The beaches in St. Johns County, along the Atlantic coast of North Florida, are important sea turtle nesting areas. Regions of these beaches differ in their historical and present anthropogenic use, which can affect the quality of nesting habitat. We recorded beach topographic profiles for three beach sites: Crescent Beach, the Archie Carr Property of Summer Haven, Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR) in July 2014 and July 2015. The purpose of this study was to compare topographic and sediment profiles among these beaches and to continue long-term monitoring of these beaches for documentation of changes in these coastal ecosystems.
Three transects were carried out at each site during low tide, beginning at the vegetation line on the dune and continuing east toward the ocean. Relative elevation was recorded along the 95m transects at an interval of one meter. Sand samples were collected at the beginning, middle, and end of each transect. We dried samples to constant mass, passed the samples through a wire sieving column, and classified according to grain size according to the Udden-Wentworth grain-size classification scheme.
Results/Conclusions
The topographic profile of the Archie Carr Property changed between July 2014 and July 2015, most noticeably with the appearance of a new beach scarp, an erosional feature. Sand grain size differed across the three sites. Sand samples collected at Crescent Beach, a site where vehicles are allowed on the beach, contained the highest mass percentage of fine (<0.250mm) and very fine (<0.125mm) sand. Sand samples at the other two sites were more heterogeneous, with GTMNERR, the most undisturbed site, having the highest mass percentage of medium (<0.500mm) sand. Grain size is an important factor for sea turtle nest site selection, and long-term monitoring of this and other attributes of these nesting beaches will provide insight into how these coastal ecosystems are changing over time, and potential solutions for mitigating the effects of rapid environmental variation at critical sea turtle nesting beaches.