From parasites to saprotrophs the important role of Chytrids and other fungi members on the Arctic ecosystem

Climate change has been shown to be reducing sea ice coverage in the Arctic this reduction of ice coverage is increasing light penetration into the Arctic Ocean and is predicted to increase primary production of phytoplankton, however this increase in light can also lead to photoinhibition and cause stress to phytoplankton, this increase stress in organism can increase the susceptibility to disease. In addition to this changes in sea ice cover allowing higher light penetration resulting in changes to environmental conditions this combined with availability of nutrients affects the seasonal composition of marine fungi.  A study by Hassett and Gradinger (2016) wanted to look at the role parasitic fungi belonging to chytridiomycota may have on phytoplankton as a response to this changing light penetration and how the community structure may shift with season and the impacts this may have to the food web.

Method

•   In order to access the impact of reduce snow coverage five areas each 5m²  were cleared of snow.
•     Samples form the experimental sites and controlled sites were collected every other day using ice cores and the photosynthetic yield was accessed.
•  To assess the abundance and diversity of the fungi community cell counts and DNA sampling were also performed.

Findings

Based on a 3 year study the authors found that the life history and abundance of Arctic marine fungi are closely link to seasonal difference in light penetration, which may trigger phytoplankton blooms but may also lead to stress in the phytoplankton. The study was the first to detail the important functional role fungi play in the Arctic marine environment and showed how the fungi community structure changed with season. The study found seasonality and host specificity of the parasitic chytirds on diatoms with parasitism occurring in April near the height of the algae bloom, Along with cell counts the authors also sequenced DNA barcodes to assess the seasonal diversity and abundance of fungi, The results showed that members of the Chytridiomycoata seasonally dominated sea ice and sediment fungal communities however distinct communities were present with different seasons.

The fungal community structure was driven by availability of nutrition and environmental conditions which resulted in major community shifts. During January and June the sea ice community was dominated by members of the group Dikarya. Dikaryotic fungi belonging to Aureobasidium and Cladosporium are halotolerant which explains how they tolerate the hyersaline condition during the period when diatom host concentrations were low. Another group included the saprotrophic Zygomycota it appears they are especially important in June when they are high in abundance allowing them to redirect carbon away from higher tropic levels and into the microbial loop highlighting the importance if fungi in marine nutrient cycling.

I think the findings of this paper are important in showing us the role parasitic fungi and other fungi groups play in the Arctic environment and their impact on the food web. The paper demonstrates for the first time the seasonality and functionality of parasitic chytrid fungi, and is very relevant in helping us understand the impact that reduce ice coverage may have in the Arctic ecosystem and how it might lead to a restructuring of the food web. I think it provides a good case for the impacts of parasitism to be incorporated into models of the marine environment which may be especially important on local scales such as the Arctic Ocean.

Hassett, B. and Gradinger, R. (2016). Chytrids dominate arctic marine fungal communities. Environmental Microbiology, 18(6), pp.2001-2009.