Thermal shock treatment for controlling exotic Caulerpa brachypus

A number of macroalgal species in the genus Caulerpa are characterised as some of the most invasive marine species in the world. There are a limited range of interventions for dealing with incursions of exotic Caulerpa species that have acceptable ecological impacts. This initial study assessed the potential to use heated seawater to kill fragments of C. brachypus , a recent invader of concern in Aotearoa - New Zealand. In the laboratory, Caulerpa fragments were exposed to heated seawater treatments of 30 to 80°C in 5°C increments for each of four experimental treatment durations of either 5, 10, 30 or 60 seconds and then cultured for one week in stable conditions. At 50°C or higher for 5 seconds or more, and at 45°C or higher for 30 seconds or longer, all fragments died, whereas below these treatment combinations most fragments remained alive, with 100% survival in the control with only a sham treatment handling. In the field, Caulerpa sod segments were submerged for 30 seconds in 40 to 70°C in 10°C increments and returned to the sea for three weeks. Segments of C. brachypus exposed to thermal shock treatments of 50, 60, and 70°C resulted in a significant loss of C. brachypus cover ( p  < 0.05), but not complete elimination. These results indicate the potential to use thermal shock for controlling invasive C. brachypus that supports the management and protection of Aotearoa - New Zealand’s unique marine ecosystems.