The structure and composition of Holocene coral reefs in the Middle Florida Keys

Open-File Report 2016-1074
By: , and 



The Florida Keys reef tract (FKRT) is the largest coral-reef ecosystem in the continental United States. The modern FKRT extends for 362 kilometers along the coast of South Florida from Dry Tortugas National Park in the southwest, through the Florida Keys National Marine Sanctuary (FKNMS), to Fowey Rocks reef in Biscayne National Park in the northeast. Most reefs along the FKRT are sheltered by the exposed islands of the Florida Keys; however, large channels are located between the islands of the Middle Keys. These openings allow for tidal transport of water from Florida Bay onto reefs in the area. The characteristics of the water masses coming from Florida Bay, which can experience broad swings in temperature, salinity, nutrients, and turbidity over short periods of time, are generally unfavorable or “inimical” to coral growth and reef development.

Although reef habitats are ubiquitous throughout most of the Upper and Lower Keys, relatively few modern reefs exist in the Middle Keys most likely because of the impacts of inimical waters from Florida Bay. The reefs that are present in the Middle Keys generally are poorly developed compared with reefs elsewhere in the region. For example, Acropora palmata has been the dominant coral on shallow-water reefs in the Caribbean over the last 1.5 million years until populations of the coral declined throughout the region in recent decades. Although A. palmata was historically abundant in the Florida Keys, it was conspicuously absent from reefs in the Middle Keys. Instead, contemporary reefs in the Middle Keys have been dominated by occasional massive (that is, boulder or head) corals and, more often, small, non-reef-building corals.

Holocene reef cores have been collected from many locations along the FKRT; however, despite the potential importance of the history of reefs in the Middle Florida Keys to our understanding of the environmental controls on reef development throughout the FKRT, there are currently no published records of the Holocene history of reefs in the region. The objectives of the present study were to (1) provide general descriptions of unpublished core records from Alligator Reef and (2) collect and describe new Holocene reef cores from two additional locations in the Middle Keys: Sombrero and Tennessee Reefs.

Suggested Citation

Toth, L.T., Stathakopoulos, Anastasios, and Kuffner, I.B., 2016, The structure and composition of Holocene coral reefs in the Middle Florida Keys: U.S. Geological Survey Open-File Report 2016–1074, 27 p.,

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Introduction
  • Methods
  • Results and Discussion
  • Acknowledgments 
  • References Cited
  • Appendix 1. Photographs and Descriptive Logs of Holocene Reef Cores from the Middle Florida Keys
Publication type Report
Publication Subtype USGS Numbered Series
Title The structure and composition of Holocene coral reefs in the Middle Florida Keys
Series title Open-File Report
Series number 2016-1074
DOI 10.3133/ofr20161074
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) St. Petersburg Coastal and Marine Science Center
Description v, 27 p.
Country United States
State Florida
Other Geospatial Florida Keys
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details