RECENT CORAL-REEF DECLINE: IS THE PAST THE KEY TO THE PRESENT?

Since the early 80’s, hurricane damage, overfishing and the die-off of grazing urchins have led to a shift in Caribbean reefs from coral to macroalgal dominance. The near extirpation of Acropora palmata by White Band Disease (WBD) has led to a fundamental shift in community structure over recent decades. In 1992, Jackson observed that Pleistocene coral reefs exhibit spatial persistence that contrasts with recent instability and reef decline. This has led to comparisons invoking the Quaternary record as a pre-anthropogenic proxy against which recent changes might be measured. Most recently, it has been stated that community shifts involving Acropora are unprecedented over the latter part of the Holocene, and perhaps longer.

Over 30 cores through shelf-edge reefs off St. Croix, Puerto Rico and Florida record A. palmata reef development starting 11,000 ybp and ending suddenly between 7,000 and 6,300 ybp. This is associated with reef backstepping and a Caribbean-wide decrease in A. palmata abundance for nearly a millenium. A second gap in the A. palmata record occurred 3,000 ago and continued for 600 years.

Seven cores through the shallow reef complex around Buck Island Underwater National Monument (USVI) record 7,000 years of reef accretion. The time-averaged reef-community structure was nearly identical to that occurring at Buck Island prior to the WBD die-off, inferring that a community doinated by A. palmata was the norm. However, the absence of A. palmata in the cores both 7.000 and 3,000 years ago verifies temporal gaps in the A. palmata record that follow the larger Caribbean trend. If we recognize that spatial persistence does not necessarily reflect temporal stability, then the presumed lack of major community shifts in the Quaternary must be reconsidered. Our ability to discriminate reef disconformities and their causes is critical to comparison of recent reef changes and the Quaternary reef record.