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The year was 1834, and the HMS Beagle was sailing through the Strait of Magellan near Tierra del Fuego, when Charles Darwin’s mind turned to kelp. “The number of living creatures of all Orders, whose existence intimately depends on the kelp, is wonderful,” he later wrote in The Voyage of the Beagle. “Often as I recurred to a branch of the kelp, I never failed to discover animals of new and curious structures.”

As Darwin rightly noted, giant kelp plays a foundational role in coastal ecosystems. Like every part of a food web, kelp provides critical nutrition for other species: in this case, sea urchins and abalone. But its role goes far beyond that. And as University of California, Santa Barbara marine scientist Robert J. Miller says, giant kelp’s key role in creating the physical structures for many coastal ecosystems has, for the most part, been poorly studied and inadequately quantified.

Drawing on data collected over 16 years at 39 coastal kelp forests off the California coast, collected by the Santa Barbara Coastal Long Term Ecological Research Project, Miller and his colleagues studied how kelp stalks affect the kelp forest understory by assessing the abundance and diversity of algae, invertebrates, and reef fishes.

The team found that where there is more kelp, there are fewer understory algae. Like in tropical rainforests, where tall trees block sunlight from reaching the forest floor, giant kelp prevent sunlight from reaching the seafloor, making it tough for smaller algae to photosynthesize and grow. Free from having to compete for space with smaller red, brown, and green algae, stationary or slow-moving invertebrates such as sponges and sea squirts thrive. The presence of so much prey also drives an increase in the abundance of predators such as fish, crabs, and lobsters.

“It affirms the role of giant kelp [and] the auxiliary ecosystem services that it provides,” says California State University, Northridge ecologist Kerry Nickols, who wasn’t involved in the study. In her research, Nickols found that kelp’s physical presence has other effects as well, such as changing water chemistry and currents, and altering the way sediment settles on the seafloor.

While researchers have long known that kelp provides more than food, “we’re just starting to understand all the benefits,” Nickols says.