733 0.072 3

1982 0.769 0.104 6 0.818 0.067 3 0.72 0.14 3 0.59 0.044 3

1981 0.708 0.080 6 0.72 0.055 3 0.697 0.104 3 0.603 0.025 3

1980 0.802 0.097 6 0.787 0.023 3 0.817 0.170 3 0.633 0.101 3

1979 1.037 0.018 8 1.014 0.018 5 1.06 0.017 3 0.783 0.068 3
14

DRTO Montastraea faveolata (continued)

1978 0.954 0.026 8 0.983 0.028 4 0.925 0.024 4 0.69 0.085 4

1977 0.611 0.062 6 0.621 0.019 3 0.6 0.105 3 0.705 0.069 4

1976 0.858 0.065 6 0.87 0.01 3 0.847 0.120 3 0.78 0.029 4

1975 0.74 0.053 7 0.77 0.044 3 0.71 0.062 4 0.62 0.067 4

1974 0.832 0.069 6 0.79 0.033 3 0.873 0.105 3 0.573 0.010 4

1973 0.746 0.027 6 0.771 0.018 3 0.72 0.036 3 0.677 0.078 3

1972 0.943 0.091 6 1.003 0.061 3 0.883 0.121 3 0.765 0.057 4

1971 0.649 0.033 6 0.702 0.037 3 0.597 0.029 3 0.71 0.053 3

1970 0.658 0.037 6 0.736 0.030 3 0.58 0.044 3 0.677 0.055 3

1969 0.578 0.048 6 0.627 0.026 3 0.53 0.07 3 0.683 0.055 3

1968 0.697 0.026 6 0.691 0.011 3 0.703 0.040 3 0.523 0.042 3

1967 0.65 0.030 6 0.72 0.003 3 0.58 0.056 3 0.467 0.049 3

1966 0.626 0.029 6 0.636 0.011 3 0.617 0.047 3 0.573 0.047 3

1965 0.919 0.073 6 0.904 0.013 3 0.933 0.133 3 0.633 0.074 3

1964 0.689 0.013 6 0.732 0.010 3 0.647 0.015 3 0.593 0.047 3

1963 0.701 0.051 6 0.719 0.005 3 0.683 0.096 3 0.69 0.017 3

1962 0.759 0.051 6 0.828 0.022 3 0.69 0.079 3 0.727 0.060 3

1961 0.803 0.051 3 0.782 0.020 3 0.537 0.015 3

1960 0.908 0.036 3 0.633 0.015 3

1959 1.086 0.125 3 0.617 0.051 3

1958 0.683 0.174 3 0.52 0.02 3

1957 0.787 0.178 3 0.593 0.023 3

1956 0.753 0.114 3 0.653 0.085 4

1955 0.723 0.126 3 0.623 0.054 4

1954 0.831 0.059 3 0.713 0.051 3

1953 0.807 0.054 3 0.743 0.040 3

1952 0.926 0.135 3 0.66 0.02 3

1951 0.93 0.029 3 0.6 0 3

1950 0.805 0.036 4 0.667 0.047 3

1949 0.83 0.064 3 0.628 0.065 4

1948 0.94 0.015 3 0.613 0.006 3

1947 0.892 0.115 3 0.733 0.025 4

1946 0.961 0.138 3 0.718 0.057 4
15

DRTO Montastraea faveolata (continued)

1945 0.801 0.0393 0.71 0.0254

1944 0.782 0.1493 0.648 0.0305

1943 1.078 0.1963 0.708 0.0495

1942 0.897 0.1253 0.71 0.0255

1941 0.924 0.1454 0.746 0.0255

1940 0.904 0.1154 0.724 0.0235

1939 0.997 0.0483 0.717 0.0353

1938 0.731 0.0854

1937 0.787 0.1624

1936 0.577 0.0173

1935 0.632 0.0753

1934 0.628 0.0303

1933 0.636 0.043

1932 0.897 0.1033

1931 0.784 0.1013

1930 0.918 0.0623

1929 0.94 0.1123

1928 0.878 0.0223

1927 1.18 0.0953

1926 1.208 0.0193

1925 1.224 0.0303

1924 0.944 0.0873

1923 0.868 0.0733

1922 1.15 0.1973

1921 0.872 0.1293

1920 0.834 0.0273

1919 0.978 0.1083

1918 0.868 0.056

3

1917 0.844 0.061

3

1916 0.984 0.0393

1915 0.912 0.0233

1914 0.727 0.0293

1913 1.054 0.0883
16

DRTO Montastraea faveolata (continued)

