Abstract
Seasonal variation in temperature fluctuations may provide corals and their algal symbionts varying abilities to acclimate to changing temperatures. We hypothesized that different temperature ranges between seasons may promote temperature-tolerance of corals, which would increase stability of a bacterial community following thermal stress. Acropora muricata coral colonies were collected in summer and winter (water temperatures were 23.4–30.2 and 12.1–23.1 °C, respectively) from the Penghu Archipelago in Taiwan, then exposed to 6 temperature treatments (10–33 °C). Changes in coral-associated bacteria were determined after 12, 24, and 48 h. Based on 16S rRNA gene amplicons and Illumina sequencing, bacterial communities differed between seasons and treatments altered the dominant bacteria. Cold stress caused slower shifts in the bacterial community in winter than in summer, whereas a more rapid shift occurred under heat stress in both seasons. Results supported our hypothesis that bacterial community composition of corals in winter are more stable in cold temperatures but changed rapidly in hot temperatures, with opposite results for the bacterial communities in summer. We infer that the thermal tolerance ranges of coral-associated bacteria, with a stable community composition, are associated with their short-term (3 mo) seawater thermal history. Therefore, seasonal acclimation may increase tolerance of coral-associated bacteria to temperature fluctuations.
Highlights
Coral-associated bacteria are critical to the health and function of coral ecosystems and coral holobiont[1,2]
To detect short-term dynamics in coral-associated bacterial communities exposed to various temperatures and to compare this variation between summer and winter, Acropora muricata coral colonies were collected from the Penghu Archipelago, in western Taiwan (Fig. 1)
Analysis of bacterial community composition was based on operational taxonomic units (OTU) with 97% nucleotide sequence identity and matrices of Bray-Curtis similarity
Summary
Coral-associated bacteria are critical to the health and function of coral ecosystems and coral holobiont[1,2]. Coral-associated bacteria are dynamic and often form stable homeostatic associations with their host[3] Changes in these bacterial communities may be an indicator of health of coral holobionts[4]. The bacterial community in corals may remain stable before and after heat stress[29,30]. Seasonal acclimation in coral-associated bacteria is unknown, as only between-season variations in the coral-associated bacterial community have been reported[31,32,33,34,35]. To better understand this phenomenon, we conducted a comprehensive study to determine effects of temperature stress on changes in bacteria with different seasonal thermal histories
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