Cultures of Cylindrotheca sp. were isolated from Subantarctic Water (SAW) off New Zealand's east coast in December 2023 and exposed to a simulated marine heatwave incubation. Three replicates were incubated under two treatments: the average summer temperature of the SAW (Control, 12.2°C) and the maximum anomaly measured at the sample site at the time of experimental design (Heatwave, +3.6°C; EU Copernicus Marine Service, 2023). The heatwave temperature was first increased by 0.6°C, followed by 3 days of 1°C increase per day to a 7-day constant period at 15.8°C. At the end of the 7 days, the temperature was decreased by 1°C for 3 days and finally returned to 12.2°C at the end of the incubation. Biomass accumulation was monitored daily by measuring the in vivo chlorophyll-a using a Turner 10-AU fluorometer. The daily growth rate of the cultures was calculated from the natural log of the chlorophyll-a measurements against time.