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All issues No 418 (2017) Knowl. Manag. Aquat. Ecosyst., 418 (2017) 14 Full HTML
Open Access
Issue
Knowl. Manag. Aquat. Ecosyst.
Number 418, 2017
Article Number 14
Number of page(s) 12
DOI https://doi.org/10.1051/kmae/2017005
Published online 29 March 2017

© M. Vilenica et al., Published by EDP Sciences 2017

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License CC-BY-ND (http://creativecommons.org/licenses/by-nd/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. If you remix, transform, or build upon the material, you may not distribute the modified material.

1 Introduction

Ephemeroptera (mayflies) is an order of aquatic insects that plays an important role in running and standing waters, representing a very large proportion of the aquatic ecosystem biomass (Brittain and Sartori, 2003; Bauernfeind and Soldán, 2012).

Water temperature, dissolved oxygen concentration, nutrients, water velocity and substrate type are the most important natural environmental factors driving freshwater communities, including mayflies (Giller and Malmqvist, 1998; Moog, 2002; Allan and Castillo, 2007; Choudhary et al., 2014). Stream insects often show longitudinal zonation along habitats following the downstream gradient in physico-chemical water properties (Vannote et al., 1980; Giller and Malmqvist, 1998; Bauernfeind and Humpesch, 2001). The majority of mayfly species prefer the meta- and hyporhithral sections (upper reaches) of the fast-flowing streams and rivers, and ecologically intact large potamal rivers (Bauernfeind and Moog, 2000; Bauernfeind and Soldán, 2012). On the other hand, crenal (spring) sections of streams, high mountains and metapotamal river sections (lower reaches) usually have low mayfly species diversity (Bauernfeind and Soldán, 2012).

The longitudinal succession of macroinvertebrate communities, including mayflies, reflects the temperature regime of a river, the differences in other environmental factors, but also the changes in food webs (Giller and Malmqvist, 1998; Moog, 2002; Schmidt-Kloiber and Hering, 2015). Consequently, changes in mayfly assemblages are often used as an important parameter to detect and assess temperature increases induced by climate change, or to assess river degradation (e.g. hydromorphological changes) and stress intensity (Schmidt-Kloiber and Hering, 2015).

Karst is a set of morphological, hydrological and hydrogeological terrain features built of water-soluble rock. Due to anthropogenic pressure and the specific hydrology and soil morphology (Sánchez‐Fernández et al., 2004), karst habitats are particularly endangered. These fragile ecosystems are inhabited by numerous rare and endangered species (Bonacci et al., 2008; Bonacci, 2009). The karstification process has resulted in a mosaic of climatic and environmental conditions with diverse physiographic traits. Geographical isolation, local influences of climate and altitude and high habitat heterogeneity may have favoured the maintenance of a high level of speciation, and a high number of discontinuous populations of phylogenetically distinct origin (Bonacci et al., 2008; Previšić et al., 2009, 2014; Ivković and Plant, 2015). The Dinaric Mountains are the largest continuous karst landscape in Europe (Mihevc et al., 2010), extending over approximately 60,000 km2, with an extremely complicated hydrological network (Bonacci and Jelin, 1988; Bonacci et al., 2013). The mountain range lies along the western Balkan Peninsula, stretching in a north-south direction from northeastern Italy to Albania (Bonacci, 2009). Freshwater karst habitats are characterized by an exceptional phenomenon: secondary calcium-carbonate deposition − tufa. Tufa is a product of the physico-chemical characteristics of water, geological bed and the present biota. The biological component is a crucial factor in the genesis and maintenance of cascade lake systems with tufa barriers (barrage lakes), such as Plitvice Lakes National Park (Srdoč, 1985).

