Diversity and abundance of rotifers during an annual cycle in the reservoir Valerio Trujano (Tepecoacuilco, Guerrero, Mexico)

Abstract

We analyzed the diversity and density of monogonont rotifers collected from 10 sites, 5 in the littoral zone and 5 in the pelagic zone, during a 1-year period from March 2010 to April 2011 in the reservoir Valerio Trujano, altitude 820 m a.s.l. (Tepecoacuilco de Trujano, State of Guerrero, Mexico). We also measured physicochemical variables such as temperature, pH, hardness, nitrates, and phosphates. The rotifers were identified to species level and quantified using a Sedgwick-Rafter chamber. We found 62 species belonging to 28 genera and 19 families, representing 22% of total species reported for Mexico. The most abundant species were Brachionus caudatus, B. falcatus, Horaëlla thomassoni, Filinia longiseta, Conochilus dossuarius, and Keratella cochlearis. The highest rotifer densities were those of B. caudatus (around 300 ind. L−1) in June and July. The common phytoplankton genera were Pediastrum, Cosmarium, Closterium, Nitzschia, Suriella, Microcystis, Oscillatoria, and Merismopedia. The species diversity of Rotifera in the reservoir ranged from 1.3 to 3.2 in both the littoral and the pelagic regions. The saprobic index varied from 1.2 to 2 in the pelagic and 1.4 to 2.1 in the littoral region of the reservoir. Nutrient levels and indicator species (Brachionus and Trichocerca) showed that the reservoir, which was nitrogen rather than phosphorus limited, is eutrophic and moderately polluted by organic matter.