Ocean Acidification: Impact of ocean acidification on survival of early life stages of planktonic copepods in the genus Calanus in the northern oceans

As the CO2 content of the atmosphere rises, part of this CO2 will dissolve into the ocean. Since CO2 is a weak acid, it will lower the ocean waters pH. Currently, most of the oceans surface waters have pH values between 7.8 and 8.1, but this could be reduced by 0.4 pH units by the end of this century. The impacts of this pH shift on marine life currently is uncertain. Although most efforts have been directed toward studying the impacts on calcifying organisms, non-calcifying plankton may also be affected. The copepod, Calanus finmarchicus, dominates the biomass of small zooplankton across the coastal and deep North Atlantic Ocean. Previous work showed that the ability of C. finmarchicus eggs to hatch became severely limited when exposed to significantly acidic seawaters. In the Gulf of Maine, C. finmarchicus is at the southern-most extent of its geographic range and hypothesized future warming of the Gulf coupled with decline of the waters’ pH values could make survival of this species in the Gulf of Maine difficult. Here, we obtained this research funding to examine, both in the laboratory and in the field, whether pH shifts would have a significant impact on the life cycle of this copepod.

The research team directly involved in sampling and analysis included:

Dr. Jeffrey Runge, University of Maine and Gulf of Maine Research Institute, zooplankton oceanographer; project leader .

Dr. John P. Christensen, Green Eyes LLC, chemical oceanographer; project co-author .

Mr. Brian Preziosi, graduate student at University of Maine at Orono

Ms. Phoebe Jekielek, graduate student at University of Maine at Orono,

Ms. Rebecca Jones, University of Maine at Orono and Gulf of Maine Research Institute.

Mr. Vincent Kelly, Green Eyes LLC

The methods for the research involved catching or raising Calanus finmarchicus from sites near the Darling Marine Center of the University of Maine, as described in the thesis, Preziosi, 2012. From these collections of zooplankton, adult females of C. finmarchicus were separated and allowed to feed on cultured phytoplankton while they released their eggs, which were separated from the females and collected (see photo below). When sufficient numbers of eggs were available, the eggs were subdivided into several batches and each batch placed in egg hatching dishes and immersed in a 20 L hatching tank of natural seawater (collected near the Darling Marine Center) for up to 6 days at a constant temperature. Each tank was equipped with a tightly sealing top, an air input line ending in a fritted-glass bubbling stone to allow a preselected gas mixture to be bubbled into the seawater tank, a siphon for sampling the waters without opening the tank, a 1 inch diameter sampling hole to allow electrodes to be inserted for occasional monitoring of conditions within the tank, and a gas vent port (see photo below). When electrodes were not used, the sampling hole was sealed using a stopper. The pH of each tank was altered from the seawater’s ambient condition by bubbling with a commercially purchased gas mixture of a preselected CO2 concentration (ranging from 350 to 15000 ppm), 20% molecular oxygen, and the remainder N2. The CO2 concentration for each cylinder of premixed gas was calculated in advance of purchase to achieve a particular pH (ranging from 8.0 to 6.9) given estimates of the salinity, alkalinity, and nutrient content of the seawaters likely to be collected for each experiment. This calculation was done with the carbonate system model of seawater using programs such as CO2SYS (Lewis and Wallace, 1995). During the incubation, seawater within the tank was sampled for salinity, alkalinity, total carbon dioxide concentration, and nutrient concentrations (nitrate + nitrite, inorganic phosphate, dissolved silicate, and ammonium concentrations). After the eggs had been incubated for a period of time sufficient for full hatching, the egg hatching dishes were removed and the proportion of eggs which had hatched were determined by microscopic counting. The pH was assessed by the carbonate system model based on the measurements of salinity, alkalinity, total carbon dioxide, and nutrient concentrations (Christensen 2012).

On this web page, the viewer can download the chemical methods used by J. P. Christensen for these experiments, as well as the chemical results for hatching experiments 1-5 and 6 -8. Additional experiments will be posted as these are finalized.

In addition, this research grant also determined what the natural pH distribution was in the Gulf of Maine in relation to the vertical and horizontal distribution of Calanus species. The oceanographic cruise was conducted on the R.V. Cape Hatteras in September of 2012. Sampling occurred generally along 3 transect lines. One was perpendicular to the coast off of New Hampshire and passed through the 300 m deep Wilkinson Basin. One was perpendicular to the coast off of Mount Desert Island and passed through the 280 m deep Jordan Basin. One paralleled the coast at about the 100-150 m depth contour. Results from this cruise will be added to this web page as they are finalized.

REFERENCES:

J. P. Christensen 2012. Carbonate System Sampling in Zooplankton Hatching Experiments as part of Ocean Acidification impacts on Zooplankton in Northern Oceans. Technical Report #12-003, Green Eyes LLC, Easton MD, 16 pp. (file OAZTCH3B.PDF on this page)

E. R. Lewis, D. W. R. Wallace 1995. Basic program for the CO2 system in seawater. BNML-61827. Brookhaven National Laboratory, Upton N. Y., 11973.

B. M. Preziosi 2012. The Effects of Ocean Acidification and Climate Change on the Reproductive Processes of the Marine Copepod, Calanus finmarchicus. U. Maine at Orono, Orono Maine, 42 pp.

Green Eyes LLC. More information and technical reports.


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