The multifaceted effects induced by floods on the macroinvertebrate communities inhabiting a sinking cave stream.

First-order sinking cave streams experience considerable hydrological variability, including spates and periods of base-flow during dry seasons. Early-summer flooding on a first-order stream sinking in Ciur-Ponor Cave (Romania) represented a suitable opportunity to test the response of the macroinvertebrate community and of basal food resources quantity and diversity to such a disturbance event. The invertebrate community and basal resources (i.e., woody debris, leaves, fine particulate organic matter and epilithon) were collected from three sampling sites, before and after the flood. The sampling strategy followed an up-downstream gradient of both species diversity and quantity of allochtonous organic matter decrease as the stream flows through the cave. From each sampling site, ten replicates of both the benthic community and basal resources (detritus and epilithon) were taken. Outside the cave, the spate reduced the invertebrate community density, instant secondary production, complexity and stability (measured as eco-exergy and specific eco-exergy). The epigean section of the stream is populated mainly by taxa characteristic of karst headwaters prone to floods that usually recolonize the streambed rapidly from adjacent habitats. This effect was corroborated with a subsequent increase of both the mass of fine particulate organic matter and of invertebrate density within the cave, following the aftermath of the flood. In the river stretch situated close to the entrance (100 m), where the flood carried both live and dead organic matter, the stability index showed that the complexity of the community was not severely disturbed, despite the high influx of surface-dwelling taxa and temporary increase in species richness. Further downstream, in the third sampling site (400 m from entrance), all measured endpoints indicated a change in community stability, suggesting that local spates can act as rejuvenating drivers in shaping the invertebrate community structure and functioning. [ABSTRACT FROM AUTHOR]