Effects of Past and Recent Severe Hurricanes on St. John, USVI Beaches and Their Ecosystems

Abstract

To better understand, prepare for and mitigate the effects that climate change induced storms are having on small Caribbean island beaches, and to determine the level of risk these beaches and their ecosystems are facing, I studied changes in beach geomorphology and vegetation profile to determine beach suitability for Hawksbill nesting pre- and post-Hurricanes Irma and Maria on selected St. John beaches in the United States Virgin Islands (USVI). This study explored whether or not the recent 2017 category 5 hurricanes Irma and Maria impacted, and if so in what way, Hawksbill nesting beaches and their nesting suitability on St. John. To study these changes, I compared the changes in beach length, width, and slope of seven north shore Hawksbill turtle nesting beaches pre- and post- Hurricanes Irma and Maria. My data came from both existing sources and from measurements and observations that I collected on site. Data from existing records came from remote site analysis using satellite images sourced from Google Earth Pro, the USVI National Park, local scholars, and from LiDAR and hurricane information obtained from the records of NOAA. Onsite data were obtained by conducting onsite assessments. Beach profile measurements (width and slope) were collected following the established protocol established in the 2010 Sandwatch Manual (Cambers & Diamond, 2010). Pre- and post- storms data for vegetation profiles include vegetation gain or loss, density, species ratios (native to non-native), root density, and shade provision. Because of a lack of records, the vegetation data were obtained from interviews with scholars local to St. John with appropriate expertise in the subject. Statistical significance of my relevant data was investigated by performing two Wilcoxon signed-rank tests on width change and nesting suitability pre- and post-storms. From literary research, and using the Hawksbill turtle (Eretmochelys imbricata) as an indicator species, I hypothesized that recent hurricanes Irma and Maria have caused beach erosion, narrowing the width of north shore beaches on the island of St. John in the United States Virgin Islands. I also hypothesized that these same storms have caused a reduction in nesting suitability by reducing areas of beach corresponding to Hawksbill nesting preference parameters. My study found that hurricanes Irma and Maria did indeed cause significant changes in beach geomorphology and backbeach vegetation. However, these changes did not manifest as reduction in beach size through erosion, but rather in beach increase due to loss of vegetation. These changes also resulted in both increases and decreases in nesting suitability for these beaches. Information resulting from this study will be useful in predicting future viability of these and other beaches as Hawksbill nesting sites, and contribute to optimum conservation planning and policy making.