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Biology

Global Warming Increases Cold-Stun in Sea Turtles

Kemp’s ridley on Padre Island national seashore along the Texas coast in the Gulf of Mexico. Photo courtesy of the nation parks service (nps.gov).

Source

Griffin, L.P., Griffin, C.R., Finn, J.T., Prescott, R.L., Faherty, M., Still, B.M. and Danylchuk, A.J., 2019. Warming seas increase cold-stunning events for Kemp’s ridley sea turtles in the northwest Atlantic. PloS one, 14(1), p.e0211503.

Background

When thinking about the impacts of global warming in marine waters, cold-stun in sea turtles seems counter-intuitive. However, ‘Cold-Stun’ occurs with warming temperatures as turtles travel farther north and are trapped in near shore waters when temperatures drop in Fall. ‘Cold-Stun’ is a state of lethargy caused by cooling water temperatures that can lead to death. When sea turtles are cold-stunned, some become stranded on coasts, and many efforts are in place to rehabilitate these turtles. All sea turtles can be affected by cold-stun, but those particularly susceptible include the Kemp’s ridley (Lepidochelys kempii), Loggerhead (Caretta carreta), and green turtle (Chelonia mydas). As sea turtles move along the east coast in the summer time, increasing temperatures are expanding their habitat further north. For the Kemp’s ridley summer time temperatures have expanded its habitat into the Gulf of Maine. As waters stay warmer longer on the New England shelf, the Kemp’s ridley stay in the Gulf of Maine longer. When temperatures drop in late fall these sea turtles start migrating south-ward, but some get trapped in Cape Cod (see map). Kemp’s ridley generally cold-stun around November, while other sea turtles like the Loggerheads cold-stun later in December.

Map of study site in the Gulf of Maine, Cape Cod at the bottom left in the box has a high incidence of stranding (Griffin et al., 2019).

Goals of Study

A recent study by Griffin et al. (2019) aimed to identify environmental factors that impact cold-stun in sea turtles and predict future instances of cold-stun. In the study, Griffin et al. (2019) used stranding information from a national database, number of hatchlings and environmental variables (ex: temperature) across the Gulf of Mexico and the east coast.

Findings

Surprisingly, the number of hatchlings in the Gulf of Mexico of the Kemp’s ridley sea turtle were not found to affect the increases in cold-stun sea-turtles along the east coast. However, higher sea surface temperature (SST) in the Gulf of Maine were found to increase instances of cold-stun. The SST during different seasons was found to be the largest driver of cold-stun in the Kemp’s ridley. Particularly, late summer to early fall SST was found to be indicative of cold-stun. Increasing temperature in late fall was the most important factor of cold-stun, followed closely by higher SST in late summer and early fall. These higher temperatures in the Gulf of Maine are thought to lead to later south-ward migration and higher instances of stranding along the east coast. Interestingly, a few SST anomalies were associated with a hurricane in the late fall (Hurricane Arthur). The authors used this opportunity to look at potential impacts of strong fall and winter storms that are predicted to increase with climate change. They hypothesized these hurricanes and strong storms either drive warm waters shoreward driving sea-turtles inland, or the associated winds force sea turtles nearshore. As a result, sea turtles get trapped in nearshore waters as temperatures drop. Although this was seen in the case of Hurricane Arthur the authors point towards future research into the effects of hurricanes and winter storms on sea turtle cold-stun. Strandings to cold-stun instances in Kemp’s ridley sea turtles were also projected into future conditions using modeled SST in the Gulf of Maine. Cold-Stun strandings of Kemp’s ridley were predicted to increase from 1,100 in Cape Cod, MA in 2014 to 2,349 in 2031. Emphasizing the importance of rehabilitation efforts to save sea turtles in the future. Griffin et al. (2019) conclude this research by stating that although cold-stun might not have a large impact on the total population every effort counts in saving this critically endangered species.

Why is this important?

Due to anthropogenic climate change, sea surface temperature is predicted to increase over the coming years. Understanding the problems this poses for many marine organisms is vital to making changes and preventing further harm. This study investigated the impact of warming sea surface temperatures on cold-stun strandings along the east coast, with a focus on the Gulf of Maine. Many cold-stun strandings occur in Cape Cod, MA and along the Florida coast. Rehabilitation centers along the east coast play a vital role in saving affected sea turtles. However, with warming temperatures, a prediction of increasing sea turtle strandings due to cold-stun will put increasing pressure on these institutions. This study states that more resources will likely be needed for rehabilitation centers in the future, providing critical information for decision and policy makers to make changes accordingly. Finally, a lot of these cold-stun sea turtle strandings occur along the Massachusetts coastline. If you ever find a sea turtle on a beach you can help by calling your local turtle rescue organization.

I’m a PhD student in the Rynearson Lab at the University of Rhode Island (URI) Graduate School of Oceanography (GSO). Broadly, my research interests are focused on human impacts on the oceanic ecosystem, particularly effects on the primary producers (phytoplankton) at the base of the food web. Specifically, my interests include phytoplankton ecology and physiology, especially relating to stressors of nutrient limitation, pollutants and human impacts. I am also interested in using molecular analyses for studies of environmental distributions within different phytoplankton functional groups and highlight differences between organisms in culture experiments. Currently, I work with cultures from regions of the ocean that are nutrient limited and will conduct laboratory experiments to help investigate how these phytoplankton survive.

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