Faunistic surveys and ecological studies involving various aquatic insect groups were recently conducted in the Dinaric Karst area, e.g. stoneflies (Popijač and Sivec, 2009), caddisflies (Previšić et al., 2007; Šemnički et al., 2012), blackflies (Ivković et al., 2013a), aquatic dance flies (Ivković et al., 2013b) and riffle beetles (Mičetić Stanković et al., 2015). However, the ecological preferences of mayfly assemblages in this region are still poorly known (e.g. Hrovat et al., 2009; Vilenica et al., 2016a, b). Matoničkin and Pavletić (1961, 1967); Habdija et al. (1994) and Habdija et al. (2004) investigated mayflies only sporadically as a part of invertebrate benthic communities. Moreover, most of the previous identifications are ambiguous, as the identification tools were not cited or current revision of sampled material is not possible.

Therefore, the main goals of this study were to

  • determine the composition, abundance and spatial distribution of mayflies;

  • determine the mayfly habitat preferences and

  • examine which environmental factors are important in structuring mayfly assemblages in the selected tufa-depositing karst freshwater ecosystem of Plitvice Lakes National Park.

2 Material and methods

2.1 Study area

Plitvice Lakes National Park is located in the Dinaric Karst region in Croatia. The Plitvice Lakes' barrage lake system consists of 16 oligotrophic, dimictic and fluvial lakes divided and interconnected by tufa-depositing barriers (Fig. 1). After the confluence, the small mountainous rivers Bijela rijeka and Crna rijeka form the Matica river, the main surface-water supplier of the lakes (Stilinović and Božičević, 1998).

The climate is transitive, moderately mountainous (Šikić, 2007). The main rainfall occurs in autumn and winter, while the air temperature during the winter drops to −25 °C and during the summer rises above 30 °C (Makjanić, 1958). The area is rich in a range of karst habitat types (Stilinović and Božičević, 1998) and well known for its high endemism, especially in freshwater (Bãnãrescu, 2004), which is why Plitvice Lakes National Park (NP) was designated as a UNESCO world natural heritage site in 1979 (Stilinović and Božičević, 1998).

Sampling was conducted in various habitats at 10 study sites. According to their altitude and habitat type, lotic habitats were classified into four categories (Fig. 1, Tab. 1):

  • Rheocrene springs of upper lotic habitats (small mountainous rivers): spring of the Bijela rijeka river (elevation 720 m) (IBR) and spring of the Crna rijeka river (675 m) (ICR).

  • Downstream sections of upper lotic habitats (small mountainous rivers): upper reaches of the Bijela rijeka river (716 m) (SBR), middle reaches of the Crna rijeka river (670 m) (SCR) and lower reaches of the Crna rijeka river (665 m) (CM).

  • Three tufa barriers, situated between upper and lower lotic habitats: Tufa barrier Labudovac (630 m) (LB), Tufa barrier Kozjak-Milanovac (545 m) (KM) and Tufa barrier Novakovića Brod (505 m) (NOB).

  • Tufa-depositing lower lotic habitats at the end of the cascade system represented by downstream sections of the canyon type mountainous stream Plitvica stream (555 m) (PP) and mid-altitude large river Korana river (390 m) (KR).

thumbnail Fig. 1

Location of Plitvice Lakes NP in Croatia and position of 10 study sites in Plitvice Lakes NP. Legend: IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod.
Table 1

Characteristics of the study sites in Plitvice Lakes National Park. Abbreviations of the study sites are presented in Figure 1.

2.2 Mayfly sampling

Mayfly larvae were sampled monthly from February 2007 to February 2008 with other macroinvertebrates using a Surber sampler (0.1 m2 surface area and 0.5 mm mesh size). In the CM, a D-frame hand net (with 0.5 mm mesh size) was used. Every month, at each site, three samples were taken, with the exception of the IBR, where four samples were taken. Samples were conserved in 80% ethanol.

2.3 Environmental factors

Physico-chemical water properties were measured monthly at each study site (Tab. 1): oxygen concentration, oxygen saturation, water temperature (using the oximeter WTW Oxi 330/SET), pH (using the pH-meter WTW ph 330), conductivity (with the conductivity meter WTW LF 330), alkalinity (by titration with 0.1 M HCl), water velocity (with P-670-M velocimeter), water depth (with handheld meter) and nutrients (ammonium by HRN ISO 70-3:1998 method, nitrates and nitrites by HRN ISO 7890-3:2001 method and orthophosphates by HRN ISO 6878:2001 method). Water velocity and water depth were measured at each sampled microhabitat. Altitude and distance from the springs were determined for each study site. Geographical coordinates were read using a GPS Garmin Oregon 550, and subsequently processed in ArcGIS software.

