Graduation Year

2014

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Pamela Hallock Muller, Ph.D.

Co-Major Professor

Kendra Daly, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Committee Member

Kathleen Lunz, Ph.D.

Committee Member

Alison Moulding, Ph.D.

Keywords

disturbance, fate-tracking, Florida Keys, Octocorallia, recruitment, Scleractinia

Abstract

Over the past several decades, rapid decline in adult stony-coral (comprising the Orders Scleractinia and Anthomedusae, specifically Family Milleporidae) cover has occurred concurrent with an increase in adult octocoral (Octocorallia/gorgonian) cover along the Florida Reef Tract. In January 2010, the Florida Keys experienced extremely cold air and water temperatures, below the lethal threshold for many reef organisms including corals. Very high stony-coral mortality occurred on some patch reefs. The newly-available space created by this disturbance event provided the opportunity for recruitment and settlement of new coral larvae and other reef organisms.

The goal of this study was to examine post-disturbance recruitment and survival of juvenile stony corals and octocorals on patch reefs in the Middle and Upper Florida Reef Tract. Permanent quadrats were established at eight patch-reef sites. Stony-coral and octocoral juveniles, visible to the naked eye and having a maximum 4 cm diameter for stony corals or 4 cm height for octocorals, were identified, measured, and photographed to track each colony through spring and fall for two years. Juvenile densities increased significantly over that time; octocoral density increased with higher significance (p<0.001) than stony-coral density (p=0.019). Overall, 48% of all juveniles observed over the course of this study were stony corals and 52% were octocorals. Stony-coral juveniles dominated the Middle-Keys sites, while octocorals dominated the Upper-Keys sites. The stony-coral juveniles were dominated by hardy and weedy, opportunistic species such as Siderastrea siderea (46%) and Porites astreoides (19%), whereas juveniles of massive, late-successional species such as Orbicella annularis were nearly absent (<3%). The octocoral juveniles were dominated by Antillogorgia spp. (25%) and Gorgonia spp. (21%).

Opportunistic and/or hardy organisms are re-populating patch-reef sites, whereas slower growing, massive stony-coral species are declining. When a reef environment is plagued with chronic stressors, such as terrestrial runoff, overfishing, high temperature fluctuations and turbidity, the succession process may be inhibited following acute disturbances such as cold-water events. Patch reefs of the Florida Reef Tract now appear to be caught in a perpetually disturbed state, which supports opportunistic and hardy taxa and inhibits recovery of slower-growing climax taxa that dominated until the past few decades.

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