1912 1.174 0.108 3

1911 0.983 0.064 3

1910 0.861 0.045 3

1909 1.056 0.030 3

1908 0.918 0.058 3

1907 0.801 0.083 3

1906 1.062 0.063 3

1905 0.843 0.070 3

1904 0.816 0.030 3

1903 0.954 0.096 3

1902 0.784 0.094 3

1901 0.788 0.094 4

1900 0.657 0.104 3

1899 0.829 0.115 3

1898 0.987 0.115 3

1897 0.932 0.099 3

1896 0.813 0.037 3

1895 0.749 0.048 3

1894 0.964 0.015 3

1893 0.859 0.030 3

1892 0.754 0.067 4

1891 0.936 0.083 3

1890 1.019 0.056 3

1889 0.806 0.005 3

Average 0.85 0.07 0.83 0.04 0.78 0.09 0.67 0.04
17

DRTO Siderastrea siderea

Year A1 Composite A1 Composite 

Error (1σ)

A1 Composite n A1 Slab 1 A1 Slab 1 Error 

(1σ)

A1 Slab 

1 n

A1 Slab 2 A1 Slab 2 Error 

(1σ)

A1 Slab 

2 n

2007 0.426 0.017 6 0.439 0.015 3 0.413 0.019 3

2006 0.381 0.033 6 0.381 0.040 3 0.381 0.026 3

2005 0.494 0.039 6 0.499 0.044 3 0.489 0.033 3

2004 0.537 0.023 6 0.542 0.020 3 0.531 0.026 3

2003 0.590 0.037 6 0.603 0.032 3 0.577 0.041 3

2002 0.530 0.027 6 0.549 0.011 3 0.511 0.044 3

2001 0.436 0.031 7 0.421 0.035 3 0.451 0.026 4

2000 0.541 0.036 8 0.54 0.029 4 0.542 0.042 4

1999 0.464 0.008 9 0.458 0.002 4 0.470 0.013 5

1998 0.518 0.036 7 0.531 0.040 3 0.505 0.032 4

1997 0.470 0.011 7 0.491 0.007 3 0.448 0.016 4

1996 0.464 0.019 8 0.472 0.020 3 0.456 0.018 5

1995 0.474 0.016 8 0.475 0.018 4 0.473 0.013 4

1994 0.469 0.027 8 0.471 0.029 4 0.468 0.025 4

1993 0.496 0.032 9 0.495 0.032 5 0.497 0.031 4

1992 0.478 0.028 9 0.473 0.028 5 0.483 0.027 4

1991 0.428 0.020 8 0.421 0.008 3 0.435 0.033 5

1990 0.409 0.028 8 0.399 0.018 3 0.418 0.037 5

1989 0.346 0.029 8 0.331 0.028 3 0.362 0.030 5

1988 0.486 0.010 8 0.48 0.003 3 0.492 0.016 5

1987 0.463 0.016 8 0.462 0.011 3 0.463 0.022 5

1986 0.508 0.023 9 0.519 0.017 4 0.496 0.028 5

1985 0.491 0.049 9 0.493 0.043 4 0.488 0.055 5

1984 0.464 0.029 7 0.462 0.024 3 0.467 0.035 4

1983 0.592 0.022 7 0.592 0.017 3 0.591 0.027 4

1982 0.522 0.020 7 0.53 0.018 3 0.515 0.022 4

1981 0.450 0.030 8 0.446 0.025 3 0.455 0.034 5

1980 0.439 0.039 9 0.426 0.038 3 0.453 0.039 6

1979 0.485 0.042 9 0.494 0.047 3 0.476 0.036 6

1978 0.431 0.015 7 0.439 0.015 3 0.422 0.016 4

1977 0.474 0.021 6 0.482 0.020 3 0.466 0.021 3
18

DRTO Siderastrea siderea (continued)

