An elevated sea temperature is considered a key abiotic stressor causing thermal stress to intertidal macroalgae and influencing their populations. Halimeda macroloba is an important CaCO₃ producer that contributes to the carbonate budget in marine ecosystems. The population decline of this intertidal algal species could lead to considerable declines in both regional and global carbonate production. However, the impact of increasing temperature on the molecular mechanisms and protein profile of calcified H. macroloba is unclear and remains to be explored. In this study, H. macroloba was exposed to 30 °C and 35 °C for 7 days. The whole protein was then extracted using 0.5% SDS and digested using trypsin before an analysis using LC-MS. The protein profile of H. macroloba was characterized using the MaxQuant program aligned with the UniProt database. A total of 407 proteins were identified, and 12 proteins were found to be significantly upregulated or downregulated in response to the elevated temperature. Cell division protein, protein kinase domain-containing protein, phospholipid transport protein, and small ribosomal subunit protein were the significant proteins identified in our dataset. The proteins associated with cell division, cellular metabolic processes, localization, oxidoreductase activity, and biosynthetic process pathways were overexpressed with a more than 2-fold change at a high temperature. An interaction map generated using STITCH revealed that the significant protein change altered the other proteins related to abiotic stress, producing energy and inducing calcification. This information could be useful in understanding how H. macroloba responds to an elevated sea temperature.

Increased seawater temperatures and nutrient loading are stressors that affect coral reefs and their microbiomes. In this study, filamentous algae were collected and exposed to different temperatures and nutrient concentrations through a laboratory experiment. Microbial DNA was extracted and analyzed using amplicon sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. In total, 1 domain, 51 phyla, 131 classes, 335 orders, 549 families, and 1905 species were identified. Proteobacteria and Bacteroidota were the dominant taxa reported. Elevated seawater temperatures and nutrient enrichment impacted microbial communities associated with turf algae under laboratory culture. Bacterial species diversity and abundance differed under different temperature and nutrient conditions. Proteobacteria and Actinobacteria were abundant in lower-temperature conditions, while Desulfobacterota, Spirochaetota, and Firmicutes were abundant in higher-temperature conditions. Ruegeria was abundant in low-temperature conditions, whereas Vibrio abundance was low. Regarding nutrient conditions, Proteobacteria and Cyanobacteria were abundant under high-nutrient conditions, while Firmicutes and Desulfobacterota were abundant under ambient-nutrient conditions. The higher nutrient concentration increased the abundance of pathogenic bacteria, such as Vibrio and Photobacterium, while Pseudoalteromonas, which is beneficial for reefs, was present under ambient nutrient conditions. This study demonstrates that temperature and nutrient enrichment can shape microbial communities under laboratory conditions, providing an experimental setting for further studies of bacterial functions and metabolic processes in natural conditions under thermal and nutrient stresses.