Acidic oceans threaten corals

Across our planet, ecosystems are changing, big and small. While I've been compiling my thoughts on small, local changes (check back next week for a series on the subject) I found a bit of news about some very drastic changes to large areas. i-f5ee914d5d59c40501c5e0c49e3532fd-coral.jpgAccording to an article in this week's Washington Post, coral reefs may be greatly affected by an increase in the acidity of the oceans, which correlate with the rising levels of carbon dioxide in the atmosphere. Scientists are estimating that the acidity level will be sufficiently deadly by the end of this century:

Scientists expect ocean pH levels to drop by another 0.3 units by 2100, which could seriously damage marine creatures that need calcium carbonate to build their shells and skeletons. Once absorbed in seawater, carbon dioxide forms carbonic acid and lowers ocean pH, making it harder for corals, plankton and tiny marine snails (called pteropods) to form their body parts.

The effects are already beginning to show, giving a rather bleak outlook for some of our most diverse ecosystems:

Stanford University marine biologist Robert B. Dunbar has studied the effect of increased carbon dioxide on coral reefs in Israel and Australia's Great Barrier Reef. "What we found in Israel was the community is dissolving," Dunbar said.

Caldeira has mapped out where corals exist today and the pH levels of the water in which they thrive; by the end of the century, no seawater will be as alkaline as where they live now. If carbon dioxide emissions continue at their current levels, he said, "It's say goodbye' to coral reefs."

The chemistry involved is quite simple: take a straw, and use it to blow into a glass of water. The amount of carbon dioxide in your breath is enough to increase the acidity of the water. You can test this with pH indicator strips, available from a variety of places, such as medical suppliers (for people or forpets... the latter cost less, and are apparently useful if your pet is prone to urinary tract infections.)

Image note: The image above (click here for a full size version) is a historical plate from the first study of Florida corals, via the NOAA Photo Library. The caption of the plate reads:

Figures 1-9, Madrepora prolifera Lamarck. In: "Report on the Florida Reefs", 1880, by Louis Agassiz. Memoirs of the Museum of Comparative Zoology at Harvard College, Vol. VII, No. 1. Plate XIX. These plates help document the oldest studies of the Florida Reefs.

Let's hope that all coral images aren't soon to be simply historical relics as well.

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What I don't get about coral: how have they survived this long? They do seem to be quite fragile: global warming/ coral bleaching/ now increased acidity. Yet over the tens (hundreds? not sure how old they are) of millions of years coral have been around, surely the world's climate has varied so widely--and been so warm--that they should have died out before.

By lostinasia (not verified) on 06 Jul 2006 #permalink

I think it is the scale of the changes happening now that are the biggest threat to the corals (which are among the most ancient animals--hundreds of millions of years.) In the past, changes could happen suddenly, but not typically to the entire planet at once. The corals survived a few major extinctions, true... but there was always a suitable pocket or two where they could survive and adapt. Perhaps there are such pockets around (I'm not sure how thorough Caldeira's mapping was) where some coral species can ride out another major extinction... but, at this rate, the reefs as we know them will be gone.

Acidification from CO2 burning is a major problem but it is not as simple as you make it sound. Normally CO2 added to the atmosphere increases slowly, so that cations produced by carbonic acid weathering balance the acidity of the increasing CO2. Therefore, global seawater did not become acidic during episodes of higher CO2 in the modern geologic record.

I pointed out the danger of CO2 induced acidification over three years ago when an experiment on marine "sequestration" of CO2 was planned offshore of Kauai. Injecting CO2 into the deep ocean is a very poor idea because it could damage reefs when the CO2 finally wells upto the surface.

g, thanks for adding the specifics. I do tend to simplify at times, especially when blogging about topics outside my realm of research.

Where did people got the idea that deep inside the earth or oceans was a safe and stable place? You'd think we'd know better by now.