Assessing rotifer diapausing egg bank diversity and abundance in brackish temporary environments: an ex situ sediment incubation approach

Abstract

The hatching of diapausing eggs from sediment samples of ponds and lakes is a fast, easy, and economical technique proven useful for the assessment of diversity and abundance of zooplankton in permanent habitats. Here, we extend and optimize this approach for temporary brackish ponds which may experience great within-year variation in salinity conditions. We studied the species and numbers of rotifers emerging from the sediments of several brackish ponds and saline lakes from Eastern Spain incubated at the full range of salinity conditions observed at the study sites. On average, 82 % of the total observed species in weekly sampling for one year were detected in a single sample of both the sediments and water column. No statistical difference was found between both methods. However, some rotifer species were only observed in the water column samples, but not in sediment hatchlings, and vice versa. We concluded that both methods are not exhaustive by themselves but are complementary. Salinity affected the estimation of both rotifer richness and the density of individuals of each rotifer species that emerged from the incubated sediments. Differences in the density of emerging animals were also found among sites and among combinations of sites and salinities. The latter result indicates that in order to obtain an estimate of the emergence rate for each rotifer species present at a site, it is necessary to incubate sediments at salinity conditions close to their local values.