Ecosystem Dynamics of Calcareous Green Algae

Calcareous green algae, chiefly represented by the genus Halimeda and related taxa, are key architects of tropical and subtropical marine ecosystems. Through rapid biomineralisation, they precipitate calcium carbonate within their thalli, contributing substantially to reef framework development and sediment generation. These algae form extensive mats, bioherms and rudstones that modulate water chemistry, influence local hydrodynamics and provide habitat complexity for diverse faunal assemblages. Their diurnal patterns of photosynthesis and calcification drive carbonate chemistry fluctuations, while interactions with co-occurring seagrasses, corals and microbial consortia underpin community resilience to stressors. Anthropogenic pressures such as ocean acidification, warming, eutrophication and habitat degradation threaten calcification rates and alter sediment budgets, with cascading effects on coastal stability and carbon sequestration. Understanding the physiological responses, population dynamics and sedimentary roles of calcareous green algae is therefore essential for predicting the future trajectories of carbonate ecosystems and for informing conservation and management strategies at regional to global scales.

Research from Nature Portfolio

Recent studies have revealed that metabolic coupling between seagrass and calcifying algae can buffer the negative impacts of rising CO₂ and temperature. Experiments manipulating carbon dioxide and thermal regimes demonstrated that photosynthetic drawdown of CO₂ by seagrass can elevate local pH and enhance the calcification rate of adjacent Halimeda species by more than two-fold under acidified conditions. This finding indicates that mixed algal–seagrass assemblages may serve as microrefugia against ocean acidification, thereby sustaining carbonate production and mitigating dissolution of existing deposits. Such community-level interactions highlight the importance of benthic habitat mosaics in maintaining carbonate factory function under future climate scenarios.

Ecosystem Dynamics of Calcareous Green Algae publication trend

The graph below shows the total number of articles in ecosystem dynamics of calcareous green algae across all publications each year (not limited to Nature Index journals).

Technical terms

Calcification: The biologically mediated precipitation of calcium carbonate within algal tissues, contributing to skeletal structure and sediment formation.

Bioherm: A mound-like carbonate build-up formed by the in situ accumulation of calcareous algae and associated organisms, analogous to coral reef structures.

Ocean acidification: The reduction in seawater pH and carbonate ion concentration resulting from uptake of anthropogenic CO₂, which can impair calcifying organisms.

Biogenic sediment: Mineral particles produced by living organisms, in this context primarily the calcium carbonate fragments generated by coralline and green calcareous algae.

References

1. Seagrass can mitigate negative ocean acidification effects on calcifying algae. Scientific Reports (2019).
2. Census Estimates of Algal and Epiphytic Carbonate Production Highlight Tropical Seagrass Meadows as Sediment Production Hotspots. Frontiers in Marine Science (2019).
3. Effect of Inorganic and Organic Carbon Enrichments (DIC and DOC) on the Photosynthesis and Calcification Rates of Two Calcifying Green Algae from a Caribbean Reef Lagoon. PLOS ONE (2016).