Long-term monitoring of astatic water bodies: microcrustaceans as indicators of hydroperiod length in ponds and pools

Abstract

Microcrustacean assemblages (Cladocera and Copepoda) from astatic ponds and pools of Castelporziano Presidential Estate were analysed to evaluate their role as indicators of functional variations related to the duration of the wet phase. Samples from a subset of 23 water bodies classified as permanent or temporary (based on observations over two decades, 1989–2010) were analysed. As a whole, 36 species of microcrustaceans were present. Hierarchical clustering allowed a clear distinction between temporary and permanent water bodies. Principal coordinates analysis (PCoA) provided a good separation of the two major hydroperiod groups along the first axis, while no correlation emerged among PCoA axes and hydrogeological setting. The correlation between species and the first PCoA axis highlighted biological indicators of hydrological change: among them, the cyclopoid copepods Macrocyclops albidus and Eucyclops serrulatus, which have no resting stages, were exclusive of permanent ponds; the calanoid copepod Eudiaptomus padanus etruscus and the cladocerans Ceriodaphnia reticulata, Scapholeberis rammneri and Coronatella rectangula were present in permanent and semi-permanent ponds; the cladoceran Daphnia chevreuxi and the calanoid copepods Diaptomus serbicus, Hemidiaptomus gurneyi and Mixodiaptomus kupelwieseri were exclusive of temporary ponds with short hydroperiod (less than 6 months). Temporary water bodies hosted a higher mean species richness (13.7 species) than permanent ones (10.3), and the difference was statistically significant. Our results highlight that: (1) the cladoceran and copepod assemblage effectively discriminate between ponds with different wet phase duration, proving to be good bioindicator; (2) small astatic water bodies play an important role in biodiversity conservation, as they host a high percentage of the species distributed over wider areas, next to species which are exclusively found in these habitats; (3) hydroperiod appears to be the main driving force in characterising microcrustacean assemblages in astatic ponds.