Structure and Functioning of Food Webs in the Communities of the Ohrid, Prespa and Skadar lakes – a Qualitative Modelling Approach

M. Pavlova1*, D. Milosevic 2, A. Talevska 3, Lachezar Pehlivanov 1 and T. Talevski 4

1 Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Sofia, Bulgaria 2 University of Montenegro, Faculty of Science and Mathematics, Department of Biology, Podgorica, Montenegro 3 University of Belgrade, Faculty of Biology, Belgrade, Republic of Serbia 4 University “St.Kliment Ohridski”, PSI Hydrobiological Institute, Ohrid, Republic of Macedonia

[email protected]

Abstract

The aim of this study was to compare the features of trophic structure of the fish communities in three large lakes on the Balkan Peninsula – the Ohrid, the Prespa and the Skadar, using innovative qualitative method for modelling the trophic webs (Loop analysis). We hypothesized, that there should be differences in both the structure and functioning of the trophic webs of fish communities in the three lakes, conditioned by differences in the main morphologic and hydro chemic features of the water bodies. Published data about species composition of the ichthyocenoses in the three lakes were used to define the trophic groups. The trophic affiliation of the fish species was referred to recent data, presented in the e-source FishBase.org. Values of trophic index were also determined according to the reference data. The models of trophic webs in the three compared fish communities were built using PowerPlay software for Loop analysis, designed in the Oregon State University, USA. Software “PRIMER v6” was used for testing the similarity among the trophic structure of the fish communities in the three lakes. Generally, six trophic groups of were defined in the compared lakes: omnivorous, zoobenthivorous, zooplanktivorous, phytoplanktivorous, macrophytivorous, and piscivorous. Representatives of the all six trophic groups were identified only in the Skadar lake, whereas, the zooplanktivorous fishes are not presented in the Prespa lake and the macrophytivorous ones – in the Ohrid lake. Nevertheless, high value of Bray-Curtis similarity (68.65% – 81.63%) between the lakes was recorded according to number of species in the six trophic groups. Significant similarity of species composition in the zooplanktivores, phytoplanktivores and macrophytivores was found in opposite to the different species composition in the omnivorous, zoobenthivorous and piscivorous groups. The elaborated models of food webs in fish communities suggest a general resemblance in their functioning in the three lakes regardless of significant diference in the trophic structure of communities. The presence of local endemic salmonid species is essential for the functioning of these lake ecosystems, but considerable overlap of their trophic niches with non-native salmonid species could be expected.

Key words: Fish communities, Trophic structure, Loop Analysis, Trophic groups, Trophic resources, Niche overlap, Ecosystem functioning

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 1 Introduction In the complete summary of the available data about the ichthyofauna of the three lakes (1)) reported 11 native and 12 introduced fish species in the Prespa Lake, respectively 21 and 7 ones in the Ohrid and 34 and 13 – in the Skadar Lake. Strong relation between the environmental conditions and the high endemism within the ichthyofauna in both the Ohrid and the Prespa Lakes was found (2). In 2004 the trophic state of the Ohrid Lake was reported as olygotrophy and the Prespa Lake was considered to be meso-eutrophic. For comparison, as reported by the same author, before 1988 the Ohrid lake was defined as high oligotrophy and the Prespa – as oligo-mesotrophy respectively. There is a opinion, that the Prespa Lake trophic state is one of the main factors for the worsening of the Ohrid’s lake state, due to the underground connection between them ( 3). According the phosphorus concentrations the Skadar Lake is mainly oligotrophic and mesotrophic (4). The predomination of the omnivorous golden carp Carassius auratus in the diet of pygmy cormorant reported for the years 1973-74 and 2006 was considered an indirect evidence for the eutrophication of the Skadar Lake (5). Furthermore, after (2) the major threats to these lake ecosystems are considered to be the anthropogenic pressures mainly through the enrichment with nutrients, shrinking of the water volumes, and the interruption of the natural migrating path of many fish species by the dams (i.e. Crni Drim dam). Moreover, introduction of allien fish species within the ichthyocenoses of the three lakes have also render an account. For the Prespa Lake, this phenomenon is considered one of the remarkable threats to the whole ecosystem (6). The qualitative modeling became a widely used method for representing the subtle ecosystems functioning to a wide audience as well as to the scientists. The Loop- modeling approach described in (7) and (8) has been used for revealing the interrelations and functioning in different ecosystems types and it was find to work quite effectively in sea and fresh water studies (9,10). Aggregation of species into groups based on their similar feeding is a desirable goal for food web modelers (11). The trophic attributes of the fish as basis for the qualitative modeling has been also successfully for revealing interrelationship among the biocenoses into the Srebarna Lake ecosystem (NE Bulgaria) (12).

