VARIATION IN ACROPORA PALMATA BLEACHING ACROSS BENTHIC ZONES AT BUCK ISLAND REEF NATIONAL MONUMENT (ST. CROIX, USVI) DURING THE 2005 THERMAL STRESS EVENT

At Buck Island Reef National Monument (BIRNM) in St. Croix, U.S. Virgin Islands, Acropora palmata (Lamarck, 1816) experienced extensive bleaching in 2005. Water temperatures at BIRNM in 2005 were higher than at any time since at least 1991, and exceeded the bleaching threshold by over 2 degrees C, causing extensive coral bleaching. Forty-four A. palmata colonies at three sites in BIRNM were sampled before, during, and after the thermal stress event. Additionally, colonies at randomly located sites on the reef shelf were surveyed to extend results over a larger portion of BIRNM; these colonies were surveyed during and after the thermal stress event. Acropora palmata colonies located in the backreef benthic zone exhibited a different response to the thermal stress event than those located elsewhere in BIRNM: backreef colonies bleached earlier and suffered greater tissue loss than those located elsewhere. We hypothesized that increased water temperature coupled with reduced water flow and increased light penetration caused higher mortality in backreef locations. Since A. palmata in the backreef benthic zone is least resistant and resilient to thermal stress events, backreef areas are a poor focal area for A. palmata marine protected areas.