Calcification and linear extension rates for Oculina arbuscula corals grown under different pCO2 levels; from the Cohen lab at WHOI in Woods Hole, MA (OA Nutrition and Coral Calcification project) on 2014-02-06 (NCEI Accession 0278116)

Acquisition Description:
Methodology as described in Ries et al. (2010):
Zooxanthellate colonies of Oculina arbuscula were collected offshore of Bogue Banks North Carolina in August 2007. After collection, the organisms were transported to the Marine Calcification Laboratory at Woods Hole Oceanographic Institution. After acclimation to the laboratory conditions, fragments of each colony were harvested and mounted on acrylic slides. Specimens were then transferred to the experimental seawaters for additional acclimation for 14 days prior to the start of the experiment.

The O. arbuscula specimens were reared for 60 days from Sept. to Nov. 2007 in four 38-liter glass aquaria filled with filtered seawater. The experimental seawaters were bubbled continuously with air-CO2 mixtures of 409, 606, 903, or 2856 ppm pCO2. Temperature was maintained at 25 +/- 1 degrees Celsius. Aquaria were illuminated 10 hours per day. Seventy-five percent seawater changes were made every 14 days. Coral fragments were fed Artemia sp. every other day. The experimental air-CO2 gas mixtures were formulated using Aalborg mass flow controllers, yielding average seawater saturation states of 2.6, 2.3, 1.6, and 0.8 with respect to aragonite. Salinity, temperature, and pH of the seawaters, and pCO2 of the mixed gases were measured weekly. Total alkalinity was measured every 2 weeks. DIC, bicarbonate ion concentration, dissolved CO2, aragonite saturation state, and pCO2 were calculated from the measured parameters. Refer to Table 1 of Ries et al. (2010) for more detail on the measured and calculated carbonate chemistry parameters, including mean, range, and standard deviation.

A buoyant weighing method was used to estimate the corals' calcification rates. Calcification rates were calculated as the percent change in buoyant weight between the beginning and end of the experiment.

Each aquarium was dosed with 137BaCO3 for 14 days at the beginning of the experiment. After 14 days, the 137Ba-enriched seawaters were replaced with seawaters of natural Ba isotopic composition. This temporary increase in the concentration of Barium-137 in the experimental seawaters resulted in a five-fold spike in the ratio of Ba-137 to Ba-138 in the coral skeletons accreted during the first 14 days of the experiment. This spike provided the baseline from which linear extension of the coral skeletons could be measured. Four coral specimens were randomly selected from each of the treatments and sectioned parallel to the growth axis. 137Ba/138Ba ratios were measured using laser ablation-inductively coupled plasma-mass spectrometry. To determine linear extension, the time elapsed from the detection of the 137Ba/138Ba spike and the outer edge of the coral skeleton was converted to distance by multiplying the elapsed time by the scan rate of the laser.