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Sea turtle nest being washed over by a wave

Wave exposure and inundation of sea turtle nesting beaches

PIs: Matt Ware (UNCW/FSU), Mariana Fuentes (FSU), Joe Long (UNCW), Simona Ceriani (FL FWC), Janice Becker (FL DEP/FSU)

Inundation and nest erosion from wave exposure, storm surge, and sea level rise are major threats to sea turtle nests – causing mortality as well as potential changes in hatchling size, morphology, locomotor function, and sex. Female turtles use several environmental cues when deciding where to nest such as beach slope, tide height, and distance from the water to reduce the chances of wave exposure. However, waves are still a common problem and increasing storm intensity and coastal development only exacerbate the issue. Identifying where and under what conditions wave exposure becomes a problem, and deciding what action to take (if any), is a common issue for sea turtle managers. For example, before we can consider any management action or intervention ranging from beach preservation to nest relocation, we need to know:

  • At what frequency or duration of exposure does wave wash-over cause significant harm to developing turtles?
  • Do these exposure thresholds vary with the developmental stage of the embryo?
  • How does this tolerance (or lack thereof) vary across species and populations?
  • What are the benefits of non-lethal levels of wave exposure, including reduced incubation temperatures, increased male hatchling production, large body sizes, and/or faster crawling speeds?
  • Would relocating nests introduce other threats which may cause as much (or greater) impact than wave exposure in their current location, such as hyperthermia, increased female hatchling production in a female-dominant population, desiccation, and increased predation or orientation?
  • How is wave exposure likely to change in the near future due to coastal development, armoring, beach erosion, hurricane frequency and strength, and sea level rise?
  • How may sea turtles naturally adjust their nesting behaviors to combat these changing beach conditions?

To help inform conservation initiatives to combat this threat, we can use beach elevation data, nest location and productivity data, and wave runup modeling to:

  1. Identify the reduction in loggerhead sea turtle hatchling production caused by wave exposure,
  2. Map out which beaches represent priority areas for conservation initiatives, and
  3. Investigate the efficacy and consequences of various management actions for the individual clutch, broader population, and coastal ecology
Map of wave exposure along a portion of the St Joseph Peninsula shoreline
Proportion of wave exposure along a stretch of the St Joseph Peninsula shoreline from 2016 to 2019. Loggerhead sea turtle nests laid during this time were typically above the most frequently exposed portions of the beach.

Following these modeling exercises, we can collect in situ information such as the frequency of wave exposure, its duration, hatchling production, and other data to close the information gaps and better inform management decisions. For example, St George Island was identified as a priority area for wave exposure impacts based on wave runup mapping in the Florida Panhandle. In 2021, we monitored wave exposure and inundation across the nesting beach throughout the nesting season to begin describing embryonic tolerance to these threats following the blueprint laid out by previous work on the Fort Morgan Peninsula of Alabama from 2016-2018.

This previous work concentrated on wave exposure, inundation, and the role of nest relocation in mitigating this threat. Though moving “at risk” nests may be a common sense approach to dealing with inundation, relocation can 1) result in the loss of developing embryos through the disruption of embryonic membranes, 2) increase the production of female hatchlings by changing the eggs’ incubating environment, and/or 3) increase predation from coyotes, foxes, raccoons, birds and other predators by moving the nest closer to their preferred hunting habitat and increasing the distance hatchlings must crawl to the water. There may also be sublethal effects such as reduced muscular development as a result of the altered incubation environment. Nest relocation on the beach or into a hatchery, beach renourishment, Leave No Trace ordinances, refugia protection, and other management actions all need to be investigated in order to determine under what circumstances each may be effective.

Publications in this project and related literature:

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