Week 5 & 6: It's all coming together

There has been a noticeable increase in phytoplankton abundance at 15 m depth, not only from flow cytometry counts but also in the volume used for filtering to get enough biomass for phytoplankton pigment analysis. Via the analysis of the pigment composition of the biomass from these filters back at the NIOZ, we will be able to determine which groups of phytoplankton and how much they are currently dominating the waters here.

In terms of the flow of organic carbon and energy up through the food chain in Antarctic waters, zooplankton are an important link between primary producers (e.g. phytoplankton) and higher level consumers (e.g. fish). One of the goals of our research is to study how zooplankton grazers respond to phytoplankton populations and how this feeds into their overwintering behaviour.

Dorsal (left) and lateral (right) view of a female C. acutus individual.

During the winter there is less primary production by phytoplankton in the surface waters (as there is hardly to no light) and so less phytoplankton for zooplankton to eat. As a consequence many copepod species (a small crustacean) migrate vertically to deeper waters where there is less predation pressure. At these depths they rely only on their lipid reserves built up over the summer to carry them through the winter and at the start of summer they will return to the surface waters to feed and breed. Our copepod of choice is a lipid rich, large sized copepod (body size 3-3.5 mm long) called Calanoides acutus that is abundant in the waters of the Western Antarctic Peninsula. By following the lipid composition of phytoplankton and C. acutus, we hope to gain a better understanding of how and when this copepod species builds up its lipid reserves. The total amount and quality of lipid reserves also influences the depth at which copepods overwinter. At a certain depth and temperature, their lipids change from a liquid to a solid phase which makes the copepod neutrally buoyant so that it does not need to consume energy by swimming to stay at this depth. The more and better quality the lipids are, the deeper they can overwinter.

To study this we use a 500 um mesh size net with which we take two depth profiles, one from 500 – 200 m and another from 200 m to the surface. By doing this we hope to separate last season’s overwintering population from the next generation.

It has not all been work however. One Saturday afternoon we took a break to explore a nearby crevasse. After squeezing through a tiny hole in the snow we found ourselves 10 meters below the surface where the natural light from above us lit up the most amazing and beautiful ice formations.

Our friendly base elephant seals seem to have found a nice comfortable spot in the middle of the road as one has been there for 4 days now only to move 90 degrees. It must be a good spot because after a few days three more elephant seals joined in and haven’t moved since, only to have a good scratch.

Today, Sunday, whilst we were writing this blog there was the first sighting of Killer Whales in the bay. We saw them up on the hill (Rothera point) from a distance swimming around the ice bergs. I hope we get a chance to see them a bit closer, but not too close…

After being here for just over a month we are getting into a routine more in line with our original research plan. Preparations have started in readiness to receive the fourth lab container (Hoop) on board the JCR (James Clarke Ross) next week, as well as the next instalment of a few of our Dutch colleagues.