Experimental Evolution Of The Coral Algal Endosymbiont, Cladocopium Goreaui, For Coral Heat Tolerance

An experiment was carried out to compare the performance of coral juveniles using cultured symbionts selected for enhanced tolerance in Cladocopium goreaui (C1) over multiple time scales.

Symbiotic cells were extracted from colonies of Acropora tenuis from Nelly Bay, Magnetic Island in 2010. The cells were isolated, cultured and maintained, then split into 16 independent replicates under an experiment to select for thermally tolerant Symbiodiniacae.

Colonies of A. tenuis were collected from Geoffery Bay, Magnetic Island In November, 2014 and transported to the National Sea Simulator facility (SeaSim) at the Australian Institute of Marine Science (AIMS). Larvae raised from A. tenuis were infected with symbionts at 22 and 28 days post spawning.

A mix of wild type (WT) strains (10 strains) and a separate mix of thermally tolerant Symbiodiniaceae (SS) with 21 generations of selection (10 strains) were used to infect coral juveniles.

The performance of SS- and WT-juveniles was compared with survival and growth rate, cell density and photosynthetic function of symbionts at three temperatures (27, 31, and 32.5°C) over short (28 days) and longer (72 days) periods of heat stress. The results of this experiment using symbionts selected after 21 generations were then compared with the results of later studies that used symbionts after 73 (Chakravarti et al. 2017) or 130 (Buergeret al. 2020) generations of selection, to test host costs or bene¿ts over varying periods of time.

Further details are presented in the paper and supplementary methods: Quigley, K.M., Alvarez Roa, C., Beltran, V.H., Leggat, B. and Willis, B.L. (2021), Experimental evolution of the coral algal endosymbiont, Cladocopium goreaui: lessons learnt across a decade of stress experiments to enhance coral heat tolerance. Restor Ecol, 29: e13342. https://doi.org/10.1111/rec.13342