Elemental ratios (C:N) and stable isotopic composition of dominant rotifer species in a tropical eutrophic alkaline–saline Lake Nakuru (Kenya)

Abstract

Rotifers dominate zooplankton biomass of many aquatic environments. However, their link to food web biomass has rarely been elucidated in alkaline-saline lakes. Variations in C content, C:N ratio and stable isotope composition (d 13 C, d 15 N) of dominant rotifer species were studied from January to December 2008 in alkaline-saline Lake Nakuru to provide insights into their bioenergetics. We established that Brachionus dimidiatus dominated in terms of abundance (80,000-100,000 9 10 3 ind m -3 ) and C-biomass. Also B. dimidiatus constituted about 60-75% of the rotifer biomass in the samples. All the rotifer species exhibited significant (P \ 0.05) seasonal differences in biomass, C and C:N ratios. Rotifers had lower mean d 13 C than course particulate organic matter, fine particulate organic matter and fish, but higher than mean d 13 C in the dominant phytoplankton species. In all species, d 13 C and d 15 N increased markedly during the rainy season reflecting the feeding onset on allochthonous food sources. The isotopic increase correlated with an increase in their C:N. Our results demonstrate that rotifers respond quickly to any increase in primary production and can cope with changes in its nature and timing.

A georeferenced dataset for occurrence records of the phylum Rotifera in Africa

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