Cylindrotheca sp. growth rates during thermal performance curve laboratory experiment

Subantarctic water off the east coast of New Zealand was collected in December 2023. Half of the water collected was incubated under 12.2°C (Control), and the other half was exposed to a 14-day mixed species marine heatwave simulation (15.8°C). Three individual populations of Cylindrotheca sp. were isolated from each treatment. After six months of maintenance under 12.2°C, a thermal performance curve experiment was performed. Triplicate cultures of the Control and Heatwave populations were grown in 30mL polycarbonate tubes (Oakridge) in Aquil medium (Price et al., 1989). The tubes were incubated in aluminium heatblocks (Thomas et al., 1963), with circulating water baths (Julabo), cooling one end and heating the other to create a thermal gradient with 10 temperatures from 10-20°C. The block was lit from below at ~85 µmol(photons)/m²/s on a 12:12 light:dark cycle. To account for minor variation in light levels, the replicates were rotated through the block each day at the same temperature. Chlorophyll was measured daily using a Turner 10-AU fluorometer. Growth rates were calculated from the slope of the natural log of the chlorophyll a against time while the replicates were in the exponential growth phase. The data was collected and analysed in 2024 as part of a Master's research project investigating the impacts of marine heatwaves on subantarctic phytoplankton.