1976 0.437 0.032 7 0.451 0.032 4 0.424 0.032 3

1975 0.452 0.045 7 0.466 0.038 4 0.437 0.051 3

1974 0.445 0.023 8 0.467 0.017 4 0.424 0.030 4

1973 0.415 0.026 8 0.419 0.030 4 0.411 0.023 4

1972 0.397 0.042 8 0.389 0.048 4 0.405 0.036 4

1971 0.36 0.025 8 0.359 0.017 4 0.361 0.032 4

1970 0.460 0.030 8 0.46 0.032 4 0.459 0.028 4

1969 0.436 0.006 8 0.435 0.004 4 0.437 0.007 4

1968 0.462 0.021 7 0.458 0.014 3 0.467 0.027 4

1967 0.449 0.010 7 0.453 0.006 3 0.445 0.014 4

1966 0.433 0.016 8 0.442 0.017 4 0.425 0.015 4

1965 0.406 0.015 8 0.398 0.006 4 0.414 0.025 4

1964 0.399 0.027 7 0.414 0.020 3 0.384 0.034 4

1963 0.436 0.026 7 0.452 0.029 3 0.419 0.024 4

1962 0.458 0.036 7 0.458 0.028 3 0.459 0.044 4

1961 0.39 0.016 7 0.391 0.011 3 0.389 0.021 4

1960 0.392 0.033 6 0.393 0.031 3 0.391 0.036 3

1959 0.537 0.030 6 0.54 0.03 3 0.533 0.030 3

1958 0.489 0.022 6 0.493 0.023 3 0.484 0.021 3

1957 0.403 0.018 6 0.41 0.01 3 0.395 0.027 3

1956 0.425 0.039 7 0.427 0.047 3 0.423 0.031 4

1955 0.403 0.005 7 0.41 0 3 0.395 0.009 4

1954 0.407 0.010 6 0.41 0.01 3 0.403 0.011 3

1953 0.431 0.069 6 0.437 0.076 3 0.425 0.063 3

1952 0.475 0.033 6 0.483 0.025 3 0.467 0.040 3

1951 0.434 0.026 7 0.453 0.023 3 0.414 0.028 4

1950 0.377 0.063 6 0.38 0.079 3 0.373 0.047 3

1949 0.422 0.048 6 0.407 0.055 3 0.437 0.040 3

1948 0.426 0.026 6 0.427 0.021 3 0.425 0.031 3

1947 0.441 0.040 7 0.44 0.04 3 0.441 0.039 4

1946 0.389 0.064 7 0.377 0.065 3 0.402 0.064 4

1945 0.353 0.027 7 0.333 0.025 3 0.373 0.029 4

1944 0.356 0.063 7 0.353 0.075 3 0.358 0.05 4

1943 0.392 0.067 5
19

DRTO Siderastrea siderea (continued)

1942 0.38 0.022 5

1941 0.343 0.055 3

1940 0.387 0.031 3

1939 0.357 0.015 3

1938 0.393 0.054 4

1937 0.373 0.022 4

1936 0.38 0.01 3

1935 0.37 0.052 3

1934 0.327 0.025 3

1933 0.34 0.051 4

1932 0.388 0.039 4

1931 0.373 0.065 4

1930 0.345 0.021 4

1929 0.38 0.034 4

1928 0.423 0.017 4

1927 0.363 0.033 4

1926 0.358 0.010 4

1925 0.31 0.02 3

1924 0.347 0.046 3

1923 0.39 0.027 3

1922 0.347 0.042 3

1921 0.34 0.01 3

1920 0.333 0.023 3

1919 0.303 0.032 3

1918 0.313 0.012 3

1917 0.36 0.044 3

1916 0.347 0.006 3

1915 0.4 0.01 3

1914 0.353 0.029 3

1913 0.403 0.006 3

1912 0.413 0.015 3

1911 0.373 0.023 3

1910 0.355 0.027 4
20

DRTO Siderastrea siderea (continued)

