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CORVALLIS - A new study shows that marine intertidal plant communities are far more sensitive than had been believed to changes in available nutrients such as nitrogen.

The research, just published by Karina Nielsen from Oregon State University in a professional journal, Proceedings of the National Academy of Sciences, suggests that short- or long-term climate changes that affect coastal upwelling, in addition to over-fishing, could have a profound effect on near-shore plant life in the ocean.

It has long been known that upwelling currents, which bring nitrates and other nutrients to the near-surface of the ocean, were a key to the growth of tiny plants called phytoplankton, and most other fish in the marine food change which ultimately depend on these phytoplankton.

"Until now, however, people thought that most open-coast seaweed communities weren't really limited by nutrient availability, especially not on wave-swept shores where coastal upwelling occurs," said Karina Nielsen, an OSU postdoctoral research associate with the Partnership for Interdisciplinary Studies of Coastal Oceans, or PISCO.

"My experiments showed that there are areas along the open-coast where seaweed communities are limited by nutrients and this changes how abundant and diverse they are, especially when animals that eat seaweeds are scarce," Neilsen said. "Knowing what causes these differences along the coast shows us how changes in ocean climate and over-exploitation of marine animals can affect intertidal communities."

The findings may help scientists identify the best locations for highly productive marine reserves, Nielsen said, and may be of particular relevance to near-shore areas in the Pacific Northwest, which have some of the most abundant and diverse temperate seaweed ecosystems in the world.

In controlled experiments off the central Oregon coast, Nielsen manipulated 42 tide pools by placing small nutrient dispensers in them, releasing nitrates and phosphates, and reducing the abundance of snails, urchins and other invertebrates. The abundance of seaweeds increased up to 35 percent, shifting the whole structure of the community.

Scientists believe that changes in climate, ranging from long-term effects such as global warming to near-term effects such as the Pacific decadal oscillation, may create major changes in current movements and upwelling in many places. It's now clearer, Nielsen said, that such changes could have significant effects on marine plant life, as well as fisheries.