Ocean Acidification Occuring Too Fast For Adaptation

Posted on 26. Jul, 2010 by Ross in Climate Change

Firstly, some good news. Ocean acidification, the evil twin of climate change, has happened in the past and creatures of the period adapted their physiologies to survive.

The bad news is that the current rate of ocean acidification far outstrips what has gone before, making generational adaption to the current rising oceanic pH far more unlikely for all but the most simple planktons.

Ocean acidification occurs due to carbon dioxide dissolving into sea water, removing it from the atmosphere but creating mild carbonic acid. Rising ocean acidity is expected to have a number of serious impacts upon worldwide aquatic ecosystems, but the main area for concern is usually the ability of simple species towards the foot of the food chain to synthesise their shells, which dissolve in acid. Calcium carbonate structures are widespread amongst zooplankton, as well as being the building blocks of corals, mollusc shells and a host of other organisms.

The fear is that disruption from ocean acidification at these lower levels of the food chain would have massive ramifications for the pyramid of predators above.

Now, scientists from Switzerland and Italy has published research in Science showing that during a previous period of comparatively rapid ocean acidification, plankton proved fairly resilient to the changes, despite some species dying out and others suffering malformation and stunted growth. The conclusions were reached after studies on ancient ocean sediments.

About 120 million years ago, during the early part of the Cretaceous period, a series of massive volcanic eruptions pumped huge amounts of carbon dioxide into Earth’s atmosphere, raising it’s concentration to about twice today’s level. Eventually, the oceans absorbed much of that carbon dioxide, which in turn significantly increased the water’s acidity. Ocean pH returned to normal about 160,000 years later.

The findings are not entirely unexpected, since planktons fast life cycle makes genetic responses to evolutionary pressures theoretically feasible within human lifetimes. The good news definitely stops there though, since the current rate of ocean acidification far outstrips the environmental conditions of the period studied, and the timescale over which the organism can adapt relative to it’s own life cycle is crucial. Likewise, longer-lived organisms such as sea snails, urchins and corals have far fewer generations over which genetic changes can be selected for successfully.

In a further dose of bittersweet news, the same study found that ocean acidification also spread progressively downwards from the surface waters into the depths over time: something not yet detected in modern times. The upside of this is that it would increase the ability of the world’s ocean’s to soak up carbon dioxide from the atmosphere. The downside is of course that no aquatic ecosystem is safe from the effects of increasing acidity over the coming century.

Image of a sea snail, urchin and coral - all at risk from ocean acidification - by Debs (