Animals and plants are optimally adapted to their surroundings. Therefore, when temperatures change due to global warming, plants and animals have to find ways of coping. One way to cope can be to relocate to areas with temperatures like those the species are used to. Another option is for the animals or plants to change the timing of seasonal events like hibernation, breeding, spawning or migration.

Marine species have to move longer
The study shows that in order to keep up with the observed climate warming over the past 50 years, the world’s plants and animals would have moved around 2.5 km each year on average to track their optimal temperatures. But regional variations mean that in many areas marine species must respond much more rapidly to the changing climate than species on land.

“Because of the faster increase of temperatures on land, you might expect the species to change quicker on land that in the sea. This study shows that this is not true at all”, says Keith Brander from DTU Aqua, who came up with the initial idea to look at how quickly species in the sea could be expected to change as a response to global warming.

“On land, species can find different temperatures by moving a shorter way than species in the ocean. For example, by relocating to higher altitudes in mountains. In the oceans, temperatures are much more even. Here, if the temperature increases, the species would have to move a much larger distance to find the right temperature”.

Figure: Burrows et al. 2011 / Alphagallileo.com

Spring temperatures arrived 5 to 10 days/decade earlier in the North Sea but by less in the Mediterranean and were delayed in the Black Sea.

Increased biodiversity in the North Sea
The average temperature in the Danish seas has increased by 1.5 ⁰C over the last 30 years and to track these changes, marine species have had to relocate.
“Some species in the Danish waters have had to move their ranges around 10 km each year during the last 50 years in order to cope with the changing water temperature,” says Keith Brander.

Surprisingly, the increasing water temperature and the species relocating have meant an increased number of animal and plant species in the North Sea:

“The numbers of the flatfish, the common sole, has been increasing in Danish waters. The sole is distributed all the way down to Africa, and thrives in the warmer Danish waters. In contrast, the European plaice is a flatfish species adapted to living in colder waters, and we see that the numbers of European plaice in Danish waters are going down compared to sole numbers. Yet, it is not a simple picture. For instance, a cold-water species, like the cod, is able to stay in Danish waters by adapting to changing temperatures by moving the time when they spawn,” says Keith Brander.