2.4 Data analysis

For all data, the Shapiro–Wilk normality test was performed. All mayfly data were log-transformed prior to analyses.

In order to determine differences in physico-chemical water properties between habitat types, one-way ANOVA for water velocity and Kruskal–Wallis H test with multiple comparisons test for other environmental factors were applied.

Non-metric multidimensional scaling analysis (NMDS) was applied to show similarities in the composition of mayfly assemblages among study sites using the Bray–Curtis similarity index. The results of the hierarchical cluster analysis are superimposed on NMDS ordination.

The relationship of mayflies to environmental factors were analysed from various aspects: (i) Kruskal–Wallis H test with multiple comparisons test and indicator value method (IndVal) were used to determine the preference of each recorded taxon for a certain habitat type, with Monte Carlo permutation test (4999 permutations) and threshold value of the proportion determining the characteristic indicator taxa of 55% (Dufrêne and Legendre, 1997); (ii) Spearman's rank correlation coefficient (R) for analysis of the relationship of mayfly assemblages (number of individuals, number of taxa) and each of the recorded species with physico-chemical water properties; (iii) Canonical correspondence analysis (CCA) with Monte Carlo permutation test of significance (with 999 permutations) was used for identification and measurement of the mayfly associations and environmental conditions. The CCA analysis included 20 taxa and 9 physico-chemical water parameters. Prior to the CCA analysis, the full draftsman's plot excluded orthophosphates and nitrites.

Analyses were performed in Statistica, version 10.0 (Statsoft Inc., Tulsa, PC-ord ver. 5.0), Primer 6 software package (Clarke and Gorley, 2006) and CANOCO for Windows (ver. 4.02) (Ter Braak and Šmilauer, 1998).

3 Results

3.1 Environmental factors

Kruskal–Wallis and multiple comparisons of mean ranks for all groups separated the four habitat types (springs, upper lotic habitats, tufa barriers and lower lotic habitats), based on their physico-chemical water properties (Tabs. 1 and 2).

Table 2

Significant differences in physico-chemical water properties between habitat types in Plitvice Lakes NP based on Kruskal–Wallis H test with multiple comparisons test. Sample size (N) = 31, ⁎⁎⁎ p < 0.001, ⁎⁎ p < 0.01, ⁎ p < 0.05.

3.2 Population aspects and relation of mayflies to environmental factors

A total of 14 mayfly species (20 taxa), belonging to 13 genera and 7 families, were recorded. Early instars or damaged specimens were identified to the genus or family level (six taxa) (Tab. 3). Springs and one tufa barrier had the lowest number (four) of mayfly species (Tab. 3). The highest diversities and abundances were recorded in the lower lotic habitats, especially at the site Plitvica stream (PP) (Tab. 3). Baetis rhodani (Pictet, 1843) and B. cf. nubecularis (Eaton, 1989) were the most widely distributed species, while Serratella ignita (Poda, 1761) was the most abundant. On the contrary, Procloeon pennulatum (Eaton, 1870) was the rarest recorded species (Tab. 3).

NMDS analysis (Fig. 2a and b) showed clustering of the sites according to habitat type. Sites located in the upper lotic habitats (IBR, SBR and SCR) were clearly separated from the tufa barriers (LB, NOB and KM) and lower lotic habitats (PP and KR), which clustered together. A single study site located in the downstream sections of the upper lotic habitats (CM) clustered with the lower lotic habitats and tufa barriers.

Preferences for a certain habitat type was significant for four mayfly species: Rhithrogena braaschi Jacob, 1974 (IndVal = 62.3, p < 0.05) for upper lotic habitats; Caenis horaria (Linnaeus, 1758) (IndVal = 55.6, p < 0.01) for tufa barriers and Centroptilum luteolum (Müller, 1776) (IndVal = 58.6, p < 0.05) and S. ignita (IndVal = 99.7, p < 0.001) for lower lotic habitats.

