Washington: Overfishing and nitrate pollution can destroy coral reefs by allowing an overgrowth of algae that can choke off oxygen and disrupt helpful bacteria.
These "macroalgae," or large algal species, can get out of control when sewage increases nitrate levels, feeds the algae, and some of the large fish that are most effective at reducing the algal buildup are removed by fishing.
Researchers from Oregon State University found that macroalgal competition decreased coral growth rates by about 37 percent and had other detrimental effects. Other research has documented some persistent states of hypoxia (oxygen deficiency), the journal Public Library of Science One reports.
"There is evidence that coral reefs around the world are becoming more and more dominated by algae," said Rebecca Vega-Thurber, Oregon assistant professor of microbiology, according to an Oregon statement.
"Some reefs are literally covered up in green slime, and we wanted to determine more precisely how this can affect coral health," added Vega-Thurber.
The new study found that higher levels of algae cause both a decrease in coral growth rate and an altered bacterial community. There are thousands of species of algae, and coral reefs have evolved with them in a relationship that often benefits the entire tropical marine ecosystem.
When in balance, some algae grow on the reefs, providing food to both small and large fish that nibble at the algal growth. But the algal growth is normally limited by the availability of certain nutrients, especially nitrogen and phosphorus, and some large fish such as parrot fish help eat substantial amounts of algae and keep it under control.
"This shows that some human actions, such as terrestrial pollution or overfishing, can affect everything in marine ecosystems right down to the microbes found on corals," Vega-Thurber said.