Coralline algae are an essential element of benthic ecosystems throughout the ocean's photic zone. Yet, the role of light in shaping the physiology of coralline algae from cold-water, low-light habitats is poorly understood. Here, we assess the calcification physiology of five cool temperate coralline algae in response to different irradiance levels over 3 months. We show that in contrast to current models focused on warmer water species, previously observed enhancement of calcification rates by photosynthesis is largely limited to lower irradiances, and that the removal of CO2 from the calcifying fluid is not the underlying mechanism of this enhancement. Instead, this most likely occurs via two processes: (1) increased ion pumping rates to elevate the calcium carbonate saturation state in the calcifying fluid; and (2) a higher daytime pH in the diffusion boundary layer that raises calcifying fluid pH. However, as irradiance increases, ion pumping becomes increasingly saturated limiting further enhancements. Our results also suggest the existence of two calcification strategies in coralline algae and indicate that magnesium incorporation is determined by the magnesium to calcium ratio in the calcifying fluid ([Mg]CF/[Ca]CF). This study adds to our mechanistic understanding of calcification in coralline algae and fills in much needed knowledge about the role of light in controlling their physiology.
|Original language||English (US)|
|Journal||Limnology and Oceanography|
|State||Published - Apr 25 2023|
Bibliographical noteKAUST Repository Item: Exported on 2023-05-12
Acknowledgements: We thank J. Van der Sman for his assistance during collection; J. Delgado and J. Brown for their help with carbon isotope measurements; Y. Tassin for creating a R script for total alkalinity analysis; and R. D'Archino for training in molecular identification. E.C.K. and C.E.C. were supported by a Rutherford Discovery Fellowship from The Royal Society of New Zealand Te Apārangi (no. RDF-VUW1701) awarded to C.E.C. Part of the research was paid for by a grant awarded to C.E.C. and W.A.N. by the Victoria University of Wellington University Research Fund. Open access publishing facilitated by Victoria University of Wellington, as part of the Wiley - Victoria University of Wellington agreement via the Council of Australian University Librarians.