Lake Mikri Prespa Research Articles

Phytoplankton and physical-chemical features of the shallow Lake Mikri Prespa, Macedonia, Greece

Phytoplankton and physical-chemical features of the shallow Lake Mikri Prespa, Macedonia, Greece

The establishment and impact of Pseudorasbora parva, an exotic fish species introduced into Lake Mikri Prespa (north‐western Greece)

Abstract The topmouth gudgeon Pseudorasbora parva Schlegel, 1842, a south‐east asian cyprinid, was introduced accidentally in the Danube Delta in Romania in the 1960s and has now achieved a pan‐Danubian distribution. P. parva has been introduced into other countries, such as Greece, usually inadvertently included with other species imported for fish farming. In 1984–85, during a study of the fish populations of Lake Mikri Prespa (north‐west Greece), several topmouth gudgeon were caught. Our aim was to study the changes in the population size of P. parva over nearly 10 years, to study its life history traits and to assess its potential impacts on native fish species. The catch per unit effort (CPUE) in spring increased significantly between 1984 and 1992. We found evidence that P. parva has established a breeding population in the lake. P. parva combines many characteristics likely to favour a successful colonization (resistance to harsh climatic conditions, early sexual maturity, extended breeding season, broad dietary spectrum). Growth in Lake Prespa, where the oldest individuals captured were 3 years old, is very similar to that observed within its native range. There is evidence for dietary overlap between P. parva and three endemic species: Paraphoxinus epiroticus prespensis, Cobitis meridionalis and Alburnoides bipunctatus ohridanus. No decline in the populations of these three species has yet been demonstrated. Other possible impacts are discussed. The successful colonization by P. parva was certainly favoured by the absence of a true piscivorous fish in the lake and by the isolation and high level of endemism of fish communities. The conservation of the many endemic species in the lake should be a priority and the introduction of exotic species should be banned.

A palaeoecological evaluation of environmental degradation in Lake Mikri Prespa, NW Greece

Sediment cores from Lake Mikri Prespa, NW Greece were examined to determine the extent and possible causes of environmental degradation in the wetland. While diatom analyses of a 210Pb-dated sediment core demonstrate that the lake does not appear to have undergone any significant changes in water quality within the last seventy years, significant variations in the sediment accumulation rate were discovered. These changes appear to be linked to changing anthropogenic pressures on the landscape involving river diversion, rural depopulation and abandonment of terracing cultivation and development of an extensive irrigation network in the catchment. It is concluded that the application of palaeoecological methods has an important role to play in the management of wetland ecosystems by providing a temporal context in which the timing, trends and nature of environmental degradation can be established and evaluated.

Dissolved and particulate trace metals in a wetland of international importance: Lake Mikri Prespa, Greece

This paper reports the dissolved and particulate trace metal distributions in Lake Mikri Prespa, wetland of NW Greece. The concentrations of Cu, Pb, Zn, Cd, Al, Fe, Mn, Ni and Cr were determined in surface and hypolimnetic waters as well as in the inputs and the outflow. Trace metals were connected with two major populations of suspended particles, identified by using the recovery ratio for two different leaching reagents, namely 0.5 N HCl and 1:1 hot aqueous HNO3. The first group is land derived entering the lake through runoff and plays a rather restricted role in its geochemistry. The second group which is more important includes authigenic carbonates, Fe and Mn hydroxides and oxides and organic rich particulates.

Trace elements and chlorinated hydrocarbons in eggs of Pelecanus crispus, a world endangered bird species nesting at Lake Mikri Prespa, North-western Greece

Eggs of the Dalmatian pelican, Pelecanus crispus, collected from 1984 to 1986 at Lake Mikri Prespa, north-western Greece, contained residues of trace elements and PCBs at low concentrations, and of DDE at rather high concentrations. DDE is negatively related to eggshell thickness. Eggshell thickness was reduced by 12–20% in comparison with the pre-1947 (before DDT use) eggshell thickness. However, this decrease did not affect the reproductive success of this species. The main fish species eaten by the Dalmatian pelican at Lake Mikri Prespa were analyzed for pollutants. All the fish contained low concentrations of residues. The contribution of the diet while the birds are on the wintering grounds is unknown. Recommendations for a monitoring programme of pollutants in eggs of the Dalmatian pelican, a world-endangered species, are proposed.

