Impact of a Warming Climate on Sea Turtle Populations Introduction
by Barry Shedrow
The most common species of sea turtle nesting on South Carolina’s beaches is the loggerhead [Caretta caretta]. The loggerhead spends most of its life offshore in marine and estuarine habitats. While the female loggerhead will briefly come ashore to lay eggs on or near her natal beach, the male loggerhead will almost never return to land after entering the sea. Sea turtles represent some of earth’s most ancient creatures. They have been around since the time of the dinosaurs (approximately 110 million years). However, sea turtle populations today are faced with two existential threats: (a) the feminization of their populations and (b) the loss of suitable nesting habitat. Both of these threats are driven by global warming.
Feminization of Sea Turtle Populations.
During incubation, sea turtle eggs are very sensitive to temperature changes within the clutch. Successful embryonic development typically occurs between 77 to 95 degrees Fahrenheit. Within this temperature range, gender is determined at a pivotal incubation temperature. For example, loggerhead eggs incubated at 84 degrees Fahrenheit will produce an even number of male and female hatchlings. Eggs that incubate above this pivotal temperature will produce more female hatchlings while eggs that incubate below this pivotal temperature will produce more male hatchlings. As the environment continues to warm and temperatures on nesting beaches rise, more female than male hatchlings will be produced. This phenomenon is known as the feminization of a population. In the southeastern US, the more southern, warmer beaches along the east coast of Florida are estimated to produce nearly 90% female hatchlings. Conversely, the more northern, cooler beaches in Georgia and the Carolinas are believed to produce closer to 55% - 60% female hatchlings. From the male sea turtle perspective, feminization of the population is a good thing because it increases his opportunities to mate. More female turtles also means greater nesting activity and a short-term increase in population. However, the diminishing number of males in a breeding population will eventually result in low genetic variation. Without sufficient genetic diversity, a sea turtle population cannot evolve in response to changing environmental conditions and will face an increased risk of extinction.
It should be noted that rising temperatures on nesting beaches are affecting turtle populations in another important way. If temperatures within the nest rise beyond the optimal range for successful incubation, thermal stress will result in increased egg mortality. In extreme cases, total clutch failure could occur. A significant reduction in hatchling production will increase the risk of extinction.
Loss of Suitable Nesting Habitat.
A significant consequence of global warming is sea level rise. The rise in sea level is mostly due to the influx of water from melting glaciers and ice caps and thermal expansion of the ocean. A primary impact of sea level rise on marine turtles is the loss of suitable nesting habitat due to inundation and/or erosion. This problem is exacerbated in locations where anthropogenic development prevents the natural landward migration of beaches. Even on currently viable nesting beaches such as Seabrook Island, incubating clutches may be at risk from sea level rise if the underlying water table rises and floods the nest from below. Compounding the threat of sea level rise are extreme weather events
driven by global warming, This increase in storm activity is expected to result in significant erosion or alteration of nesting beaches.
Protect Our Sea Turtles.
• Don’t buy items made from critically endangered hawksbill shell. • Reduce your carbon footprint.
• Choose responsibly caught seafood.
• Say NO to plastics.
• Leave no trace on the beach.
• Choose sunscreen carefully.
• Shield lights from the beach.