Benthic calcareous macroalgae are vital primary producers and reef-builders in global reef ecosystems. Light availability is a critical factor for their growth, and reductions in light due to human activities pose significant challenges to their reproduction. However, there is limited research in this area. Here, we investigated the proteomic and physiological responses of the green macroalga Halimeda opuntia and the red microalga Amphiroa fragilissima under different light intensities. In H. opuntia, we observed no significant variation of Chl a and Fv/Fm values but a decrease in tissue carbonate content and calcification rate. In contrast, A. fragilissima showed increased Chl a and Fv/Fm values, and an elevated calcification rate. The two species exhibited distinct strategies in response to light limitation, as reflected by the differential enrichment of processes such as translation, signal transduction, peptidases, membrane trafficking, and exosome in H. opuntia, and transporters, photosynthesis, oxidative phosphorylation, nitrogen metabolism, and exosome in A. fragilissima. Both species downregulated proteins related to photosynthesis, light harvesting, and carbon fixation, likely as an adaptive response to reduced light input. Notably, H. opuntia upregulated plasma membrane-type Ca²⁺-ATPase and intracellular carbonic anhydrase (CA) to enhance the concentration of calcifying ions, thereby sustaining calcification under low light. On the other hand, A. fragilissima appeared to allocate more energy to calcification through the upregulation of glycolysis, the TCA cycle, and oxidative phosphorylation. Our findings reveal distinct strategies for maintaining growth and calcification under low light conditions between the two macroalgae. This suggests a potential advantage for Halimeda in adapting to future reductions in ocean light availability.
 

Proteomics，Light, reef, calcification, Macroalgae