4.2 Effects of the initial marine heatwave on bacteria
Symbiotic bacteria play a crucial role in coral reef ecosystems by maintaining a balanced bacterial community (Ziegler et al., 2017). However, environmental changes, especially temperature fluctuations, can alter the composition of these bacterial communities, particularly in response to temperature fluctuations (Ziegler et al., 2017, Lima et al., 2020; Zhu et al., 2022). Our findings indicate that after the initial marine heatwave, there was a significant increase in the abundance of a bacterial family called u. Legionellaceae, with functional predictions suggesting their potential as “Potentially Pathogenic” and “intracellular parasites”. Legionellaceae are commonly found in coral reef ecosystems and have associations with coral pathogens (Vega et al., 2009), indicating that assumed beneficial bacterial groups within the coral symbiont community may transition into potentially pathogenic and intracellular parasites under high-temperature conditions (Sweet et al., 2013; McDevitt-Irwin et al., 2017).
At the end of the first recovery phase, Leptospira ,Halomonas desiderata , and u. Flavobacteriaceae maintained a relatively high abundance. Leptospira is an intracellular parasite commonly found in the environment (Kavela et al., 2023), and is speculated based on FAPROTAX predictions, to have detrimental effects on corals. Marine heatwaves can lead to increased nitrogen and nitrate levels in coral reef areas (Howells et al., 2012; WIEDEMANN et al., 2013; Grottoli et al., 2018). Halomonas desiderata are opportunistic microbes that form a symbiotic relationship with corals, residing on the coral surface and utilizing organic matter present in the coral reef area, which helps corals resist invasion by pathogenic microorganisms (Wang and Shao, 2021). The symbiotic relationship between Flavobacteriaceae and corals is complex and sensitive (Meyer et al., 2016; Vega et al., 2008; Sweet et al., 2011; Certner and Vollmer, 2018). However, based on functional predictions, the primary function of u. Flavobacteriaceae in this study was an organic matter decomposition. These results indicate that during the recovery period, although potentially pathogenic bacterial groups are present within the core community, beneficial bacterial groups rapidly increase to aid in coral recovery (Sun et al., 2023).