Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Calcification rates of Porites corals collected from a naturally high-Ωar reef and a naturally low-Ωar reef incubated at three Ωar conditions.

These data were originally published in figure 2 of:
H.C. Barkley, A.L. Cohen, D.C. McCorkle, Y. Golbuu. Mechanisms and thresholds for pH tolerance in Palau corals. Journal of Experimental Marine Biology and Ecology, 489, 7-14 (2017). doi:10.1016/j.jembe.2017.01.003

Coral collection: Coral plugs were collected in December 2012 from massive Porites colonies at a naturally low-Ω_ar reef site (7.324 N, 134.493 E; mean Ω_ar = 2.3; n = 78) and a naturally high-Ω_ar reef site (7.268 N, 134.522 E; mean Ω_ar = 3.7; n = 75). At each reef site, small skeletal cores (diameter = 3.5 cm) were removed from massive colonies (one core per colony) at 2-3m depth using underwater pneumatic drills, and cores were cut with a lapidary table saw to approximately 1 cm below the tissue layer. The plugs were affixed to nylon square base screws with marine epoxy, secured to egg crate racks, and returned to their original reefs to allow the corals to recover from the coring procedure. All corals survived two months of recovery on the reef and on all corals living tissue had fully overgrown the sides of the plugs so that no underlying skeleton was exposed. Corals were recovered in February 2013.

CO₂ manipulation experiment: Corals from two reefs were cultured at three CO₂ levels for eight weeks in March to May 2013 (n = 10 corals per treatment, n = 60 corals total). The corals were individually incubated in independently manipulated plastic cups (volume = 750 ml) to increase statistical power. Cups were placed within a large, temperature-controlled water bath. The corals were maintained at mean (± SD) temperatures of 29.4C ± 0.1C. Light was provided by LED aquarium lights (Coralife) at average levels of 334 ± 48 umol photons m^-2 s^-1 (measured by an underwater quantum sensor, LI-COR) on a 12h:12h light:dark schedule. Corals were fed live Artemia brine shrimp larvae every other evening by pipetting 1 ml of concentrated brine shrimp in filtered seawater into each cup. Coral cups were cleaned weekly to prevent algae overgrowth.

Mean pH (total scale)/Ω_ar levels for the three treatment conditions were 7.98/3.0, 7.83/2.3, and 7.60/1.5. In each coral cup, carbon system chemistry was regulated using a combination of flow-through pre-equilibrated water and bubbling of mixed air/CO₂ gas. Incoming seawater (filtered to 0.35 um) from the reef was aerated and split into three header tanks. In the low-CO₂ header tank, water was bubbled with air. In the mid-CO₂ and high-CO₂ header tanks, CO₂ levels were regulated by a pH controller (Drs. Foster and Smith) connected to a solenoid valve that introduced CO₂ gas into the header tank through a column diffuser. Water was siphoned from the three header tanks into each coral cup at a rate of approximately 375 ml per hour. Each coral cup was also bubbled with either compressed air (low CO₂ treatment) or mixed compressed air and CO₂ gas (mid and high CO₂ treatment) controlled by pairs of mass flow controllers (Aalborg Instruments) at approximately 200 ml per minute. Low alkalinity levels in the source water to the Palau International Coral Reef Center (drawn from within the lower-alkalinity Rock Islands) prevented Ω_ar in the low-CO₂ condition (Ω_ar = 3.0) from reaching values that were as high as those measured on the barrier reef site (Ω_ar = 3.7).

To characterize the carbonate chemistry in each cup, total alkalinity (TA), pH, temperature, and salinity were measured weekly. Spectrophotometric pH measurements were made with 2 mM m-Cresol purple indicator dye using a spectrometer with a 100 mm flow cell (Ocean Optics, mean precision = 0.005) following procedures in Clayton and Byrne (1993) and Dickson et al. (2007) and using the equation of Liu et al. (2011). Samples for TA were collected in 20 ml glass vials and poisoned with saturated mercuric chloride. Automated gran titrations for TA were run on duplicate 1 ml samples using a Metrohm Titrando 808 and 730 Sample Changer (mean precision = 4 umol/kg), and TA values were standardized to certified reference materials obtained from Andrew Dickson [Scripps Institution of Oceanography (Dickson, 2001)]. Salinity was measured in each cup using an YSI salinity probe, and temperatures were measured using an Omega thermocouple (accuracy = 0.1 degree C). Full CO₂ system parameters were calculated from temperature, salinity, TA, and pH using CO2SYS (Lewis and Wallace, 1998) with the constants of Mehrbach et al. (1973) as refit by Dickson and Millero (1987).

