By JEANETTE WYNEKEN

The planet’s climate changes; it has done so throughout Earth’s history. Those environmental changes can affect all life stages of sea turtles, including egg survival and the reproductive success of adults, in addition to affecting food quality and availability.

Some climate models predict that many marine turtle nesting sites could become warmer, drier, and subject to more severe storms as climate change progresses. Dry sand can increase unsuccessful nesting attempts (false crawls), cause nest chambers to collapse while being excavated, and dehydrate and destroy nests. Conversely, wetter sand caused by storms and wave runup can suffocate sea turtle embryos or lower hatching success. Sea turtle eggs incubate more rapidly at warmer temperatures up to a point, but as the upper thermal limit is approached (~34 C [~93 F] for most species) development slows, and higher heat can cause embryos to perish. Temperature also affects sex ratios, with warmer incubation resulting in a preponderance of female hatchlings, a demographic problem that could become catastrophic over time if insufficient numbers of males are produced.

Warming seas and estuaries are likely to undergo ecological shifts as well, such as losses of basic or intermediate links in food chains; these losses could in turn affect the habitats used by juvenile turtles and alter how they move from one developmental habitat to another as they mature. Those same factors may also have an impact on the abundance, quality, and distribution of adult turtle feeding grounds. However, changes in sea level and storm severity are the climate components most likely to have direct, near-term effects on sea turtle reproduction, causing nest inundations and the loss of turtle nesting sites to rising seas. Researchers are already beginning to see such effects at many armored beaches in Florida, U.S.A., and elsewhere (see “Coastal Armoring and Rising Seas Put a Squeeze on Turtles” in SWOT Report, vol. XII).

The effects of climatic shifts seem dire for sea turtles. Yet history across geological time can provide perspective and even some hope. Turtles appeared on Earth about 220 million years ago, with several marine lineages persisting for millions of years and through many major climate change events, including the Mesozoic and Cenozoic interglacial and glacial periods. Today’s seven species of marine turtles arose ~20–70 million years ago; the oldest ones arose around the time of the K–T or Cretaceous–Tertiary mass extinction event caused by an asteroid some 66 million years ago. Their ancestors evolved from stock that lived in much warmer times, compared with more recent millions of years characterized by cooler seas and beaches. What extant turtles now face is a different (generally warmer) thermal trajectory accompanied by a more rapid onset. The question is whether ancestral resiliencies that allowed sea turtles to thrive to the present will be sufficient to carry them past the current threat posed by climate change.

Sea turtles can elicit tricky questions from those curious about their mysterious lives and natural histories. And even sea turtle specialists can struggle to answer some of the most seemingly basic questions about sea turtle biology and conservation. If you are among the many specialists who have stumbled to concisely answer things such as “How many sea turtles are there?,” “How old do turtles get?,” or “Where do baby turtles go?,” then this feature is for you. Our hope is to set the record straight about often-asked questions with answers written by top experts who will prepare you to respond like an expert yourself. Moreover, we hope that for those questions about sea turtles that may still have no firm answers, this series can pique SWOT readers’ curiosity and drive them to conduct the research needed to solve the mysteries.

This article originally appeared in SWOT Report, vol. 16 (2021). Click here to download the complete article as a PDF.

What Does Climate Change Mean for Sea Turtles?

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