Significant differences between abundances were recorded for two mayfly species. According to Kruskal–Wallis H test and multiple comparisons of mean ranks for all groups, abundances of Rh. braaschi were significantly different between the tufa barriers and springs (p < 0.05), and between the tufa barriers and upper lotic habitats (p < 0.05), as this species was absent from the tufa barriers and was most abundant in the upper lotic habitats (Tab. 3). Abundances of S. ignita strongly differed between the lower lotic habitats and other habitat types: springs (p < 0.01), tufa barriers (p < 0.01) and upper lotic habitats (p < 0.05). The species was absent from the springs, present in very low numbers in tufa barriers and upper lotic habitats and highly abundant in the lower lotic habitats (Tab. 3).

The eigenvalues for the first two CCA axes (Fig. 3) were 0.373 and 0.224 and accounted for 53.2% of the variability in species–environment relations, while the eigenvalues accounted for 80.1% of the overall variability. The Monte Carlo permutation test showed that the species–environment ordination was statistically significant (first axis: F-ratio = 4.876, p = 0.002; overall: trace = 1.122, F = 3.048 and p = 0.002), indicating that mayfly assemblages were significantly related to the tested set of environmental variables. Axis 1 was related to water temperature (R = 0.646) and pH (R = 0.632) and Axis 2 to ammonium concentrations (R = 0.690), indicating that these were the most important parameters in explaining patterns of the mayfly assemblages.

The number of mayfly taxa (S) was positively correlated with conductivity (R = 0.21, p < 0.001), alkalinity (R = 0.19, p < 0.001) and the concentration of nitrate ions (R = 0.14, p < 0.01). The number of mayfly individuals (N) was positively correlated with conductivity (R = 0.18, p < 0.001), alkalinity (R = 0.16, p < 0.01), concentrations of ammonium (R = 0.13, p < 0.01) and nitrate ions (R = 0.19, p < 0.05), water temperature (R = 0.11, p < 0.05) and water velocity (R = 0.12, p < 0.05). A negative correlation was determined between mayfly abundance and water depth (R = −0.17, p < 0.001). Significant correlations with physico-chemical water properties were recorded for 13 species (Tab. 4).

Table 3

Mayfly abundance (shown as a number of individuals per m2) and distribution in Plitvice Lakes NP: (a) springs and upper lotic habitats, (b) tufa barriers and lower lotic habitats. Abbreviations of the study sites are presented in Figure 1.

thumbnail Fig. 2

NMDS analysis of the study sites in the different habitat types in Plitvice Lakes NP based on the composition of mayfly fauna shown (a) pooled per study site and (b) per microhabitat. Study sites: IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod.
thumbnail Fig. 3

F1 × F2 plane of CCA analysis showing 20 mayfly taxa, 10 study sites encompassing 31 microhabitats in Plitvice Lakes NP and nine selected environmental variables. Legend: Study sites (black circle symbols): IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod. Environmental factors (green arrow symbols): T max = maximum water temperature (°C); O2 = O2 (mg L−1); pH = pH value; Con = Conductivity (µS cm−1); Al = Alkalinity (mg L−1 CaCO3); Vel = Water velocity (cms−1); Dep = Water depth (cm); NO3 = Nitrates (mg L−1); NH4 = Ammonium (mg L−1). Taxa (red triangle symbols): A = juvenile Baetidae, B = Alainites muticus, C = juvenile Baetis sp., D = Baetis cf. nubecularis, E = Baetis rhodani, F = Centroptilum luteolum, G = Procloeon pennulatum, H = juvenile Caenis sp., I = Caenis horaria, J = juvenile Ephemerellidae, K = Serratella ignita, L = Torleya major, M = Ephemera danica, N = juvenile Heptageniidae, O = Ecdyonurus submontanus, P = Rhithrogena braaschi, R = juvenile Leptophlebiidae, S = Habrophlebia lauta, T = Paraleptophlebia submarginata, U = Siphlonurus croaticus.
Table 4

Spearman's rank significant correlation coefficient (R) for mayfly species and physico-chemical water properties in Plitvice Lakes NP. Sample size (N) = 366, ⁎⁎⁎ p < 0.001, ⁎⁎ p < 0.01, ⁎ p < 0.05.

