Strong Symbiodiniaceae Influence on Coral Gene Expression Under Ocean Acidification and Warming

Area of Science:

• Marine Biology
• Coral Reef Ecology
• Genomics

Background:

• Coral reefs face severe threats from ocean acidification and warming.
• Coral responses to environmental change are influenced by their symbiotic partnerships and history.

Purpose of the Study:

• To investigate the holobiont (coral host, algal symbionts, and bacterial communities) response of Siderastrea siderea to simulated future ocean conditions.
• To examine how symbiont type influences coral phenotype, symbiotic community structure, and gene expression under stress.

Main Methods:

• Exposure of Siderastrea siderea to various ocean acidification and warming scenarios for three months.
• Analysis of holobiont phenotypes, including lipid content and calcification rates.
• Assessment of algal symbiont and bacterial communities.
• Examination of coral host gene expression profiles.

Main Results:

• Siderastrea siderea exhibited moderate stress responses with no significant shifts in algal symbiont or bacterial communities under tested conditions.
• Coral gene expression was predominantly influenced by the hosted Symbiodiniaceae genus (Durusdinium trenchii vs. Cladocopium goreaui), not experimental treatments.
• Corals hosting D. trenchii showed higher lipid content but reduced calcification rates compared to those hosting C. goreaui.
• Extreme acidification conditions, not projected for this century, led to reduced growth rates and downregulation of calcification genes.

Conclusions:

• Symbiotic relationships fundamentally shape coral responses to environmental change, potentially determining future reef persistence.
• Coral acclimatization strategies are strongly mediated by their associated symbionts.
• While moderate climate change effects were observed, extreme conditions pose significant challenges to coral skeletal production.