Macroinvertebrate Communities of sub-Mediterranean Intermittent Rivers in Bulgaria: Association with Environmental Parameters and Ecological Status

. Intermittent rivers and ephemeral streams drain more than 50% of the land surface on Earth. Yet, their ecology remains insufficiently understood. In Bulgaria, temporary rivers are typically small- or medium-sized rivers (national type R14), flowing in areas with subMediterranean climate. We present the first data focused explicitly on macrozoobenthos from intermittent rivers in four Bulgarian river basins within the drainage of the Aegean Sea. We identified 114 taxa from nine rivers (5÷33 taxa/site), with abundance varying between 61 and 994 ind.m-2. The most common were taxa of Ephemeroptera and Chironomidae, followed by the crab Potamon ibericum. There were considerable differences among macroinvertebrates at different sites at taxon level, with similarities among samples increasing when using lower taxonomic resolution. The distinctness of communities was likely a reflection of the high variability in environmental conditions and local human impacts. Redundancy analysis identified key groups for the sites with fast flow (e.g. Ephemeroptera, Trichoptera, Plecoptera, Coleoptera and Diptera Varia, taxa associated with altitude and the higher share of stone substrata). Most of the river sites were classified as having high ecological status according to the Bulgarian legislation. Only the sites in the Vrabcha and Dereorman Rivers were with moderate status; these were the sites with the lowest taxon richness. We could speculate that the structuring of the benthic community was affected by other factors that have not been accounted for in the present study, i.e. great annual fluctuations in river flow, characteristic for R14, or by loading with nutrients or other pollutants.