Abstract
Corals, specifically the Atlantic staghorn coral, Acropora cervicornis, have become more vulnerable to disturbance events such as storms and disease and predation outbreaks. Since its population declines due to a wide spread disease event in the early 1980s, limited long-term monitoring studies describing the impact of current threats and potential recovery have been completed. The aim of this study was to document the impacts of environmental (tropical storms, increased wind) and biological (disease and predation) threats on A. cervicornis to further understand its dynamics and potential for recovery. Two high-density A. cervicornis patches (greater than 1 hectare each) were surveyed tri-annually (winter, summer, fall) from 2008-2016. Acropora cervicornis percent cover, canopy height, census of individuals (fragments, colonies and masses), and prevalence and occurrence of disease, predation, and bleaching were evaluated within permanent 3.5 m radial plots. Temporal variability was observed in mean percent live cover at both patches and resulted in an overall loss of tissue. Frequent disturbances such as tropical storms, hurricanes, and disease events caused increased, prolonged, and widespread mortality. Periods void of disturbance allowed for recovery and growth. Prevalence and occurrence of disease and predation were highly variable between monitoring events. They were also found to be significantly higher on masses (individuals ≥ 1.5 m) than on colonies and during summer surveys. These data indicate that substantial length of time between major disturbance events are necessary for recovery and growth of this species. The implication from these results is that given the current rates of growth, recruitment, and storm frequency, natural species recovery is unlikely unless larger scale issues are addressed such as climate change and ocean warming, which could reduce the intensity and frequency of disease and predation.
Highlights
Acropora cervicornis is a fragile, vulnerable, and dynamic species that has been known to change in abundance and/or cover quickly in response to disease outbreaks, tropical disturbances, or climatic events (Shinn, 1976; Antonius, 1977; Davis, 1982; Knowlton et al, 1990; Schopmeyer et al, 2012; Miller et al, 2014a) and was frequently found lining the fore reef of many Caribbean, Florida, and Gulf of Mexico coral reefs
Acropora cervicornis populations became spatially and regionally isolated following a multi-decadal white band disease outbreak starting in the 1970s which left the surviving populations most commonly distributed as individual colonies or much smaller patches (Gladfelter, 1982; Bythell et al, 1989, 1993; Aronson and Precht, 2001; Acropora Biological Review Team, 2005)
Across the 8 years of the study, abundance and health of A. cervicornis were surveyed within 27 plots at BCA and 31 plots at Scooter, five plots at BCA never had A. cervicornis so were not included in the analysis
Summary
Acropora cervicornis is a fragile, vulnerable, and dynamic species that has been known to change in abundance and/or cover quickly (e.g., weeks to years) in response to disease outbreaks, tropical disturbances, or climatic events (Shinn, 1976; Antonius, 1977; Davis, 1982; Knowlton et al, 1990; Schopmeyer et al, 2012; Miller et al, 2014a) and was frequently found lining the fore reef of many Caribbean, Florida, and Gulf of Mexico coral reefs. Acropora cervicornis populations became spatially and regionally isolated following a multi-decadal white band disease outbreak starting in the 1970s which left the surviving populations most commonly distributed as individual colonies or much smaller patches (Gladfelter, 1982; Bythell et al, 1989, 1993; Aronson and Precht, 2001; Acropora Biological Review Team, 2005) This dramatic decline leads to its listing as threatened under the United States Endangered Species Act (US ESA; National Marine Fisheries Service, 2006) and as critically endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species (Aronson et al, 2008). One region where numerous large patches of A. cervicornis exist today is within the Southeast Florida Coral Reef Ecosystem Conservation Area and in Broward County, FL, at the northern-most extent of this species’ range (Vargas-Ángel et al, 2003; Walker et al, 2012; D’Antonio et al, 2016)
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