Bleaching damage spreads beyond corals.

Tiny marine organisms known as foraminifera exhibit damage similar to that observed in bleached coral reefs, reports Pamela Hallock, an oceanographer at the University of South Florida in St. Petersburg.

Both foraminifera and coral play an important role in the global ecosystem. As these organisms "are very important sources of organic matter and calcium carbonate production . . . such [bleaching] phenomena could affect the global carbon cycle and the oceanic food chain," Hallock says. Foraminifera and coral filter carbon dioxide out of the atmosphere. If their numbers decline, then atmospheric concentrations of this greenhouse gas could potentially increase.

Many foraminifera, like many coral, live in a symbiotic relationship with microorganisms that provide their hosts with not only nourishment, but also color (SN: 12/8/90, p.364). A host organism that has lost its symbiotic companion turns white, or bleaches, and its health declines.

In the first documented study of bleaching in foraminifera, Hallock examined four species of the genus Amphistegina collected from Florida reefs. These species live on the loose rubble bottom in water approximately 20 meters deep.

Hallock found that while most of the population appeared normal throughout the winter months, bleaching began to occur and then increase during spring 1992. Bleaching peaked in June and July, with 85 percent of the population showing total or partial loss of color.

While damaged foraminifera began to regain color as fall approached, the bleaching appears to have had severe effects on reproduction and adult mortality. "There were very few juveniles in the population at a time when you would expect them to be [abundant]," Hallock says.

In the laboratory, bleached foraminifera produce significantly fewer young, and up to 30 percent of these may be deformed or nonviable, the study shows.

Laboratory studies indicate that bleaching can be induced by increasing the organisms' exposure to ultraviolet light. Hallock speculates that the bleaching she observed may have resulted from a minute increase in ultraviolet exposure related to Mt. Pinatubo's eruption in 1991.