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Tolerance of a Key Arctic Krill Species to Ocean Acidification

Paper Reviewed
Venello, T.A., Calosi, P., Turner, L.M. and Findlay, H.S. 2018. Overwintering individuals of the Arctic krill Thysanoessa inermis appear tolerant to short-term exposure to low pH conditions. Polar Biology 41: 341-352.

Thysanoessa inermis, one of the most abundant krill species inhabiting the northern waters of the Atlantic Ocean, play an important role in the Arctic food web by transferring energy from phytoplankton to higher trophic-level species. However, in the words of Venello et al. "little is known of the chemical habitat occupied by Arctic invertebrate species, and of their responses to changes in seawater pH" associated with so-called ocean acidification. Consequently, Venello et al. say "understanding krill responses to ocean acidification is essential for predicting the future of Arctic ecosystems." And thus they set out to conduct an experiment to gain knowledge in this regard.

In doing so, they collected adult T. inermis specimens from Kongsfjord, located on the west coast of Spitsbergen, Svalbard, Norway, during the spring month of April. This particular krill species overwinters in Kongsfjord, and according to the authors may therefore be "particularly sensitive to environmental changes, as low food availability [during overwintering] may increase their sensitivity to [ocean acidification] stress."

Once collected, the krill were transported to a laboratory where they were acclimated and then exposed to four seawater pH treatments for a period of seven days: ambient (pH 7.96) or reduced (pH of 7.70, 7.65 or 7.28). Measurements pertaining to organism standard metabolic rate (measured as oxygen consumption) and energy metabolism markers (adenosine triphosphate and L-lactate) were conducted at the end of the experimental period to estimate krill tolerance under the three levels of reduced seawater pH.

In discussing their findings, Venello et al. report "we found no significant physiological impacts of ocean acidification on overwintering individuals of T. inermis from the Arctic fjord of Kongsfjord." More specifically, they write "low pH does not significantly affect T. inermis' physiology when considering individuals' metabolic rates and metabolite concentrations." In other words, they found that the krill were able to "maintain aerobic metabolism and that energy metabolism was not compromised at different pH levels, i.e., maintenance of metabolic rates came at no apparent energetic cost as there was no observable differences in adenosine triphosphate concentration or evidence supporting an increase in anaerobic metabolism."

Commenting on the significance of their work, the four researchers say their results "suggest that overwintering individuals of T. inermis may possess sufficient ability to tolerate short-term low pH conditions due to their migratory behavior, which exposes T. inermis to the naturally varying carbonate chemistry observed within Kongsfjord, potentially allowing T. inermis to tolerate future ocean acidification scenarios." Thus, it would appear that this important krill species will have no problem maintaining its key ecosystem role under any of the ocean acidification scenarios projected for this region of the ocean in the future.

Posted 20 July 2020