Indonesian reefs fell prey to fires

The fires that swept through Indonesian rain forests late in 1997 apparently laid waste to some marine ecosystems in the area, as well.

Before 1997, more than 100 species of hard corals made up the reefs surrounding the Mentawai Islands, an archipelago that runs parallel to the southwestern coast of Sumatra. In December of that year, a massive bloom of phytoplankton known as a red tide occurred in the region, says Nerilie J. Abram of the Australian National University in Canberra. After the bloom had run its course, the phytoplankton’s rapid decomposition robbed the water of its dissolved oxygen. The effect asphyxiated almost all the fish and corals in the reefs fringing a 400-kilometer-long stretch of the Mentawai Islands.

Upwelling currents of cool, deep water–chock-full of algae-nourishing nitrates and phosphorus–fueled the red tide. However, analyses of chemical isotopes in coral samples show that the reefs experienced similar water temperatures–and therefore probably similar nitrate and phosphorus concentrations–without ill effects on several occasions during the past 7,000 years.

In 1997, however, strong winds brought dense plumes of smoke from the wildfires to the reef. Besides sending millions of tons of planet-warming carbon dioxide into the atmosphere (SN: 11/9/02, p. 291: Wildfire Below: Smoldering peat disgorges huge volumes of carbon), the fires released about 11,000 metric tons of iron, another algal nutrient, says Abram. Even if only a fraction of 1 percent of that iron rained down on the Mentawai Islands region, it would have been enough to fuel the reef-killing red tide. Abram and her colleagues report their analyses in the Aug. 15 Science.


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