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 wet phase duration. The cladoceran and copepod fauna of the Estate (42 species) is very well known; rarefaction curves demonstrated that a percentage between 91 and 95% of total species richness was collected so far. Samples from a subset of 22 water bodies classified as permanent or temporary (based on observations over two decades, 1989-2001) were analysed. As a whole, 36 species of microcrustaceans (22 cladocerans and 14 copepods) were present in the 22 sampling sites. Hierarchical clustering allowed a clear distinction between temporary and permanent water bodies. Principal coordinate analysis (PCoA) provided a good separation of the two major hydroperiod groups along the first axis, which explained over 41.3% of total variation. The separation, tested by means of ANOSIM, showed to be significant, while no correlation emerged among PCoA axes and hydrogeological setting (i.e. hydrogeochemistry). The correlation between species and the first PCoA axis evidenced some possible biological indicators of hydrological changes: the cyclopoid copepods Macrocyclops albidus and Eucyclops serrulatus, which have no resting stages, in permanent ponds, accompanied by the calanoid copepod Eudiaptomus padanus etruscus and the cladocerans Ceriodaphnia reticulata, Scapholeberis ramneri and Coronella rectangula which are 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 six months). Finally, temporary water bodies hosted a mean species richness (13.7 species) higher than permanent ones (10.3), and the difference was statistically significant (p<0.05). Our results highlight that (1) cladocerans and copepods possess a high power in discriminating ponds with different wet phase duration, showing to be very good bioindicators; (2) small astatic water bodies play an important role in biodiversity conservation, as they host high percentages of species distributed in wider areas, besides of species exclusive of these habitats, and exhibit a higher alpha-diversity than permanent ponds; (3) hydroperiod appears to be the main driving force in characterizing microcrustacean assemblages in astatic ponds