Fungal infections on phytoplankton —cryptic perturbation of phytoplankton growth, recycling and sedimentation—

• Applicant: Isabell Klawonn, Ph.D.
• Subject Area: Oceanography
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 427631835

Fungi are one of the most diverse but least studied microbial groups in marine waters. A fungal subgroup, shortly referred to as chytrids, occurs as parasites on phytoplankton, imposing a strong pressure on phytoplankton growth, bloom development and population dynamics. Parasitic chytrids have been reported for all major phytoplankton groups and seem to emerge preferentially in coastal regions with high phytoplankton biomass and productivity. Their impact on biogeochemical cycles and ecosystem functioning, however, is poorly known and not yet quantified. The herein proposed Emmy Noether Junior Research Group will elucidate the functional and quantitative role of parasitic fungi on phytoplankton productivity and element cycling in brackish and marine waters. Our objectives focus on parasitic fungi by (1) studying phytoplankton–chytrid interactions on a single-cell level, (2) exploring their integrative role in aquatic food webs and (3) revealing their impact on remineralisation and sedimentation processes. Our comprehensive approach will include experimental work on phytoplankton–fungi co-cultures as well as field-sampled plankton communities, spanning from single-cell up to mesoscale-scale flux measurements across the water column. Essentially, we will follow the fate of phytoplankton-derived carbon and nitrogen, while being transferred and recycled through pelagic food webs within the photic zone during chytrid infections, and eventually exported as sinking detritus to the seabed. The project outcome shall foster a holistic understanding, including underlying mechanisms and magnitudes, of the role of chytrids at the base of aquatic food webs and productivity. Given the potential significance of parasitic fungi in moderating aquatic productivity, sinking fluxes and also harmful algae blooms in the coastal ocean, the obtained data shall be linked to local and global element cycling, and implemented in future ecosystem management decisions.

• DFG Programme: Independent Junior Research Groups