Ecophysiology of Marine Macroalgae in Elevated CO2 Environments

Marine macroalgae occupy critical positions in coastal ecosystems as primary producers, habitat formers and mediators of biogeochemical cycles. Their ecophysiological responses to rising atmospheric CO2—and the associated decline in seawater pH—drive shifts in community composition, productivity and ecosystem services. Under elevated CO2, some species benefit from increased substrate for photosynthesis, often downregulating energy-intensive bicarbonate uptake and reallocating resources to growth and reproduction. By contrast, calcifying algae face dissolution stress and reduced calcification rates, which can undermine reef building and structural complexity. Interactions with light availability, nutrient status and natural pH fluctuations further modulate these effects, leading to species-specific and context-dependent outcomes. Understanding the mechanistic basis of carbon acquisition, nutrient interactions and stress tolerance is essential to predict future changes in coastal food webs, bioproductivity and carbon sequestration potential.

Research from Nature Portfolio

Recent studies have provided mechanistic insight into how inorganic carbon physiology underpins species-level responses to elevated CO2. One investigation along volcanic CO2 seeps revealed that macroalgae capable of using both CO2 and bicarbonate exhibit increased CO2 utilisation and enhanced abundance in acidified waters, whereas obligately calcifying species decline. Physiological groupings based on δ13C proxies offer predictive power for community shifts under ocean acidification scenarios. Another study on the temperate kelp Ecklonia radiata demonstrated that natural diel pH fluctuations currently benefit juvenile growth and photosynthesis, but these positive effects are abolished or reversed when mean pH is reduced to levels anticipated later this century. This finding highlights the dual role of macroalgae as both modifiers and responders to their carbonate environment, with implications for the resilience of kelp forests under future ocean acidification.

Ecophysiology of Marine Macroalgae in Elevated CO2 Environments publication trend

The graph below shows the total number of articles in ecophysiology of marine macroalgae in elevated co2 environments across all publications each year (not limited to Nature Index journals).

Technical terms

Carbon-concentrating mechanism (CCM): A suite of cellular processes that actively accumulate inorganic carbon in the form of CO2 or HCO3− to enhance photosynthetic efficiency.

Ocean acidification: The decrease in seawater pH resulting from absorption of atmospheric CO2, which alters carbonate chemistry and can impair calcification.

Bicarbonate (HCO3−): The dominant form of dissolved inorganic carbon in seawater, which can be utilised by many macroalgae via specialised transporters or enzyme-mediated conversion.

Partial pressure of CO2 (pCO2): A measure of the concentration of CO2 gas in seawater, influencing the availability of dissolved CO2 for photosynthesis.

δ13C values: The ratio of stable carbon isotopes in algal tissue, used as a proxy to infer reliance on CO2 versus bicarbonate sources.

References

1. Inorganic carbon physiology underpins macroalgal responses to elevated CO2. Scientific Reports (2017).
2. Ocean acidification reverses the positive effects of seawater pH fluctuations on growth and photosynthesis of the habitat-forming kelp, Ecklonia radiata. Scientific Reports (2016).
3. Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza. Biogeosciences (2018).
4. Responses of macroalgae to CO2 enrichment cannot be inferred solely from their inorganic carbon uptake strategy. Ecology and Evolution (2018).