PLANKTONIC CILIATES IN PEAT PONDS OF DIFFERENT ACIDITY (E POLAND)

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

ABSTRACT

The aim of the investigations was to determine the composition and abundance of the planktonic ciliates occurring in three small peat ponds of different acidity – from 3.2 to 6.2 (south-eastern Roztocze, E Poland). The highest diversity and density of ciliates were noted in high pH (>6) pond, the lowest in low pH ponds. The seasonal changes of ciliate communities in three ponds were quite similar, reaching peak values in October during the mass development of small Scuticociliatida and Prostomatida. The density throughout July was the lowest. Probably in peat ponds the biggest factors limiting the degree of the presence of planktonic ciliates are the pH, conductivity and concentrations of total phosphorus and organic matter.

Key words: peatlands, ponds, pH, plankton, ciliates.

INTRODUCTION

Peat-storing wetlands are important freshwater habitats and provide important habitats for often endemic flora and fauna and are in danger of destruction due to human uses, such as drainage for agriculture or excavation of peat [12,21]. As a bog has limited external drainage, the surface is frequently covered with small ponds. Small peat ponds with low pH, high concentrations of humic matter have low levels of inorganic nutrients and their typical brown water colour reduces light penetration, thus primary productivity is usually low. Low pH is a biological effect of peat-moss (Sphagnum) occurring around ponds or even expanding over its water table from of a mat with water pH about 3.0-5.0 [19,20]. The limnology of this unique lentic system, in spite of the possessing interesting ecological attributes, is poorly understood worldwide. Planktonic ciliates ecology in these specific ecosystems is understudied compared to other aquatic systems such as lakes, streams and rivers.

An abiotic factor important in the classification of peatlands is pH [21]. However, the role of pH in structuring of zooplankton communities has rarely been examined explicitly in peatlands. The studies of the effect of changing pH on zooplankton communities have been concentrated on rotifers [4,6,7]. To date, the taxa composition of planktonic ciliates in small peat ponds has not been investigated because it is difficult to compare the results obtained. Ecology and spatial distribution of ciliates have been studied only in humic lakes [2,3,15,18]. This studies indicate that with increased acidity, both the abundance, biomass and species richness decreased. However, studies in acid lake in central France indicate that the major role in the development of communities of microorganisms play the high concentration of organic carbon [1]. Up to the present, the research focused on ciliates in relation to chemical factors in small peat ponds are not common.

The detail aims of the present study were: identification of taxonomic diversity of planktonic ciliates communities in relation to pH, conductivity, TP and TOC in three small peat ponds of different acidity (from about 3.2 to 6.2).

MATERIAL AND METHODS

Studies have been carried out in three small peat ponds: Nowiny 1 (N1), Nowiny 2 (N2) and Jęzior (J) (area <0.9 ha, mean depth 1.0-2.5 m) of different acidity (from 3.2 to 6.2) (Table 1). The ponds are located in south-eastern Roztocze (E Poland). All of the ponds adjoins a highmoor and transitional peatlands formed by Sphagnum and covered by Carex acutiformis Ehrhart., Carex gracilis Curt., Drosera spp. and Equisetum limosum (L.). In spring (May), summer (July) and autumn (October) 2005 eight samples were collected from each pond with a 5-litre Bernatowicz sampler, every 0.5-metre. Samples were taken on two stations: pelagic – located in the deepest part of each ponds and littoral. Samples from all layers were pooled together, mixed and 500 cm^-3 sample was fixed with Lugol’s solution (0.2% final concentration). Three sub-samples of 50 cm^-3 volumes were settled for at least 24 h in plankton chambers. Ciliates were enumerated and identified with an inverted microscope at 400 - 1000 x magnification [10]. The entire content of each Untermöhl chamber was surveyed. Ciliate biomass was estimated by multiplying the numerical abundance by the mean cell volume calculated from direct volume measurements using appropriate geometric formulas [8].

All data collected were analysed statistically by means of GLM and CORR procedures of SAS Programme. One-way ANOVAs were run on abundance and biomass data to separately assess the protozoan variability caused by the ponds (N=24). Canonical Correspondence Analysis (CCA) was performed to relate water chemistry variables to ciliate occurrence.

RESULTS

From all of the studied ponds, the highest pH values was noted in Jęzior pond (pH>6) and the lowest in Nowiny 1 pond (pH=3.2). Conductivity and TP reached the highest values in higher pH pond. Only content of total organic carbon reached the highest values in low pH pond. The chemical properties of water were significantly different in ponds (ANOVA, F_11.23=12.673, P<0.01) (Table 1).

