The effect of the sampling scale on zooplankton community assessment and its implications for the conservation of temporary ponds in south-west Spain

Abstract

1. The zooplankton (rotifer and microcrustacean) assemblages of temporary ponds in the Doñana National Park (south-west Spain) have been compared in two surveys of contrasting scales that resulted in the same number of samples: an extensive survey of 36 ponds sampled in May 1998 (or widespread survey) and a survey of nine ponds sampled four times over 2 years (or cumulative survey). 2. The total number of microcrustacean and rotifer taxa was larger in the cumulative survey (43 and 41 taxa, respectively) than in the widespread survey (39 and 34, respectively). Crustacean assemblages became less alike throughout the cumulative survey. 3. The presence of invertebrates (Coleoptera, Odonata, Heteroptera and crayfish) and aquatic vertebrates (fish and salamanders) was recorded as an estimate of potential predator impact on zooplankton. Several pond features (water depth, conductivity, pH, chlorophyll a concentration, distance to the nearest permanent pond and to the marsh) were also measured in both surveys. 4. A combination of these environmental factors was more strongly related to the similarity matrices derived from the zooplankton assemblages of the cumulative survey (Rho = 0.7) than to those of the widespread survey (Rho < 0.4). The distance of ponds to the marsh was an important factor in explaining this correlation as well as the strongest factor in the ordination of crustacean assemblages following a CCA. 5. Predation by exotic fish in long-hydroperiod ponds where overflow drains to the nearby marsh (fish source) is the mechanism likely to explain the changes in crustacean composition recorded in the cumulative survey. 6. The cumulative survey was more suitable for the study of zooplankton diversity as it rendered a higher number of taxa and gave more insight into the mechanisms that explain taxon richness. Thus, conservation strategies in temporary habitats require a scale of observation that includes long temporal changes. Copyright © 2006 John Wiley & Sons, Ltd.