At a UN-organized meeting in Bonn, experts are discussing the plight of endangered sea turtles. Expert Colin Limpus told DW climate change is just the latest human-made factor making life tough for turtles.
DW: Why are turtles on the agenda?
Marine turtles have a number of very critical issues related to climate change. The first is ‘temperature dependent sex determination’. The sex of the hatchlings is determined by the temperature of the nest half-way through incubation. And a warm beach creates mostly females, and a cool beach creates mostly males. One of the concerns with rising global temperatures is that we will shift potentially into an all-female producing population in a number of places. So this is a concern of the effect of rising temperatures.
The second big issue is that turtles nest on sandy beaches. That's the only place they can lay their eggs. And sea levels rise, then nesting areas could potentially see a rise in the water table, flooding of the nesting sites and loss of eggs as a result.
Additionally, the increasing the intensity of hurricanes or cyclones: the more intense a cyclonic disturbance, the greater the destructive effect when the cyclone crosses coastal waters. So this leads to dramatic changes and the loss of critical habitat in coastal areas and the feeding areas for sea turtles. And major damage to a feeding area, may take years to recover. So any change in the frequency and intensity of these events is going to be detrimental.
Are we already seeing signs of these things already happening?
Yes, we can see the effects of major floods and cyclones. Part of the problem is judging which way this could go with our turtle population. A lot of studies try to predict on the basis that the population is static and will not shift. But if we look at what has happened over the last 10 to 12,000 years in Australia, for example, today, nesting beaches have multiple species nesting in places where 10,000 years ago it was dry land, and the nearest beaches would have been 900 kilometers away. We've gone through a major climate change from the ice ages through to the present, and sea turtles survived that. They did it by changing where they breed. So it's a challenge for how the turtles will respond. Will they stay where they are right now and suffer the consequences? Or can the population shift to areas that are suitable for them as change occurs? We have to consider how fast they can adapt with a rapid change in climate compared to what they went through in the past.
So we are probably talking about a faster climate change than what we have seen to date?
That's what some people are saying. If that's the case, it may challenge the capacity of turtles to do adapt. On the other hand, there are areas of their biology that we have not really investigated very well. A turtle comes back to the area where it's born. Recent research suggests that they don’t necessarily go back to the same beach where they were born, but go back to the region. So that suggests that as a turtle grows up, it choosing where it wants to breed. It may be able to make choices and may respond to changes, and choose a different site maybe within hundreds of kilometers of where it was born. So it could choose a beach with the right temperatures and stability.
But we don't know? And what can we do about it?
No but I guess I have some confidence that these animals, which have survived the past millions of years, have come through many climate change events. They’ve survived the catastrophic events that caused the demise of the dinosaurs. But in the past they didn't have to deal with human impacts. All of our sea turtles are listed as threatened species. It's going to depend on how we help them. Obviously the broader community has to address the issue of climate change. We need to start looking at how we manage temperatures of beaches, how we tackle the recovery of foraging areas, sea grass pastures, coral reefs. We need to keep them viable. We have to look at the sediment runoff that comes with floods, because that has a very big negative impact. How do you stop that soil eroding from your farmlands? These are all things we can do to soften the impact on turtles.
Why should we be worried about marine turtles in general, what role do they play in the ecosystem?
That depends on in which society you ask that question. A person living in Berlin might say “can't see much point in it.” If you were talking to an indigenous person in northern Australia, they would talk about the iconic value of the turtles in terms of totemic animals that are an integral part of their religious culture. And there are areas where it is the primary source of red meat for the community, so for them as a food resource and a cultural thing, very important. In the area where I grew up, the eco-tourism around turtles is the primary cash flow for the district economy for about five months of the year. Tourists come to look at nesting turtles. So the people in the business community would see it as an important economic component. As a biologist I see them as an integral part of the ecosystem. The loggerhead turtles have a function in the regulation of the density of shellfish in some areas, they feed on them. The green turtles are herbivores feeding on sea grass and their activity promotes the turnover of nutrients in a sea grass pasture. So turtles have lots of significance to different parts of the world.