Climate change impacts on marine reptiles

The turtles, sea snakes and crocodiles of the Great Barrier Reef are affected by climate change because their body temperatures are controlled by the environmental temperature (except for the leatherback turtle). Thus many of their biological processes are affected by temperature, increasing their vulnerability to climate change impacts.

Turtles

Of all the marine reptiles on the Reef, turtles are the most vulnerable to climate change. Six of the world's seven species of marine turtles visit or live on the Great Barrier Reef. It is predicted increased temperatures will significantly affect their reproductive processes and food resources.

Temperature plays a critical role in marine turtle reproduction. The beginning of a turtle's breeding cycle depends to some extent on the air temperature. Once the eggs have been laid, their development into a hatchling requires a temperature range between 25 and 33 degrees celcius.

The sex of turtles is also determined by the temperature of the sand where the eggs have been laid. Therefore, any increases to air and sea temperatures will alter turtle breeding seasons and patterns, egg hatching success and the sex ratio of the populations.

The predicted sea level rise is likely to threaten marine turtles' nesting areas around the Great Barrier Reef. Four of the six species nest on beaches, cays and islands and as the sea rises this could erode those areas, and see less available space. It is expected turtles will move around until they find a suitable nesting spot. However, due to coastal development, available space is becoming increasingly limited.

An increase in cyclone severity could impact turtle nests, as they are usually made during cyclone season. However, these impacts are likely to be localised to only a few nesting areas with each cyclone. The extent of the impact will depend on the timing of the cyclone. For example, a severe cyclone at the end of nesting season may cause less damage than a small cyclone at the height of the nesting season.

More rainfall may lead to more nesting success for turtles as it is difficult for a female turtle to build a nest in loose, dry sand. Evidence shows a marked improvement in nest building success following major rain events.

Seagrass is a food source for some marine turtles and as the effects of climate change may reduce the amount and spread of seagrass, its availability to turtles may decrease.

Sea snakes

Sea snakes' body temperature is completely reliant on the sea temperature due their small body mass and surface area. However, little is known about tolerance levels and where sea snakes live and move based on their preferred sea temperature.

Crocodiles

The estuarine crocodile is the only crocodile species on the Great Barrier Reef. Like turtles, temperature is an important factor in the development of crocodile hatchlings. Nesting periods, sex determination and the running and swimming speed of a hatchling are environmentally-determined, and influenced by temperature. Water levels and temperature also affect breeding behaviour in estuarine crocodiles; predicted increases in each of these could change the timing and patterns of mating.

While currently estuarine crocodiles are most likely to be found in the northern parts of the Great Barrier Reef, higher air and sea temperatures could see populations move further south.

The estuarine crocodile nesting season coincides with cyclone season on the Great Barrier Reef. Therefore, cyclones can sometimes result in localised flooding of crocodile nests. This could mean eggs are washed away, restricted access to nesting sites for crocodiles and a loss of available nesting area.