Stay in the know about wildlife, water quality, and ecosystems on Sanibel and Captiva Islands and in Southwest Florida

Does Beach Renourishment Affect Sea Turtle Hatchling Success?

June 11, 2024
Installing Loggers 1600

Following the first-ever renourishment of all of Sanibel’s beaches this year with sand trucked in from a sand mine in Moore Haven to offset impacts from Hurricane Ian, many beachgoers have questioned whether or not sea turtle nesting will be affected.

As part of a study that SCCF started in 2021, the sea turtle team is analyzing how the sand’s characteristics relate to hatchling emergence success through loggers installed at nests on Sanibel and Captiva.

In June of 2021, the sea turtle team launched a project investigating how variation in sand grain size, color, compaction, and bulk density influences temperature, moisture, and water flow through the nest chamber.

“We are also evaluating subsequent impacts on embryonic development and hatchling production,” said Coastal Wildlife Director Kelly Sloan.

Trucks hauled 400,000 tons of sand to Sanibel’s beaches from December 2023 through April 2024. Photo by City of Sanibel

Since 2021, 111 nests have been outfitted with temperature, moisture, and water level loggers on Sanibel and Captiva and over 1,000 unhatched eggs have been staged to identify when development ended.

“Sand samples are taken at each site, along with beach profile metrics such as elevation and slope,” said Sloan.

Preliminary analyses from data collected in 2021-2022 suggest that there were significantly different sand grain sizes on Sanibel and Captiva, and these varying sediment characteristics may impact the rate of water flow and temperature within the nest chamber, possibly resulting in decreased emergence success. The elevation gain associated with renourishment projects may also be an important variable affecting hatch success.

Sand placement projects have been occurring regularly on Captiva Island between 1961 and 2021. Sand for those projects is typically dredged from an offshore borrow site and piped onto the beach.

Sand for Captiva’s 2021 renourishment project is piped onto the beach after being dredged from an offshore borrow site. Photo by Larry Richardson

Notably, the average annual hatch success on Captiva was found to be generally about 20% lower than non-nourished stretches of Sanibel (2014-2020) when nests with any external losses are removed (i.e. depredation, tidal washovers, etc.). This 20% reduction in hatchlings represents an important potential obstacle to loggerhead population recovery.

“This year, we will also be able to compare previous years’ data to determine any impacts or benefits from the renourishment project that occurred on Sanibel,” said Sloan.

Why are beaches renourished?

Along the coast of Florida, beach erosion due to storms, hurricanes, and sea level rise is becoming increasingly common. Natural processes have been radically changed as humans develop the coast, and interruptions in sediment transport on naturally dynamic beaches prevent normal sand migration patterns.

One of the anthropogenic responses to shrinking shorelines is beach renourishment.

Beach renourishment is considered a “soft” measure that can help replace lost sand and is a common response to erosion.

While the addition of sand to an erosional beach can benefit sea turtles by creating nesting habitat, questions have been raised concerning the direct and indirect effects of beach renourishment on nesting turtles.

“For example, changes in the physical properties of non-native sand may alter critical characteristics of the nest microclimate, such as sand temperature, moisture, gas exchange, and porosity,” said Sloan.  “These shifts in incubation environments raise real concerns about incubation time, clutch viability, hatchling fitness, and hatchling sex ratios.”

The results from studies assessing how the hydric, which determines the amount of water available in the sand, and the physical properties of the sand on natural and renourished beaches have produced varied results over space and time, suggesting the effects may be somewhat site-specific.


Archives by Month