1909 0.323 0.070 3

1908 0.327 0.025 3

1907 0.34 0.017 3

1906 0.297 0.031 3

1905 0.417 0.095 3

1904 0.46 0.036 3

1903 0.437 0.025 3

1902 0.44 0.053 3

1901 0.377 0.015 3

1900 0.413 0.015 3

1899 0.397 0.021 3

1898 0.457 0.012 3

1897 0.363 0.015 3

1896 0.347 0.015 3

1895 0.393 0.059 3

1894 0.403 0.012 3

1893 0.323 0.021 3

1892 0.403 0.110 3

1891 0.433 0.083 3

1890 0.39 0.046 3

1889 0.383 0.074 3

Averagee 0.41 0.03 0.45 0.03 0.45 0.03
21

DRTO Diploria strigosa

Year C1 C1 Error (1σ) C1 n MK MK Error (1σ) MK n

2007 0.713 0.040 3 0.552 0.090 3

2006 0.832 0.063 4 0.556 0.023 3

2005 0.724 0.040 5 0.598 0.105 3

2004 0.666 0.064 5 0.556 0.030 3

2003 0.701 0.056 6 0.604 0.058 3

2002 0.743 0.086 6 0.574 0.037 3

2001 0.683 0.026 6 0.604 0.045 4

2000 0.777 0.089 6 0.567 0.039 5

1999 0.788 0.091 6 0.561 0.017 5

1998 0.685 0.063 6 0.548 0.040 5

1997 0.637 0.047 6 0.583 0.041 5

1996 0.753 0.036 6 0.657 0.086 5

1995 0.763 0.021 6 0.674 0.111 5

1994 0.758 0.104 6 0.659 0.083 4

1993 0.675 0.060 5 0.641 0.099 5

1992 0.663 0.020 5 0.582 0.071 5

1991 0.748 0.034 5 0.59 0.121 3

1990 0.792 0.042 5 0.604 0.102 3

1989 0.835 0.014 5 0.595 0.067 4

1988 0.742 0.088 5 0.582 0.037 3

1987 0.786 0.043 4 0.512 0.059 3

1986 0.726 0.064 4 0.564 0.057 3

1985 0.711 0.081 4 0.488 0.058 3

1984 0.729 0.039 4 0.561 0.017 3

1983 0.721 0.046 4 0.554 0.037 3

1982 0.772 0.033 4 0.513 0.027 3

1981 0.742 0.025 4 0.531 0.043 3

1980 0.83 0.02 3 0.607 0.092 3

1979 0.818 0.003 3 0.686 0.115 3

1978 0.645 0.012 4 0.747 0.027 3

1977 0.766 0.021 4 0.633 0.062 4

1976 0.688 0.026 3 0.614 0.042 4
22

DRTO Diploria strigosa (continued)

1975 0.725 0.074 3 0.594 0.084 4

1974 0.783 0.037 3 0.526 0.051 3

1973 0.757 0.040 3 0.552 0.051 3

1972 0.733 0.025 3

1971 0.76 0.040 3

1970 0.733 0.051 3

1969 0.735 0.013 3

1968 0.626 0.021 4

1967 0.857 0.020 4

1966 0.854 0.006 3

1965 0.704 0.022 3

1964 0.666 0.033 3

1963 0.706 0.009 3

1962 0.665 0.024 4

1961 0.683 0.026 5

1960 0.818 0.026 4

1959 0.765 0.013 4

1958 0.648 0.039 4

1957 0.71 0.035 3

1956 0.637 0.025 3

1955 0.617 0.006 3

1954 0.697 0.035 3

Average 0.73 0.04 0.59 0.06