The number of ciliate taxa visibly differed in particular ponds. The number of ciliate taxa - 4 was significantly lower in the low pH pond (pH=3.2) compared to the high pH ponds were found from 9 to 14 of planktonic ciliate species (pH=5.0 and pH=6.2) (ANOVA, F_11.23=11.917, P<0.01). Further, protozooplankton species diversity was relatively low and included seven groups: Oligotrichida (3 species), Prostomatida (3 species), Peritrichida (2 species), Scuticociliatida (2 species), Pleurostomatida (2 species), Colpodea (1 species) and Haptorida (1 species) (Table 2). In ciliate community three taxa: Strombidium viride, Strombilidium spp. and Cinetochilum margaritaceum were the most frequent species. The mean numbers of planktonic ciliates were significantly different between examined ponds (ANOVA, F_11.23=13.117, P<0.01). The lowest density was observed in low pH pond and it was 5 ind. cm^-3, being a little higher in pH=5.0, up to 12 ind. cm^-3, and the highest – 23 ind. cm^-3 in high pH pond (Fig. 1). However, the greatest biomass of ciliates occurred in low pH pond – 19.2 ng cm^-3 and the lowest in high pH pond – 15 ng cm^-3 (ANOVA, F_11.23=11.112, P<0.01) (Fig. 2). The composition of ciliates changed in particular ponds. In low pH pond (pH=3.2) the species belonging to mixotrophic Oligotrichida (Strombidium viride, Strombilidium spp.), predators Haptorida (Lacrymaria olor) and bacterivorous Scuticociliatida (Cinetochilum margaritaceum), constituted 78%, 12% and 10% of the total numbers of the ciliates, respectively. In pond with pH=5.0 species belonging to Oligotrichida (Strombidium viride), Scuticociliatida (Cinetochilum margaritaceum) and Pleurostomatida (Amphileptus cleparedei), constituted 46%, 26% and 13% of the total numbers of the ciliates and the other orders from 4% to 7%. In high pH pond (pH=6.2) Scuticociliatida (Cinetochilum margaritaceum, Cyclidium sp.), Oligotrichida (Strombidium viride) and Peritrichida (Vorticella convallaria-Komplex and Vorticella microstoma-Komplex) constituting 46%, 18% and 13% of the total numbers, respectively. The other orders of ciliates reached 3% to 9% of the total population (Fig. 3). The dynamics of ciliate communities in three ponds were quite similar, reaching peak values in October during the mass development of small Scuticociliatida and Prostomatida. The density throughout July was the lowest.

In studied ponds two similar groups of planktonic ciliates with different structures were found (CCA – Canonical Correspondent Analysis). The first group was from a pond with low level of pH and the second group from the pond with a pH close to neutral. In studied ponds, classification of environmental changes (CCA) has shown that axis 1 is most closely related to the pH, conductivity and total organic carbon and reflects the reaction of ciliates to these factors, while axis 2 is more closely related to the total phosphorus in the water. In the CCA diagram axis 1 accounted for 70% of the total cumulative variance. Axis 2 accounted for only 5% of the variance in the ciliate data (Fig. 4).

DISCUSSION

This study is one of the first to examine the effects of pH on planktonic ciliates from a peatlands. Changes in pH resulted in significant changes in the density, biomass and species composition of ciliates. In the investigated ponds, the number of species of ciliates grew together with the increase in pH. This characteristic dependence was observed in acid lakes [5]. In studied ponds were found from 4 to 14 ciliate taxa. These values were similar to those noted in humic lakes (from 1 to 15 ciliate taxa) [15]. From 1 to 12 species were found in wetland acid lakes [12]. The abundance of ciliates found in studied ponds are generally much lower than values reported in the literature [14,15]. The lower number of ciliates in peat ponds might result from the fact that the infiltration of peat and suspension in water in connection with humus limits the penetration of light, and precisely this factor influences to a large degree the autotrophic and mixotrophic microorganisms constituting the potential food for the ciliates [1]. In pond with a low pH values, ciliate communities were mainly composed of Oligotrichida (>60µm) (Strombidium viride, Strombilidium spp. However, together with the increased pH, conductivity and concentrations of total phosphorus, there was increased density of Scuticociliatida (Cinetochilum margaritaceum), Peritrichida and small Oligotrichida (<50µm). The high proportion of larger (>50µm) ciliates in low pH pond agrees well with earlier observations from freshwaters [14]. Beaver and Crisman [2] observed that smaller ciliates of 20-30µm size were progressively replaced by larger ciliates with increasing acidity. Members of the Oligotrichida dominate numerically in oligotrophic lakes, whereas the Scuticociliatida dominate the communities of higher trophic states [2]. Nutrient addition has been reported to bring about a change from Oligotrichida to Scuticociliatida and Peritrichida [3]. The increase in biomass in low pH pond has been due to increases in some mixotrophic Oligotrichida. This order is a significant component and often dominate in ciliate communities in lakes of different trophic status. Beaver and Crisman [2,3], have show that there is a definite domination of Oligotrichida in water with a pH<5 level. In turn, investigations carried out in recent years have shown a significant increase in the abundance of Prostomatida, Hypotrichida and Peritrichida in reservoirs with very low pH [17]. Maximum densities of ciliates have often been observed during mid or late summer and autumn in humic lakes[16]. In investigated ponds the dynamics of ciliate communities reaching peak values in autumn during the mass development of small bacterivorous Scuticociliatida and Prostomatida. The density throughout summer was the lowest. Mixotrophic Oligortichida dominated during summer. The low densities of ciliates in the summer could be related to higher predation caused by high densities of macrozooplankton. In three investigated ponds, the conductivity and content of total organic carbon correlated positively with the ciliate numbers. A significant correlations were observed in humic lakes [1,15]. In fact, the conductivity (beside content of calcium) is one of the factors which determine pH of the water. Likewise, only in pond with a high pH level and TP content there existed a significant correlation between the abundance of ciliates and the total phosphorus concentration. The higher density of ciliates in high pH pond may be confirmation of the presence of their advantageous feeding conditions [9].

CONCLUSIONS

1. In general, the number of species of ciliates, density and biomass grew together with the increase in pH.

2. Probably in peat ponds the most important factors limiting the degree of the presence of ciliates are not only pH of the water but conductivity, total phosphorus and organic matter contents.

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Accepted for print: 17.10.2007

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