Exposure to global change and microplastics elicits an immune response in an endangered coral

Global change is increasing seawater temperatures and decreasing oceanic pH, driving declines of coral reefs globally. Coral ecosystems are also impacted by local stressors, including microplastics, which are ubiquitous on reefs. While the independent effects of these global and local stressors are well-documented, their interactions remain less explored. Here, we examine the independent and combined effects of global change (ocean warming and acidification) and microplastics exposures on gene expression (GE) and microbial community composition in the endangered coral Acropora cervicornis. Nine genotypes were fragmented and maintained in one of four experimental treatments: 1) ambient conditions (ambient seawater, no microplastics; AMB); 2) microplastics treatment (ambient seawater, microplastics; MP); 3) global change conditions (warm and acidic conditions, no microplastics; OAW); and 4) multistressor treatment (warm and acidic conditions with microplastics; OAW+MP) for 21 days after which corals were sampled for genome-wide GE profiling and ITS and 16S metabarcoding. Overall A. cervicornis GE responses to all treatments were subtle; however, corals in the multistressor treatment exhibited the strongest GE responses, and gene ontology enrichment analyses showcased that genes associated with innate immunity were overrepresented in this treatment. 16S analyses showcased that microbiomes were dominated by the bacterial symbiont Aquarickettsia and were stable, suggesting that A. cervicornis exhibited remarkably low variability in community composition, and future work should focus on functional differences across these bacterial communities as well as the influence of viruses in these responses. Overall, results suggest that local stressors present a unique challenge to endangered coral species under global change.

全球变化正导致海水温度升高、海洋pH值下降，进而引发全球珊瑚礁的退化。珊瑚生态系统同时受到各类本地胁迫因子的影响，其中微塑料（microplastics）在珊瑚礁上无处不在。尽管这两类全球与本地胁迫因子的单独效应已有充分研究，但二者的交互作用仍较少被探索。本研究探讨了全球变化（海洋变暖与酸化）及微塑料暴露的单独与联合效应，对濒危珊瑚鹿角轴孔珊瑚（Acropora cervicornis）的基因表达（gene expression, GE）与微生物群落组成的影响。我们将9个基因型的珊瑚切割为断枝后，分别置于4种实验处理组中培养21天：1）对照组（天然海水，无微塑料；AMB）；2）微塑料处理组（天然海水，添加微塑料；MP）；3）全球变化处理组（暖化与酸化环境，无微塑料；OAW）；4）多胁迫处理组（暖化与酸化环境，添加微塑料；OAW+MP）。培养结束后，采集珊瑚样本进行全基因组基因表达谱分析，以及ITS与16S元条形码测序。整体而言，鹿角轴孔珊瑚在各处理组中的基因表达响应均较为微弱；但多胁迫处理组的珊瑚展现出最强的基因表达响应，且基因本体（gene ontology, GO）富集分析显示，该组中与先天免疫相关的基因显著富集。16S分析结果显示，珊瑚微生物组以共生细菌Aquarickettsia为优势类群，且群落结构稳定，表明鹿角轴孔珊瑚的微生物群落组成变异程度极低。未来研究应聚焦于这些细菌群落间的功能差异，以及病毒在该响应过程中的作用。综上，研究结果表明，在全球变化背景下，本地胁迫因子对濒危珊瑚物种构成了独特的生存挑战。