Using B isotopes and B/Ca in corals from low saturation springs to constrain calcification mechanisms

Ocean acidification is expected to negatively impact calcifying organisms, yet we lack understanding of their acclimation potential in the natural environment. Here we measured geochemical proxies (δ(11)B and B/Ca) in Porites astreoides corals that have been growing for their entire life under low aragonite saturation (Ω(sw): 0.77–1.85). This allowed us to assess the ability of these corals to manipulate the chemical conditions at the site of calcification (Ω(cf)), and hence their potential to acclimate to changing Ω(sw). We show that lifelong exposure to low Ω(sw) did not enable the corals to acclimate and reach similar Ω(cf) as corals grown under ambient conditions. The lower Ω(cf) at the site of calcification can explain a large proportion of the decreasing P. astreoides calcification rates at low Ω(sw). The naturally elevated seawater dissolved inorganic carbon concentration at this study site shed light on how different carbonate chemistry parameters affect calcification conditions in corals.