Coral calcification analysis: Calcification rates were measured using both buoyant weight (Davies, 1989) and alkalinity anomaly (Chisholm and Gattuso, 1991) techniques. Buoyant weights for each coral were collected at the beginning of the experiment, after three weeks in experimental CO₂ conditions, and then weekly during weeks four to eight. Corals were weighed using a balance with a weigh-below hook (Sartorius GC803S), which allows for beneath-balance weighing of coral plugs that remain entirely submerged in experimental cups maintained at treatment Ω_ar levels. Wet weight data were converted to dry weights using an aragonite density of 2.93 grams per cubic centimeter and the density of seawater determined using a standard of known weight and density. Repeated buoyant weight measurements on the same coral yielded mean precision estimates of ± 0.03 g.

Day/night alkalinity depletion experiments were conducted at the end of the eight-week experiment. Water flow to each coral cup was stopped during this time but gas bubbling was continued in order to maintain pH levels. Samples for TA were collected for each coral cup at the beginning and end of two four-hour periods (one four-hour period during the day and one at night). Alkalinity depletion incubations were simultaneously run in control cups containing only filtered seawater (n=3 per experiment). Because the net change in TA values in control cups was within analytical precision (mean = 3 umol per kilogram), coral calcification was assumed to be the only process impacting the alkalinity in the cups, where two moles of alkalinity were consumed for every one mole of calcium carbonate produced. TA pre and post incubation was determined following the titration procedure described in section 2.2 with samples run in triplicate.

Calcification rates for both buoyant weight and alkalinity anomaly measurements were normalized to coral tissue surface areas. Surface areas were measured following the general procedure for aluminum foil wrapping, in which the weight of aluminum foil needed to cover the entire surface of the coral skeleton is converted to area using a calibration curve (Marsh 1970). However, skeletons were wrapped with electrical tape instead of aluminum foil because the use of electric tape provided tighter control and minimization of tape overlap, which can significantly overestimate surface area. The area of each coral skeleton occupied by living tissue was wrapped in electrical tape that was subsequently carefully trimmed to eliminate any overlay. The weight of tape used to cover the coral tissue for each skeleton were converted to surface areas using a weight-to-area calibration, where ten pieces of electrical tape of known area were weighed to build a weight-per-unit area curve. Replicated electrical tape surface area estimates on ten coral skeletons produced a mean precision of 0.43 square cm, or ~1% of calculated surface areas.

Parameter names have been modified to comply with BCO-DMO naming conventions.

text copied from the NSF award abstract:

Much of our understanding of the impact of ocean acidification on coral reef calcification comes from laboratory manipulation experiments in which reef organisms are removed from their natural habitat and reared under conditions of calcium carbonate saturation (Omega) predicted for the tropical oceans at the end of this century. By comparison, there is a paucity of in situ data describing the sensitivity of coral reef ecosystems to changes in calcium carbonate saturation. Yet emerging evidence suggests there may be critical differences between the calcification response of organisms in culture and the net calcification response of a coral reef ecosystem, to the same degree of change in calcium carbonate saturation. In the majority of cases, the sensitivity of net reef calcification to changing calcium carbonate saturation is more severe than laboratory manipulation experiments predict. Clearly, accurate predictions of the response of coral reef ecosystems to 21st century ocean acidification will depend on a robust characterization of ecosystem-scale responses and an understanding of the fundamental processes that shape them. Using existing data, the investigators show that the sensitivity of coral reef ecosystem calcification to Delta calcium carbonate saturation conforms to the empirical rate equation R=k(Aragonite saturation state -1)n, which also describes the relationship between the rate of net abiogenic CaCO3 precipitation (R) and the degree of Aragonite supersaturation (Aragonite saturation state-1). By implication, the net ecosystem calcification (NEC) response to ocean acidification is governed by fundamental laws of physical chemistry and is potentially predictable across space and time. When viewed this way, the existing, albeit sparse, dataset of NEC reveals distinct patterns that, if verified, have important implications for how different coral reef ecosystems will respond to 21st century ocean acidification. The investigators have outlined a research program designed to build on this proposition. The project expands the currently sparse dataset of ecosystem-scale observations at four strategically placed reef sites: 2 sites in the Republic of Palau, Caroline Islands, Micronesia, western Pacific Ocean; a third at Dongsha Atoll, Pratas Islands, South China Sea; and the fourth at Kingman Reef, US Northern Line Islands, 6 deg. 23 N, 162 deg. 25 W.  The four selected sites will allow investigators to test the following hypotheses: (1) The sensitivity ("n" in the rate equation) of coral reef ecosystem calcification to Delta Aragonite saturation state decreases with decreasing Aragonite saturation state. By implication, the rate at which reef calcification declines will slow as ocean acidification progresses over the course of this century. (2) The energetic status of the calcifying community is a key determinant of absolute rates of net ecosystem calcification ("k" in the rate equation), which, combined with n, defines the Aragonite saturation state value at which NEC approaches zero. By implication, the shift from net calcification to net dissolution will be delayed in healthy, energetically replete coral reef ecosystems and accelerated in perturbed, energetically depleted ecosystems. and (3) The calcification response of individual colonies of dominant reef calcifiers (corals and algae) is weaker than the measured ecosystem-scale response to the same change in Aragonite saturation state. By implication, processes not adequately captured in laboratory experiments, such as bioerosion and dissolution, will play an important role in the coral reef response to ocean acidification.

