2.2 Experimental design
To simulate the impact of heatwaves on corals, a heatwave treatment was conducted by manipulating the seawater temperature over a specific period (Fig. 1). Coral nubbins were randomly divided into 6 aquariums, each with a capacity of 20L. Two experimental groups were established: the control group (“C”) and the heatwave group (“H”), based on historical high-temperature extremes recorded in Xuwen over the past 10 years (source: http://gd.cma.gov.cn).
From day 1 to day 5, a microcomputer digital thermostat (XH-W1308, Tyrell, Shenzhen, China) was used to gradually increase the seawater temperature from 26 °C to 32 °C, representing the first heatwave. Subsequently, from day 6 to day 10, the seawater temperature was reduced back to 26 °C, simulating the first recovery period. Starting from day 11 to day 15, the seawater temperature was increased again to 32 °C to model a second heatwave. Finally, from day 16 to day 20, the seawater temperature was lowered to 26 °C to simulate the second recovery period. In the control treatment, the seawater temperature was maintained constantly at 26 °C throughout the entire exposure period.
Specific dates were assigned as “day 5” (end of the first heatwave), “day 10” (end of the first recovery period), “day 15” (end of the second heatwave), and “day 20” (end of the second recovery period), and were denoted as “A”, “B”, “C”, and “D”, respectively. From each group, three corals were randomly selected for sampling.
Fig. 1. Design of the culture experiment.