If sea level rise continues to more than 7 millimeters per year, mangroves are in danger of drowning. A little sea level rise is no problem for an average mangrove forest. But if it goes too fast, then everything gets drowned out.
Mangroves can withstand a maximum sea level rise of 7 millimeters per year, above that threshold the trees and shrubs in this (sub) tropical ecosystem drown. This is the conclusion of an international group of geologists and biologists 7 June in Science, based on 78 drill cores.
Sea levels are currently rising by 3.4 millimeters per year, but in a business as usual scenario this will rise to 10 millimeters per year in 2100. Then there is only one thing left for a mangrove forest: migrating inland. But given the human coastal use, that is not possible in most places.
“Beautiful and relevant research,” says Utrecht mangrove researcher Job de Vries, not involved in the study. “Previous work has been done to determine the effect of sea level rise on mangroves using boron cores, but these researchers are now taking a global look at the Early Holocene for the first time, when the world awoke from the last Ice Age. And that is special. “
That de-icing of the world began some twenty thousand years ago. Initially, the sea level rise therefore rose extremely quickly, but the rise became weak in the middle of the Holocene, some ten to seven thousand years ago, slowly diminishing with some fluctuations here and there. Especially during the latter period of stabilization, mangroves had to migrate further inland.
To find out how mangroves reacted to sea-level fluctuations at the time, the researchers analyzed sediment from 78 cores from all over the world. They are looking specifically at so-called vertical accretion, a process in which the soil on which mangrove forests grows rises due to sedimentation processes.
“This is mainly because the roots are very good at retaining sediment,” explains De Vries. “The more sediment that flows onto land due to tidal action, the more it will rise. And sea level rise is driving that process. “
Thus mangroves can adapt their own environment to some extent. Until that found sea level rise of an average of 7 millimeters per year is reached. Above that, mangroves have to migrate. “In principle, they are very good at that,” says De Vries. “The interface between sea and land is” their “habitat, all other plant species are outcompeted.”
In the past, that was indeed not such a problem, the researchers also conclude. But in the modern world there is simply no more room for this. Almost all relevant square meters have been taken up by humans. That would mean that the mangrove ecosystems, which are already being cut down to make way for shrimp farming, for example, would get a new threat: drowning.
“That’s not a nice prospect,” says De Vries. “Mangroves are not just dirty, muddy places for mosquitoes. They are important nurseries for ocean species, play an important role in coastal protection by weakening wave energy and storing enormous amounts of CO2. When drowning, all CO2 is released from the muddy soil and the trees. “
Translated from: Bionieuws.nl