Integrating top-down control by parasitic protists and fungi into the ecological dynamics of freshwater phytoplankton blooms

Freshwater lakes provide us with many services such as a supply of freshwater for our homes and recreation. Within freshwater lakes, microalgae, photosynthesising single cells, increase in numbers throughout the spring and summer. Different species of algae "bloom" at different times of the year and are usually a normal part of the lake ecosystem. However, sometimes these blooms can become a nuisance, produce toxic chemicals (such as blue-green algae), or simply turn the water a green pea soup colour, shading out other plants. Blooms of algae may impact on all life within the lakes. With increasing nutrient inputs from sewage and agriculture, increasing temperature and extreme whether events, algal blooms are happening more frequently and with longer duration. What controls these blooms is largely attributed either bottom-up factors (availability of light, temperature, nutrients) or top-down factor (predation and grazing by zooplankton). One less known top-down control of algae is parasitism. Algae are parasitised by many different organisms. The most well-known are tiny single-celled species of fungi called Chytrids that infect cells of algae killing them. There are also diverse groups of other life such as different species of single celled protozoa that may control algae numbers through parasitism. Many parasites of algae within the UK are not well known and only described from microscope observations in the last century. This project will use cutting edge DNA sequencing technology combined with microscopy and flow cytometry to identify and count parasites of algae within the lakes of Lake district UK. It will look at samples across different seasons and from 20 different lakes. It also will track parasite abundance and diversity across the lifetime of an algal bloom. The project will look at the impact these parasites have on blooms of algae, showing how their numbers increase and decrease in relation to their algal hosts. This will enable us to increase our knowledge of top-down controls on blooms of algae, learning more about their ecology and will helpi us to better understand, predict and manage algae and the health of freshwater ecosystems.