It would be illegal to dump a common aquarium algae in any body of water in California under a bill before the state legislature. Caulerpa taxifolia, once given away free as a decorative addition to aquariums, is now banned by the Noxious Weed Act in the U.S. — but it can still be purchased illegally on the Internet. Set loose in the wild, the invasive weed smothers plant life and can turn stretches of sea into dead zones. Last summer, Southern California experienced the first outbreak of the weed in North America. In related news, an international group of scientists unveiled a broad plan last weekend to tackle the global problem of invasive species at the annual meeting of American Association for the Advancement of Science.