Thrilled to see our latest paper “Efficient carbon recycling between calcification and photosynthesis in red coralline algae” out in Biology Letters, and on the front cover!

This paper is from the work of former PhD student Jinhua Mao, who used radioactive isotopes of carbon and calcium to track carbon processing in coralline algae – globally distributed calcified red seaweeds that create biodiverse reef habitats. We have previously shown that coralline algae reefs are important for blue carbon storage (see James et al 2024 Glob Change Biol and Mao et al 2020 Global Change Biol), but the calcifying nature of coralline algae complicates carbon fluxes. Counter-intuitively (but the chemistry works out!), calcification actually releases carbon dioxide – not great from a carbon storage perspective. But if that carbon dioxide can then be used by the organism, the amount ultimately released will be much less. That is exactly what we show here – 40% of the carbon released from calcification is internally recycled for use in photosynthesis!

You can read the full paper here (open access)

Efficient carbon recycling between calcification and photosynthesis in red coralline algae

J Mao, HL Burdett and NA Kamenos

Red coralline algae create abundant, spatially vast, reef ecosystems throughout our coastal oceans with significant ecosystem service provision, but our understanding of their basic physiology is lacking. In particular, the balance and linkages between carbon-producing and carbon-sequestering processes remain poorly constrained, with significant implications for understanding their role in carbon sequestration and storage. Using dual radioisotope tracing, we provide evidence for coupling between photosynthesis (which requires CO₂) and calcification (which releases CO₂) in the red coralline alga Boreolithothamnion soriferum (previously Lithothamnion soriferum)—a marine ecosystem engineer widely distributed across Atlantic mid-high latitudes. Of the sequestered HCO₃ ⁻, 38 ± 22% was deposited as carbonate skeleton while 39 ± 14% was incorporated into organic matter via photosynthesis. Only 38 ± 2% of the sequestered HCO₃ ⁻ was transformed into CO₂, and almost 40% of that was internally recycled as photosynthetic substrate, reducing the net release of carbon to 23 ± 3% of the total uptake. The calcification rate was strongly dependent on photosynthetic substrate production, supporting the presence of photosynthetically enhanced calcification. The efficient carbon-recycling physiology reported here suggests that calcifying algae may not contribute as much to marine CO₂ release as is currently assumed, supporting a reassessment of their role in blue carbon accounting.