Ecology and Vulnerability

Loggerhead Sea Turtle

A 2017 global review of papers focused on turtles and climate change recommendations focusing on the following areas: more data on individual species responses to climate change through skewed sex ratios, improvements to species distribution models including fine-scale climate and population-specific physiological variables and physiology, and actions that increase species resilience and mitigate climate threats (Butler, 2019).

Juvenile ocean-stage sea turtles (i.e., Green Sea Turtles, Kemp’s Ridley Sea Turtles, Loggerhead Sea Turtles) are projected to increase along the North Atlantic coast and in the Northern Atlantic Ocean based on simulated data from 1993 to 2017, making sea turtle conservation a priority along the Atlantic Coast due to climate change (Putman et al., 2020). A study testing phenological shifts of four sea turtles, two that are RSGCN (Loggerhead and Green Sea Turtles), projected that phenological shifts will likely not be enough to overcome the negative impacts due to warming sands on nesting grounds and sea water temperature from climate change (Fuentes et al., 2024).

Few studies were found on the impacts of climate change on sea turtles in the northeastern U.S.; therefore, many of the resources and information presented below are out of region but may provide useful context for how sea turtles are responding to climate impacts elsewhere and guide targets for similar studies for Northeast populations.

Shifts in Range, Elevation, or Depth

In Europe, Loggerheads have started nesting further north than previously documented, with northern hatchlings experiencing lower survival success (Maffucci et al., 2016)

Shifts in Phenology

A global study on nesting phenology for Loggerhead Sea Turtles shows that temperature dependent responses to climate change are stronger in populations nearer to the poles than in the equator (Mazaris et al., 2013). This could hold for other behavioral responses to climate change and would be important for the Northeast, the northern range limit for this species. Additional research on Loggerhead nesting phenology showed that hatching success is greater for temperate populations and likely to increase in temperate regions as temperatures increase (Pike, 2014).

Changes in Population

Climate variables such as humidity, air temperature, and accumulated precipitation influenced hatchling production in Florida, while sea surface temperature and wind speed did not (Montero et al., 2018). Similarly, in Brazil, air temperature and precipitation were the main climatic variables that led to high nest production (Montero et al., 2019). In Turkey, sea surface temperature was a stronger predictor than air temperature of nest temperature (Girondot et al., 2015). Larger swings in temperature during incubation led to lower mass in hatchling. Loggerhead Sea Turtles (Horne et al., 2014). In a Loggerhead rookery in Cabo Verde, warmer sand temperatures increased female sex ratios, smaller hatchlings, and increased predation by ghost crabs when hatchlings left the nest for the ocean (Martins et al., 2020). From Loggerhead nests sampled in Florida at Archie Carr National Wildlife Refuge during 2007-2011, researchers projected that a combination of sea level rise from climate change and land use changes from development would decrease available nesting beach area by 43% by 2050 (Reece et al., 2013). Modeling terrestrial and aquatic environments in the Mediterranean Sea showed that anthropogenic variables and sea surface temperature over 25°C decreased nesting probability (Mancino et al., 2022). Compounding effects such as these indicate the need to protect shorelines in current and projected range areas of sea turtles. A study on the Loggerhead beach nesting habitat in Greece estimated a loss of 11-71% of the habitat due to a 0.2-1.3 meter climate-induced sea level rise prediction (Katselidis et al., 2014). In addition to losing beach habitat, sea turtle nests are at risk for increased flooding. A controlled study of the six stages of incubation found that flooding during the early and late stages (near hatchling) and long-term exposure to flooding increased hatchling mortality (Limpus et al., 2020). The impacts of sea level rise on Loggerhead Sea Turtle nests in Alagadi, Northern Cyprus, from 2012-2016 was estimated at 36.5-44.1%, 43.3-49.4%, and 62.1-67.4% flooding of nests with rising sea level 0.48m, 0.63m, and 1.2m respectively (Varela et al., 2019). 

Indirect Effects

Other negative impacts on Loggerhead juveniles and adults from extreme climate events, such as cold stranding, have been recorded in Mexico and California; multiple factors increased the risk of strandings, such as increased disease vulnerability, predation, entanglement, and reduced swimming abilities from cold water, reducing body temperatures below optimal thermal ranges (Salinas-Zavala et al., 2020). A multi-species study in Australia investigated the indirect effect of seagrass loss due to extreme climatic events; Loggerheads were not negatively impacted, presumably due to their generalist diet (Nowicki et al., 2019). The combination of direct and indirect effects of climate change on Loggerhead Sea Turtles' nesting behavior is studied more than other life stages.