Spatial heterogeneity and long-term dynamics of cladoceran ephippia in a monsoonal reservoir, driven by hydrology and eutrophication

Abstract

Most freshwater Cladocera produce ephippia to survive harsh episodes in their life cycle. Ephippia represent the dormant community in sediments and allow tracing population dynamics and community succession with environmental change in water bodies in time. As reservoirs are created by damming rivers, the species composition and structure of a dormant cladoceran community are expected to depend on trophic state as well as on hydrological conditions. We collected ephippia from sediments in the transition and lacustrine zones of Liuxihe reservoir, a warm-water impoundment in southern China. High species richness with low abundance was found in the transitional zone, while high abundance was found at the lacustrine zone. Ephippia identified Daphnia galeata as the first Cladocera colonizer of the newly created water body, but littoral or small sized species—Scapholeberis sp. and Bosmina sp. fast increased and became dominated from damming till the end of 1970s. Medium-sized pelagic species—Moina micrura and D. galeata—increased from 1975 onwards, corresponding to an increase in diatom abundance with slight eutrophication and hydrological shift due to the construction of two small dams in the upstream zone of the feeding rivers. A two-way stepwise linear regression analysis showed that spatial variables explained 33% of ephippial total abundance while diatom abundance explained 5.2%. Hydrological conditions in the dry season (October to next March) were unrelated to total ephippial abundance but explained 37.5% in the wet season (April to September). We conclude the distinct longitudinal gradient and vertical variation of the dormant community provide useful information for understanding of long-term dynamics of site-specific hydrological processes, primary productivity and hydrologic events.