Oceans in Crisis - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 187

above the neutral level (of pH 7.0)—so it is not 'acidic' (rather, it is less
basic). Nevertheless, for the creatures that live in the seawater it is the
amount of change from the status quo that matters. The pH scale is
logarithmic, not linear, and so a change from 8.4 to 8.3 means some
30 per cent more hydrogen ions in the water. It is also roughly the
amount of change in ocean carbon chemistry that took place between
glacial and interglacial phases of the Ice Ages—only we are heading
beyond interglacial levels into uncharted territory.
How much of a problem is this for sea life? After the relative sim-
plicity of the chemistry, the biological effects prove more compli-
cated. The building of calcium carbonate skeletons takes place within
biological tissues, and so the chemical micro-environment (or per-
haps more accurately the nano-environment) is controlled not just by
the chemistry of the seawater around them, but by the ability of vari-
ous organisms to control the chemistry within their tissues, and thus
to counteract changes in external circumstances.
Hence, biologists have been scrambling in recent years to find out
what rising acidity levels would do to different types of marine crea-
ture by keeping them in tanks in which different amounts of carbon
dioxide have been dissolved, or by observing what happens when sea-
water is naturally made more acid—where volcanic gases escape from
submarine volcanic vents for instance. These studies show that rising
acidities can interfere with the formation of calcium carbonate skel-
etons, but that different types of organism have different tolerances.
Let us take a couple of examples. Coral reefs are being observed
particularly closely because of their enormous ecological importance.
They are, like the tropical rain forests on land, storehouses of much of
the oceans' biodiversity, some 25 per cent of all marine species being
crammed into about a tenth of 1 per cent of ocean area. They are
remarkable, counter-intuitive biological systems. Their diversity is
predicated upon the elaborate architectural framework built by the