In the same way canaries were once used to warn miners of dangerous gases, the changing behaviour and population demographics of seabirds and marine mammals are clear indicators of the effects of climate change on our oceans — and there is a growing body of research to prove it.
To analyse the main trends that are emerging, and identify research gaps, a team of top researchers from Norway, Tasmania, the US and SA — led by Prof Pierre Pistorius, head of the Marine Apex Research Unit at Nelson Mandela University — undertook the mammoth task of analysing all the research in this area from across the world.
“This is the most extensive meta-analysis that has been done on the impact of climate change on seabirds and marine mammals to date,” Pistorius said.
Their findings — recently published in leading ecology journal Ecology Letters — showed that seabirds and mammals are being affected directly by an increase of extreme weather events, like storms and heatwaves, and indirectly by shifts in their prey, as a result of rising sea temperatures.
And, in many cases, their numbers are declining.
“Cold-blooded animals like fish respond much faster to the actual physical characteristics of climate change, such as increasing temperatures,” Pistorius said.
What this means is that marine prey, including fish, krill or squid, quickly move to cooler waters, and seabirds and mammals, especially those that breed on land, have to travel much further to feed.
If there is not enough food, reproduction rates drop.
The review also found that the effects of climate change on these animals were most pronounced at the North Pole, but it also showed this was where the most research had been carried out, with the fewest studies being conducted in the tropics.
“In the Arctic, there have been some drastic changes over a very short period, and that’s been documented to have influenced a lot of marine mammals in these waters,” Pistorius said.
The study showed that animals with a narrow thermal range — meaning they can only thrive under certain temperatures, such as polar bears — were affected much more by climate change than animals with a wider thermal range, like migrating seabirds.
A significant gap was the limited research on climate change effects on cetaceans, which include whales and dolphins.
“To measure the impact of climate change, you have to have baseline information, and there’s simply not enough known about many cetacean species.
“So there could be massive changes, but it will go totally unnoticed because we know so little about these species,” Pistorius said.
Because seabirds and seals breed on land, they are easier to study.
“We also looked at the amount of time that is required to confidently state that it’s climate change that has influenced the animal, and not just normal climatic variability.
“We concluded that, overall, a steady period of 19 years is roughly what is needed to confidently attribute a change to climate change.
“This time period varies geographically though, and in some areas like the North Pole, where conditions are changing so fast, a shorter period of time is needed.”
Closer to home, Pistorius and other NMU researchers have also been conducting research into changes in prey distribution and feeding areas for seabirds along SA’s coastline and on Indian Ocean islands, including Reunion and the Seychelles, to identify important habitats.
This helps to inform marine spatial management and the design of marine protected areas.
“It is sometimes difficult to separate the influence of climate change from fisheries, as we know that fisheries also have a big impact on the prey base of many marine predators.
“We know both of them are coming into play, but just to what extent each of those are important is difficult to assess.”
But what they do know for sure is that marine management approaches need to keep up with a changing ocean.
“Conventional static boundaries on marine protected areas are probably not the best approach in the face of climate change because of ongoing changes in oceanographic conditions and associated ocean productivity.
“Having marine protected areas with dynamic boundaries is going to become increasingly important in the face of climate change.”
To discuss these and other marine challenges, Pistorius and many of the world’s top marine researchers are gathering in Nelson Mandela Bay until October 15 for the 12th Western Indian Ocean Marine Science Association Scientific Symposium to share knowledge, experience and solutions.
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