Global microbialization of coral reefs

Area of Science:

• Marine biology
• Ecology
• Microbiology

Background:

• Microbialization describes a shift in ecosystems towards increased microbial biomass and energy utilization.
• Coral reefs are experiencing microbialization due to overfishing and eutrophication, which promote fleshy algae growth over corals.
• The DDAM (dissolved organic carbon, disease, algae, microorganism) feedback loop is proposed to explain algal competitive advantage.

Purpose of the Study:

• To test the DDAM feedback loop predictions across multiple ocean basins.
• To investigate the relationship between algal cover, dissolved organic carbon (DOC), and microbial communities on coral reefs.

Main Methods:

• Analysis of over 400 samples from 60 coral reef sites across three ocean basins.
• Correlation analysis of reef algal cover with DOC concentrations and microbial abundances.
• Metagenomic analysis of microbial communities and their metabolic potential for carbohydrate degradation.

Main Results:

• Reef algal cover positively correlated with lower DOC concentrations and higher microbial abundances.
• Copiotrophic microbial taxa were more abundant on reefs with turf and fleshy macroalgae.
• Microbial communities on algal-dominated reefs shifted to less efficient carbohydrate metabolism pathways (Entner-Doudoroff and pentose phosphate).

Conclusions:

• The DDAM feedback loop is consistent across ocean basins, confirming its role in coral reef microbialization.
• Shifts in microbial metabolism on algal-dominated reefs increase hypoxia and CO2 release, threatening coral reef health.
• Overfishing and eutrophication drive microbialization, leading to detrimental changes in coral reef ecosystems.