The role of macroalgae in modulating coral calcification: Mixed species responses in a changing reef environment
Date
2025Author
Manikandan, B.
Sawant, P.
Maurya, P.K.
Pal, A.
Naik, T.A.
Ravindran, J.
Paul, S.
Lad, T.
Prabhudesai, S.
Jayakumar, K.
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The ever increasing dominance of macroalgae on coral reefs is posing new challenges for coral growth and reef resilience. As a part of the continuous coral community monitoring program in Gulf of Mannar Marine Biosphere Reserve (GoMBR) in India, we observed that a few species of macroalgae were persistent throughout the year and remained in physical contact with corals. The effects of such competitive macroalgal interaction on the functional traits of corals are least understood. A series of insitu experiments were conducted to investigate the impact of three macroalgal species on the calcification rates of two Indo-Pacific corals, Acropora muricata and Porites lutea, through alterations in seawater carbonate chemistry. The experimental results showed that macroalgae increased the pH and aragonite saturation state (?arag) throughout the day, that remained stable at night. This created a conducive environment for the corals to maintain their net calcification even at night. However, the corals A. muricata and P. lutea displayed a mixed response, wherein the net calcification rate of the former was enhanced and the latter was significantly reduced in the presence of macroalgae, irrespective of the species. Such disparity in the calcification rates between coral species indicates both affirmative and detrimental effects of coral-macroalgal interactions, highlighting the significance of considering the species-specific interactions between corals and macroalgae in the context of climate change and coral-macroalgal phase-shifts.
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