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Protozoa in stream biofilms.

Protozoa are single-celled eukaryotes with animal-like traits of motility (ability to move) and phagotrophy (feeding on living or dead organic matter). They can be divided into four main types based on appearance: amoebae, ciliates, flagellates, and apicomplexans. Apicomplexans live inside the cells of other animals, causing diseases such as malaria and toxoplasmosis. Amoebae, ciliates and flagellates are found virtually everywhere that liquid water is present, including soils, lakes, rivers, the ocean, and stream biofilms, and are important components of aquatic ecosystems.

Protozoa are the most abundant and diverse group of phagotrophic organisms in the biosphere. About 40 000 species of protozoa have been described, and it is estimated that some 200 000 species may exist. They are major consumers of bacteria, and are an important food source for other protozoa and animals (such as rotifers, insects and fish larvae). They have important roles in carbon cycling and mineralisation of nutrients in microbial food webs, contribute to decomposition of leaf litter in streams, and graze upon biofilm material. The role and significance of protozoa in stream biofilms has been little studied, however, and is not well understood.

One of the objectives of the stream biofilm project is to investigate the trophic interactions between biofilms and protozoa, and assess the significance of biofilm-associated protozoa for stream health and restoration. This involves measuring diversity of protozoa in a variety of stream habitats, ranging from pristine bush streams to degraded urban streams, investigating the influence of protozoan grazing on biofilm composition, structure and function, and assessing the influence of biofilm composition and nutritional quality on protozoa abundance, diversity and feeding activity.

Biofilm-associated protozoa are collected by swabbing rocks with sponges, or using a special brush-syringe sampling device. Protozoan communities differ in streams in different states of degradation. In Cascade Stream biofilms, the most commonly found protozoa are small bacterivorous and detritus-feeding ciliates, and amoebae. Stoney Creek and Opanuku Stream biofilms have the most species-rich protozoan communities, with many small and large crawling ciliates, algae and diatom consumers, attached suctoria, and flagellates. Pakuranga Stream biofilms are characterised by free-swimming and crawling ciliates, carnivores, and consumers of bacteria and detritus.

>> learn more about our investigation of protozoan diversity in stream biofilms

 

 

 

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Stream Biofilm Research Group
School of Biological Sciences
The University of Auckland
3a Symonds Street
Auckland, New Zealand
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streambiofilmgmail.com

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© Stream Biofilm Project, The University of Auckland 2008-2010
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