Effects of ocean acidification (pHtotal~7.8) on calcification, photosynthesis, carbon and nitrogen contents and carbon isotopic signatures on Halimeda opuntia grown at tropical carbon dioxide seeps (NERP TE 5.2, AIMS)

Brief description

This dataset consists of one csv data file from field derived experiments at tropical carbon dioxide seeps in Papua New Guinea, measuring the response parameters: calcification, photosynthesis, carbon and nitrogen contents and carbon isotopic signatures on Halimeda opuntia grown under ocean acidification conditions.

The aim of this study was to investigate the effects of ocean acidification on Halimeda opuntia grown under ocean acidification conditions at tropical carbon dioxide seeps. Therefore we tested several response parameters to try to understand how the calcareous alga is capable of growing under ocean acidification conditions.


Method:

At several locations in Milne Bay Province, Papua New Guinea, volcanic CO2 is seeping out of the seafloor (Fabricius et al. 2011). The seep sites are located at Dobu Island and Upa-Upasina (Normanby Island) close to the shore in shallow water of ~1–15 m depth and extend over an area of ~20 by 100 m with different intensities of bubble activity within this area. Control reefs were allocated several hundred meters away from the seep sites with no impact of the seep activity on their seawater carbonate system. The bubbles, which consist of pure CO2, ascend to the surface and mix with the ambient seawater, changing the carbonate chemistry. This study was confined to areas where seawater chemistry was altered to levels projected for a vast part of the globe for the end of this century (‘representative concentration pathway’ RCP6.0 to RCP8.5 scenarios) (Moss et al. 2010).

Calcification rates in the light and dark, as well as net photosynthesis and respiration rates, were measured in-situ at control (pHtotal = 8.17) and seep sites (pHtotal = 7.77). Branches 5 – 8 cm in height and with ~20 phylloids of H. opuntia were collected and retained at the site of collection until incubations commenced. Light incubations were conducted in-situ at 5 m water depth at midday. Specimens were placed into 0.5 L clear Perspex chambers, simultaneously at control and seep sites, by two separate SCUBA diving teams. After ~3 h incubation under ambient light, incubation chambers were retrieved and a water subsample was directly analyzed for total alklinity. Oxygen concentration was determined in each incubation chamber including two blank incubations per treatment (to correct for seawater production/ respiration) with a hand-held dissolved oxygen meter (HQ30d, Hach, USA). Light intensities of incubation conditions were recorded by two light loggers (Odyssey, New Zealand) each at control and seep site. Photosynthetically available radiations (PAR) was dependent on weather conditions and averaged 259 and 281 µmol photons m-2 s-1 for H. opuntia incubations. Dark incubations were conducted on board the research vessel for ~3 h in the evening. The incubation chambers were filled with water from the site of origin of the plants (control vs. seep site). Chambers were placed in black plastic bins (45 L) with lids for darkening and flow-through seawater for temperature control. Rates of calcification were determined with the alkalinity anomaly technique (Chisholm and Gattuso 1991). Calcification rates (in µmol L-1 C h-1 gFW-1) and oxygen fluxes (in µg O2 h-1 gFW-1) were calculated in relation to blank incubations and standardized to the fresh weight (FW) of the plants. Daily net calcification rates were calculated by 12h of daylight and 12h of darkness.

Apical phylloids of dried Halimeda spp. were crushed with mortar and pestle and the homogenate was analyzed for total carbon (Ctot) and total nitrogen (N) on a Flash EA 1112 elemental analyzer (Thermo Fisher Scientific, USA). In addition, organic carbon (Corg) contents were measured after acidifying the sample with 150µL concentrated HCl to drive out Cinorg. Inorganic carbon content was calculated by subtracting Corg from Ctot. Stable isotope signatures were measured in a subset of these samples using a Delta S mass spectrometer (Thermo Fisher Scientific, USA) coupled with the elemental analyzer.

Further details can be found in the publication:

Vogel, N., Fabricius, K. E., Strahl, J., Noonan, S. H. C., Wild, C. and Uthicke, S. (2015), Calcareous green alga Halimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps. Limnology and Oceanography, 60: 263–275. doi: 10.1002/lno.10021


Format:

This dataset comprises a single csv file, Vogel_acid_opuntia.csv.


Data Dictionary:

The columns of the Vogel_acid_opuntia.csv are described below:
- Species: Halimeda opuntia
- Treatment: Site of collection/ measurement, seep site or control reef
- Light calcification: calcification in light, given in µmol L-1 C h-1 gFW-1
- Dark calcification: calcification in darkness, given in µmol L-1 C h-1 gFW-1
- Net calcification: 12xlight+12xdark calcification, given in µmol L-1 C d-1 gFW-1
- Net photosynthesis: oxygen production in light, given in µmol L-1 O2 h-1 gFW-1
- Dark respiration: oxygen respiration in darkness, given in µmol L-1 O2 h-1 gFW-1
- Gross photosynthesis: oxygen production – dark respiration, given in µmol L-1 O2 h-1 gFW-1
- Ctot: total carbon content, given in molar %
- Corg: organic carbon content, given in molar %
- Cinorg: inorganic carbon content (Ctot-Corg), given in molar %
- N: total nitrogen content, given in molar %


References:

Chisholm JRM, Gattuso JP (1991) Validation of the alkalinity anomaly technique for investigating calcification and photosynthesis in coral-reef communities. Limnol Oceanogr 36:1232-1239

Fabricius KE, Langdon C, Uthicke S, Humphrey C, Noonan S, De'ath G, Okazaki R, Muehllehner N, Glas MS, Lough JM (2011) Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change 1:165 - 169

Moss RH, Edmonds JA, Hibbard KA, Manning MR, Rose SK, van Vuuren DP, Carter TR, Emori S, Kainuma M, Kram T (2010) The next generation of scenarios for climate change research and assessment. Nature 463:747-756

Notes

K.E. Fabricius, J. Strahl, S.H.C. Noonan, C. Wild, S. Uthicke