Assessing the trophic status of Lake Mikri Prespa, Greece

Lake Mikri Prespa is a shallow water basin characterized by unstable thermal stratification, primary dimictic condi­ tions and clinograde distribution of dissolved oxygen. The nutrient concentrations are high, indicating a trend towards eutrophication. Total phosphorus input calculated on the basis of the export coefficient accounting for land-uses and other sources is estimated to be of the order of 1 5 x 106 kg yr A mathematical model is applied to assess the trophic status of Lake Mikri Prespa in the light of development projects recently undertaken in its catchment area. Evaluation of the trophic status reveals that the critical and permissi­ ble loading for Lake Mikri Prespa are 0.07 and 0.03 gm^y 1, respectively. Present loading of the lake is estimated at 0.27 gm-2y-' indicating that the lake is already at a dangerous level. On the basis of the employed O.E.C.D. relationships, Lake Mikri Prespa is presently classified as mesotrophic to eutrophic.

Simultaneous determination of gillnet selectivity and population age-class distribution for two cyprinids

A new indirect method for estimating gillnet selectivity is proposed. Using data on the distribution of fish length for each age class plus length distribution for each mesh size, it is possible to calculate, simultaneously, both the selectivities and the proportion of each age class in the population. This new method is applied to two species of cyprinid caught in Lake Mikri Prespa, North-Western Greece.

Do parasites confer a disadvantage to hybrids? : A case study ofAlburnus alburnusxRutilus rubilio, a natural hybrid of Lake Mikri Prespa, Northern Greece.

This paper is the second of three studies of a natural hybrid,Rutilus rubilioxAlburnus alburnus found in Lake Mikri Prespa in Northern Greece. It compares the parasite load of the hybrid to that of its parents, focussing onDactylogyrus spp.,Diplozoon sp.,Bolbophorus confusus andPomphorhynchus bosniacus. The hybrid's gill tissue is parasitised almost exclusively by the parentalDactylogyrus. It follows that theDactylogyrus group constitutes an excellent biological marker for hybridisation. Furthermore, the hybrid is characterised by the following two features: 1. high susceptibility to parasitic infections, 2. important role of ecological components in the recruitment of parasites: for monoxenous parasites (Dactylogyrus spp.), the spatial position of the hybrid and for heteroxenous parasites (P. bosniacus), the trophic position. The parasitology of this particular hybrid may be useful as a model for the properties and fitness of hybrids in general.

Biometrical and biological features of Alburnus alburnus×Rutilus rubilio natural hybrids from Lake Mikri Prespa, northern Greece

Morphometric and meristic characteristics of a rare hybrid between the Adriatic roach. Rutilus rubilio, and the bleak, Alburnus alburnus, discovered in Lake Mikri Prespa, north‐western Greece are described. Axis 1 and 2 of a discriminant analysis using all morphometric and meristic features explains 99.5% of the total variability of the hybrid and both its parents. No back‐crossing is detected in the discriminant analysis: all hybrids found are F1 fish. Age and length of the hybrid and its parents were measured; the best‐fit growth model is the logistic curve. Growth of the hybrid is faster than that of the Adriatic roach and slightly faster than that of the bleak: this indicates heterosis. Problems in the systematics of genera of European cyprinids are discussed.

