Differential responses of zooplankton assemblages to environmental variation in temporary and permanent ponds

Permanent and temporary wetlands in Mediterranean shrublands represent unique repositories of biodiversity, which are increasingly threatened by human-induced habitat loss. The zooplankton of a permanent (P1) and a temporary pond (T35) in the Natural Reserve of Castelporziano, a rare residual stretch of such a shrubland in Central Italy (Latium), was investigated to: (1) expand and deepen knowledge of these endangered freshwater habitats, which represent a crucial component of Mediterranean biodiversity; (2) identify environmental controls regulating the development of zooplankton communities of each environment; and (3) highlight differences in the adaptive responses of the zooplankton community in relation to the different ecological conditions experienced by permanent and temporary habitats. Despite summer desiccation in T35, the two ponds exhibited a relative homogeneity in hydrological and physico-chemical dynamics. Zooplankton assemblages contained 41 total taxa, of which 32 were found in P1 and 28 in T35. Out of the 41 taxa identified, 22 (> 50%) were exclusively present in one of the two ponds. On a yearly basis, the community dynamics of P1 seemed to be conditioned by physical and chemical factors and by hydrological cycle characteristics, while the community of T35 responded to algal blooms, food competition and predator/prey equilibria rather than correlating to abiotic factors. The main differences amongst zooplankton assemblages were observed over short time scales and occurred both within and between seasons, highlighting the role of some structural taxa that dominated the average composition of the community throughout the year, and the importance of "quick-response" taxa in determining the short-term composition and structure variation of pond zooplankton. A year-round cyclic community succession peculiar to each pond is described

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

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

Zooplankton response to flooding of a drought refuge and implications for the endangered fish species Craterocephalus fluviatilis cohabiting with alien Gambusia holbrooki

Disruption to a river's natural flow regime changes its ecological character, which becomes unfavourable for previously adapted biota. The zooplankton particularly are affected, and survival of larval and juvenile fish is largely determined by their availability. Alien fishes can also impact on recruitment in native fishes, sometimes through competition. In this regard, the invasive eastern Gambusia Gambusia holbrooki is linked to the decline of several fish species. It can have a substantial influence in shaping plankton communities, which implies that it competes with native fish that rely on the microfauna. The effects of river regulation and over abstraction of water in the Murray-Darling Basin, south-eastern Australia, were exacerbated by drought from 1997 to 2010. Consequently, the endangered Murray hardyhead Craterocephalus fluviatilis underwent substantial population decline and extirpations. The purpose of this study is to determine if a link exists between zooplankton response to flooding of a drought refuge and the recruitment success of C. fluviatilis in the presence of G. holbrooki. Flooding triggered sharp and substantial increases in the zooplankton and their eggs, which was the sole food of C. fluviatilis. This apparently benefitted the recruitment of C. fluviatilis, and sometimes alleviated diet overlap with G. holbrooki. Conversely, the zooplankton in a nearby non-flooded refuge was low in abundance and diversity, and all fish species were extirpated. The findings indicate that the flooding of drought refugia with relatively small volumes of water can be timed with ecological cues that would otherwise be desynchronized in highly regulated rivers, particularly during drought. © 2013 Springer Science+Business Media Dordrecht.Scotte D. Wedderburn, Karl A. Hillyard, Russell J. Shie