Coral-Macroalgal Interactions in Reef Ecosystems

Coral reefs represent dynamic interfaces where reef-building corals and macroalgae vie for space, light and nutrients. Following disturbance events such as bleaching, storms or overfishing, macroalgae can proliferate and establish persistent algal beds that hinder coral settlement and survival. Interactions are mediated by direct contact, chemical warfare (allelopathy), alteration of microbial communities and physical shading. Some fleshy macroalgae release metabolites that induce coral bleaching or disrupt symbiotic algal communities, while crustose coralline algae may facilitate coral recruitment. Herbivorous fishes and invertebrates play a crucial role in regulating macroalgal abundance, thus maintaining coral dominance. Feedback mechanisms can lock reefs into alternative stable states dominated by macroalgae, with profound implications for biodiversity, fisheries and coastal protection. Recognising the drivers and outcomes of these interactions is essential to inform restoration efforts, local management and broader strategies aimed at enhancing reef resilience under climate change.

Research from Nature Portfolio

A foundational study investigated the allelopathic capacity of brown macroalgae in direct contact with scleractinian corals. Crude extracts from several species of the genus Lobophora were shown to induce bleaching in selected coral hosts through polyunsaturated alcohol compounds. Field observations, however, revealed that allelopathic effects occur sporadically in situ, suggesting that physical overgrowth, herbivore pressure and microbial processes may modulate the realised impact of chemical interactions. This work underscored the complexity of coral–macroalgal interfaces and emphasised the need to integrate chemical assays with ecological surveys to predict persistence of regime shifts in reef ecosystems.

Coral-Macroalgal Interactions in Reef Ecosystems publication trend

The graph below shows the total number of articles in coral-macroalgal interactions in reef ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Allelopathy: Chemical inhibition or stimulation of one organism by biochemicals produced by another, often at the direct contact interface.

Macroalgae: Multicellular photosynthetic algae, commonly called seaweeds, that form fleshy or calcareous thalli on reef substrates.

Scleractinian corals: Reef‐building stony corals possessing a calcium carbonate skeleton and a symbiotic relationship with photosynthetic dinoflagellates.

Coral microbiome: The assemblage of bacteria, archaea and microeukaryotes associated with coral tissues, influencing health and stress response.

Regime shift: A persistent change in ecosystem structure and function, here describing the transition from coral‐dominated to macroalgal‐dominated reef states.

References

1. Chemically Mediated Interactions with Macroalgae Negatively Affect Coral Health but Induce Limited Changes in Coral Microbiomes. Microorganisms (2023).
2. Sea‐weeding: Manual removal of macroalgae facilitates rapid coral recovery. Journal of Applied Ecology (2023).
3. Biodiversity of macroalgae does not differentially suppress coral performance: The other side of a biodiversity issue. Ecology (2024).
4. Allelopathic interactions between the brown algal genus Lobophora (Dictyotales, Phaeophyceae) and scleractinian corals. Scientific Reports (2016).