Context The well studied fish community composition in the three lakes favors analyzes of its trophic structure. Fish trophic attributes description would be usefull for clarifying the functional integrity in the three ecosystems. Hence it would be beneficial for proposing all stakeholders’ evidence based decisions for the sustainable use of these valuable ancient lakes.

Methodology applied Data about species composition of the ichthyocenoses in the three lakes (1) were used to define the trophic groups. The trophic affiliation of the fish species and the trophic index was referred to recent data, presented in the e-source FishBase.org with the cited references. The models of trophic webs in the three compared fish communities were built using PowerPlay software for Loop analysis, designed in the Oregon State University, USA. The similarity checking among the trophic structure of the fish communities in the three lakes was made using “PRIMER v6” software (13, 14).

Results obtained Three types of food components were can be indicated for the fish species in the target lakes after the referent data (FishBase.org): • food: zooplankton, macrozoobenthos, fish; • Plant food: phytoplankton, macrophytes, phytobenthos; • Detritus.

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 2 Three main trophic levels are defined in the food composition of the studied fishes: 1) Primary producers (i.e., phytoplancton, macrophytes and phytobenthos); 2) First order consumers (mainly benthic and plankton invertebrate ) and 3) Second order consumers (fishes Table 1. Affiliation of the ichthyofauna species content according to (1) to the six trophic groups’ defined at the three lakes studied with references given. Legend: PRSL- the Prespa Lake, OHRL- the Ohrid Lake, SKDL- the Skadar Lake; P.O. Genus- personal observations, referred to the genus/ family observed.

Species Abbreviation Mainfood References PRSL OHRL SKDR

Acipenser naccarii Bonaparte, 1834 -1841 Anac MZB (15) 0 0 1 Acipenser sturio Linnaeus, 1758 Astu MZB (15) 0 0 1 Alburnoides ohridanus (Karaman, 1928) Aohr MZB (16) 0 1 1 Alburnoides prespensis Karaman, 1924 Apre MZB (16) 1 0 0 Alburnus belvica Karaman, 1924 Abelv Omni (17) 1 0 0 Alburnus scoranza (Heckel et Kner, 1858) Asco Zpl (15, 20, 21) 0 1 1 Alosa fallax (Lacepède, 1803) Afal Zpl (15, 20, 21) 0 1 1 Alosa sp. Zpl (15, 20, 21) 0 0 1 Ameiurus nebulosus Lesueur, 1819 Aneb Omni (22) 0 0 1 Anguilla anguilla (Linnaeus, 1758) Aang MZB (15) 1 1 1 Barbatula zetensis (Šorić, 2000) Bzet MZB P.O. Genus Barbatula 0 0 1 Barbatula sturanyi (Steindachner, 1892) Bstu MZB P.O. Genus Barbus 0 1 0 Barbus prespensis Karaman, 1924 Bpre MZB (15, 19) 1 0 0 Barbus rebeli Köller, 1925 Breb MZB (15, 19) 0 1 1 Carassius gibelio Bloch, 1782 Cgib Omni (15) 1 1 1 Chondrostoma ohridanus Karaman, 1924 Chohr MZB (15) 0 1 0 Chondrostoma prespense Karaman, 1924 Chpre MZB (15) 1 0 0 Chondrostoma scodrensis Elvira, 1987 Chsco MZB (15) 0 0 1 Citharus linguatula (Linnaeus, 1758) Ciling PR (15) 0 0 1 Cobitis ohridana Karaman, 1928 Coohr MZB (15) 0 1 1 Cobitis meridionalis Karaman, 1924 Comer MZB (15) 1 0 0 Ctenopharyngodon idella Valenciennes 1844 Ctide Mph (15) 1 0 1 Cyprinis carpio Linnaeus, 1758 Ccarp Omni (15) 1 1 1 Dicentrarchus labrax (Linnaeus, 1758) Dlab PR (15, 23) 0 0 1 Gambusia holbrooki Girard, 1859 Ghol MZB (24) 1 1 1 Gasterosteus gymnurus Cuvier, 1829 Ggym MZB (25) 0 0 1 Gobio ohridanus, Karaman, 1924 Gohr MZB (15) 0 1 0 Gobio skadrensis Karaman, 1936 Gsca MZB (15) 0 0 1 Hypophthalmichthys molitrix Valenciennes 1844 Hmol phpl (15, 26, 27 ) 1 0 1 Hypophthalmichthys nobilis Richardson, 1845 Hnob phpl (15, 26, 27 ) 0 0 1 Lepomis gibbosus Linnaeus, 1758 Lgib Omni (28) 1 1 0 Liza ramada Risso, 1826 Lram Omni (27) 0 0 1 Megalobrama terminalis Richardson, 1844 Mter MZB (28) 0 0 1 Mugil cephalu Linnaeus, 1758 Mceph Omni (29); (30) 0 0 1 Mylopharyngodon piceus Richardson, 1845 Mpuc Zpl (31) 0 0 1 mykiss Walbaum, 1792 Omyk PR (32) 1 1 1 Pachychilon pictum (Heckel et Kner, 1858) Ppic MZB (15, 16) 0 1 1 Parabramis pekinensis, (Basilewsky, 1855) Ppek MZB (28) 1 0 0 Pelasgus minutus Karaman, 1924 Pmin MZB (15) 0 1 1 Pelasgus prespensis Karaman, 1924 Ppre MZB (15) 1 0 0 Perca fluviatilis Linnaeus, 1758 Pflu Omni P.O. Perca fluviatilis 0 0 1 Phoxinus limaireu Schinz, 1840 Plim MZB (26) 0 1 1 Pleuronecte sflessus Pallas, 1811 Pfle MZB (21, 35) 0 0 1 Pomatoschistus montenegrensis Miler & Šanda, Pomon MZB (36) 0 0 1 2008 Pseudorasbora parva Temminick & Schlegel, Pparv omni (26) 1 1 1 1846

