Vertical change of cladoceran ephippial densities in the sediments of Lake Nanyi and its correlation with the nutrients

Abstract

We examined the vertical variations of cladoceran ephippia in the sediments (1-28 cm) of Lake Nanyi. Nine cladoceran ephippia (Daphnia similoides sinensis, Daphnia galeata, Daphnia pulex, Ceriodaphnia sp., Moina micrura, Bosmina sp., Scapholeberis sp., Leydigia leydigii and Chydorus sp.) were identified. The ephippial densities of Daphnia species and small cladocerans ranged from 0 to 2.0 ind·g-1 DM and from 0 to 10 ind·g-1 DM, respectively. D. similoides sinensis and Ceriodaphnia sp. were respectively dominant species of large and small cladocerans in the sediments of Lake Nanyi. The ephippial densities of D. similoides sinensis had a significant negative correlation with total phosphorus content of sediments in the 1# sampling site of Lake Nanyi and had positive correlations with total nitrogen and total phosphorus contents in the 3# sampling site. In three sampling sites (except for total nitrogen contents in the 2# sampling site), there were significant positive relationships between the ephippial densities of Ceriodaphnia sp. and both total nitrogen and total phosphorus contents. Our results suggested that eutrophication and fish predation affected the historical succession of cladoceran community structure in Lake Nanyi.