PLANKTONIC CILIATES IN DEPRESSION RESERVOIRS CREATED AS A RESULT OF THE GROUND SUBSIDENCE (POLESIE LUBELSKIE, EASTERN POLAND)

Tomasz Mieczan
Department of Hydrobiology, University of Agriculture in Lublin, Poland

ABSTRACT

The abundance and species composition of ciliates were analysed in pelagic zone of two depression reservoirs: Nadrybie and Szczecin (Polesie Lubelskie, eastern Poland) from May to November 2002. Totally 21 ciliates species were found in Szczecin reservoir and 24 in Nadrybie reservoir. The mean abudance of ciliates was 31 ind. ml^-1 in Szczecin reservoir and 26 ind. ml^-1 in Nadrybie reservoir. Ciliates communities in both reservoirs were dominated by Scuticociliatida (Cinetochilum margaritaceum) and Peritrichida (Vorticella sp.). Densities and species composition of ciliates showed clearly changes. In both reservoirs the correlation between ciliates density and conductivity, pH, TP and TOC was found.

Key words: plankton, ciliates, depression reservoirs.

INTRODUCTION

The ecological role of planktonic ciliates as trophic links between bacteria and pelagic zooplankton has been increasingly appreciated during recent years [8]. Ciliates graze on autotrophic and heterotrophic pico- and nanoplankton and functioning as prey for larger zooplankton, contribute to the remineralization and cycling of nutrients [4, 11, 19]. They play a pivotal role in the indication of pollution degree in lakes [17].

Up till now, no research on plankton ciliates in depression reservoirs has been carried out. Thas why the goal of these research was to study temporal fluctuation in species composition, numbers of planktonic ciliates and their relation to physical and chemical parameters in two depression reservoirs located in Polesie Lubelskie Region (eastern Poland).

STUDY AREA

Nadrybie and Szczecin are situated in the Łęczna-Włodawa Lakeland (eastern Poland). They are relatively small, shallow depression reservoirs (surface area 30 ha and 105 ha, max. depth 1.5 m and 0.7 m, respectively). They were created in 1984 and 1993, respectively, as a result of the ground subsidence on the area of the “Bogdanka” hard-coal mine. The reservoirs are supplied with seepage water from adjacent agricultural areas. They have well-developed phytolittoral, typical of small lakes. It occupies 60% in Szczecin reservoir and 75% in Nadrybie. A total of 53 vascular plant species were found, 40 in Szczecin reservoir and 37 in Nadrybie, which represented four ecological communities: amfiphytes, helophytes, elodeids and pleuston. The helophytes were dominated by Typha angustifolia in Szczecin and by Phragmites australis in Nadrybie reservoir, the elodeids by Ceratophyllum demersum and Polygonym amphibium, respectively [16].

MATERIAL AND METHODS

Three samples were taken in pelagic zone in the middle water column by means of a 5-litre Bernatowicz sampler [3]. Samples were pooled together, carefully mixed and 500 ml sample was fixed with Lugol’s solution and stored in the dark at 4°C. Each sample was condensed to 5-15 ml and ciliates were determined and counted at a magnification 500x. Four microscopic slides were preparated from each sample and examined. Taxonomic identifications were based mostly on Foissner et al. [8].

The following physical and chemical factors were studied: visibility, pH, O₂, conductivity, TOC and biogens (TP, PO₄, N-NH₄, N-NO₃). Visibility, pH, O₂ and conductivity was determined in situ using the Secchi disc and electrode Jenway 3405 and remaining factors were analysed in the laboratory, according to Hermanownicz et al. [9].

RESULTS

The physico-chemical properties of water were similar and only visibility, oxidability, TP, PO₄ and TOC were significantly different between reservoirs and their particular values are presented in table 1. These parameters confirmed eutrophic status of the reservoirs and were similar to that observed in eutrophic lakes in Łęczyńsko-Włodawskie Lakeland [15].

A total number of 24 ciliates species were found in plankton samples. The biggest number – 24 species, were found in Nadrybie reservoir, a little less – 21 species in Szczecin reservoir (tab. 2). Only the Nadrybie reservoir seem to have the characteristic (exclusive) species. There were the following species: Actinobolina radians, Disematostoma tetraedricum and Frontonia sp. The highest number of species was noted in May and November while the lowest one in June.

The mean abudance of ciliates was 31 ind. ml^-1 in Szczecin reservoir and 26 ind. ml^-1 in Nadrybie reservoir.