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 3 Rhodeus amarus (Bloch, 1782) Rham Phpl (15) 1 1 1 Rutilus albus Maric, 2010 Rutalb Omni (17) 0 0 1 Rutilus ohridanus (Karaman, 1924) Rutoh Omni (15) 0 1 0 Rutilus prespensis Karaman, 1924 Rutpr Omni (15, 17) 1 0 1 Salaria fluviatilis Asso, 1801 Saflu MZB (15) 0 0 1 aphelios, Kottelat,1997 Safe PR (15) 0 1 0 Karaman, 1928 Sabal PR (15) 0 1 0 Salmo farioides Karaman, 1937 Safar PR (15) 0 0 1 Salmo letnica Karaman, 1924 Salet PR (15) 1 1 0 Poljakov, Filip & Basho 1958 Salum PR (15) 0 1 0 Cuvier, 1817 Samar PR (15) 0 0 1 Salmo ohridanus Steindachner 1892 Saohr PR (15) 0 1 0 Salmo peristericus Karaman, 1938 Saper PR (15) 1 0 0 (Heckel, 1851) Saobt PR (15) 0 0 1 fontinalis Mithchill, 1815 Safon PR (37) 0 0 1 Scardinius knezevici (Bianco & Kottelat, 2005) Scknez Omni (38) 0 1 1 Silurus glanis Linnaeus, 1758 Sigla Omni (15) 1 0 0 Squalius prespensis Fowler, 1977 Sqpre Omni P.O. genus Squalius 1 0 0 Squalius squalus Bonaparte, 1837 Sqsqu Omni (15) 0 1 0

Squalius platyceps Zupancic, Maric, Naseka & Sqplat Omni (39) 0 0 1 Bogutskaya, 2010

Telestes montenegrinus (Vuković, 1965) Tmont MZB (15) 0 0 1 Thymallus thymalus Linnaeus, 1758 Ththy MZB (20) 0 0 1 Tinca tinca Linnaeus, 1758 Ttin MZB (15) 1 0 1

Six trophic groups were identified among the focused fish species (Table 1) according the predominating food component as follows: Group 1: Piscivores, i.e. predaceous fishes; Group 2: Phytoplanktivores (feeding mainly on planktonic algae); Group 3: Macrophytivores (feeding maily on submerged high plants); Group 4: Zoobentivores feeding mainly on macrozoobenthos); Group 5: Zooplanktivores (feeding mainly on zooplankton); Group 6: Omnivores (feeding on more than one trophic level (for example, Ohrid bleak Alburnus belvica which main food consists equally from phyto- and zooplancton).

Figure 1. Percent representation of the six trophic groups in the ichthyocenoses of the Prespa, ohrid and Skadar Lakes. Legend: PRSL- the Prespa Lake, OHRL- the Ohrid Lake, SKDL- the Skadar Lake; zpl- zooplanctivores; pr- predaceous; mph- macrophytivores; phpl- phytoplanctivores; mzb- macrozoobenthivores; omni- omnivores. The full range of trophic groups is represented in the Skadar Lake only (Fig.1). The absence of both the groups of zooplanktivores and macrophytivores might be attributed to the lake trophic state. The oligo-mezotrophy suggests low levels of nutrient concentrations (40) reflected by specific dynamics

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 4 and seasonal successions of the zooplankton groups (41). After this study, the copepodite character of the lake zooplankton is considered an indicator for good trophic conditions in the pelagic zone but the dynamics of zooplankton quantity probably favors the large number of omnivorous fish species (Fig. 3). These species have to appear as opportunists and to supplement their diet with other trophic components in the periods of low zooplankton density.

