Innate Immune Responses in Coral Ecosystems

Corals possess a sophisticated innate immune system that underpins their survival in dynamic marine environments. Unlike adaptive immunity, their defences rely on germline‐encoded receptors and cellular effectors to detect and neutralise pathogens and to maintain homeostasis with beneficial microbes. Key components include pattern recognition receptors such as Toll-like receptors, downstream signalling via transcription factors like NF-κB, and effector mechanisms including antimicrobial peptides, melanin synthesis and phagocytosis by amoebocytes. These responses are integrated within the coral holobiont—a consortium comprising the animal host, photosynthetic algal symbionts and a diverse microbiome. Fluctuating temperatures, nutrient availability and microbial challenges disrupt this balance, often tipping the holobiont towards dysbiosis, bleaching or disease. Recent advances have illuminated both the molecular networks governing coral immunological memory and the environmental modulation of immune competence, offering new avenues for reef conservation and resilience enhancement.

Research from Nature Portfolio

Studies in the past two years have revealed how nutritional status modulates coral immunity. Work on a model sea anemone demonstrated that starvation leads to downregulation of genes involved in cellular respiration and innate immune pathways, accompanied by a marked decrease in NF-κB protein levels and heightened susceptibility to bacterial infection. This finding underscores the critical link between energy reserves and host defence in early-diverged marine metazoans. In parallel, experiments with a Mediterranean thermophilic coral species have shown that exposure to elevated temperatures combined with bacterial lipopolysaccharide challenge suppresses TLR-NF-κB activation, while heat shock protein 70 activity increases. This dual stress model elucidates how global warming may undermine pathogen recognition and signal transduction, thereby compromising coral health. Foundational research across divergent Caribbean corals has further dissected holobiont metatranscriptome responses to thermal stress, identifying lineage-specific gene expression adaptations in both host and algal symbiont and revealing roles for bacterial associates in supplementing metabolic demands during heat exposure. Together, these studies establish a framework for predicting coral resilience under compound stressors.

Innate Immune Responses in Coral Ecosystems publication trend

The graph below shows the total number of articles in innate immune responses in coral ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Innate immunity: The non-specific, first line of defence using germline-encoded receptors and effector mechanisms to detect and eliminate pathogens rapidly.

Holobiont: The coral host together with its symbiotic algae and associated microbial community, functioning as an integrated biological unit.

Pattern recognition receptor (PRR): A molecule such as a Toll-like receptor that recognises conserved microbial molecules and initiates immune signalling.

NF-κB: A transcription factor central to the regulation of immune and stress responses, activating genes involved in inflammation and cell survival.

Phagocytosis: The process by which specialised cells engulf and digest pathogens or debris, a key effector mechanism in innate defence.

References

1. Starvation decreases immunity and immune regulatory factor NF-κB in the starlet sea anemone Nematostella vectensis. Communications Biology (2023).
2. Global warming-related response after bacterial challenge in Astroides calycularis, a Mediterranean thermophilic coral. Scientific Reports (2024).
3. Elucidating gene expression adaptation of phylogenetically divergent coral holobionts under heat stress. Nature Communications (2021).
4. Impact of rising seawater temperature on a phagocytic cell population during V. parahaemolyticus infection in the sea anemone E. pallida. Frontiers in Immunology (2023).
5. First insights into the Aurelia aurita transcriptome response upon manipulation of its microbiome. Frontiers in Microbiology (2023).