Ecological role of fungal parasites on benthic diatoms of polar coastal waters

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Parasitism was recently identified as an ecologically immensely successful, and probably the most abundant mode of biotic interactions and nutrition in the world ocean’s pelagic zone, while the Polar Regions and benthic habitats remain largely unstudied. Chytrids are zoosporic true (basal) fungi that play an ecological key role as lethal parasites in the aquatic food web such as controlling phytoplankton blooms, and serving as trophic link between inedible phytoplankton and zooplankton via the so-called “mycoloop”. Benthic diatoms dominate - as so called microphytobenthic communities - marine soft bottom shallow waters as i) high primary producers, ii) control barrier for oxygen and nutrient fluxes at the sediment/water interface, and iii) stabilizer of sediment surfaces against hydrodynamic erosion. However, whether and to what degree parasitic chytrids affect marine benthic diatoms in Polar Regions, yet, have to be studied, as well as the presence of the mycoloop in marine environments. Therefore, the main questions of the present proposal are: How relevant are parasitic interactions in polar benthic diatoms, and does global warming has the potential to change these interactions? This fundamental gap of knowledge will be closed with a focus on the following goals to be studied for the first time: (i) to survey benthic diatoms in Potter Cove (Antarctica) and Kongsfjorden (Arctic) for the presence and diversity of parasitic chytrids using a variety of microscopic and molecular tools such as single cell and Illumina Amplicon sequencing. (ii) To evaluate the unknown infection rate by specific chytrids using a combination of field identification, culture and culture-independent methods to address the relative infection rate and identity of these parasites as well as their hosts via molecular detection tools (including FISH and RT qPCR). These data are essential for understanding and linking functional mechanisms to key biotic interactions. (iii) To evaluate climatic change conditions (warming) as potential driver for stimulation or inhibition of parasitism in Polar benthic diatoms with consequences for microphytobenthic structure and function; (iv) To establish parasite-host systems by which biotic interactions (e.g., host recognition, biochemical/molecular parasite-host interactions) can be studied under controlled and manipulated environmental conditions; We hypothesize that chytrids play an ecologically important, but so far largely overlooked role in biotic interactions with diatoms at the base of benthic food webs, in particular of the Polar Regions.