Project Update: Wave Exposure of Sea Turtle Nests

Identifying inundation and erosion hot-spots in the Florida Panhandle

Inundation and nest erosion from wave exposure, storm surge, and sea level rise are major threats to sea turtle nests – causing localized mortality of eggs, as well as potential changes in hatchling size, morphology, locomotor function, and sex. Nesting females use several environmental cues 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 modifications (e.g., seawalls and upland construction) 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. To help managers with this decision, this project used 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, and
  • 2) map out which beaches in the Florida Panhandle represent priority areas for conservation initiatives.
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.

From 2016 to 2019, reported wave exposure affected 42% of loggerhead nesting stretching from the Florida-Alabama state line east to Bald Point State Park – 1,665 nests were washed over and an additional 1,200 nests were either partially or completely washed away. On average, the nests which were washed over produced 46% fewer hatchlings than nests which were otherwise undisturbed. By comparison, predated nests produced 28% fewer hatchlings, on average, than their undisturbed counterparts.

 Number of NestsHatching Success
(%, mean ± SD)
Emergence Success
(%, mean ± SD)
Undisturbed210478.1 ± 29.776.3 ± 30.2
Washed Over166532.7 ± 38.630.5 ± 37.5
    
Partial Wash-Out79NANA
Complete Wash-Out112100
Hatching and emergence success for undisturbed and wave-exposed nests in the Florida Panhandle from 2016 to 2019. Number of nests and complete and partial wash-outs are derived from the full dataset (n = 6,773). Hatching and emergence success from undisturbed and washed over nests were evaluated from a subset of the available data (n = 2,947). Productivity from partially washed-out nests is impossible to determine without a known clutch size prior to erosion.

The wave runup model had an 89% accuracy when determining the presence or absence of wave exposure during a nest’s 2-month incubation. When mapped across the Florida Panhandle and considering the number of nests laid per beach, the model suggested the following beaches represent the highest priority for conservation initiatives:

  • St Joseph Peninsula State Park
  • St Joseph Peninsula
  • St George Island
  • Cape San Blas
  • Cape St George Island

Together, these 5 beaches represent 60% of the loggerhead nesting in the region. Significant losses from wave exposure on these beaches can dramatically affect hatchling production for the entire Northern Gulf of Mexico loggerhead sea turtle population.

Nesting beach Priority Category (C) based on loggerhead sea turtle nesting frequency (A) and the proportion of nest locations exposed to modeled wave wash-over (B). The choice of conservation initiative will vary based on nesting frequency and wave exposure. For example, beaches with frequent nesting and high wave exposure will need different initiatives than those with low wave exposure (D).

There is still a lot of work to be done. This model is just one step in the larger efforts for sea turtle conservation in the Florida Panhandle and elsewhere. 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?

Certainly plenty to keep us busy for awhile, so stay tuned for updates from the sea turtle community!

The manuscript for this work is currently under review for the special section “Remote Sensing Applications for Sea Turtle Conservation” in the journal Remote Sensing. The link to the article will be listed here once it is available!

For similar work, check out:

Published by Ware Research

I'm a coastal ecologist with a PhD in Biological Oceanography from Florida State University in the Marine Sea Turtle Research, Ecology, and Conservation Group (FSU MTRECG), as well as a PADI Master SCUBA Diver Trainer. My current research with sea turtles in Florida and the Gulf of Mexico, past research with coral reef restoration, and diving background have taken me all over the world - which is a mixed blessing with my photography hobby! Enjoy the posts on this site, check in often to stay up-to-date on my research, and please email me (mw15w@my.fsu.edu) if you have any questions about anything on this site!

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