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St. Petersburg Coastal and Marine Science Center

Coral Reef Ecosystem Studies (CREST)

Research: Holocene Coral-Reef Development

A reef core collected from Dry Tortugas National Park.
Figure 1. A reef core collected from Dry Tortugas National Park. Numbers indicate the depth of penetration into the reef in feet. [larger version]

  Mendenhall postdoctoral researcher Lauren Toth operates an underwater hydraulic drill to collect a coral-reef core from Crocker Reef
Figure 2. Mendenhall postdoctoral researcher Lauren Toth operates an underwater hydraulic drill to collect a coral-reef core from Crocker Reef (this research was conducted under permit # FKNMS-2013-097). [larger version]
Map of the Florida Keys Reef Tract
Figure 3. Map of the Florida Keys Reef Tract (FKRT), which includes the Florida Keys National Marine Sanctuary (FKNMS; white boundary), Dry Tortugas National Park, and Biscayne National Park. The reef tract can be divided into 6 sectors based on geological and hydrographic variability (modified from Shinn et al. 1989). Points on the map indicate the sites that were previously cored by USGS researchers (yellow) and the new coring sites included in this study (red). [larger version]

The coral reefs of the Florida Keys Reef Tract (FKRT) are an invaluable natural resource. They protect shorelines by reducing wave energy, provide critical habitat to associated marine life, and contribute nearly $3 billion annually to local economies. Over the last several decades, coral reefs around the world have declined as a result of a variety of local- to global-scale perturbations; the reefs along the FKRT are no exception to this trend (Toth et al. 2014). With the continuing threat of climate change and other anthropogenic disturbances, the future of Florida's coral reefs is uncertain. One way to gain insights into the future trajectories of Florida's coral reefs is to investigate how they responded to environmental disturbances in the past (Toth et al. 2012; Toth 2013).

Cores collected from coral reef frameworks (Fig. 1) can provide valuable records of reef development across millennial timescales. Using underwater hydraulic drilling (Fig. 2), USGS researchers have been collecting cores from the reefs of the Florida Keys since the early 1970s. As a result, USGS-Saint Petersburg has amassed an extensive archive of coral reef cores (Reich et al. 2012; http://olga.er.usgs.gov/coreviewer/). We are synthesizing records of existing reef cores and new cores collected during the course of this study (Fig. 3), to better understand the spatial and temporal trends in the development of Florida's reefs during the Holocene. The study is divided into three main parts: reconstructions of Holocene reef accretion, coral-reef paleoecology, and paleoenvironmental reconstructions.

Holocene Reef Accretion

We are using a combination of radiocarbon and U-series dating techniques to determine whether the timing of reef decline differed across the FKRT as a result of environmental differences. We will also calculate reef-accretion rates during the Holocene epoch, the period since the last glacial time, from ~10,000 years ago to present. Reef accretion is a measure of the net vertical growth of the reef over time that incorporates both calcification and erosion. By better understanding how reef accretion changed in response to environmental changes in the past, we can make predictions about how Florida's reef may respond to changes in climate, water quality, and sea-level rise in the future. This work compliments other studies in CREST that are investigating calcification rates and reef-scape biogeochemical processes on today's reefs.

Coral-Reef Paleoecology

We are using core records to reconstruct the species composition of reefs during the Holocene to determine how modern reef assemblages compare to the assemblages of the past. We are also analyzing Holocene coral skeletons to determine if coral growth rates have changed through time. We will compare these paleoecological data with our records of reef accretion to determine what ecological changes may have characterized changes in reef growth in the past.

Paleoenvironmental Reconstructions

We are working with the Reef History and Climate Change team in CREST to reconstruct environmental conditions on Florida’s reefs during the Holocene using geochemical archives from coral skeletons. We are also using the dating records from the cores to develop a model of sea-level changes on the FKRT over the last 10,000 years. This will allow us to directly measure the impact of environmental variability on the history of Florida’s reefs.

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