A “red tide” of blooming algae stretched more than 20 miles along the coast near La Jolla, Calif., in spring 1995. Blooms can be harmless, such as this one (the dinoflagellate Noctiluca scintillans), but blooms of some algae, including Alexandrium, can harm human health, coastal economies, and marine ecosystems. Algal blooms occur naturally, but have become much more common in recent years, sometimes due to human activities that put excess nutrients into the water. (Photo courtesy of Peter Franks, Scripps Institution of Oceanography)[back]
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