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Scientists use satellite images of the kelp canopy (here, as seen from underwater) to track this important ecosystem over time (Credit: Stuart Halewood)

I remember an analogy from one of my marine science classes, that studying the ocean is sometimes like trying to study a forest by dropping a bucket from a helicopter. It explains why we know comparatively little about ocean ecosystems, even when they’re situated close to populous areas of land, like the forests of giant kelp (Macrocystis pyrifera) in the Santa Barbara Channel off California. These kelp ecosystems are important because they provide food and habitat for a variety of fish and other species. And now a group of scientists led by the University of California, Santa Barbara found a new way to study the kelp, which enabled them to look at long-term changes in this ecosystem for the first time. (Their results appear in Marine Ecology Progress Series.)

The scientists were able to use images of the area made by the Landsat 5 satellite from 1984 through 2009. (Scientists were not previously able to use the extensive collection of imagery because of the cost; in 2009, Landsat images were made freely available.) “Giant kelp forms a dense floating canopy at the sea surface that’s distinctive when viewed from above,” the researchers wrote. They used the imagery to document the changes in the kelp forests over time and found that, during most years, the forests go through an annual cycle, rapidly growing in spring and summer and dying back during the winter. In some regions, huge waves limit the kelp’s growth, while in others they are held back by a lack of nutrients.

“We know from scuba observations that individual kelp plants are fast-growing and short-lived,” says study co-author Kyle Cavanaugh of UCSB. “The new data show the patterns of variability that are also present within and among years at much larger spatial scales. Entire kelp forests can be wiped out in days, then recover in a matter of months.”

Kelp biomass off Santa Barbara, 1984-2009, as measured by the Landsat 5 satellite (Credit: NASA; SBC LTER Site)

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