4 Discussion

Aquatic organisms in Plitvice Lakes NP are confronted with specific environmental conditions, such as low nutrient availability, low water temperature and high alkalinity, which also most likely resulted in a relatively low diversity of mayfly assemblages (e.g. Hrovat et al., 2009; Vilenica et al., 2016a, b). The results obtained from the mayfly fauna are in accordance with data obtained from physico-chemical analyses of the water. Our results clearly indicate differences in physico-chemical water characteristics throughout Plitvice Lakes NP. As expected, the lowest variations were recorded in the springs and spring zones, where environmental conditions are stable regardless of stream type (Jones and Mulholland, 2000). On the other hand, sites situated downstream of the barrage-lake system, and sites at tufa barriers and in the lower lotic habitats, showed higher fluctuations in environmental factors. In accordance with the literature (e.g. Berner and Pescador, 1988; Bauernfeind and Soldán, 2012), the lowest mayfly species' richness was recorded in the springs and spring areas. Mayfly diversity is usually highest in meta- and hyporhithral stream sections (upper reaches) (Bauernfeind and Soldán, 2012). However, downstream sections of lower lotic habitats had the most diverse mayfly assemblages due to the rhithral character, more suitable environmental conditions (e.g. higher water temperature), a variety of available microhabitats and food resources (see also in Vilenica et al., 2014). Generally, tufa barriers were a less favourable habitat than the lower lotic habitats, which could be due to the more prominent fluctuations in oxygen concentrations, water temperature and available nutrients. On the other hand, tufa barriers were a more favourable habitat type than upper lotic habitats, due to the higher amount of organic matter. The barriers are situated between lakes, which is why they represent natural lake outlet habitats where organic matter accumulates, thus enhancing conditions for detritivorous insects such as mayflies (Obelić et al., 2005; Šemnički et al., 2012; Ivković et al., 2013a).

Similar to the previously investigated freshwater systems of the Dinaric Karst (Vilenica et al., 2016b), water temperature and pH were amongst the most important variables that determined mayfly assemblages and their distribution (e.g. Gerhardt, 1990; Moog, 2002; Petrin, 2011; Bauernfeind and Soldán, 2012). In addition, habitat type (springs, upper lotic habitats, tufa barriers and lower lotic habitats) and ammonium concentrations also played an important role.

The NMDS analysis showed a grouping of mayfly assemblages according to habitat type (see also in Siegloch et al., 2014; Lencioni and Spitale, 2015), with a clear separation of upper lotic habitats from lower lotic habitats and tufa barriers. In addition to differences in the physico-chemical water properties, upper lotic habitats differed from tufa barriers and lower lotic habitats in the microhabitat composition. In the upper lotic habitats, microhabitats mainly consisted of pebbles, sand, angiosperms and bryophytes, while in tufa barriers and lower lotic habitats, pebbles/tufa, bryophytes on tufa, tufa with detritus and silt dominated.

Several of the recorded species showed a significant preference for habitat type. To date, larvae of Rh. braaschi have been recorded in the rhithral sections (upper reaches) of brooks and smaller rivers lying at elevations from 600 to 1000 m (Bauernfeind and Soldán, 2012). The distribution of this species in Plitvice Lakes NP was in accordance with its known habitat preferences (Jacob, 1974; Vidinova, 2003; Bauernfeind and Soldán, 2012), in the springs and upper lotic habitats, at sites with a low and constant water temperature. On the other hand, our results indicate that tufa barriers are less favourable for the species, which should be investigated in more detail. The limnophilic (lentic) species C. horaria, predominantly inhabiting the lakes (Bauernfeind and Soldán, 2012), was recorded at the tufa barriers but in low abundance. As much higher abundances of this species were recorded in the surrounding lakes (Vilenica et al., 2014), low numbers of larval specimens at the tufa barriers are most likely the consequence of drift from upstream lakes (Sertić Perić et al., 2011). Two eurytopic and eurythermic species, C. luteolum and S. ignita, found most commonly in habitats with moderate (<18 °C) and warmer water (≥18 °C) (Schmidt-Kloiber and Hering, 2015), preferred the lower lotic habitats in Plitvice Lakes NP, where such conditions were recorded.

