In this talk, we will provide an overview of the research we are currently undertaking to understand the influence of the environment, particularly ocean acidification, on the growth and calcification of crustose coralline algae (CCA) in the Great Barrier Reef (GBR) and the Caribbean. A first step towards this goal is to understand the mechanisms and patterns of calcification, growth and mineralogical composition. We are making significant progress to unravel the molecular basis of CCA calcification and have now identified RNA molecules (transcriptomes) involved in biomineralization and other key processes (T. Page work). Because biomineralization in the CCA occurs in the cell walls, we are studying the monosaccharide constituents of the cell wall and their potential role in calcification (E. Bergstrom work). Understanding the influence of environmental variability on the calcification process requires fundamental research on species boundaries and phylogeny of the corallines, as well as knowledge of the distribution of species across reef habitats. This knowledge allows us to examine in more detail the influence of water quality, seasonality and upwelling (Caribbean) on CCA calcification and mineralogical composition and to obtain growth and calcification estimates of CCA along the GBR. There is considerable variability in CCA responses to ocean acidification and our recent experiments suggest that this variability may also be explained by their evolutionary history. This work is critical for advancing our understanding of anthropogenic influences on CCA ecology and the critical roles they play in reef ecosystem functioning, in particular their contribution to reef framework construction.