Environmental problems from practicing agriculture in Prespa National Park, Greece

Prespa National Park is situated at the northwestern corner of Greece bordering Yugoslavia and Albania and covers 25,690 ha of which 8,114 ha are lake. The remaining area is forest, rangeland and arable land in the vicinity of twelve villages. The objectives of the park authority are to preserve the wetland with its special fauna of rare bird species, its flora, the geomorphological formations of the lake and the natural environment. The nucleus of the park is comprised by Lake Mikri Prespa and the surrounding wetland. It is in this wetland that an exceptional assemblage of rare and endangered species breed. However, the park is recently undergoing rapid development of its agroecosystems in terms both of higher subsidiary energy inputs, notably irrigation, and of acreage, i.e. of substituting some of the wetland for cropland. The objective of this study was to assess the potential environmental hazards from practicing agriculture in the park and to propose measures of abatement. Assessment was based on field surveys, administration documents and interviews. Cropland is not intensively used at present. Two thirds is covered by winter cereals and the remaining by other row crops (beans and potatoes). There are no deciduous orchards. Practices are carried out without regard for environmental conservation. Farmers' attitudes towards the wildlife range from indifference to hostility because they attribute the lag in their economic development to the past restrictions imposed by the National Park Administration. The main environmental consequences from the ongoing agricultural development in Prespa are assessed to be a dramatic increase of nonpoint agricultural pollution of the lake, with phosphorus and pesticides as the primary pollutants. Moreover, accidents in the use of pesticides may lead to immediate deterioration of the nucleus wildlife habitats. Since irrigated agroecosystems are there to stay and grow in subsidiary energy, measures are needed to prevent harmful consequences. Such measures are the alleviation of the land ownership problem, adoption of cultural practices to limit soil erosion, rational use of chemical fertilizers and pesticides and education of farmers. It is concluded that the internationally invaluable natural ecosystems of the park are definitely threatened by the development of the irrigated agroecosystems. The measures proposed will limit this threat and at the same time will help to perpetuate the productivity of the agroecosystems themselves.

Land Cover/Use Analysis of Prespa National Park, Greece

Prespa National Park in Greece is an important breeding-area for rare and endangered waterbird species, but people living within the Park and using its resources create serious conservation problems. An environmental management plan which will regulate mainly the human activities within the Park is therefore necessary. Such a plan should be based on a land cover/use analysis of the area, for which much of the necessary information, in the form of a thematic map, has been collected by interpreting blackand-white aerial photographs. The procedure involved the development of a classification system, transferring the interpreted data onto a base-map, field-checking the results, and tabulating the area measurements with the pertinent errors.Of the total Park area (25,690 ha), 66.5% is classified as terrestrial (forestland, rangeland, agricultural land whether irrigated, non-irrigated, or abandoned, wet meadows/marshland, barren and eroded land, and urban areas), and the remainder as aquatic (water, reedbeds). The most extensive category in the Park is forestland, much of which is seriously degraded. Rangeland provides forage for sheep and goats, being also degraded owing to uncontrolled grazing. Wet meadows/marshland are invaluable as waterbird breeding and feeding habitats, but the present use of this category as grazing fields, and its proximity to agricultural land and to the existing irrigation/drainage system, have all had negative impacts on the resource. Irrigated land is almost half of the cultivated area.The abandoned agricultural land is interspersed within the forestland and is a result of the human population decline in the area, while barren and eroded land has resulted from prolonged land misuse. Twelve old villages are distributed over the Park, being visually unobtrusive. Lake Mikri Prespa is the main water-body and covers almost the entire nucleus of the Park. Extensive reedbeds are found along the lakeshores, which are the main breeding habitats of certain waterbirds. As land cover/use analysis of the Park has shown much serious environmental degradation, conservation measures should be undertaken urgently.

Study of communities of Monogenea Dactylogyridae parasites of the Cyprinidae in Lake Mikri Prespa (northern Greece). Description of 3 new species from an endemic Barbus: Barbus cyclolepis prespensis Karaman, 1924

In this paper are described 17 species of Monogenea Dactylogyridae, parasites of Cyprinidae from lake Mikri Prespa, in Greece: 14 species have been already reported in mediterranean region; 3 new species have been harvested on an endemic Barbus, B. cyclolepis prespensis, Dactylogyrus balkanicus n. sp., Dactylogyrus crivellius n. sp., Dactylogyrus prespensis n. sp. For these communities of Dactylogyrus, we discuss some problems of parasite specificity, speciation and biogeography. From the morphological types, we suggest for D. crivellius and D. prespensis an allopatric speciation and for D. balkanicus, a synxenic sympatric speciation.