Understanding Earth's Underwater Forests: Kelp Demography Off The Coast Of California

Within the Point Loma kelp forest community off the coast of San Diego, researchers have been conducting long term ecological kelp studies over three decades. The goal of their research is to evaluate the roles of large-scale, low frequency oceanographic processes on the demography patterns of the area's most conspicuous species of kelp. These processes range from seasonal climate variability to episodic nutrient-rich La Ninas and warm water, nutrient-poor El Ninos.

"As expected, we found considerable differences in the habitat adaptations of the specific kelps over large temporal and spatial scales," says marine ecologist Paul Dayton from UCSD. "Standard experiments of the type that ecologists often do at small scales give different results under different oceanographic climate conditions."

By repeating experiments over an extended period of time and in different areas, researchers were able to observe certain changes within the community that occur from episodic shifts in nutrients and temperature. For instance, during the nine-year study, Macrocystis species were not affected by competitive effects from other species of kelp. On the other hand, Pterygophora californica, an important understory species, exhibited reduced growth and reproduction by the light-limited conditions and competition with Macrocystis during La Nina periods when Macrocystis thrived. When El Nino conditions led to poor Macrocystis growth, the understory kelps did much better.

"By doing small scale experiments over large scales, researchers can gain a much more realistic understanding of oceanic ecosystems," says Dayton.

Although their research found that small-scale events in coastal zones driven by local processes (e.g. competition, disturbance and dispersal) were important, Dayton et al have concluded that the most lasting effects on the kelp communities were the result of very large-scale, low-frequency events, such as the El Nino and especially the La Nina phenomena.

"Statistics analyzing small-scale experiments can give the illusion of power, but our study shows that they might lack generality because very different patterns appear over larger scales," concludes Dayton.

Research was funded by the National Science Foundation, Pew Charitable Trust, California Sea Grant College Program, UCSD, and the City of San Diego.

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