Search for: All records

Abstract Microbiomes are essential features of holobionts, providing their hosts with key metabolic and functional traits like resistance to environmental disturbances and diseases. In scleractinian corals, questions remain about the microbiome's role in resistance and resilience to factors contributing to the ongoing global coral decline and whether microbes serve as a form of holobiont ecological memory. To test if and how coral microbiomes affect host health outcomes during repeated disturbances, we conducted a large‐scale (32 exclosures, 200 colonies, and 3 coral species sampled) and long‐term (28 months, 2018–2020) manipulative experiment on the forereef of Mo'orea, French Polynesia. In 2019 and 2020, this reef experienced the two most severe marine heatwaves on record for the site. Our experiment and these events afforded us the opportunity to test microbiome dynamics and roles in the context of coral bleaching and mortality resulting from these successive and severe heatwaves. We report unique microbiome responses to repeated heatwaves inAcropora retusa,Porites lobata, andPocilloporaspp., which included: microbiome acclimatization inA. retusa, and both microbiome resilience to the first marine heatwave and microbiome resistance to the second marine heatwave inPocilloporaspp. Moreover, observed microbiome dynamics significantly correlated with coral species‐specific phenotypes. For example, bleaching and mortality inA. retusaboth significantly increased with greater microbiome beta dispersion and greater Shannon Diversity, whileP. lobatacolonies had different microbiomes across mortality prevalence. Compositional microbiome changes, such as changes to proportions of differentially abundant putatively beneficial to putatively detrimental taxa to coral health outcomes during repeated heat stress, also correlated with host mortality, with higher proportions of detrimental taxa yielding higher mortality inA. retusa. This study reveals evidence for coral species‐specific microbial responses to repeated heatwaves and, importantly, suggests that host‐dependent microbiome dynamics may provide a form of holobiont ecological memory to repeated heat stress. 

Abstract Nutrient availability drives community structure and ecosystem processes, especially in tropical lagoons that are typically oligotrophic but often receive allochthonous inputs from land. Terrestrially derived nutrients are introduced to tropical lagoons by surface runoff and submarine groundwater discharge, which are influenced by seasonal precipitation. However, terrigenous inputs presumably diminish along the onshore–offshore gradients within lagoons. We characterized nutrient availability in the lagoons of a tropical high island, Moorea, French Polynesia, using spatially distributed measurements of nitrogen content in the tissues of a widespread macroalga during the rainy season over 4 yr. We used synoptic water column sampling to identify associations among macroalgal nutrient content and the composition of inorganic macronutrients, dissolved organic matter, and microbial communities. We paired these data with quantifications of land use in nearby watersheds to uncover links between terrestrial factors, aquatic chemistry, and microbial communities. Algal N content was highest near shore and near large, human‐impacted watersheds, and lower at offshore sites. Sites with high algal N had water columns with high nitrite + nitrate, silicate, and increased humic organic matter (based on a fluorescence Humification Index), especially following rain. Microbial communities were differentiated among nearshore habitats and covaried with algal N and water chemistry, supporting the hypothesis that terrigenous nutrient enrichment shapes microbial dynamics in otherwise oligotrophic tropical lagoons. This study reveals that land–sea connections create nutrient subsidies that are important for lagoon biogeochemistry and microbiology, indicating that future changes in land use or precipitation will modify ecosystem processes in tropical lagoons.