The densities of ciliates showed clearly marked seasonal changes. In Szczecin reservoir they fluctuated from 8 ind. ml^-1 in April to 42 ind. ml^-1 in November. During this period Scuticociliatida (Cinetochilum margaritaceum) and Prostomatida (Coleps hirtus) constituted 75% of the total numbers of the ciliates. Two lower peaks were observed in May and August (fig. 1, 2). At this time Peritrichida (Vorticella convallaria) and Scuticociliatida (Cinetochilum margaritaceum) dominated, constituting 50% of the total numbers of the ciliates.

Density of ciliates in Nadrybie reservoir ranged from 3 ind. ml^-1 in Juny to 26 ind. ml^-1 in November, and showed several maxima (May, August, November). The highest peak was noted in November with dominance of Scuticociliatida (Cinetochilum margaritaceum) (95%). Slightly lower peak was observed in May with domination of Peritrichida (Vorticella convallaria) (fig. 1, 2). In July and August (Szczecin and Nadrybie reservoirs) more numerously occurred Haptorida (Didinium nasutum), and mixotrophic Oligotrichida (Strombidium sp.) with symbiotic zoochlorellae.

Occurrence and abundance of ciliates were clearly correlated with chemical conditions. The significant high correlation between pH, conductivity, PO₄, TP, TOC and ciliate numbers were found in both reservoirs (tab. 2).

In Szczecin and Nadrybie reservoirs bacteriovorous and omnivorous taxa predominated in the trophic structure of ciliates. In Szczecin reservoir the highest numbers of bacteriovores was noted in October. In Nadrybie reservoir the highest numbers of bacteriovores was noted in May and November, omnivores in June.

DISCUSSION

The ciliate species composition in both reservoirs was similar to the reported in other papers [1, 2, 14, 18]. According to Finlay [7] global distribution of ciliates corresponds well with the notion that microorganisms are ubiquitous of their small size and high abundance which generate high levels of random dispersal.

The densities of ciliates showed clearly marked seasonal changes. In the reservoirs the peaks in spring and autumn were probably determined by abiotic water factors. They were observed also in eu- and hypertrophic lakes [18, 19]. Beaver and Crisman [2] found that protozoan abundance tended to increase with increasing lake productivity. The present study clearly showed that ciliates abundance correlated with reservoirs productivity, too. Wišckowski et al. [20] demonstrated that concentration of appropriate food (bacteria, nanoflagellates and algae) are probably the major regulator of abundance, biomass and diversity of planktonic ciliates. Very high densities of ciliates in spring in Nadrybie reservoir might have been caused by the phytoplankton density.

Beaver and Crisman [2] found that small bacterivorous ciliates, mainly Scuticociliatida are typical of eutrophic lakes. Also omnivorous Coleps hirtus and Vorticella sp. dominated in pelagial of lakes of pH>7 and their importance increase with eutrophication [10]. In July and August more numerously occurred Haptorida (Didinium nasutum). This species feeds mainly on Coleps hirtus and Halteria gradinella [5]. In both reservoirs its increasing density can be related to the increase of Coleps hirtus and Halteria gradinella abundance. Also mixotrophic Strombidium sp. with symbiotic zoochlorellae was the more abundant species in July and August. The genus often dominates in ciliates communities in trophically different freshwater ecosystems. These results are in good agreement with the statement of Kalinowska [12], Mieczan [14], Takamura et al. [18].

In Szczecin and Nadrybie reservoirs bacteriovorous taxa predominated in the trophic structure of ciliates. Their increased density can be related to the increased organic matter. Spring and autumn peaks of bacteriovorous seem to be a common pattern [12, 13, 14]. A slight proportion of algaevorous ciliates could have been caused by problems with getting the food – the dominating were filamentous and colonial algae, inaccessible for ciliates.

CONCLUSIONS

Diversity and species compositions of ciliates showed clearly seasonal changes. In both reservoirs bacteriovorous ciliates occurred in the highest number. A slight proportion of algaevorous ciliates could have been caused by problems with getting the food – the dominatig were filamentous and colonial algae, inaccessible for ciliates. In both reservoirs the correlation between ciliates abundance and conductivity, pH, TP and TOC was found.

ACKNOWLEDGEMENTS

I am very grateful to prof. Ryszard Kornijów for valuable suggestions for improvement of the manuscript.

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