Adaptation strategies of relatively high-latitude marginal reef corals in response to severe temperature fluctuations.

The large seasonal temperature fluctuations caused by global warming and frequent marine heatwaves pose new challenges to survival of relatively high-latitude marginal reef corals. However, the adaptation strategies of high-latitude marginal corals are not fully understood. We employed integrated approach to investigate the response mechanism of hosts, Symbiodiniaceae, and symbiotic bacteria of marginal reef corals Acropora pruinosa and Pavona decussate in response to large seasonal temperature fluctuations. The coral holobiont maintained a high level of immunity to adapt to seasonal pressure by increasing Symbiodiniaceae energy supply. The symbiotic Symbiodiniaceae of two coral was dominated by C1 subgroup, and was stable across seasons. The α-diversity of symbiotic bacteria P. decussata and A. pruinosa in summer was higher than that in winter. The symbiotic bacterial community of two coral reorganized during different seasons. Scleractinian corals improve adaptability to seasonal stress by increasing energy supply to maintain high levels of immunity, increasing symbiotic bacterial α-diversity, and changing dominant bacteria. This study demonstrates the adaptation strategies of marginal reef corals to seasonal temperature fluctuations and provides novel insights into the study of the adaptation of corals and relatively high-latitude coral refuges in the context of global warming and intensified marine heatwaves.