Home Archived October 29, 2018
(i)

South Florida Information Access (SOFIA)


publications > paper > sedimentary petrology of a declining reef ecosystem, florida reef tract (u.s.a.)

Sedimentary Petrology of a Declining Reef Ecosystem, Florida Reef Tract (U.S.A.)

Barbara H. Lidz1 and Pamela Hallock2

Abstract

Lidz, B.H. and Hallock, P., 2000. Sedimentary petrology of a declining reef ecosystem, Florida Reef Tract (U.S.A.).
Journal of Coastal Research, 16(3), 675-697. West Palm Beach (Florida), ISSN 0749-0208.

Abstract
Introduction
Methods
Results
Discussion and Interpretations
Conclusions
Acknowledgments
Literature Cited
Appendix 1
Appendix 2

Petrologic evaluation of biogenic sediments collected shelf-wide along the Florida reef tract in 1989 revealed three principal components: coral, the calcareous green alga Halimeda, and mollusc. The dominant grain was dependent in part upon local morphology that controlled composition and vitality of the biota. Either Halimeda or mollusc grains prevailed in sands off the upper Keys, In the middle and lower Keys, Halimeda grains prevailed nearshore and coral grains offshore. Comparison with similar analyses of samples collected in 1952 and 1963 indicates that, over 37 years, the relative abundance of molluscan grains more than doubled in the upper Keys and that of particulate coral tripled in the middle Keys. These changes can be interpreted in the context of physical and biological events that affected Florida Keys reefs over that period of time. In the 1970s, outbreaks of extremely cold water killed even representatives of the hardiest coral species. In the 1980s, black-band and white-band diseases decimated the major reef-building acroporid corals, and the pivotal herbivore, Diadema antillarum, disappeared. Although Diadema is a major coral bioeroder, the sea urchin is also essential to healthy reef growth. The increase in coral debris in the middle Keys may be related to Hurricane Donna in 1960, but it is also consistent with the prediction of accelerated bioerosion by boring organisms in response to increased plankton productivity. Plankton productivity is stimulated by nutrients from Florida Bay and by well-documented eutrophication of nearshore environments. In the upper Keys, where reefs are somewhat removed from bay and nearshore influence, a relative decrease in coral debris over the 37 years may reflect proliferation of algae and algae-grazing molluscs as well as suppressed rates of bioerosion in the absence of Diadema.

Human activities have substantially increased the natural flux of fixed nitrogen to coastal systems worldwide. Waters in the Florida Keys are no exception. Spatial and temporal trends in sediment constituents are compared to a previously published model that predicts the response of benthic biota to changes in nutrient supply. As adapted to interpret changes observed in reef-tract sediments, the model provides insights into the natural nutrient gradient along the Florida reef tract.

Additional Index Words: Bioerosion; biogenic carbonates; coral, Halimeda, and mollusc debris; coral reefs; Diadema antillarum; ecosystem alteration; effects of environmental change; geologic indicator; nutrification; quantification of reef health; regional geomorphology.


1U.S. Geological Survey
Center for Coastal Research
600 4th St. South
St. Petersburg, FL 33701,
U.S.A.
2Marine Sciences Department
University of South Florida
140 Seventh Ave. South
St. Petersburg, FL 33701,
U.S.A.



| Disclaimer | Privacy Statement | Accessibility |

U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/publications/papers/sedpetro/index.html
Comments and suggestions? Contact: Heather Henkel - Webmaster
Last updated: 04 September, 2013 @ 02:04 PM (KP)