Abstract:
Three experiments were performed at Davis Station, East Antarctica 77 degrees 58' E, 68 degrees 35' S to determine the effects of ocean acidification on natural assemblages of Antarctica marine microbes (bacteria, viruses, phytoplankton and protozoa). Incubation tanks (minicosms) were filled on the 30/12/08, 20/01/09 and 09/02/09 with sea water that was filtered through 200 microns mesh to remove metazoan grazers. The pH of the contents of each tank was then adjusted by adding calculated amounts to CO2 saturated sea water to achieve and maintain CO2 concenrtations that encompassed atmospheric concenrtations from pre-industrial to post-2100. As 6 tanks were available the 3 x current CO2 treatment was duplicated to indicate the variance among replicate tanks. Instead, responses were analysed to determine trends among concentrations. The microbial communities were incubated for 10, 12 and 10 days, in experiments 1, 2 and 3 respectively. Chemical and biological parameters were measured every second day to determine concentrations of macronutrients, particulate and dissolved organic carbon, pigment composition, dissolved oxygen, concentrations of phytoplankton, protozoa, bacteria (and viruses) using flow cytometry, light and electron microscopy, lipids, rates of primary, bacterial production and microzooplankton grazing.
These data have been collected as part of ASAC project 40 (ASAC_40), and Terrestrial Nearshore Ecosystems project 8A.
The excel spreadsheet contains:
Separate sheets reporting the results from each of the 3 experiments run at Davis Station in the 2008/09 summer.
Abbreviations are as follows:
Nutrients: NO3 =nitrate, PO4 = Phosphate, Si = silicate
Primary production and respiration were determined from oxygen microelectrodes: net photosynthesis from oxygen increase during exposure to light and respiration determined from net decrease in oxygen in the absence of light.
Photosynthetic parameters were also measure using 14C bicarbonate as a trace for Carbon uptake, these being: maximum photosynthetic rate) Pmax, Photosynthetic efficiency (Alpha) and saturating light intensity (Ek).
Flow cytometry was used to count 7 microbial parameters: pico phytoplankton (Picos) nanophytoplankton in two regions (Nano R2 and Nano R3).
Cryptophytes, high DNA bacteria (HDNA_bact) and low DNA bacteria (LDNA_bact).
Microscope cell counts identified a range of taxa/groups that comprised greater than 1% of the total phytoplankton abundance: unidentified nanoplankton (UNAN), small pennate diatoms (Pennate less than 10 microns) and other taxa as specified.
Organic material measurements including: Particulate organic carbon (POC), Particulate organic nitrogen (PON) particulate carbon to nitrogen ratio (C:N), Dissolved organic carbon (DOC)
Intermittent measurements were also made of rates of herbivory and bacterivory and rates of phytoplankton and bacterial growth in 3 of the 6 tanks.
Photosynthetic pigments were measured and are given only for experiment 1 so far (other to come later): Beta-Beta carotene (BB carotene), Chlorophylls c1 (Chl c1), c2 (Chl c2), c3 Chl c3), a (Chl a), b (Chl b), Chlorophyllide a (Chlidea), diadinoxanthin (Ddx), Diatoxanthin (dtx), Chl a epimer (epi), Fucoxanthin (Fuc), 19'-hexanoyloxyfucoxathin (Hex), Methyl Chlorophyllide a (MeChlidea), Magnesium divinyl pheaoporphyrin monomethyl ester (MgDVP), Phaeophytin (Phaeo), Violaxanthin (viola) and total pigment concentration. CHEMTAX will also be performed using these pigments to study CO2-induced changes in phytoplankton community structure.
Purpose:
Antarctica is likely to be amongst the first regions of the earth to be affected by ocean acidification due to the high solubility of CO2 in cold water and the upwelling of high CO2 water off the Antarctic coast. Yet little is known regarding the effect of ocean acidification on Antarctic biota, especially marine microbes and particularly non-calcifying taxa. Virtually without exception, studies that have looked at such effects have done so by bubbling the samples with at the target CO2 concentration. Though easy and convenient as a means of adjusting sea water pCO2 it is a practice not recommended by the EPOCA guidlines for experiments studying the biological effects of ocean acidification experiments. This study aims to determine the responses of natural communities of Antaerctic marine microbes to changes in pH from the pre-industrial era (1800s) to concentrations predicted for the atmosphere by the end of this century 2100.
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