Considering their water temperature requirements, the majority of the mayfly species recorded in the current study were eurytherms (Schmidt-Kloiber and Hering, 2015), with the exception of the warm stenotherms P. pennulatum and C. horaria (Bauernfeind and Soldán, 2012; Schmidt-Kloiber and Hering, 2015). Accordingly, these two species were recorded only at sites with the highest water temperatures, namely the tufa barriers (max. temp. NOB 22.9 °C; LB 20.5 °C; KM 22.9 °C) and lower lotic habitats (max. temp. KR 19.8 °C; PP 15.4 °C). Several additional species recorded in the lower lotic habitats and tufa barriers were also correlated with higher water temperatures, such as the eurythermic S. ignita, two species preferring moderate water temperatures (<18 °C), Ephemera danica Müller, 1764 and Torleya major (Klapálek, 1905) (Kamler, 1965; Céréghino and Lavandier, 1998; Bauernfeind and Soldán, 2012; Schmidt-Kloiber and Hering, 2015), and B. cf. nubecularis. Since the taxonomic status of the latter species is unresolved, its ecological preferences cannot be compared.

Another environmental factor strongly influencing mayfly assemblages was pH. Majority of mayfly species inhabit freshwaters with a neutral to alkaline pH, whereas they are highly sensitive to low pH values (e.g. Gerhardt, 1990; Petrin, 2011). pH values of the karst streams and rivers usually range from 6.5 to 8.5, due to the geological effects of karst substrate (Štambuk-Giljanović, 2005). In accordance with the recorded pH range (6.8–8.9), the majority of mayfly taxa recorded in our study preferred a neutral to alkaline environment (Jazdzewska and Górczynski, 1991; Schmidt-Kloiber and Hering, 2015), with Rh. braaschi and B. rhodani inhabiting sites with a neutral pH and C. horaria, E. danica and T. major preferring sites with a more alkaline pH.

Conductivity and alkalinity also had a strong influence on both diversity and abundance of mayflies in Plitvice Lakes NP, with e.g. B. rhodani (Dolisy and Dohet, 2003), Alainites muticus (Linnaeus, 1758) (López-Rodríguez et al., 2010) and Rh. braaschi tolerating higher values and C. horaria, E. danica and T. major selecting sites with lower values.

The requirement for an adequate oxygen content in water is commonly high in mayflies (Bauernfeind and Soldán, 2012). Generally, oxygen concentrations in karst rivers fluctuate between 10 and 12 mg/L (Štambuk-Giljanović, 2005). In the current study, the water was well oxygenated (average in the range 10.1–11.1 mg/L) though several species, such as C. luteolum, E. danica and C. horaria, exhibited a correlation with lower concentrations of dissolved oxygen. These species usually inhabit slow-flowing or standing water bodies (Bauernfeind and Soldán, 2012; Schmidt-Kloiber and Hering, 2015), often associated with lower oxygen concentrations compared to fast flowing streams (Giller and Malmqvist, 1998; Wetzel, 2001). As such, they were generally more abundant in the downstream sections of lower lotic habitats, Plitvica stream and Korana river, on sandy substrates with lower water velocity.

Plitvice Lakes NP is an oligotrophic freshwater system (e.g. Habdija et al., 2004; Špoljar et al., 2007). However, several sites (springs and lower lotic habitats) exhibited slightly higher concentrations of nitrates and ammonium ions due to increased demands of tourism for waste disposal in recent decades (Petrik, 1961; Matoničkin and Pavletić, 1967). This may have had a positive effect on the algal growth (Fried et al., 2003) and quantity of food, making these sites more suitable habitats for a higher abundance and higher number of mayfly taxa. Nevertheless, the values of nitrates and ammonium could increase more in the near future. This should be taken in account while protecting this valuable karst river system and its communities. Two species were correlated with ammonium concentrations, B. cf. nubecularis with higher and Siphlonurus croaticus Ulmer, 1920 with lower values, indicating higher and lower tolerance, respectively. The potential sensitivity of S. croaticus to ammonium should be further studied.

