Coral response to climate change

Work with colleagues Karl Castillo and Jack Weiss (UNC) has shown that growth rates for the reef-building coral Siderastrea siderea have changed over the past century.  However, the rate and direction of change appears to vary across reef zones, with forereef colonies exhibiting the most severe decline, nearshore colonies exhibiting a moderate decline, and backreef colonies exhibiting a moderate increase.  Most strikingly, forereef colonies, which a century ago exhibited the fastest rates of growth of the three reef zones, now exhibit the slowest rates of growth (Castillo, Ries, and Weiss, 2011). We are presently trying to determine why – READ MORE 

Modeling the calcification response to ocean acidification

Biological calcification responses to CO2-induced ocean acidification vary widely across taxa, with species exhibiting positive, threshold-positive, neutral, parabolic, threshold-negative, and negative responses (Ries et al., 2009; see below).  A generalized physicochemical model of calcifying fluid, based upon the premise that many marine calcifiers induce calcification by removing protons from their calcifying fluids, is able to generate a comparably broad range of calcification responses to CO2-induced ocean acidification.  Measurements of the calcifying fluid of the temperate coral Astrangia poculata with pH microelectrodes reveal that the coral maintains a substantially elevated pH (~10) at the site of calcification relative to its ambient seawater (~8).  This suggests that the coral is indirectly utilizing bicarbonate (HCO3) as a source of carbon in its calcification, via conversion to CO32- within its high-pH calcifying fluid.  The microelectrode measurements also revealed that the coral maintained a fixed external:internal proton ratio of approximately 85:1 under both control and acidified conditions (Ries, 2011) – READ MORE

Responses of marine calcifiers to CO2-induced ocean acidification

My work with colleagues David Fike (Washington University), Tim Lyons (UC Riverside), Lisa Pratt (Indiana University), and John Grotzinger (Cal Tech) has found that sulfur isotopes from Namibian carbonates suggest that low seawater sulfate conditions (and thus low atmospheric oxygen) persisted into terminal neoproterozoic time, just prior to the Cambrian radiation of animal life (Ries et al., 2009) – READ MORE

Calcite-aragonite seas

My dissertation research showed that three species of scleractinian corals reared in experimental “calcite seawater” (mMg/Ca < 2) produce up to one-third of their skeleton as the calcite, rather than the aragonite, polymorph of calcium carbonate (Ries et al., 2006) – READ MORE

Mg-fractionation in biogenic calcite

My colleagues and I have shown that most high-Mg calcite secreting marine organisms incorporate Mg into their skeletal calcite in proportion to the concentration of Mg in their ambient seawater (Stanley, Hardie, & Ries, 2010; Ries et al., 2008; Ries et al., 2006; Ries, 2006; Stanley, Ries, & Hardie, 2005; Ries, 2004; Stanley, Ries & Hardie, 2002). This finding supports the use of Mg/Ca ratios in fossil calcitic organisms to reconstruct ancient seawater Mg/Ca ratios and suggests that most modern high-Mg calcite secreting taxa produced low-Mg calcite during calcite sea intervals of the geologic past – READ MORE