Figure 2. UPGMA cluster analysis dendrogram for the Bray- Curtis similarities among the number of species in each trophic group in the ichthyofauna of the three lakes studied. On the other hand, it is clearly visible, that the main food resource for fish in the three focused lakes comes from the macrozoobenthic communities. High value of Bray-Curtis similarity index among the lakes was reported according to the species number in the each of the six trophic groups defined. Significant similarity of the species composition in the trophic groups of Zooplanctonivores, Phytoplanctonivores and Macrophytivores was also found. Diferent composition of the trophic groups of omnivorous, macrozoobenthivorous and predaceous fish was reported in each lake. The trophic indexes graphs for the three lakes (Fig. 3) represent significant differences among the functioning of the three fish communities. The predaceous trophic group in the all lakes consists of 5 species, but the non-native O. mykkis is the only common species in the three of them. On the other hand, the herbivorous fishes are well presented in the Skadar Lake only. According to (42), macrophyte vegetation in the lakes provides habitats, food, spawning ground, nursery and a shelter from predators for a large number of fishes. In spite of the similar number of macrophyte species reported, our analysis shows important role of the high plant communities as a food resource for fish mainly in the Prespa and the Skadar Lake, where the macrophytivorous fishes from the East complex are presented. Qualitative Loop analysis The models show resemblance in functioning of the trophic webs in the Ohrid and the Skadar Lakes (Fig. 4). The first main difference between the two lacustrine trophic webs lies in the greater presence of the herbivorous fishes in the Skadar Lake. The second distinction is in the fish species within the predaceous complexes. In the Ohrid Lake, three different primary producers were found in the fish food: phytoplankton, macrophytes and phytobenthos. In both the Skadar and the Prespa lakes the phytoplankton and macrophytes predominate in the diet of the fish consumers of 1st order.In the Prespa Lake very important significance of the macrophytivorous fish is found. The basis for division within this group might be found in the primary producers in the fish diet. The macrozoobenthos seems to be the most available trophic resource in the two lakes. On the whole, in all three lakes the salmonid fishes are found to be key species being the top predators. The presence of local endemic species of salmonid complex is essential for the functioning of the three lake ecosystems since they have evolved in the evolution on place along with their trophic resource. In the Skadar lake some migrant marine species (such as: D. labrax C. linguatula) are included as key species, together with the freshwater salmonid complex. Trophic niche overlap of the local salmonids with the introduced Rainbow O. mykiss might be expected (Fig. 5c).

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 5

Prespa Lake

Skadar Lake Figure 3. Trophic index values (minimal, maximal and average) for the fish species from the three lakes. Legend: for the abbreviations of the genus and species names - see tabl.1; the green lines represents the Herbivores trophic level, the red ones - the Predators trophic level.

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 6

(a) (b) Figure 4. The Ohrid and the Skadar Lake trophic web general- (a) and prediction with increasing the level of significance of Macrozoobenthos factor (b) Legend: Zpl- zooplankton; Phpl- phytoplankton; DOM- dissolved organic matter; Mphy- macrophytes; hxv- sun light; Mzb- macrozoobenthos, Phb- phytobenthos, ZplvF- zooplanctivorous fish; MzbvF- macrozoobenthivorous fish; OmniF- omnivorous fish; PrF- predaceous fish; the red circles means dincreasing of the level of significance of the relative factor and the yellow ones- decreasing of it.

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 7

(a) (b) (c) Figure 5. The PrespaLake trophic web general- (a), prediction with decreasing the level of significance of macrophytivorous fish trophic group factor (b) and simplified trophic relation among the omnivorous Ohrid bleak and the native and non-native- salmonid species. Legend: Zoopl- zooplankton; Phpl- phytoplankton; DOM- dissolved organic matter; Mphy- macrophytes; hxv- sun light; Mzb- macrozoobenthos, Phb- phytobenthos, ZplvF- zooplanctivorous fish; MzbvF- macrozoobenthivorous fish; OmniF- omnivorous fish; PrF- predaceous fish; Abelv- A. belvica;Sper- S. peristericus; Omyk- O. mykkis; the red circles means increasing of the level of significance of the relative factor and the yellow ones- decreasing of it.

BALWOIS 2012 - Ohrid, Republic of Macedonia - 28 May, 2 June 2012 8 Conclusions

The functioning of the presented trophic webs is influenced of the trophic state of the three studied lakes. The oligotrophic Ohrid Lake fish community functioning differs significant from these in the meso- and eutrophic Skadar and Prespa Lake The trophic web in the deep oligotrophic Ohrid Lake with poorly developed vegetation might be regarded as a primary stage in the evolution of trophic relationships in the lacustrine ecosystem. At the opposite end is the shallow eutrophic Prespa Lake overgrown with macrophytes. The Skadar Lake occupies intermediate position with two clearly separated zones – a large shallow area overgrown with macrophytes and a deep zone with less developed vegetation. The habitat diversity there is a prerequisite for development of both the types of the trophic webs.

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