Microbial diversity and diatom ingestion by ciliated protozoa in a river in
Dorset, UK
Summary
Ciliated protozoa are key grazers of many autotrophic microbes, including cyanobacteria and
diatoms. Due to quick turnover rates of ciliate populations, they are also able to rapidly occupy
existing ecological niches and open up new niches, which are made readily available for rare and
encysted species of ciliate (cryptic species) but also for other species such as microscopic
invertebrates.
This study will investigate the diversity of free living ciliated protozoa in a lowland chalk river in
Dorset, UK, and will consider the impact of seasonal temperature change and water velocity on
ciliated protozoa feeding on diatoms on the riverbed. In addition, niche partitioning in relation
to cell size of ciliates ingesting diatom cells will be considered, highlighting the importance of
this for multiple species of ciliate to successfully coexist in a small habitat.
Background Research
Microbial diversity plays an integral part in maintaining ecological function of freshwater
ecosystems (Finlay et al. 1997, Finlay and Esteban 1998). Ciliated protozoa are able to not only
occupy a variety of previously established ecological niches, but also to continuously open up
new niches by influencing the chemistry and nutrient cycles of their environment (Finlay and
Esteban 1998). In this sense, they are essentially changing the conditions of the environment in
which they live, allowing other species to also thrive in the habitat. This provides a continuous
turnout of species in the environment, all occupying a specific niche in the ecosystem.
Ciliated protozoa are key grazers in aquatic ecosystems, feeding on a range of microbial prey
including heterotrophic bacteria, cyanobacteria and diatoms. As a result, ciliated protozoa are
important in nutrient transfer between the microbial loop and macroscopic food webs (Azam et
al. 1983, Fenchel 2008), as they themselves are fed upon by microscopic metazoa such as
copepods and cladocerans (Schmid-Araya et al. 2016).
Ciliate communities are usually able to thrive with many species sharing the same habitat,
however this poses the question of how so many species are able to coexist without competing
for food sources. To mitigate competition between species in a feeding patch, many ciliate
communities exhibit niche partitioning, with very little overlap in food preference between
ciliate species (Epstein et al. 1992, Finlay et al. 1993).
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