Scientists predict that the effects produced by anthropogenic (human-induced) climate change could be the trigger of the sixth, and fastest, mass extinction of species on Earth, with 15-37% of species going extinct by 2050 [7]. The fifth Intergovernmental Panel on Climate Change (2014) reported that global temperature will rise between 3.7°C to 4.8°C above pre-industrial levels by 2100 if current greenhouse gas emissions are not curbed [8]. This change would be catastrophic to species’ biology with changes to sea level, ocean chemistry, species interactions and habitat loss [7].
The decline of Hawksbill turtles is the result of a large list of different threats, including poaching and pollution [2], however, climate change poses risk to the entire population and could be the tipping point for their extinction.
The decline of Hawksbill turtles is the result of a large list of different threats, including poaching and pollution [2], however, climate change poses risk to the entire population and could be the tipping point for their extinction.
Rising Sea LevelsOne of the primary consequences of climate change is sea level rise. Oceans absorb about 90% of the total heat energy in the climate system [8]; therefore rising temperatures will have a dramatic effect. As ocean waters warm, they expand, and in combination with melting glaciers, sea level could rise by one metre by 2100 [8].
Sea level rise poses great risk to Hawksbill turtles as it reduces the amount of available nesting habitat, and for the turtles that do nest, the risk of inundation and destruction of the reef is greatly increased [3]. Furthermore, increased ocean temperatures are predicted to increase the severity of weather events such as storms, which will also lead to heightened beach erosion and inundation [3]. Change in Ocean CurrentsHawksbill turtles rely on ocean currents for migration and feeding, such as hatchlings moving long distances to pelagic nursery habitats for the first five years of their development [3]. The adult turtles also decide to breed based on whether the offshore currents will support this dispersal of their young [9].
Climate change is predicted to alter and weaken current ocean circulations as warming surface waters inhibit deep water formation11. This will disrupt turtles as they will have to alter their movements and possibly have to shift their range and timing of nesting [10]. |
Breeding and Egg IncubationThe physical development of Hawksbill turtles faces direct, negative consequences of climate change. All marine turtles are vulnerable to increased temperature as they are seasonal breeders with temperature-dependent sex determination [9]. This means that the temperature of the sand in which the eggs are buried influences the embryo development, sex, and phenotype. Successful embryo development is limited to an incubation temperature range of 25°C to 34°C, with cooler sand producing more male hatchlings and warmer sand producing more females [9]. Rising temperatures mean that turtles could face large shifts in female biased sex ratios, severely reducing breeding potential.
Increased sand temperatures also shorten the incubation time of eggs, meaning hatchlings have lower residual yolk mass, higher rates of physical abnormalities and generally have poorer performance [9]. Habitat DestructionAnother aspect of climate change that threatens marine ecosystems and hence, Hawksbill turtles, is ocean acidification. High levels of the greenhouse gas, carbon dioxide, are absorbed by ocean waters and a chemical reaction produces carbonic acid, which lowers the pH level of the water [8]. The IPCC reports that since the start of the industrial era, oceans have become about 26% more acidic [8]. This acidity, along with reduced carbonate, can have a devastating effect on marine organisms as their ability to build skeletons and shells is reduced while existing ones begin to dissolve [10].
Hawksbill turtles are a species closely associated with coral reefs as they rely heavily on them for food and protection [2]. Coral reefs are predicted to experience the most degradation by ocean acidification as it will reduce the ability of coral polyps to survive and build reefs (this is called coral bleaching) [12]. |