Abstract. Initial conditions can generate differences in the biotic composition of spatially disjunct communities, but intense, large-scale perturbations have the potential to reduce or eliminate those historical differences. The latter possibility is of particular concern with respect to coral reefs, which have undergone dramatic changes in the last 25-30 years. This paper reports a case in which two reef systems with different biotic histories were recently perturbed to a single, novel state.We compared millennial-scale records of species dominance from reefs in Bahia Almirante, a coastal lagoon in northwestern Panama, to previously published records from reefs in the shelf lagoon of Belize. Reef cores extracted from Bahia Almirante at 5-10 m water depth revealed that the Panamanian reefs were persistently dissimilar from the Belizean reefs for at least 2000-3000 years prior to the last several decades. The Panamanian reefs were dominated continuously by branching finger corals, Porites spp. (primarily P. furcata). Shifts from the Ponfes-dominated state to dominance by other coral species were rare, were restricted to small areas, and lasted for decades to centuries. The Belizean reefs were dominated continuously by the staghorn coral Acropora cervicornis in the same depth range during the same period. Excursions from the Acropora-dominated state were again rare and spatially localized. Populations of Ac. cervicornis in the Belizean lagoon were nearly extirpated by an outbreak of white-band disease in the late 1980s, and changes in water quality were apparently detrimental to branching Porites in Bahia Almirante in recent decades. These large-scale perturbations caused the two reef systems to converge on a third, historically unprecedented state: dominance by the lettuce coral Agaricia tenuifolia. Ag. tenuifolia possesses life-history attributes and environmental tolerances that enabled it to become dominant in both disturbed ecosystems. Although the two phase shifts to Ag. tenuifolia differed in both their general mechanisms and specific causes, they had the effect of eliminating the salient difference in benthic composition between the Panamanian and Belizean reefs. The changes in species composition thus obliterated the influence of several thousand years of reef history.

Beginning in the late 1980s, white‐band disease nearly eliminated the staghorn coral Acropora cervicornis from reefs in the central shelf lagoon of Belize. The lettuce coral Agaricia tenuifolia replaced Acropora cervicornis in the early 1990s, but anomalously high water temperatures in 1998 caused severe bleaching and catastrophic mortality of Agaricia tenuifolia. The short‐lived transition in dominance from Acropora cervicornis to Agaricia tenuifolia left an unambiguous signature in the fossil record of these uncemented lagoonal reefs. Analysis of 38 cores, extracted from 22 sampling stations in a 375‐km2 area of the central lagoon, showed that Acropora cervicornis dominated continuously for at least 3000 years prior to the recent events. Agaricia tenuifolia occasionally grew in small patches, but no coral‐to‐coral replacement sequence occurred over the entire area until the late 1980s. Within a decade, the scale of species turnover increased from tens of square meters or less to hundreds of square kilometers or more. This unprecedented increase in the scale of turnover events is rooted in the accelerating pace of ecological change on coral reefs at the regional level.

Populations of the staghorn coral, Acropora cervicornis, collapsed throughout the Caribbean region from the late 1970s through the 1990s. We tested the hypothesis that this recent, multidecadal interruption in coral growth was a novel event in the late Holocene. Eight cores, extracted from a lagoonal reef in Discovery Bay, Jamaica dated to 440-1260 CalBP and consisted almost entirely of A. cervicornis rubble. The A. cervicornis in the cores showed significantly less internal bioerosion than A. cervicornis from modern death assemblages in Discovery Bay, indicating generally shorter post-mortem exposure at the sediment-water interface in the past. A. cervicornis grew continuously and was buried rapidly during the millennium preceding the 1980s, with the exception of a possible hiatus in growth and burial at some point 300-600 years ago. In the 1980s, a combination of perturbations, which included overfishing and (possibly) other forms of human interference, caused an unprecedented disruption in the growth and burial of staghorn coral populations in Discovery Bay.

Beginning in the late 1980s, white-band disease nearly eliminated the staghorn coral Acropora cervicornis from reefs in the central shelf lagoon of Belize. The lettuce coral Agaricia tenuifolia replaced Acropora cervicornis in the early 1990s, but anomalously high water temperatures in 1998 caused severe bleaching and catastrophic mortality of Agaricia tenuifolia. The short-lived transition in dominance from Acropora cervicornis to Agaricia tenuifolia left an unambiguous signature in the fossil record of these uncemented lagoonal reefs. Analysis of 38 cores, extracted from 22 sampling stations in a 375-km 2 area of the central lagoon, showed that Acropora cervicornis dominated continuously for at least 3000 years prior to the recent events. Agaricia tenuifolia occasionally grew in small patches, but no coral-to-coral replacement sequence occurred over the entire area until the late 1980s. Within a decade, the scale of species turnover increased from tens of square meters or less to hundreds of square kilometers or more. This unprecedented increase in the scale of turnover events is rooted in the accelerating pace of ecological change on coral reefs at the regional level.

PBS&J, together with its collaborators (the University of South Florida and Terra Ceia Consulting LLC), developed a unique and comprehensive methodology for identifying bacterial sources in environmental waters. These methods are at the cutting edge of bacteria source detection and remediation. Although the approach was developed and tested throughout Florida, it can be applied anywhere in the country.The methodologies consist of three main parts, that when combined, comprise the DecisionSupport Tool. The tool was developed to facilitate the identification of bacterial sources and the implementation of bacterial total maximum daily loads (TMDLs). The over arching strategy is based on the "Annapolis protocol" recommended by the World Health Organization (WHO) (2003) and the "phased monitoring approach" recommended by the National Research Council (NRC) (2004) to address elevated bacterial levels in recreational waters. The WHO (2003) and NRC (2004) strategies recognize that the use of water quality indicator organisms (IOs), such as fecal coliforms, E. coli, and enterococci to assess water quality and predict human health risk, is confounded by many variables. A weight-of-evidence approach is therefore recommended to compensate for the uncertainty associated with the various tests and observations currently used by regulatory agencies. The overall approach described here uses a combination of information: (a) bacterial IO data to target specific locations with likely fecal contamination; (b) site-specific field surveys to identify the sources of contamination and assess them based on their potential risk of infection to humans; and (c) microbial source tracking (MST) to detect source-specific microbes to assist in the prioritization and implementation of management actions to address bacteriological water quality impairments.1. Microbial Water Quality Assessment. The first step of the Decision-Support Tool prioritizes water bodies with known bacterial impairments at the basin (watershed) or sampling station level. This is accomplished by categorizing water quality conditions at each location based on IO concentrations (e.g., fecal coliforms) from existing monitoring data. This step focuses the investigation by prioritizing monitoring locations based on their respective microbial water quality assessment (MWQA) rating, resulting in a significant saving of time and money.2. Contaminant Source Surveys. Once the MWQA has been used to prioritize impaired water bodies or specific sites within the basins, a weight-of-evidence approach is used to compile a comprehensive contaminant source survey (CSS) of the major potential bacteria sources within an impaired watershed. Relevant information may be collected through historical data analysis, field surveys, intensive one-on-one interviews with local stakeholders, public workshops, field reconnaissance, and, if necessary, microbial source tracking. The intensity of the CSS is based on the results from step 1 (MWQA classification). Since local stakeholders participate in al...

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