Dataset: Anemone photochemistry assessed via active chlorophyll a fluorescence by pulse amplitude modulation (PAM) fluorometry after acute heating across a range of temperatures (28–36°C) in a controlled Coral Bleaching Acute Stress System (CBASS)

In the fall of 2022, Aposymbiotic (lacking Symbiodiniaceae) sea anemones, Exaiptasia diaphana were used for initial algal infections by two strains of algae, Symbiodinium necroappetens and Breviolum minutum.

For both algal strains, previous work (not related to this project) had established different lines of thermally naïve (i.e., wild-type, WT hereafter) and thermally selected (TS hereafter) cell lines. Briefly, each alga was first placed into uni-cellular culture and then subjected to a long-term thermal adaptation trial, using the ratchet heating method. Replicate cultures were subjected to a chronic heating protocol wherein temperature was increased in 1 degree Celsius (°C) increments while monitoring algal growth. A subset of the fastest growing isolates at each temperature were then shifted into the next higher temperature and growth was monitored for approximately one month. This process was repeated until negative growth was noted in each algal strain. Thermally selected algae were then grown at the highest temperature for which growth remained positive for 80 generations (32°C for S. necroappetens and 31°C for B. minutum). After maintaining cultures at these elevated temperatures for approximately one year, thermally selected cultures were then shifted back to the naïve growth temperature (28 °C) for three months.

Anemones harboring each WT and TS alga were then grown under low and high light conditions in 2022 (50 µmol photons m-2 s-1 and 220 µmol photons m-2 s-1, respectively) for two months prior to acute heating experiments that began in January 2023. All animals were fed brine shrimp and cleaned once per week until experimental work began. To test the response to acute heating, anemones were subjected to four temperatures (28, 32, 34, and 36 °C) for six hours within two Coral Bleaching Automated Stress Systems (CBASS). All acute heating trials were run under the respective growth light level for each set of anemones with the same aquarium LED lights used for the initial photoacclimation period described above. After six hours of heating at each temperature, anemones where shifted into the dark and held for dark acclimation for 25 minutes. Following dark acclimation, the maximum quantum yield of photosystem II (Fv/Fm) was recorded with a pulse amplitude modulation fluorometer (Diving PAM, Walz). Fv/Fm readings were taken from each anemone before (Time zero) and after six hours of heating.