Beach sediment properties in a mixed system and potential effects on nesting loggerhead sea turtles (Caretta caretta) in southwest Florida

Southwest Florida beaches have undergone erosional reshaping due to frequent hurricanes and subsequent beach nourishment using diverse imported sediments. Beach sediments vary in grain size, mineral composition, and angularity in a mixed system of quartz sands and shelly gravels. These changes have likely altered nesting habitats for hundreds of loggerheads (Caretta caretta) and other sea turtle species. The goal of this long-term study is to monitor sediment variations over the turtle nesting season and assess potential relationships with female nest building and hatching success. Nest temperature data suggests that Southwest Florida produces more male hatchlings than other regions of comparable latitude and sediment dynamics contribute to heat retention.

During the 2025 nesting season, predetermined stations were established on Estero Island and Bonita Beach at regular intervals of ~ 4 km to determine sediment characteristics over time and space. Samples were taken in three zones: the dune boundary, the mid-beach, and the high tide line. Quart-sized samples were collected at both 0 cm (surface) and 40 cm (average loggerhead turtle nest depth). They were dried to quantify moisture content, burned in a muffle furnace to deduce organic content, sieved, and analyzed with a Malvern Panalytical Masterizer to determine grain size distributions.

Preliminary data from the Bonita Beach stations show a lower moisture content (4.37%) than Estero Island (7.90%). Organic content percentages showed a similar trend where Bonita Beach had an average of 0.77% versus Estero Island’s 2.80%. Further analyses of grain angularities, sediment temperatures, and carbonate contents are ongoing. Understanding how sediment characteristics may affect nesting success can help explore the influence of anthropogenic activity, inform sustainable nourishment practices, and support the conservation efforts of nesting sea turtles.