Ecology and Vulnerability

Green Sea Turtle

Juvenile ocean-stage sea turtles (i.e., Green Sea Turtles (Chelonia mydas), Kemp’s Ridley Sea Turtles (Lepidochelys kempii), Loggerhead Sea Turtles (Caretta caretta) 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 of which 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). As noted above, there were few studies 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

Potential future Green Sea Turtle range shifts while foraging in the southern Atlantic Ocean are possible with rising surface temperatures and bathymetry showing whole water temperature column warming along the South American coast (Franco et al., 2020).

Shifts in Phenology

Green Sea Turtle nesting phenology at Cabuyal, Costa Rica, was not affected by oceanographic conditions (sea surface temperature and chlorophyll) but did influence the number of days between successful nesting events and nesting abundance (Valverde-Cantillo et al., 2019).

Changes to Morphology or Physiology

While Green Sea Turtles currently do not nest in the Northeast, this information is relevant to populations of sea turtles that use northeastern marine waters. Researchers used a combination of remote sensing and ground truthing to estimate the impacts of sea level rise on Green Sea Turtle nests in Alagadi, Northern Cyprus, from 2012-2016; they projected a 33.2-43.5%, 42.3-47.0%, and 57.1-59.1% flooding of nests with sea level rise 48m, 0.63m, and 1.2m respectively (Varela et al., 2019). Another study on sea level rise in Turkey revealed that, for nesting locations documented between 2016 and 2018, the extreme sea level rise scenario of 1.2 m would result in 1/3 of nesting habitat loss and 18% of nest loss due to climate change (Sonmez et al., 2021). Green Sea Turtle egg viability is reduced by less than 10% after a 1 to 3-hour nest inundation of sea water, and viability is reduced 30% after 6 hours of inundation (Pike et al., 2015). This shows that not only does losing nest habitat to sea level rise negatively impact sea turtles, but does so during short-term flooding events.

A study on ocean heatwaves, by modeling the direct impacts of nesting vs. the indirect effects of food availability, demonstrated that over the simulated lifespan of Green Sea Turtles (80 years), decreases in food availability were stronger than direct temperature effects on turtles; overall, heatwaves occurring every 5 years vs. 20 years lowered female egg production by 20% over their lifetime (Stubbs et al., 2020). Another by-product of extreme heatwaves was studied in Shark Bay, Australia, between 2007-2012; seagrass and Green Sea Turtle health were assessed, and researchers found post-heat wave seagrass die-offs equated to declining Green Sea turtle health (Thomas et al., 2015). A multi-species study in Australia (during 1999-2015) investigated the indirect effect of seagrass loss due to extreme climatic events; Green Sea Turtles were negatively impacted, presumably due to their foraging needs for seagrass (Nowicki et al., 2019). Green Sea Turtle reproductive success did not decrease following the El Nino Southern Oscillation (ENSO) in the Pacific from 2015 to 2016 (Santidrian Tomillo et al., 2020). In Costa Rica, nesting success was correlated with deeper nesting depths and lower nest temperatures. Green Sea Turtles had a higher nest success rate than both Olive Ridley Sea Turtles and Leatherback Sea Turtles, whose nest success declined as they reached their higher thermal tolerance limit (Santidrian Tomillo et al., 2017). Temperature-dependent sex determination studies (both field and laboratory) since then have found that Green Sea Turtles have an approximate 50% male-to-female ratio at temperatures between 27.1C and 30.6C and that, due to long generational times, there is a lack of genetic adaptations to rising temperatures (Tilley et al., 2019). The authors argued that temporal and spatial shifts in these species are needed to overcome future climate change impacts.