Broader Impacts: Ocean acidification threatens the livelihoods of 500 million people worldwide who depend on coral reefs to provide habitable and agricultural land, food, building materials, coastal protection and income from tourism. Yet data emerging from ocean acidification (OA) studies point to critical gaps in our knowledge of reef ecosystem-scale responses to OA that currently limit our ability to predict the timing and severity of its impact on different reefs in different parts of the world. Using existing data generated by the investigators and others, this project will address a series of related hypotheses, which, if verified by the research, will have an immediate, direct impact on predictions of coral reef resilience in a high CO2 world. This project brings together expertise in coral reef biogeochemistry, chemical oceanography and physical oceanography to focus on a problem that has enormous societal, economic and conservation relevance. In addition to sharing the resultant data via BCO-DMO, project data will also be contributed to the Ocean Acidification International Coordination Centre (OA-ICC) data collection hosted at the PANGAEA Open Access library (http://www.pangaea.de).

NSF Climate Research Investment (CRI) activities that were initiated in 2010 are now included under Science, Engineering and Education for Sustainability NSF-Wide Investment (SEES). SEES is a portfolio of activities that highlights NSF's unique role in helping society address the challenge(s) of achieving sustainability. Detailed information about the SEES program is available from NSF (https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=504707).

In recognition of the need for basic research concerning the nature, extent and impact of ocean acidification on oceanic environments in the past, present and future, the goal of the SEES: OA program is to understand (a) the chemistry and physical chemistry of ocean acidification; (b) how ocean acidification interacts with processes at the organismal level; and (c) how the earth system history informs our understanding of the effects of ocean acidification on the present day and future ocean.

Solicitations issued under this program:
NSF 10-530, FY 2010-FY2011
NSF 12-500, FY 2012
NSF 12-600, FY 2013
NSF 13-586, FY 2014
NSF 13-586 was the final solicitation that will be released for this program.

PI Meetings:
1st U.S. Ocean Acidification PI Meeting(March 22-24, 2011, Woods Hole, MA)
2nd U.S. Ocean Acidification PI Meeting(Sept. 18-20, 2013, Washington, DC)
3rd U.S. Ocean Acidification PI Meeting (June 9-11, 2015, Woods Hole, MA – Tentative)

NSF media releases for the Ocean Acidification Program:

Press Release 10-186 NSF Awards Grants to Study Effects of Ocean Acidification

Discovery Blue Mussels "Hang On" Along Rocky Shores: For How Long?

Discovery nsf.gov - National Science Foundation (NSF) Discoveries - Trouble in Paradise: Ocean Acidification This Way Comes - US National Science Foundation (NSF)

Press Release 12-179 nsf.gov - National Science Foundation (NSF) News - Ocean Acidification: Finding New Answers Through National Science Foundation Research Grants - US National Science Foundation (NSF)

Press Release 13-102 World Oceans Month Brings Mixed News for Oysters

Press Release 13-108 nsf.gov - National Science Foundation (NSF) News - Natural Underwater Springs Show How Coral Reefs Respond to Ocean Acidification - US National Science Foundation (NSF)

Press Release 13-148 Ocean acidification: Making new discoveries through National Science Foundation research grants

Press Release 13-148 - Video nsf.gov - News - Video - NSF Ocean Sciences Division Director David Conover answers questions about ocean acidification. - US National Science Foundation (NSF)

Press Release 14-010 nsf.gov - National Science Foundation (NSF) News - Palau's coral reefs surprisingly resistant to ocean acidification - US National Science Foundation (NSF)

Press Release 14-116 nsf.gov - National Science Foundation (NSF) News - Ocean Acidification: NSF awards $11.4 million in new grants to study effects on marine ecosystems - US National Science Foundation (NSF)

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.