In search of an undersea kelp forest's missing nitrogen

Plants need nutrients to grow. So scientists were surprised to learn that giant kelp maintains its impressive growth rates year-round, even in summer and early fall when ocean currents along the California coast stop delivering nutrients.

Lobsters and sea stars are important contributors to the kelp forest nitrogen cycle. Photo: Katie Davis

To sustain growth rates, kelp requires many nutrients, especially nitrogen, but changes in ocean currents reduce the availability of such nutrients each year beginning in May. As a result, kelp forests face a potential shortage of nitrogen just as long summer days are poised to fuel algal growth, said lead author Joey Peters.

Peters and his co-authors, UC Santa Barbara marine ecologists Dan Reed and Deron Burkepile, saw the local community of sea-bottom invertebrates as a likely additional nitrogen source. Indeed, it turned out that these invertebrates, especially lobsters and sea stars, are an important part of the nitrogen cycle in coastal ecosystems. Waste from the invertebrates is a consistent component of the "missing nitrogen."

"This study reveals how environmental change can affect subtle ecosystem dynamics in kelp forests," said David Garrison, a program director in NSF's Division of Ocean Sciences. (National Science Foundation)

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