"Fronds of giant kelp, buoyed by their gas-filled pneumatocysts, wave like pennants in the current of Monterey Bay, California," wrote George Cathcart of his image, a winning selection in the Portraits of Planet Ocean Flickr contest. Giant kelp (Macrocystis pyrifera) is large, brown algae that grows in dense forests along coasts around the world. Long stalks anchor each plant to the seafloor, and they grow meters high like giant trees towards the surface. Kelp forest ecosystems are home to a variety of animals, including seals, sea lions, whales, sea otters, gulls, terns, snowy egrets, great blue herons, cormorants, and shore birds. See more winning photos.