Subfossil Cladocera from surface sediment reflect contemporary assemblages and their environmental controls in Iberian flatland ponds

Abstract

Cladoceran subfossils from surface sediments have been recognized as useful and reliable ecological indicators in freshwater ecosystems. Nevertheless, investigations concerning the relationships between contemporary and sedimentary assemblages are scarce in the Mediterranean region and no studies are available from Iberian flatland ponds. Here, we explore the concordance between present-day Cladocera assemblages and their sedimentary remains from 25 ponds distributed across a vast heterogeneous region in the Iberian Plateau. Overall, this study aims at identifying sediment biological proxies with good capacity to track long-term changes in Iberian flatland ponds. We found a total of 15 and 18 taxa in the contemporary and sedimentary samples, respectively, with daphniids dominating water column samples whereas the majority of the remains recovered from surface sediments were from chydorids. In accordance with previous work, we found that subfossil Cladocera properly reflect the contemporary assemblages from which they are derived. Similarly, our results showed not only analogous environmental controls structuring contemporary and sedimentary assemblages (mainly pH and soluble reactive phosphorous), but also a similar proportion of explained variance in the two. Although there were several taxa occurring only in contemporary samples (Diaphanosoma brachyurum, Moina rosea, Macrothrix hirsuticornis, Scapholeberis sp. and Simocephalus sp.), we found that subfossil assemblages were significantly more rich, diverse, equitable and heterogeneous, indicating that an integrated sample of surface sediment from each pond may supply enough information for assessing cladoceran composition and the numerous drivers controlling their assemblage structure.