Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef

Abstract

Abstract. The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21 st century. This increase will reduce the 2 concentration of CO3-of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage.Using the large 2650 m 3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcificafion of coral reef organisms at the commtmity scale. Our experimental design was to obtain a long (3.8 years) time'series of the net calcificafion of the complete system and all relevant physical and chemical variables (tem•rature, salinity, light, nutrients, Ca 2+, pCO2, TCO2, and total alkalinity). Periodic additions of NaHCOz, Na2CO•, and/or CaC12 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcificafion in response to our manipulations of the saturation state. We show that the net community calcificafion rate suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcffication on coral reefs at the ecosystem level. We compare the sensitivity of cal½ification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification •een the years 1880 and 2065 A.D. based on our longterm results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. in the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.

Coral reefs and changing seawater carbonate chemistry

“…Community was dominated by Amphiroa fragillisma, a coralline algae that secretes high-Mg calcite (22% MgCO 3 ). Calcification goes to 0.0 at Ω arag = 1.7 ± 0.2 (data from Langdon et al [2000] and other Biosphere 2 results). sediments would not readily dissolve.…”

“…At the time they thought such a clear chemical control on the calcification rate could only mean that the calcification was abiotic. We now know that many calcifying organisms also respond linearly to changing IAP or saturation state [Langdon et al, 2000].…”

“…A simple example is a sediment mixture of Amphiroa (highMg calcite with 22% MgCO 3 ) and coral (aragonite) fragments that is exposed to increasing pCO 2 levels, and maintained at 25°C. Based on the Biosphere 2 experiments described above [Langdon et al, 2000], the high-Mg calcite would begin to dissolve once Ω hmc = 1, which would occur when pCO 2 ≈ 1000 µatm. At that point, Ω arag = 1.7, so the aragonite Figure 5.…”

Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

“…Although numerous experimental and field studies show that increasing CO 2 and decreasing aragonite saturation state (X ar ) lead to decreased coral calcification rates and increased dissolution rates of carbonate substrates, the predicted point in time at which an individual reef ecosystem will shift from net accretion to net dissolution varies across studies and ecosystems (Silverman et al 2007;Ohde and van Woesik 1999;Langdon et al 2000Langdon et al , 2003Andersson et al 2009;Shamberger et al 2011;Shaw et al 2012;Andersson et al 2014). While the global distribution of coral reefs is governed by light availability, temperature, nutrients and X ar (Kleypas et al 1999), at the local scale, the conditions that determine coral reef calcification, distribution and community composition are much more complicated.…”

Vibrational spectroscopic characterization of growth bands in Porites coral from South China Sea

“…There is a long history of research of mineral phases in the marine environment, especially for coral carbonates [10][11][12], and the spectral characteristics of coral have been analyzed using FT-Raman and Fourier transform infrared spectroscopy (FTIR) [13][14][15]. Because minor elements such as Mg, Sr, Mn and U are incorporated into calcium carbonate from seawater during formation and mineralization of biogenic CaCO 3 , changes in the composition of calcium carbonate will lead in changes in the spectra.…”