Bad HABit

Arrive a month later, and they might have missed it. In late 2008, marine biologists were able to witness first-hand the devastating impact of a massive algal bloom on coral reefs in the Gulf of Oman. The episode may be a picture of things to come, as researchers predict that harmful algal blooms (HABs) will become more common in the future.

Marine researchers have become increasingly worried about HABs, which occur when otherwise benign species of marine plankton begin to reproduce wildly. The blooms can suffocate and poison sea life, and make seafood unsafe for humans to eat. Many scientists believe HABs are on the rise due to pollution of coastal waters, the spread of exotic plankton species by ships, and climate change. And they worry that more blooms could topple sensitive ecosystems already stressed by other problems.

In November, 2008, a multinational research team got a case study of the havoc wreaked by a HAB. As the scientists were surveying the extensive reefs that fringe the coasts of Oman and the United Arab Emirates, a marine dinoflagellate named Cochlodinium polykrikoides began running amok; the swarm eventually covered more than 500 square kilometers.  A month later, after the bloom had peaked, the researchers returned to two study sites to see what had happened.

The results were dramatic, a team led by Andrew G. Bauman of the United Nations University in Canada reports in the Marine Pollution Bulletin. The bloom had killed nearly all branching corals in the genera Pocillopora and Acropora, and substantially reduced fish populations. The study “provides the first evidence of the potential for HAB events to cause rapid declines in and changes in structure of coral reef assemblages within the Indian Ocean,” the authors note. “The effects are very similar” to damage done by severe bleaching events caused by warming seas, they add. It’s not clear if or when the reefs might bounce back.

Now, the question is how many other reefs may suffer the same experience. Plankton species that are some of the prime culprits in HABs appear to be increasing their global distribution, so HABs could cause “the permanent alteration of the structure and function” of other coral reefs too. David Malakoff | September 28, 2010

Source: Bauman, A., Burt, J., Feary, D., Marquis, E., & Usseglio, P. (2010). Tropical harmful algal blooms: An emerging threat to coral reef communities? Marine Pollution Bulletin DOI: 10.1016/j.marpolbul.2010.08.015

Image © simon gurney