Exploring The Underwater Forests Of The Pacific Ocean

Mark Dunphy -

Forests of giant kelp, or Macrocystis pyrifera, are found in temperate coastal regions and are among the most productive ecosystems on Earth.  In a melding of data from the beneath the waves and from the skies above, researchers have developed a method for studying how environmental factors affect the kelp forests.

The results have allowed scientists to look at changes in giant kelp across hundreds of square miles in California’s Santa Barbara Channel over 25 years, from 1984 through 2009.  The findings are published in the current issue of the journal Marine Ecology Progress Series.

Obtaining a quarter-century of imagery from the same satellite, in this case the Landsat 5 Thematic Mapper, is unprecedented, says David Siegel of the University of California at Santa Barbara (UCSB), one of the paper’s co-authors.

“A satellite mission that goes on for more than 10 years is rare,” says Siegel. “One that continues for more than 25 years is a miracle.”

Until recently, the high cost of Landsat images limited their use in research. Then in 2009 the Landsat image library was made available at no charge.  “In the past, it wasn’t feasible to develop long time-series using Landsat images,” says Kyle Cavanaugh of UCSB, the paper’s lead author. “Once these data were released free of charge, however, we could access hundreds of pictures that show an area over time.”

Images from the Landsat 5 satellite provided the researchers with a view of how giant kelp forests change over time across a broad geographic region.

“Giant kelp forms a dense floating canopy at the sea surface that’s distinctive when viewed from above,” write the scientists in their paper. “Water absorbs almost all incoming near-infrared energy, so the kelp canopy is easily differentiated using its near-infrared reflectance signal.”

In southern California, giant kelp is found primarily on shallow rocky reefs distributed in patches. The plants’ numerous fronds extend upward in oceans and bays, forming a canopy at the surface.  The plants grow to lengths of more than 100 feet, at a rate of up to 18 inches per day.

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