What happens when the ocean is too warm for the Hawksbill Sea Turtle?
Climate change and rising sea temperatures are causing Hawksbill Sea Turtles to remain on the critically endangered species list. But why is this happening?
To be critically endangered a species has to be at very high risk of extinction in the wild. But, before a species can be declared critically endangered it has to surpass the status of endangered by meeting certain criteria. The International Union for Conservation of Nature Red List has a set of five different criteria that need to be looked at when assessing a species to be considered critically endangered. These criteria include a species: initial population size, decline in population, geographic range, and if their range is restricted for any reason (1). All of these criteria are analyzed quantitatively to determine the probability of the species becoming extinct in the wild.
According to the World Wildlife Fund’s endangered species list there are currently sixteen critically endangered species as of 2020. Out of seven species of sea turtles, three are considered endangered, and one is considered critically endangered (2). Since 1970 the Hawksbill Sea Turtle (Eretmochelys imbricata) found predominantly in tropical reefs of the Indian, Pacific, and Atlantic Oceans has been considered critically endangered.
Hawksbill Sea Turtle/ Carey de Concha by U.S. Fish and Wildlife
Hawksbill Sea Turtle populations are faced with a double threat that are causing decreases in their population numbers. The first threat that initially landed them on the endangered species list is their beautiful shells that capture the attention of poachers. But most recently, what is keeping the Hawksbill Sea Turtle on the critically endangered species list is the impact of rising ocean temperatures on their breeding grounds (3).
Gender in sea turtles is determined by temperature in the middle third of the incubation process. In order for there to be a 50% chance of male birth and a 50% chance of female birth the water the turtles breed in needs to remain as close to 81.86°F as possible. In warm temperatures, sea turtles give birth to 100% females. This trend of warm temperatures and female births has been seen almost 99% of the time with Hawksbill Sea Turtle populations. So, if only females are being born then there are no males for them to reproduce with. With the warming of the ocean in recent times this has a drastic alteration on the Hawksbill Sea Turtles sex ratios (4).
Around 80% of the excess warmth from the rising surface temperatures due to climate change is absorbed by the ocean resulting in thermal expansion. This thermal expansion can produce anywhere between 18 to 60 cm in sea level rise by the year 2100. When Hawksbill Sea Turtle nesting takes place there should be sufficient space above the high tide line and there should be adequate beach vegetation for clutch shading. If sea levels continue to rise there won’t be sufficient space and vegetation for nesting, making these species further susceptible to future climate changes. Areas especially vulnerable to this are low lying narrow coastal and island beaches susceptible to costal squeeze (5). If a nesting habitat is located between the sea and a sea wall or barrier then as the sea level rises the water takes over the nesting habitat. The nesting habitat then can’t move or migrate up land because of the sea wall blocking it.
Costal Squeeze Diagram by Eastern Solent Costal Partnership
The conservation of marine turtles and the full understanding of the impact of climate change on these species is essential because they play big roles in maintaining marine and costal ecosystems. Hawksbill Sea Turtles primary prey are sponges. By controlling sponge populations the turtles contribute to reef health because the sponges compete for reef space. The nesting of sea turtles on beaches provides nutrients for costal vegetation and sea turtle grazing on the costal vegetation plays a part in keeping it healthy. The Hawksbill Sea Turtle also has important cultural roles in terms of their values to indigenous communities, and educational roles in learning about marine ecosystems (3).
Some efforts that are being put into place to conserve sea turtle populations are stricter laws in regard to the dumping of pollutants and waste into the ocean, eliminating nest disturbances by decreasing public access to beaches and decreasing artificial light, and decreasing turtle deaths caused by commercial fishing with stricter net regulations. But what can you do to help sea turtle populations? You can reduce the amount of waste you produce by using reusable items, you can participate in costal clean-ups, if you come across a sea turtle nest don’t disturb it, and you can fill in holes you find on the beach that could end up being obstacles for sea turtles trying to get to the ocean.
Sources:
(1) International Union for Conservation of Nature. (n.d.). Background & History. Retrieved March 4, 2020, from https://www.iucnredlist.org/about/background-history
(2) World Wildlife Fund. (n.d.). Endangered Species Directory. Retrieved March 4, 2020, from https://www.worldwildlife.org/species/directory?direction=desc&sort=extinction_statu
(3) Fuentes, M., Limpus, C., & Hamann, M. (2010). Vulnerability of sea turtle nesting grounds to climate change. Global Change Biology, 17(1), 140–153. doi: 10.1111/j.1365-2486.2010.02192.x
(4) Glen, F., & Mrosovsky, N. (2004). Antigua revisited: the impact of climate change on sand and nest temperatures at a hawksbill turtle (Eretmochelys imbricata) nesting beach. Global Change Biology, 10(12), 2036–2045. doi: 10.1111/j.1529-8817.2003.00865.x
(5) Hamann, M., Fuentes, M., Ban, N., & Mocellin, V. (2013). Climate Change and Marine Turtles. The Biology of Sea Turtles, Volume III Marine Biology, 353–378. doi:10.1201/b13895-14
Katelyn Fournier 