Preparations for Experimentation!
Updated: Apr 11, 2020
It’s hard to believe it’s already the first week of July. That means we’ve been at Palmer Station for almost three months now with our krill! We collected our krill on our way to Palmer Station and upon arrival, placed them in four different diet treatment tanks where they would undergo a long-term feeding experiment. The premise of our project is to understand if the overwintering diet of juvenile krill affects their physiology over the course of the winter. Every five weeks we conduct a series of experiments on subsamples of krill from our treatment tanks to see how exposure to varying diets is affecting their physiological development. These experiments each last for about a week and they are our “time point experiments.”
Next week we run our “time point 2” tests, and there is a lot of work that we have to do this week to ensure we are properly prepared for the intensive week of experimentation. In this blog I will outline what a week in the life of three Antarctic krill scientists looks like getting ready for one of these time points.
1. Particle free seawater, particle free seawater and more particle free seawater! About half of our experiments require the use of particle free seawater. What is particle free (PF) seawater? Well, PF seawater is just seawater that has been filtered through a 0.2 micron filter. This prevents any particles such as bacteria, phytoplankton or detritus from screwing with our experiments. PF seawater is also necessary for the preparation of our diatom cultures that we feed our krill!
2. Foily preparing our GF/F filters.“GF” stands for glass fiber and the second “F” indicates the filter pore size, which is 0.7 µm. We use these bad boys to collect the organic matter found in our experiments. What kind of organic matter do we care about? Poop and food! We weigh the krills’ fecal pellets (poop) as well water samples from their respective food treatments on pre-ashed and pre-weighed GF/F filters. Pre-ashing and pre-weighing these filters is important to ensure we get the correct weights of our samples. Pre-ashing involves putting the filters into a muffle furnace at 450˚C (842˚F!) for two hours and then making sure they have sufficient time to cool before taking them out to weigh them. The last step is very important so that we don’t have to spend the rest of the season here at Palmer Station with singed eyebrows. After weighing the filters, we wrap each individual filter in a piece of aluminum foil and label it with a unique filter ID number. We use at least 50 filters for each time point, which means we spend a lot of hours cutting tin foil and wrapping filters…..the things we do for science!
3. Acid washing our phytoplankton culture carboys. Carboys are large containers that we use to grow our phytoplankton. We want our cultures to grow at their max potential and be comprised of primarily diatoms, so we must ensure that the containers we grow them in are sparkling clean and uncontaminated. To achieve this goal, we wash each carboy with a diluted hydrochloric acid solution and then rinse them three times with ultrapure water. We let these carboys air dry before adding PF seawater, vitamins and minerals, and a subculture of diatoms.
4.Labeling EVERYTHING. When conducting experiments, it is important that all of the instruments and containers we are using are properly labeled. In order to make sure our experiments run as smoothly as possible, we must label everything from the scintillation vials we keep our fecal pellet samples in to the 15 mL Falcon tubes that we store krill in for later dissections. One day while labeling scintillation vials Julia asked me, “how many times in your life have you written out all of the numbers from 500-600? It feels weird to me…I don’t think I have done it very often!” Although it’s a lot of labeling, it feels good knowing we are going to be well prepared and organized for next week.
5. Finally, we must set up all of our experiment stations. Each time point consists of egestion (pooping rate), ingestion (feeding rate), respiration, fatty acid absorption and reproductive development experiments. There are a lot of tools we must get ready and work areas we must prepare for these experiments. Our egestion, ingestion and fatty acid absorption experiments all require five-gallon buckets that we use for our experimental replicates, which means they must be rinsed with PF seawater and set aside for future use. The krill used for the respiration experiments are placed into individual bottles and the oxygen concentration of the water is measured over a 48-hour period using a special oxygen sensor that is attached to the bottle. The software to run this program must be calibrated with the water in the bottles prior to experimentation. Lastly, for our reproductive development experiments we are preserving krill in a formaldehyde solution so they can later be sexed and staged. Prior to preservation, 15 mL Falcon tubes must be set aside and prepared for our wonderful krill that sacrificed their lives for science.
It’s a lot of hard work preparing for each one of our time point experiments, but it is also very rewarding. We are trying to accomplish a lot down here at Palmer Station, and even though there have been a couple of experimental hurdles we have had to troubleshoot, we have already seen some pretty cool results! I’m very curious to see how things change as the season progresses.