Fig. 5. Thermal gradients demonstrate a temperature-dependent decline in single-cell F_v/F_m of Symbiodinium CCMP2467. (A) Thermal linear gradients with slopes between 0.1 and 2.5 °C mm⁻¹ were supplied along the horizontal axis of the heat-stage and accessed via the RTD array. The flow rate of the cooling liquid was 150 μl min⁻¹ and the flow direction was from T1 to T6. A power limit of 400 mW for each heater was used. (B) The linearity of the thermal gradient was verified via a thermally responsive liquid crystal sheet (cross-over temperature: 30 °C), which was placed onto a coverslip via immersion oil and then mounted onto the heat-stage. The temperatures measured with the RTDs are indicated as well as the temperature zones defined for cell experiments (‘inlet’, ‘middle’, ‘outlet’). (C) Exposure of Symbiodinium CCMP2467 to linear temperature gradients produced in (B) for 6 h. Note the reductions in F_v/F_m for the inlet, middle and outlet areas as compared to pre-stimulus assessment of F_v/F_m at 25 °C. (D) Histograms of F_v/F_m, before and after exposure to the linear temperature gradient. Note the progressive shift of normal distributions towards lower average values of F_v/F_m the closer the cells are to the outlet, the location with the highest temperature in the gradient.