Double the danger for the Mediterranean

Climate change is particularly harsh on the sea due to warming and acidification

Seagrass meadow in the Mediterranean © Gronk / CC-by-sa 3.0
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The "bathtub of Europe" is facing difficult times: Climate change causes particularly high warming and acidification in the Mediterranean, as a European marine research project shows. Already, the acidity of the water has risen by up to ten percent, by the end of the century it could even be 150 percent. Marking ecosystems such as the seagrass beds and coral reefs are in acute danger, the researchers warn.

For three and a half years, 100 researchers from 12 countries focused on just one topic: the Mediterranean and its response to climate change. In the Mediterranean Sea Acidification in a Changing Climate (MedSeA) project, they conducted long-term studies in a wide variety of marine environments, analyzed water samples, and observed changes in animals and plants.

Warm and sour to the bottom

Now the researchers have presented the first results of this EU-funded project - and these are not very encouraging. "Previously, we knew almost nothing about the combined effects of warming and acidification in the Mediterranean, and now it is clear that they are a double threat to our marine ecosystems, " explains Project Coordinator Patrizia Ziveri of the Autonomous University of Barcelona.

The studies showed that the Mediterranean has already warmed by 0.75 degrees in the last 25 years - and not just on the surface, but into the deep water layers. The reason is a circulating current typical of this fast-inland sea, as the researchers explain. It brings the heat, but also dissolved CO2, relatively quickly from the surface into the depth.

A research diver explores the seabed in the Mediterranean Sea. © MedSeA / Nicholas Blakemore

Mass extinction in the summer

And in the near future, the Mediterranean will be even warmer: By 2050, the scientists predict an increase in water temperatures by up to 1.5 ° C in the eastern part. In the summer, the average surface temperatures could soon surpass the 29 C mark, the researchers said. The ecological consequences of this development are already visible: The distribution areas of many species have moved further northwards from the south-east coast, and in the summer mass extinctions of heat-sensitive animal species have begun. display

This development is further reinforced by the increasing acidification of the Mediterranean: in the period between 1993 and 2013 alone, the pH value of the water has dropped by more than ten percent, according to the researchers. If CO2 continues to be emitted at the same rate, acidification will increase by 30 percent between 2010 and 2050. By the end of the century, the Mediterranean could even be 150 percent more acidic, so their forecast.

Unique seagrass meadows are in acute danger

"For some species, life will be very difficult, biodiversity will decline, and some species will die out, " the scientists describe the consequences of this development. Among the losers of development are the seagrass beds a magnificent and unique habitat for countless fish, crustaceans and plankton species. They still cover around 50, 000 square kilometers of the seabed in the Mediterranean.

"These biodiversity hotspots have thrived for millennia and have been used extensively by the people of the area, " say Ziveri and her colleagues. "But now they are facing the decline." The very slowly growing aquatic plants are extremely sensitive to the warming of seawater. According to estimates of the researchers, only ten percent of the underwater meadows could be left over by 2050 too little to maintain this habitat.

Massive beach-washed light jellyfish in Tunisia Nader Sahli / CC-by-sa 3.0

Consequences also for humans

However, warming and acidification will not only have consequences for the flora and fauna - humans will also be affected: for some important seafood, such as mussels, the Mediterranean might k In the future, be too angry, their decline would then be a whole industry. In 2012, 153, 000 tonnes of this seafood were harvested, which corresponds to a value of 225 million euros, the scientists said.

And yet another striking Mediterranean species is in acute danger: the red coral (Corallium rubrum). It has been used by Mediterranean cultures to make jewelery for thousands of years, but it too could disappear because of acidification.

Jellyfish plagues soon the rule

A problem for fishery and tourism alike are the increasingly frequented jellyfish along the Mediterranean coast. The cnidarians benefit from the warmer water and spread more and more. In 2012, a mass increase of the poisonous light-colored jellyfish Pelagia noctiluca on the Spanish Mediterranean coast caused problems, thousands of people were netted, helpers fished more than 4, 000 kilograms of these jellyfish off the coast. If such events accumulate, more and more holidaymakers could stay away, the researchers say.

"To protect these intriguing ecosystems, human society around the world must reduce fossil fuel emissions - that's clear, " says James Orr of the French Laboratoire des Sciences du Climat et de l'Environnement. Because not only remote seas and coasts are affected by climate change, but all - and especially the Mediterranean Sea.

(MedSeA Project, 16.06.2014 - NPO)