California’s costly battle to eradicate invasive 'killer algae' from coastal lagoons

In 2000, a home-aquarium enthusiast illegally discharged the ornamental seaweed Caulerpa taxifolia into a storm-water system, allowing the species to reach Southern California’s coastal waters. First detected in Agua Hedionda Lagoon near San Diego and later in Huntington Harbour near Los Angeles, the algae’s ability to fragment and survive in cool, damp conditions sparked fears of a widespread invasion. State officials, guided by the Centre for Invasive Species Research, responded by covering contaminated zones with large tarpaulins, securing them with sandbags and pumping chlorine beneath to eradicate the plants.

While the chemical treatment eliminated the algae, it also resulted in collateral damage to fish and other marine organisms. The intensive operation lasted six years, ending in 2006, and incurred expenses exceeding US$7 million. The episode illustrates how a seemingly harmless aquarium species can become a major ecological threat when introduced to new habitats.