Seasonal dynamics of zooplankton in Lake Huetzalin, Xochimilco (Mexico City, Mexico)

We quantified the seasonal changes in the zooplankton abundances collected from the Huetzalin Lake (Mexico City, Mexico) for two years (February 2003-January 2004 and then March 2005-February 2006). Selected physicochemical variables (Secchi depth, temperature, pH, conductivity, dissolved oxygen, phosphorus, nitrogen, carbon and chlorophyll a concentration) were also measured at the time of zooplankton collection. The data on zooplankton abundances and the physicochemical variables were subjected to multiple correlation analysis and we also derived Shannon-Wiener species diversity index. Secchi depth ranged from 9 to 65 cm. Generally the lake was alkaline (pH 7-12). The conductivity ranged from 500-1000mScm(-1), while the mean water temperature was 20.5 degrees C. Dissolved oxygen levels were generally > 3 mg L-1 and were higher in the winter than warmer months. Nitrates (90-95 mu g L-1) and phosphates (.2-.5 mg L-1) indicated that the water was eutrophic. Chlorophyll a levels ranged from 143 to 696 mu g L-1 during the study period. The zooplankton community was dominated by rotifers (46 species), followed by cladocerans (9 species) and there were only two copepod species. The dominant rotifer species were Brachionus angulans, Brachionus calyciflorus, Brachionus havanaensis, Brachionus quadridentatus, Lecane bulla and Polyarthra vulgaris. Rare rotifer species in Lake Huetzalin were Lecane ohioensis, Dicranophorus forcipatus, Lecane pyriformis, Lindia torulosa, Pleurotrocha petromyzon and Brachionus durgae. Highest densities (occasional peaks of 400 ind L-1) of B. quadridentatus occurred between April and December, while B. havanaensis reached peak densities, during June to October. e. calyciflorus reached densities higher than 1240 ind L-1 during May-September. Cladoceran and copepod densities in Lake Huetzalin were much lower than that of the rotifers. This study confirmed the earlier findings that Xochimilco system of canals is dominated by rotifers and the crustacean zooplankton have much lower abundances possibly due to predation from fish. (C) 2009 Elsevier GmbH. All rights reserved.