The sizes, maturity stages and biomass of mayfly assemblages colonizing disturbed stream bed patches in central Kenya
2002
Mathooko, Jude Mutuku
The sizes, maturity stages and biomass of mayfly species colonizing disturbed patches on the stream bed surface of the Naro Moru River, Kenya, were determined from June 1993 to January 1994. All maturity stages I–VI⁺ were present in the pre‐disturbance mayfly assemblages. Colonization of the disturbed patches by mayflies of different maturity stages was continuous, but slow or fast depending on the season and species. The overall post‐disturbance maturity structure of the mayflies colonizing the disturbed patches did not demonstrate any distinct pattern. The majority of Caenis nymphs colonizing the patches in wet season II (November–January) were in emerging maturity stage VI⁺, whilst the majority of the individuals of Afronurus and Choroterpes (Euthraulus) populations matured from stage I in the wet seasons to stage VI⁺ in the dry season. Furthermore, the majority of the individuals of Baetis (Nigrobaetis) sp.1 were maturing to stages IV–VI during the wet seasons. Small‐sized mayfly individuals (body length <3.0 mm) of all mayflies colonized the disturbed patches in the majority of numbers. However, although having the highest densities, they contributed a very low biomass compared with the fewer large‐sized nymphs. There was no size gradation in the colonization of the disturbed patches, since all sizes were sampled at all times but in differing proportions. Colonization of the patches by mayflies was not size‐ or maturity stage‐specific. Size distribution patterns could be useful in assessing which mayfly size‐spectra are more or less susceptible to disturbance in streams.
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