Impacts of ocean acidification and burrowing urchins on within-sediment pH profiles and subtidal nematode communities

Rising carbon dioxide levels in the atmosphere will affect the ocean carbonate system, resulting in a predicted future decrease in the pH of seawater by 0.3-0.5 units. To investigate whether the presence of a burrowing urchin, Echinocardium cordatum, might influence the impact of ocean acidification on subtidal sediment pH profiles and nematode community structure an experiment was conducted using subtidal sediment, with urchins present or absent and seawater at either pH 8.0 (ambient) or 7.5. The presence of urchins, and a reduction in pH, both had significant effects on within-sediment pH profiles. Where urchins were present sediment profiles were more consistent and sediment pH was lower than that of the overlying seawater. There were significant differences in nematode abundance between treatments. The primary effect was a higher abundance of nematodes in replicates with urchins in natural seawater. All treatments had similar nematode community structure and diversity. Ocean acidification could therefore lead to changes in nematode communities in subtidal sediments affected by burrowing urchins.

Climate change could stop corals fixing themselves

Climate change is depriving coral reefs across the globe of the building materials used to make their shells. Current plans to curb greenhouse gas emissions may not be enough to fix the problem, according to new research.

The daily life of corals is a constant battle against erosion. The reef builders patch up holes in their shells, left by nibbling sea creatures, using a mineral called calcium carbonate. To keep up with repairs, corals in the wild usually require three times as much of the mineral as sheltered corals grown in laboratories.

Atmospheric CO2 stabilization and ocean acidification

We use a coupled climate/carbon-cycle model to examine the consequences of stabilizing atmospheric CO2 at different levels for ocean chemistry. Our simulations show the potential for major damage to at least some ocean ecosystems at atmospheric CO2 stabilization levels as low as 450 ppm. Before the industrial revolution, more than 98% of corals reefs were surrounded by waters that were >3.5 times saturated with respect to their skeleton materials (aragonite). If atmospheric CO2 is stabilized at 450 ppm only 8% of existing coral reefs will be surrounded by water with this saturation level. Also at this CO2 level 7% of the ocean South of 60°S will become undersaturated with respect to aragonite, and parts of the high latitude ocean will experience a decrease in pH by more than 0.2 units. Results presented here provide an independent and additional basis for choosing targets of atmospheric CO2 stabilization levels.

Talk on “Ocean acidification scoping workshop and research directions”

The talk on “Ocean acidification scoping workshop and research directions” given by Chris Langdon (University of Miami) at the Ocean Carbon and Biogeochemistry Workshop 2008 (held in Woods Hole in July 2008) is available on the OCB web site.

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