Mayfly assemblages were also influenced by water velocity, and the majority of species preferred habitats with the higher water speed. This was not surprising since large number of mayfly species inhabit well oxygenated running waters with moderate to high current, having a certain preference for specific water velocity (Schmedtje and Colling, 1996; Bauernfeind et al., 2002; Menetrey et al., 2008; Bauernfeind and Soldán, 2012). Water velocity also influences the distribution of organic matter (Habdija et al., 2004; Miliša et al., 2006), which is another factor having an impact on mayfly distribution (e.g. Williams and Hynes, 1974; Fjellheim, 1996; Habdija et al., 2004). In the studied hydrosystem, water velocity was inversely proportional to water depth, therefore the rheo- to limnophilic E. danica and Paraleptophlebia submarginata (Stephens, 1835) and limno- to rheophilic Habrophlebia lauta Eaton, 1884 preferred sites with greater water depth and lower water velocity. On the other hand, B. cf. nubecularis and B. rhodani preferred sites with lower water depth and greater velocity. Thus, the highest diversity and/or abundance of mayflies in Plitvice Lakes NP were recorded at study sites with greater water velocity and lower water depth (e.g. Tufa barrier Novakovića-Brod) and with higher pH and water temperature (e.g. lower lotic habitats), which is in accordance with the habitat preferences of most mayfly species (e.g. Bauernfeind and Humpesch, 2001; Bauernfeind and Soldán, 2012).

In conclusion, the mayfly assemblages of Plitvice Lakes NP clearly reflected the high heterogeneity of the investigated karst hydrosystem, where their significant preferences for certain habitat types and physico-chemical water properties were recorded. Due to the specific abiotic factors, such as relatively low annual water temperature, high alkalinity and low productivity (e.g. Habdija et al., 2004; Špoljar et al., 2007), herbivorous and detritivorous mayflies encounter poorer food resources (Bauernfeind and Soldán, 2012). This leads to relatively low species richness in the karst system of Plitvice Lakes NP (Hrovat et al., 2014; Vilenica et al., 2016a). Nevertheless, some interesting faunistic aspects were recorded, such as taxonomically intriguing species of Baetis from the alpinus group, which presents intermediate morphological characteristics between Baetis alpinus Pictet, 1845 and B. nubecularis (see also in Vilenica et al., 2014, 2015). Future investigations should focus on a detailed taxonomic revision of B. alpinus group. Furthermore, species with a wide (e.g. B. rhodani, C. horaria, S. ignita), patchy (e.g. E. submontanus, S. croaticus) and Balkan (e.g. Rh. braaschi) distribution (Bauernfeind and Soldán, 2012; Schmidt-Kloiber and Hering, 2015) were identified. Since the presence or absence of certain mayflies was strongly influenced by the physico-chemical water properties, this study confirmed that they are a powerful tool as descriptors of their environment. Future studies should include systematic ecological study throughout the entire Plitvice Lakes NP area, encompassing the lakes and a wider range of microhabitats. Due to the very sensitive bio-dynamics of tufa deposition in this hydrosystem, long-term monitoring of the inhabiting species should be also conducted. Despite the specifics are in the hydrology of the Dinaric Karst system, the current study showed that the standard methodology for mayfly assemblage monitoring is applicable.

