Cyanobacterial Dynamics in Coral Reef Ecosystems

Cyanobacteria are photosynthetic prokaryotes that play a pivotal role in coral reef biogeochemistry by fixing nitrogen, contributing to primary production and forming biofilms and benthic mats. In oligotrophic reef settings, they supply bioavailable nitrogen through heterogeneous nitrogen fixation, sustaining diverse reef communities. Under favourable conditions—elevated nutrient inputs, warmer temperatures and reduced herbivory—some species proliferate into extensive mats that alter light regimes, outcompete reef‐building corals and release dissolved organic carbon (DOC) into the water column. These mats may produce toxins, inhibit coral recruitment and modify microbial assemblages, triggering ecological feedbacks that reinforce reef degradation. Understanding cyanobacterial dynamics is essential for reef management, as shifts towards mat dominance undermine reef resilience, affect fisheries and pose risks to human health via water‐borne toxins.

Research from Nature Portfolio

Laboratory and field experiments have quantified nutrient uptake by benthic cyanobacteria during runoff events, demonstrating that opportunistic filamentous species rapidly assimilate pulses of nitrate, ammonium and phosphate, often matching or exceeding uptake by co‐occurring algae and corals. Observations on Caribbean reefs have revealed that several reef fish—including angelfish, parrotfish and surgeonfish—actively graze benthic cyanobacterial mats, suggesting a previously underappreciated top‐down control mechanism. In contrast, seasonal mat blooms in a Fijian no‐take reserve were found to suppress overall herbivory, as common reef grazers avoided mat‐covered substrata, indicating that once mats reach high cover they can resist consumption and disrupt grazing functions. High‐resolution sequencing of mat types has shown that even within a single bloom, mats comprise complex consortia of Oscillatoriales and other bacterial taxa, highlighting their ecological plasticity and resilience.

Cyanobacterial Dynamics in Coral Reef Ecosystems publication trend

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

Technical terms

Cyanobacteria: Photosynthetic, nitrogen‐fixing prokaryotes that form biofilms, mats and symbioses on reefs.

Benthic cyanobacterial mat (BCM): A dense, often multi‐species layer of cyanobacteria and associated microbes growing on the reef surface.

Nitrogen fixation: The enzymatic conversion of atmospheric dinitrogen into bioavailable ammonia by diazotrophic organisms.

Dissolved organic carbon (DOC): Organic molecules released into water by organisms, which fuel microbial respiration and alter nutrient cycles.

Oligotrophic: Describes environments with low concentrations of nutrients, particularly nitrogen and phosphorus.

References

1. Nitrogen and phosphorus uptake rates of different species from a coral reef community after a nutrient pulse. Scientific Reports (2016).
2. Reefs under Siege—the Rise, Putative Drivers, and Consequences of Benthic Cyanobacterial Mats. Frontiers in Marine Science (2018).
3. Nitrogen fixation and diversity of benthic cyanobacterial mats on coral reefs in Curaçao. Coral Reefs (2018).
4. Cyanobacteria in Coral Reef Ecosystems: A Review. Journal of Marine Sciences (2012).
5. High dissolved organic carbon release by benthic cyanobacterial mats in a Caribbean reef ecosystem. Scientific Reports (2015).
6. Consumption of benthic cyanobacterial mats on a Caribbean coral reef. Scientific Reports (2019).
7. First insights into the impacts of benthic cyanobacterial mats on fish herbivory functions on a nearshore coral reef. Scientific Reports (2021).
8. High diversity of benthic cyanobacterial mats on coral reefs of Koh Tao, Gulf of Thailand. Coral Reefs (2022).
9. 11-yr of coral community dynamics in reefs around Dahab (Gulf of Aqaba, Red Sea): the collapse of urchins and rise of macroalgae and cyanobacterial mats. Coral Reefs (2020).