Arctic zooplankton can adapt to a changing Arctic climate
Top image: Zooplankton sampling in Billefjorden in March 2013. Photo: Janne E. Søreide/UNIS.
Lauris Boissonnot studied the effects of an earlier sea ice retreat on the key Arctic zooplankter Calanus glacialis. Her master thesis reveals that the species is able to adapt to a changing climate.
29 August 2013
This herbivorous Calanoid copepod which is endemic to the Arctic can represent up to 90% of the zooplankton biomass in Arctic shelf seas and Svalbard fjords. C. glacialis is a relatively large copepod (~4 mm) and is a key component of the Arctic marine food web due to its high biomass and its unique ability to convert low-energy carbohydrates and proteins from algae into high-energy wax ester lipids.
This grazer feeds intensively on the primary production during the short, but productive Arctic summer. In winter, it migrates down to deeper waters, entering diapause, a state of highly reduced metabolism, to survive the long, dark and food-poor Arctic winter. If it is external cues, internal triggers or a combination that triggers start and end of the diapause, is not known.
Higher primary production
A warmer climate with less extensive ice cover will lead to higher total primary production in the Arctic, which has the potential to increase the overall secondary production. However, altered climate conditions will affect timing, quantity and quality of ice algal and phytoplankton food sources with extensive implications for grazers.
Depending on the grazers’ ability to adapt to these new conditions, the population could survive or be replaced by smaller and less energy-rich organisms in a warmer Arctic with negative consequences for the entire lipid-driven Arctic marine food web.
Lauris Boissonnot studied the effects of food and light on the development of C. glacialis during the winter-spring transition. Fieldwork was conducted monthly in Billefjorden from February to May. Parallel to the field investigations, a lab experiment was run in the cold room at UNIS.
In this experiment, Lauris investigated the development and growth (lipid accumulation) of C. glacialis under different food and light regimes. She exposed developmental stage 4 of C. glacialis (an important overwintering stage of C. glacialis) to four different treatments: (1) light and no algal food, (2) light and food, (3) darkness and no food and (4) darkness and food.
The lipid analyses were performed at the Alfred Wegner Institute for polar and marine research in Bremerhaven, Germany under the supervision of Dr. Martin Graeve.
External environmental factors important
Results showed that light and food are important external cues for triggering ”wake up” and growth of overwintering C. glacialis. From February to April, food was the most important factor. Fed copepods accumulated lipids and developed to the next development stage, stage 5, while those starved lost lipids and only a few individuals developed to stage 5.
In field (Billefjorden), the C. glacialis population was dominated by developmental stage 4 with very few stage 5 individuals present from February to end of April suggesting that these copepods were food limited and thus did not grow and develop to stage 5. Billefjorden was covered by sea ice from February to June this year and first in May algal food became plentiful here.
Lauris results suggest that C. glacialis reacts rather quickly to new environmental conditions. In a context of an earlier sea ice break-up and thus earlier spring bloom, it is therefore likely that C. glacialis is able to adjust its growth and life strategy to this new primary production regime. However, it remains to see whether less sea ice and a longer productive season may favour smaller and more temperate zooplankton that may outcompete the larger long-lived and more lipid-rich Arctic zooplankton such as C. glacialis.
Lauris defended her thesis successfully at the University Pierre et Marie Curie (UPMC) in Paris, France on 25 June 2013. Her supervisors were Janne E. Søreide, UNIS and Stéphane Gasparini, UPMC.