Temporary fragmentation of a marginal lake and its effects on zooplankton community structure and organization

R Nadai,R Henry

doi:10.1590/s1519-69842009000400009

Abstract

A river lateral lake (Coqueiral Lake marginal to Paranapanema River in its mouth zone into Jurumirim Reservoir, São Paulo, Brazil) presented fragmentation into four small isolated bodies of water during a prolonged drought period, disrupting the link with the river. The aim of this work was to compare the temporal modifications on zooplankton community structure (total abundance, species richness, and diversity) in the four water bodies. Zooplankton samplings and abiotic factor measurements were made in two periods--during isolation phase of the lake in relation to river and after re-establishment of hydrologic connectivity. A concentration effect on zooplankton abundance was recorded with drought progression, but without significant modifications in species richness and diversity. When the river inundation pulse occurred, a reduction in total zooplankton density was observed due to the dilution effect and a significant increase in species richness and diversity was recorded. Lateral water influx from the river to the lacustrine environment acts as a temporary disturbance factor on the zooplankton community structure. Zooplankton species composition presented some modifications between the two periods. Zooplankton organism drift in water from the river to the lake, removal of individuals from the aquatic macrophytes, and eclosion of resting eggs from sediment are probable factors that can increase zooplankton species richness immediately after lateral pulse inundation with water by the river.

Highlights

Fragmentation of the great biomes is apparently an irreversible process
Surface water samples were taken for zooplankton every three months (April, July and October, 2000; February and May, 2001) by bucket from 12 sites in Coqueiral Lake (3 sites each in “fragments” A and C, 4 sites in fragment B, and 2 sites in fragment D, Figure 2)
The lowest levels in Coqueiral Lake were recorded in the drought period (April, July and October), with depths significantly increasing after reconnection to the Paranapanema River

Summary

Introduction

Fragmentation of the great biomes is apparently an irreversible process. In The Amazon, deforestation changes tropical rain forest into a mosaic of forested vegetation, where habitat quality for some species is severely affected. Fragments are remnants of natural vegetation surrounded by a variable area (the matrix) with agricultural characteristics or pasture. In function of their degree of isolation, size, and distance in relation to other fragments, a set of consequences on biota can be detected (Saunders et al, 1991). Habitats become less favourable to species and decrease their aptitudes, and a consequent reduction in species richness is expected.

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Conclusion