• Kim Bernard

Growing Antarctic Diatoms – A blog I wish had existed a few months ago

Updated: Apr 11

I’m not well-known for my “green thumb”… In my teens I was given a love palm, I think by a boyfriend at the time, how sweet. I killed it. In my twenties a guy I was dating gave me a cactus (not sure what message he was trying to give me). No one kills a cactus though, so should be a safe bet. I killed it. Last year I over watered my rosemary and under watered my begonias… Thankfully my partner in crime is actually good at keeping green things alive, so he resurrected them for me.


When I wrote my proposal to look at the effect of diet on the overwinter health and condition of juvenile Antarctic krill, I mentioned that I would feed the krill in half of my treatments a diatom culture. I left it at that. When I got funded and the enormous excitement that followed finally settled, I realized that I had to get over my inability to grow green things, and fast. I reached out to my friend and colleague, Dr. Jodi Young of the University of Washington, asking for some advice. As luck would have it, she had also just been funded to do research in Antarctica and was sending a team down to Palmer Station the summer before my winter field season. They would collect diatoms in the peak of their growth season (spring) and keep a culture growing for me at Palmer until I arrived in the early autumn.


The diatom culture started by Jodi’s team, Hannah Dawson and Susan Rundell, was then taken care of by students working in the Palmer Antarctica Long-Term Ecological Research program, Jack Conroy and Schuyler Nardeli when Hannah and Susan left. It was loving passed from one group to the next until I arrived at Palmer in April this year and it was handed over to me. [Thanks so much Hannah, Susan, Jack and Schuyler!] Out of the blindingly bright light emitted from the incubator as our Lab Manager, Hannah James, opened the door I was greeted by four 10-L carboys of greenish-brownish gunk. I starred at them and said a silent prayer. Then I quickly closed the incubator door. There were two things I knew I had to do this winter – keep the krill alive and keep their food alive. I hoped I was up for the challenge.

The bright lights of the incubator where we keep our diatom cultures. In this photo you will see two of the 8-L carboys that were recently started, so not very green and gunky. The two smaller bottles have more diatoms in them and are our back-up stocks for just-in-case. Photo credit: Kim Bernard.

In the first week after we arrived at Palmer Station, there were some problems with power and the incubator did not come back on after brief power outage. Because it sits inside our wonderfully warm laboratories the temperature inside the incubator rapidly climbed from 0˚C to 16˚C. I almost cried. Convinced they were dead or dying, I tried to come up with other solutions to feed the krill. In a last-ditch attempt, I took 1 L of the sad culture and gently placed it into a glass 1-L bottle. I fed it some nutrients (more on that below), put it back into the incubator at 0˚C and held my breath. After a few days of constant checking on the thing, I finally started to see signs of life. Had I, the killer of all green things, finally been able to grow something?! I had. Since that glorious day, I have kept that culture going and we have been able to feed the krill. Wooh!


So, how does one grow an Antarctic diatom culture? For our purposes, which are essentially to grow enough to feed the krill every 2-3 days, it’s actually pretty straightforward. I imagine that if I were growing these diatoms to research them it might be a little more complicated. In the interest of providing some guidance to anyone else out there who might find themselves in the same situation (daunted by the idea of growing microscopic plants, yet needing to do it none-the-less), below follows our protocol (or recipe)…

Ingredients:

  • 1 x healthy diatom culture (it helps to have it already started by a team of actual phytoplankton ecologists*)

  • 1 x f/2 media kit (I use the one from Bigelow Labs)

  • 10 % Hydrochloric acid (in deionized water, DI) – i.e. an acid bath

  • Clear polycarbonate carboys (I use these ones)

  • Glass beaker

  • Pipette and pipette tips

  • Incubator set at 4˚C (we’re using this warmer temperature to get the diatoms growing fast enough so that we can feed our krill regularly) full lights for a 12-hour on and 12-hour off light regime

Method:

  1. Check on your growing diatom culture every day.

  2. Gently invert the carboy to resuspend the diatoms that have sunk to the bottom – don’t worry, they are still alive.

  3. Open the lid to let a bit of new air in.

  4. When the diatom culture looks like it’s pretty dense, it’s time to sub-culture it.

  5. First you need to have prepared particle-free seawater (PFSW) by filtering regular seawater through a 0.2 µm inline polycap filter (I use this one).

  6. Fill an acid-washed (this is what the acid bath is for) and triple DI-rinsed 8-L clear polycarbonate carboy with 6 L of PFSW.

  7. Now the fun part. Add the f/2 media in the following concentrations: 1 mL/L nitrate 1 mL/L silicate 1 mL/L phosphorus 1 mL/L trace metals 0.5 mL/L vitamins (yes, even diatoms need vitamins)

  8. Gently mix the PFSW with the f/2 media and place the carboy into the incubator so that the contents can reach the same temperature as that in the culture carboy (you don’t want to shock the diatoms when they get added – although apparently they are okay going up to 16˚C, but I would recommend this).

  9. After a few hours, retrieve the carboy of PFSW and f/2 media and the carboy with the diatom culture from the incubator.

  10. Gently mix the carboy with the diatom culture to resuspend those sinking diatoms.

  11. Carefully pour 2 L of the culture into the new carboy with PFSW + f/2 media. I do this in batches of 500 mL using an acid-washed glass beaker.

  12. It’s important not to contaminate your new or old cultures, so be clean throughout the whole process.

  13. Put a label of the contents of your new carboy and the date and then put it back into the incubator and wait a few days.

  14. Yup, it’s as easy as that. If I can do it, you can do it.

* If you need help getting to this point, I know a great phytoplankton ecologist I could put you in touch with… Maybe I’ll try it myself when spring rolls around and the diatoms come back in full bloom, but for now I’m keeping these babies going.


Kirsten Steinke pipettes trace metals to add to the new cultures (in the three 8-L carboys on the left) while Julia Fontana watches. Photo credit: Kim Bernard.