Functional diversity of heterotrophic flagellates in aquatic ecosystems
ABSTRACT There is a lack of taxonomic resolution due to methodological problems in most ecological reports despite the significant contribution of heterotrophic flagellates (HF) to the carbon cycle of most aquatic ecosystems. The determination of HF species on a quantitative level is difficult, especially for most athecate and aloricate taxa. The dominant taxonomic groups among heterotrophic nano-and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomastigids, apusomonads) seems to be surprisingly similar. HF among Protista incertae sedis, often neglected in ecological studies, were abundant in all investigated habitats. The taxonomic variety of HF reflects the large diversity of functions of HF such as predominant bacterivory, herbivory, carnivory, detritivory and omnivory, respectively. Typical benthic HF can contribute significantly to pelagic HF communities especially in limnetic and marine coastal waters. High tolerances to changes in salinity give rise to the assumption that several species are able to live in both marine and freshwater habitats. The functional diversity of HF is discussed with respect to the feeding ecology, life strategies, tolerances to extreme abiotic and biotic conditions and distribution patterns. Considering the strong predation pressure by metazoans and protists on HF communities, many morphological and behavioural features of HF may be explained as predator avoidance mechanisms.