Journal of Environmental Biology

Seasonal variations in zooplankton abundances in the Iturbide

reservoir (Isidro Fabela, State of Mexico, Mexico)

Author Details

S.S.S. Sarma

(Corresponding author)

Laboratory of Aquatic Zoology, Division of Research and Postgraduate Studies,

National Autonomous University of Mexico, Campus Iztacala, Av. de los Barrios No.1, AP 314,

Postal Code 54090, Los Reyes, Tlalnepantla, State of Mexico, Mexico

e-mail: sarma@servidor.unam.mx

Lidia Rosario Osnaya-Espinosa

Laboratory of Aquatic Zoology, Division of Research and Postgraduate Studies, National Autonomous

University of Mexico, Campus Iztacala, Av. de los Barrios No.1, AP 314, Postal Code 54090, Los

Reyes, Tlalnepantla, State of Mexico, Mexico

Claudia Romina Aguilar-Acosta

Laboratory of Aquatic Zoology, Division of Research and Postgraduate Studies, National Autonomous

University of Mexico, Campus Iztacala, Av. de los Barrios No.1, AP 314, Postal Code 54090, Los

Reyes, Tlalnepantla, State of Mexico, Mexico

S. Nandini

Laboratory of Aquatic Zoology, Division of Research and Postgraduate Studies, National Autonomous

University of Mexico, Campus Iztacala, Av. de los Barrios No.1, AP 314, Postal Code 54090, Los

Reyes, Tlalnepantla, State of Mexico, Mexico

Publication Data

Paper received:

25 February 2010

Revised received:

28 July 2010

Accepted:

23 September 2010

Abstract

This study was undertaken to quantify the seasonal variations of zooplankton (rotifers, cladocerans and copepods) and selected physico-chemical variables (temperature, pH, conductivity, Secchi disc transparency, dissolved oxygen, ammonia, nitrate and phosphate concentrations) in the Iturbide dam. Monthly zooplankton samples (50 l filtered through 50 ?m mesh, in duplicates from each of the 4 stations) were collected from February 2008 to January 2009. Simultaneously physico-chemical variables were measured. The zooplankton samples were fixed in 4% formalin in the field. In general, the temperature ranged from 9 to 16^oC, rarely exceeding 20^oC. Secchi transparency was nearly 100% since the reservoir was shallow (<2 m) even during the rainy seasons. Dissolved oxygen was generally high, 13-18 mg l^-1. Nitrate levels (10 to 170 ?g l^-1) were low while phosphates were relatively high (9 to 35 ?g l^-1). The Iturbide reservoir was dominated by rotifer species. We encountered in all, 55 taxa of rotifers, 9 cladocerans and 2 copepods. The rotifer families Trichocercidae and Notommatidae had the highest number of species (7 each) followed by Colurellidae and Lecanidae (6 and 5 species, respectively). Trichocerca elongata, Ascomorpha ovalis, K. americana, K. cochlearis, Lepadella patella and Pompholyx sulcata were the dominant rotifers during the study period. On an annual average, rotifer density ranged between 50-200 ind. l^-1. Among crustaceans Chydorus brevilabris and Macrothrix triserialis were most abundant. The maximal density of these cladocerans was about 50 ind. l^-1. Copepods were much lower in numbers (<20 ind. l^-1). In general the density of zooplankton was higher during summer months (April to July) than during winter. Shannon-Wiener diversity index varied from 1.0 to 4.3 depending on the site and the sampling period. Based on the data of Secchi transparency and nutrient concentrations, the Iturbide reservoir appeared to be mesotrophic.

Key words

Rotifera, Cladocera, Copepoda, Limnology, High altitude reservoir

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