ABSTRACT: We investigated the fate of fragments of the invasive seaweed Caulerpa taxifolia from southern California, USA, after exposure to chlorine (10, 15, 50, 125 ppm Cl^- at 20 to 23°C and 10 to 11°C) or temperature shock (7 to 10°C,72°C). Chlorine bleach is currently being used to eradicate C. taxifolia in southern California. At temperatures favorable to growth, ~70% of the fragments survived at chlorine concentrations below 50 ppm; 1 fragment survived at 50 ppm, and nonesurvived at 125 ppm. Within 2 wk, many of the surviving fragments regenerated. After 4 mo of cold treatments, even C. taxifolia not receiving chlorine treatments failed to regrow, despite unusual chloroplast migration into belowground tissues.Re-establishment of a favorable temperature regime did not result in regrowth over a 3 mo period. Acclimation of C. taxifolia to cold waters did not improve its survival. When exposed to 72°C seawater for 60 and 120 min, all fragments but one diedwithin 2 wk. Despite presumably being from a single clone, C. taxifolia exhibited a highly variable response to treatments. Based on these results, chlorine concentrations in eradication treatments should be maintained at 125 ppm for at least 30min in both the water column and in the sediments to reach stolons and rhizoids. Fragments of C. taxifolia are unlikely to survive or grow at ambient temperatures (8 to 10°C) off the open coast of northern California.