If no action is taken now to reduce greenhouse gas emissions, macroalgal forests and spermatophytes, including Posidonia oceanica, a higher plant endemic to the Mediterranean, will be threatened with extinction by 2100. Global warming threatens to reduce by 80-90% the amount of habitat suitable for the survival of these species worldwide, which will only be able to find refuge in the polar regions. This is the conclusion of a study published in the journal Nature Communications and carried out by the Universities of Helsinki and Pisa, the Istituto superiore per la protezione e la ricerca ambientale (Ispra) and the Centre of Excellence for Australian Biodiversity and Heritage (CABAH).
Using statistical models, the researchers mapped the distribution of 207 species, 185 brown macroalgae and 22 spermatophytes, from 2015 with annual projections until the end of the century. They are currently abundant along the coasts (macroalgae cover 2.63 million sq.km and spermatophytes 1.65 million sq.km) and are essential for marine life, producing oxygen through photosynthesis, storing carbon dioxide, helping to maintain a high level of biodiversity, acting as ‘nurseries’ for many commercially important fish and crustacean species and protecting against coastal erosion.
“The problem is global; macroalgal forests populate rocky coasts all over the world, from the shore to a few tens of metres deep,” explains Professor Lisandro Benedetti-Cecchi of the Department of Biology at the University of Pisa. “In the Mediterranean, they are mainly made up of arborescent brown algae of the genus Cystoseira, plants whose leaves rise a few tens of centimetres above the seabed, forming veritable miniature forests. Together with Posidonia oceanica, the tree-like algae are a reservoir of energy that fuels the functioning of the entire coastal marine system and ultimately our life on land.”
However, the effects of climate change will be uneven across the world, with areas likely to lose or gain biodiversity. However, the overall impact will be negative. Researchers estimate that macroalgae forests and spermatophytes will decline mainly in Europe, the Baltic Sea, the Black Sea, the Pacific coast of South America, the Korean peninsula and the north-west and south-east coasts of Australia.
“Climate change studies usually focus on the terrestrial environment, while the ocean remains relatively unexplored,” concludes Professor Lisandro Benedetti-Cecchi. This work aims to reverse the perspective and quantify the global changes affecting the marine ecosystem.