Two researchers in an inflatable boat glided out onto Batiquitos Lagoon in Carlsbad, California, August 15, looking for eelgrass, an underwater plant that provides a nursery for fish, crabs, shrimp and other sealife. The boaters, equipped with sonar and diving gear, also were looking for any sign of Caulerpa, an invasive seaweed that can spread rapidly and choke out the native eelgrass. Nicknamed “killer algae,” Caulerpa taxifolia turned up in Carlsbad’s nearby Agua Hedionda Lagoon in 2000 and was eliminated only after an intensive, multi-year, $7 million battle. Since then, the invader, which may have been dumped from a home aquarium, has been absent along the North County coastline. However, last year, small amounts of a slightly different but equally destructive species, Caulerpa prolifica, were found in San Diego Bay and efforts are underway to eradicate it.