The Secret Life of Parasitic Sea Ice Fungi

Afternoon sampling on the Barrow fast ice. Photo: Brandon Hassett Arctic sea ice is teeming with life, some of which is very much a mystery. Scientists know quite a bit about organisms like the glassy diatoms, chlorophyll-rich algae and whipping flagellates that call sea ice home. But little is known about another component of the icy microcosm: parasitic fungi.

University of Alaska Fairbanks (UAF) scientist Rolf Gradinger and his graduate student Brandon Hassett are embarking on a two-year project to uncover the secrets of parasitic sea ice fungi. As part of their project—The Diversity, Seasonality and Function of Parasitic Fungi in Arctic Sea Ice—Hassett and Gradinger recently traveled to Barrow Alaska to collect data that will shed light on the diversity of these fungi, their abundance, seasonal variations and roles in the ecosystem. The National Science Foundation supports this work.

Chytridiacious fungi parasitizing diatom cells.  Arrow: a mature fungal sporangium with cleaved endogenous zoospores attached at the terminal end of a diatom (May 2013). Photo: Brandon Hassett

This month, at the start of the data collection, Gradinger and Hassett chatted with Field Notes about what they hope to learn about the secret life of parasitic sea ice fungi.

Field Notes (FN): What roles do sea ice fungi play in the Arctic ecosystem?

Rolf Gradinger (RG): Sea ice plays a critical role in structuring life in Arctic marine systems. It’s a platform for seals, for birds, polar bears, and also for people.

But it’s also the platform for a lot of biologic activity within the ice during the periods of ice cover, specifically between the end of February and the period of ice melt. Within the ice exists a microcosm of microbes and algae that live in brine channels found in between individual ice crystals. One square meter of sea ice might be home to billions of algae and hundreds of thousands of small animals that feed on these algae. Fungi play a multitude of roles in aquatic systems. The ones we are interested in are those that are parasites on algae in the ice.

Brandon Hassett (BH): In the past 10 years, people have started to acknowledge the role of fungi in aquatic systems. Most of this works has been championed in freshwater systems. We’re finding that fungi are really important in breaking down recalcitrant substances and are also important parasites.

FN: You say little is known about sea ice fungi. What do you hope to learn with this two-year project?

BH: We really just want to find out who the players are—in other words, we want to assess the fungi diversity. We also want to know what they’re doing. We know they are parasitizing diatoms, but we want to know at what abundance and what rate they are actually consuming primary producers. And then we also want to know how they are parasitizing—how they penetrate through the diatom cell wall.

RG: For the freshwater environment, the paper by Grami et al. (2011) introduced a completely new term to focus on the role of fungi in aquatic systems. That’s called the “mycoloop”. What they realized was that most of the phytoplankton was actually parasitized by fungi rather than bacteria, as traditionally believed. These fungi are releasing spores that are consumed by the flagellates, ciliates and copepods and then incorporated into the food web.

So, we have two basic hypotheses, that: (A) these kind of parasitic fungi are very common within Arctic sea ice, and (B) that the mycoloop, as described in the freshwater environment, will also exist in the Arctic marine environment.

Brandon Hassett and bear guard Michael Donovan use an ice agar on the Barrow fast ice.  Multiple holes are drilled adjacently so a sediment grab can be deployed through the ice. Photo: Kyle Dilliplaine

FN: How will you collect samples and other data during your trip to Barrow, Alaska? BH: We want to assess these communities over time. So I’m traveling to Barrow from the middle of winter (January) to the ice melt period several times to take a baseline of what’s in the ice. We’ll take ice cores and will melt them down to make basic observations and take samples for detailed analysis including photography.

Our first question is what is in the ice?

An extracted ice core awaiting temperature measurements. Photo: Brandon Hassett

We’re taking two different approaches to answer that. The first is a very traditional microbiology approach where we’ll try to culture these organisms onto media and characterize their life history. Our other approach is a more modern metagenomic approach, where you extract and sequence all of the DNA from the water and ice sample. This lets you assess who is there without bias. and at what time, based on the sorting of sequence data.

Once we know who’s in the sea ice, the second step is to understand what parasites are doing. To do that, we plan to grow algae in a tank here at UAF, and maintain and record their growth over time. Then in a second tank we’ll introduce the parasitic fungi and compare the algae’s biomass over time, if it decreases over time or not.

Often times, there’s a very small window of ambient environmental conditions that favors the development of parasitism. So the temperature, salinity and all these conditions in the tank should be very close to those physical conditions in Barrow to theoretically induce parasitism. We have good facilities here at UAF. We have a cold room and the materials where we can replicate the temperature, as well as light conditions similar to ice conditions. When we go to Barrow we’ll be recording all of that data so we can replicate them here in the lab.

FN: What does this study contribute to the Arctic research community? 

RG: In some ways this project is true scientific exploration. Brandon will go up to Barrow and whatever he finds will likely be new to science because they [fungi] are not described. So it’s a very exciting project. I’m extremely curious to see what we learn in this study because if it turns out that all of our ideas, hypotheses and objectives are right on, it will really have an impact on the way we look at Arctic sea ice from the biological perspective and will stimulate new research.

For more information on Gradinger and Hassett’s research in to Arctic sea ice fungi, visit: –Alicia Clarke