Title

Coral Growth Records from Southeast Florida: A History of Anthropogenic Influence

Event Name/Location

11th International Coral Reef Symposium, Fort Lauderdale, Florida, July 7-11, 2008

Document Type

Conference Proceeding

Publication Date

7-2008

Abstract

Coral skeletal growth records of extension, density, and calcification from Southeast Florida reveal a three-decade period of stress spanning ca. 1940 to 1970. The period is characterized by dramatically decreased annual extension rate and increased skeletal bulk density. No similar periods of growth departures of this intensity or duration are present in locally collected corals dating back to 1694. Coral growth from a total of 80 corals exhibits strong correlation with master chronologies indicating a common growth response to one or a combination of environmental limiting factors. Near-shore shallow-water corals in Southeast Florida are affected by a number of stresses including freshwater drainage and coastal runoff. The 30-year period of high skeletal densities and low extension rates matches with a 30-year period of increased freshwater discharge, at times, an order of magnitude greater than normal. Construction of the four major South Florida canal systems diverted waters from Lake Okeechobee in the 40s, 50s, and 60s to the ocean. Comparison of temporal patterns in coral extension with environmental variables reveals a positive correlation between extension rate and salinity (represented by sea water density). The direct cause may be linked to influences from freshwater discharge such as high turbidity and decreased light penetration, salinity, or deleterious water quality. Further analysis of skeletal chemistry will help to identify specific limitations on the growth potential of these corals. Since the early 1970’s, growth rates have generally increased relative to the historical average; however, the frequency of single-year stress bands has also risen. Increased growth rates coincide with warmer temperatures and stress bands likely resulting from partial bleaching when temperature thresholds are exceeded. This research has applications to better understanding coral stress and recovery with particular regard to watershed management.

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