Carbon Dioxide Erodes Marine Ecosystems: Research Suggests How Sea Life Will React to Acidification

Article excerpt

If carbon dioxide emissions don't begin to decline soon, the complex fabric of marine ecosystems will begin fraying--and eventually unravel completely, two new studies conclude.

The diversity of ocean species thins and many survivors' health declines as the pH of ocean water falls in response to rising carbon dioxide levels, scientists from England and Florida reported February 18. What's more, affected species aren't restricted to those with shells and calcified support structures--features particularly vulnerable to seawater acidification.

Jason Hall-Spencer of Plymouth University in England and his colleagues have been collecting data from marine sites off Italy, Mexico and Papua New Guinea, where high concentrations of carbon dioxide percolate out of the seabed from volcanic activity below. Directly above these C[O.sub.2] seeps, pH plummets to 7.8 or below, a value that is expected to occur widely by 2100 and which is substantially lower than the normal level for these areas, 8.1. The sites offer a preview of what may happen to seafloor ecosystems as C[O.sub.2] levels continue to rise.

Compared with nearby normal-pH sites, species richness in low-pH zones was diminished by 30 percent, Hall-Spencer reported. "Coral and some algae are gone. And the sea urchins are gone," he said. Fish may be present, but unlike in areas with a normal pH, they won't deposit their eggs there.

Although seagrasses appear to survive just fine in the low-pH seawater, close inspection showed that fish had nibbled the fronds, Hall- Spencer found. He identified one likely explanation: At low pH, these grasses no longer produced the phenolic defense compounds that typically deter grazing animals.

His team also transplanted a host of healthy marine species to sites with a gradient of pH values leading up to an Italian seep, then monitored the immigrants' health for a year.

Even shelled animals initially survived from fall to spring, in some cases bumping up their calcification rate in an attempt to cope with the corrosive waters. …