Acknowledgements

The comprehensive macroinvertebrate study at Plitvice Lakes NP was conducted on the basis of permissions of Ministry of Environmental and Nature Protection of Republic of Croatia (RN: 532-08-02-1/7-06-3; 532-08-02-1/7-06-3). The authors would like to thank Andreja Komljenović, Martina Krbavčić, Sanja Žalac, Bruno Polak and Matija Šimac for their essential assistance during field surveys. Many thanks to Ivančica Krulik, Mirjana Jelenčić and Sanja Sviben for assistance in sorting the collected material. We also thank Dr. Anita Belančić for literature loan. The study is a result of projects No. 119-1193080-1206 (PL: M. Kučinić) and No. 119-1193080-3076 (PL: M. Kerovec) supported by the Croatian Ministry of Science, Education and Sports. Many thanks to Prof. Dr. Mladen Kerovec for financial support, and Dr. Ana Previšić, Dr. Helen Barber James, Dr. Jasna Lajtner and Dr. Andreja Brigić for their comments and advice. We would also thank the reviewers for their useful comments and suggestions that markedly improved this manuscript.

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Cite this article as: Vilenica M, Mičetić Stanković V, Sartori M, Kučinić M, Mihaljević Z. 2017. Environmental factors affecting mayfly assemblages in tufa-depositing habitats of the Dinaric Karst. Knowl. Manag. Aquat. Ecosyst., 418, 14.

All Tables

Table 1

Characteristics of the study sites in Plitvice Lakes National Park. Abbreviations of the study sites are presented in Figure 1.

In the text
Table 2

Significant differences in physico-chemical water properties between habitat types in Plitvice Lakes NP based on Kruskal–Wallis H test with multiple comparisons test. Sample size (N) = 31, ⁎⁎⁎ p < 0.001, ⁎⁎ p < 0.01, ⁎ p < 0.05.

In the text
Table 3

Mayfly abundance (shown as a number of individuals per m2) and distribution in Plitvice Lakes NP: (a) springs and upper lotic habitats, (b) tufa barriers and lower lotic habitats. Abbreviations of the study sites are presented in Figure 1.

In the text
Table 4

Spearman's rank significant correlation coefficient (R) for mayfly species and physico-chemical water properties in Plitvice Lakes NP. Sample size (N) = 366, ⁎⁎⁎ p < 0.001, ⁎⁎ p < 0.01, ⁎ p < 0.05.

In the text

All Figures

thumbnail Fig. 1

Location of Plitvice Lakes NP in Croatia and position of 10 study sites in Plitvice Lakes NP. Legend: IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod.
In the text
thumbnail Fig. 2

NMDS analysis of the study sites in the different habitat types in Plitvice Lakes NP based on the composition of mayfly fauna shown (a) pooled per study site and (b) per microhabitat. Study sites: IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod.
In the text
thumbnail Fig. 3

F1 × F2 plane of CCA analysis showing 20 mayfly taxa, 10 study sites encompassing 31 microhabitats in Plitvice Lakes NP and nine selected environmental variables. Legend: Study sites (black circle symbols): IBR = Bijela rijeka river spring, SBR = Bijela rijeka river upper reaches, ICR = Crna rijeka river spring, SCR = Crna rijeka river middle reaches, CM = Crna rijeka river lower reaches, KR = Korana river, PP = Plitvica stream, KM = Tufa barrier Kozjak-Milanovac, LB = Tufa barrier Labudovac, NOB = Tufa barrier Novakovića Brod. Environmental factors (green arrow symbols): T max = maximum water temperature (°C); O2 = O2 (mg L−1); pH = pH value; Con = Conductivity (µS cm−1); Al = Alkalinity (mg L−1 CaCO3); Vel = Water velocity (cms−1); Dep = Water depth (cm); NO3 = Nitrates (mg L−1); NH4 = Ammonium (mg L−1). Taxa (red triangle symbols): A = juvenile Baetidae, B = Alainites muticus, C = juvenile Baetis sp., D = Baetis cf. nubecularis, E = Baetis rhodani, F = Centroptilum luteolum, G = Procloeon pennulatum, H = juvenile Caenis sp., I = Caenis horaria, J = juvenile Ephemerellidae, K = Serratella ignita, L = Torleya major, M = Ephemera danica, N = juvenile Heptageniidae, O = Ecdyonurus submontanus, P = Rhithrogena braaschi, R = juvenile Leptophlebiidae, S = Habrophlebia lauta, T = Paraleptophlebia submarginata, U = Siphlonurus croaticus.
In the text

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