How does rising atmospheric CO2 affect marine organisms?

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Coral Reef Diversity and Global Change
Chadwick-Furman, N.E. 1996. Reef coral diversity and global change. Global Change Biology 2: 559-568.

What was done
The author reviews what is known about the evolution of reef-building corals over the past 240 million years and uses this knowledge to infer potential impacts on coral reef diversity based upon predictions of global climate change in terms of sea level and temperature and levels of ultraviolet radiation.

What was learned
Any future rise in sea level will likely benefit the world's coral reefs as "many coral reefs have already reached their upward limit of growth at present sea level, and may be released from this vertical constraint by a rise in sea level." In addition, the author notes that rising sea levels may allow "more water circulation between segregated lagoons and outer reef slopes," which could "increase the exchange of coral propagules between reef habitats and lead to higher coral diversity in inner reef areas." She also points out that, in the past, coral reefs have survived sea level rises of "more than twice the rate" that is predicted by current ocean-atmosphere general circulation models.

As for changes in sea surface temperatures, the 1-3C warming predicted by global climate models for the next century may cause higher rates of coral mortality, but it may also positively effect coral diversity, especially in reefs that are in "latitudinally marginal areas, which presently are temperature limited." However, the author notes, "some marginal reefs which experience wide variation in temperature (both extreme lows and highs), as in the Arabian Gulf, may be negatively impacted by increased temperature."

The effects of increased irradiation, also predicted to increase by climate models, are less clear, and are referred to by the author as "poorly understood" and "largely unknown."

What it means
On the whole, the future of coral reefs, in terms of biodiversity, appears bright. As summarized by the author, "coral reefs are likely to survive predicted rates of global change," with a much more immediate threat to their welfare being "regional anthropogenic stress" due to pressures that "are most intense near human population centers."

Reviewed 1 July 1999