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Ocean Acidification Series

Ocean Acidification: The Unknown Reality of Climate Change

Plankton Life Already Weakened by CO2

The Luck of the Fish: for How Long?

Finding a Cure Despite Uncertainties

The Hopes of Ecosystem Modelling

Plankton Life Already Weakened by CO2

Wave in Brittany, France- credit: Laurene Mainguy

By Laurene Mainguy, May 2009

With the 2008 Monaco Declaration, the international scientific community is sending another CO2 warning signal to policymakers. Ocean scientists fear that current global warming mitigation policies won't suffice to prevent marine ecosytem degradation.

''I don't think that if you follow the Kyoto protocol, it will prevent ocean acidification,'' declared Long Cao, an oceanographer at the Carnegie Institute.

As excess CO2 dissolves in the ocean, the seawater becomes more acidic and less saturated in calcium carbonate minerals. Despite uncertainties, scientists say many small marine organisms may be severely affected.

John Raven, the former chair of the Royal Society working panel on ocean acidification, said some species may do better than others in high CO2 oceans. ''Clearly some present-day organisms progeny will be doing better, at least relative to other organism progeny which may no longer exist and may be extinct- say in 2100 or 2200. So yes, there will certainly be winners,'' he said.

Yet, Raven said it is absolutely necessary to cut down CO2 emissions to keep the planet as we now know it, with good air and oxygen, clean water to drink, quality food to eat, and nice places to relax. '' And even if you don't go there, I find that just knowing they are there is quite pleasant. I've never been to Yellowstone but there is nothing like Yellowstone, is there?!'' he said.

Raven has studied marine plankton at the University of Dundee, Scotland, for 38 years, but only recently he and his peers have made the connection between high CO2 emissions and changes in plankton physiology.

 

Plankton refers to microalgae (phytoplankton) and microscopic animals (zooplankton). Both are essential because they constitute the basis of the marine food web: they process nutrients for other microorganisms and feed larger animals like crustaceans and fish.

Foraminifera Neogloboquadrina pachyderma- credit: www.foraminifera.eu

Phytoplankton species that need calcium carbonate to build their shells may be affected quite badly, Raven said. With high CO2 concentrations in the seawater, some species may no longer be able to build their shells. Even those who could would be prone to dissolution and become vulnerable to predators and perhaps viruses, he added.

Such changes are already happening. Australian scientists found that the shells of foraminifera plankton are already 30 percent lighter than before the industrial revolution.

Minuscule pteropod like marine snail,s which make up penguins' diet, are also at risk. ''They often have tiny shells. It does seem to be essential for them, although it's quite difficult to establish completely what's the calcium carbonate is doing," Raven said. Gretchen Hofman, a researcher a the University of California-Santa Barbara, told United Press International that if marine snails were to go extinct, ''the impact on the food chain would be catastrophic.''

Raven said about 10 percent of all phytoplankton might be directly threatened by CO2 . But it might be more than that. ''The problem is, if something has a hard shell it's much easy to collect it. Even though it may fall to pieces, at least you've got the bits and pieces of the shell there. Whereas if another organisms falls to pieces, it's just slime, it's hard to identify.''

 

Shell-less marine snail (pteropod) credit: Arthur Anker

CO2 could also have indirect effects on phytoplankton. Most of the world ocean is already short of phosphorus and nitrogen, Raven said, so phytoplankton is already competiting with bacteria and fungi for those nutrients.

 

With high CO2 concentrations, the situation could become worse. Phytoplankton may be forced to excrete more organic carbon, the fundamental food for bacteria and fungi. Bacteria and fungi populations could get much bigger, and the competition for nutrients much tougher. ''How big a problem it really is in the real world is quite difficult to analyze, but theoretically it is a problem,'' Raven said.

A question that remains unanswered is whether plankton could adapt to higher CO2 pressures. ''These experiments are really quite difficult to run, they involve the organisms being kept for preferably hundreds of generations. Thatâ€ôs the length of time at which adaptation starts to occur,'' Raven said.

Some studies about freshwater phytoplankton have shown mixed results, but nothing has been found about marine organisms. Yet. ''It's quite a technical feat to keep the organisms going over that length of time. It's very time intensive, to make sure they are okay. You have to come in every day and look at them, every weekend... So, it is quite tough,'' he said.

More about the ocean acidification series:

Part 1: Ocean Acidification: The Unknown Reality of Climate Change

Part 2: Plankton Life Already Weakened by CO2

Part 3: The Luck of the Fish: for How Long?

Part 4: Finding a Cure Despite Uncertainties

Part 5: The Hopes of Ecosystem Modelling