Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Benthos-drift relationships as proxies for the detection of the most suitable bioindicator taxa in flowing waters – a pilot-study within a Mediterranean karst river Mirela Sertić Perić a, ⁎ , Renata Matoničkin Kepčija a , Marko Miliša a , Sanja Gottstein a , Jasna Lajtner a , Zrinka Dragun b , Vlatka Filipović Marijić b , Nesrete Krasnići b , Dušica Ivanković b , Marijana Erk b a University of Zagreb, Faculty of Science, Department of Biology, Division of Zoology, Rooseveltov trg 6, 10000 Zagreb, Croatia b Ruđer Bošković Institute, Division for Marine and Environmental Research, Bijenička cesta 54, 10000 Zagreb, Croatia ARTICLE INFO Keywords: Urban influence Contaminant pathway Protected landscape Amphipoda Physico-chemical parameters Metal contamination ABSTRACT Mediterranean karst aquifers are sensitive systems vulnerable to contamination, exhibiting high rates of diversity and endemicity. In the present pilot-study, we aimed to detect the most suitable bioindicators of contaminant accumulation and mobilization within a Mediterranean karst river (Krka River, Croatia), whose lowermost sections belong to a designated protection area (national park). To meet our goal, we sampled water, drift and benthos (macroinvertebrates and periphytic microfauna) at the two Krka River sites, located upstream and downstream from town Knin and its urban influences. We compared: 1) environmental conditions (water physico-chemical parameters, trace- and macro- element concentrations); 2) abundance and diversity of periphyton and macroinvertebrate taxa constituting benthos; and 3) macroinvertebrate benthos-drift relationships between the two sites. Despite higher values of all measured physico-chemical parameters, and most trace- and macro-element concentrations at the urban-influenced site, the concentrations of contamination indicators (i.e., COD, nutrients, metals) at both sites were generally low. This is likely a result of specific “self-purification ability” of the Krka River, mediated by relatively high contaminant retention po- tential of the underlying tufa (i.e., calcareous) and/or macrophyte substrates. Between-site differences in water quality further affected the spatial variation of macrozoobenthos, drift, and periphytic microfauna. We suggest that increased COD and orthophosphate concentration, and macrophyte presence at the urban-influenced site, supported higher densities and diversity of benthic organisms dominated by eurivalent (i.e., contamination-tolerant) taxa. The most numerous macroinvertebrate taxa in benthos were amphipod Gammarus balcanicus and the representatives of the endemic Dinaric karst taxa - gastropods Emmericia patula and Radomaniola curta germari, and another amphipod Echinogammarus acarinatus. Although we expected to observe significantly increased drift at the urban-influenced site due to the degraded environmental conditions, it was not observed. The observed benthos-drift patterns suggest that freshwater amphipods (i.e., gammarids), which were found most numerous in drift, could be considered as the most suitable bioindicators of a contaminant (i.e., metal) accumulation and mobilization within karst aquifers comparable to Krka River. 1. Introduction Karst aquifers are attributed as extremely sensitive systems vul- nerable to contamination – primarily because of their permeability, and highly fragmented and heterogeneous structure (Watson et al., 1997). Mediterranean karst aquifers (e.g., on Iberian, Apennine and Balkan peninsulas) exhibit high rates of diversity and endemicity (Bănărescu, 2004; Klobučar et al., 2013; Tierno de Figueroa et al., 2013; Previšić et al., 2014; Ivković and Plant, 2015), and have thus been identified as “hotspots of biodiversity” and “hyper-hot candidates for conservation https://doi.org/10.1016/j.ecoenv.2018.07.068 Received 22 January 2018; Received in revised form 6 June 2018; Accepted 18 July 2018 Abbreviations: T, temperature; DO, dissolved oxygen; Cond, conductivity; TDS, total dissolved solids; Alk, alkalinity; TWH, total water hardness; N-NO 2 - , nitrite; N- NO 3 - , nitrate; P-PO 4 3- , orthophosphate; COD, chemical oxygen demand; SE, standard error; M-W U-test, Man-Whitney U-test ⁎ Corresponding author. E-mail addresses: msertic@biol.pmf.hr (M.S. Perić), rmatonic@biol.pmf.hr (R.M. Kepčija), marko.milisa@biol.pmf.hr (M. Miliša), sanja.gottstein@biol.pmf.hr (S. Gottstein), jasna.lajtner@biol.pmf.hr (J. Lajtner), zdragun@irb.hr (Z. Dragun), vfilip@irb.hr (V.F. Marijić), nkrasnic@irb.hr (N. Krasnići), djuric@irb.hr (D. Ivanković), erk@irb.hr (M. Erk). Ecotoxicology and Environmental Safety 163 (2018) 125–135 0147-6513/ © 2018 Elsevier Inc. All rights reserved. T