Seasonal Variation of Microalgae Diversity in Lake Abaya, Ethiopia

Damtew Etisa*, Roman Nega and Woinshet Lule

Microbial Biodiversity Directorate, Ethiopian Biodiversity Institute, Ethiopia

Biodiversity Institute, P. O. Box 30726 Addis Ababa, Ethiopia, Email:

demtewetisa@gmail.com Chlorophyta and Bacillariophyta phylum respectively in Lake Abaya.

Keywords: Microalgae; Season; Variation; Abaya Lake

Introduction

Aquatic environments are subject to high temporal variability, with frequent reorganization of the relative abundance and species composition of phytoplankton as a result of the interactions between physical, chemical and biological variables [1]. The microalgae community in a lake may vary both spatially and temporally [2]. The reduction in numbers or change in species composition of microalgae could lead to a reduction in zooplankton abundance [3]. Suggest that a number of factors limit microalgae growth in lakes and reservoirs. Factors such as water level, meteorological factors like solar radiation, photoperiod, rainfall, wind velocity, etc., and hydrological conditions (inflows and outflows) have great influence on the rate of primary production in lacustrine and flowing waters. The fertilizers applied on the agricultural lands with a view to boost crop yield eventually find their ways into nearby water bodies and pollute them [4]. There are numerous descriptions of the seasonal periodicity of microalgae communities and the possible factors controlling their periodic changes in fresh water lakes [3]. The diversity of a phytoplankton community can be used to characterize its structure. This structure is determined by the number of species present, their physiological properties and by the genetic potential of the organisms making up the community [5]. The seasonal fluctuations in microalgae abundance and species composition in any water body is due to differential response of different species to changing levels of light, temperature, nutrients, grazing pressure, onset of parasitic infection, extracellular metabolites of plants and animals with a change in season during a course of year [6]. As demonstrate microalgae productivity follows essentially the same pattern in turbid as in clear waters except that the productivity profiles are compressed, due to the rapid attenuation of light. Blooms of blue-green algae are favored by the high temperature of the warmer months of the year [7, 8].

Lakes are one of humanity’s most important re- sources, especially in the tropics, where they are often viewed as highly productive biological systems [9]. They are critical to the survival of local communities as they are the actual and potential sources of food and income. Furthermore, their range of variations in morphometry, physical and chemical features offers opportunities for superb comparative limnological studies. African lakes exhibit considerable seasonality related to alternations of warm, wet, cooler and dry seasons. Records of microalgae composition, assemblages and seasonal variations are quite few considering the size, peculiarity and importance of the lake and its biodiversity [10]. Ethiopia is rich in both natural water bodies such as rivers, lakes and reservoirs compared to other east African countries [10]. As the community vicinity mentioned Lake Abaya found in silte woreda and the water from the lake is the major source of drinking, swimming, washing and irrigation. Animals found in the Lake are Hippopotamus, fish, different flamingo and other birds around the lake. The Siltie Agriculture woreda taken 1250 koroso fish from Sebeta Research Center and inoculated to this lake. Microalgae (planktonic or suspended algae), one of the major biological components of aquatic ecosystems, play important roles in water bodies, not only as primary producers and hence as the base of food chains, but also as one of the dependable indicators of lake fertility and environmental changes [2]. In addition, microalgae are good indicators of environmental change due to their quick response to changes in environmental pressures such as nutrient availability [11]. They act as primary producers and represent themselves as a direct food source for other aquatic animals. They constitute the basic components of the aquatic food chain. Chemical and hydro-physical characteristics of water affect diversity and structure of the micro-algal communities of these lakes [12]. The seasonality of microalgae assemblages and their productivity in relation to environmental factors coupled with biological interactions have received attention [10, 13] explained that many microalgae declines have occurred in tropical regions.

Phytoplankton dynamics is regulated not only by changing physical and chemical factors but also by biological factors such as grazing by zooplankton [14]. Most zooplanktons are phytoplankton consumers and thus contribute, along with other factors, to the reduction of phytoplankton numbers [5]. If its size is large, the zooplankton can be assumed to have a great influence on the phytoplankton community. Since each species of grazer has its own preference for particular food organisms, selection preference has an effect on the composition of the phytoplankton community. Those species of phytoplankton, which are not preferred as food by the zooplankton, are able to rapidly become dominant [15]. Microalgae represent the largest, yet one of the most poorly understood groups of microorganisms on earth. As happens with plants relative to terrestrial animals, microalgae represent the natural nutritional base and primary source of bulk nutrients in the aquatic food chain [16]. A large number of studies have been made on the community structure and primary production of microalgae in various East African lakes including those found in Ethiopia. In Ethiopia there are a lot of lakes and reservoirs. However, very few attentions have been given to the biodiversity of microalgae in the lakes, reservoirs and ponds of the country. Especially no studies reported on the seasonal variation of microalgae in Lake Abaya. Therefore, this study attempts to assess the seasonal variation of microalgae in Lake Abaya found. However, studies on seasonal variation of microalgae diversity in Lake Abaya still lacking. The aim of this study was to investigate seasonal pattern of microalgae variation by abundance of major groups with emphasis on the dominant microalgae species.

Results

In this study, a total of 5 major phylum and nearly 42 genera of microalgae were identified from composite samples taken from the Lake. Namely, Cyanophyta (blue green algae), Chlorophyta, Bacillariophyta (Diatoms), Euglinophyta, and Charophyta were the most dominant phylum identified during the study period, of which 17 were Chlorophyta, 11 were blue green algae,10 were Bacillariophyta, 3 were Euglinophyta and 1 were Charophyta phylum. Season and the presence and absence of microalgae at the selected site.

Discussion

The dominance of Chlorophyta and Diatom indicate it is indicators of good water quality and dissolved oxygen concentration and high enough to support aquatic life. This is true by author of Reynolds CS, et al. [1]. In terms of frequency the phylum obtained from all study period revealed that Bacillariophyta (2944 cells/count) distributed in highest proportion than Chlorophyta (2934 cells/count) and Cyanophyta (394 cells/count) respectively. The common Chlorophyta throughout the study season (period) were represented by Chlamydomonas (2512 cells/count), Bacillariophyta; Nitzschia (1277 cells/count) and Cyanophyta; Cylindrospermopsis sp. (198 cells/count). As previously strengthen by Fenta AD, et al. [23], variation of microalgae between lakes; is due to the difference in water quality, changes in physico-chemical characteristics of any water mass lead to concomitant qualitative and quantitative changes in microalgae organism. Therefore, the result investigated shows that Lake Abaya was characterized by eutrophic mainly as a result of high nutrient loading from surface runoff from around vicinity agriculture, vegetable, and concrete road constructed for community around the lake dweller. Over the first season of the study period Chlorophyta, Bacillariophyta, Cyanophyta and Euglinophyta were the four dominant phyla respectively 56.97%, 37.97%, 2.8% and 2.26% of the total abundances and variation of the study. This shows that it is almost similar with the study in Burullus Lagoon, in Egypt. Among the dominant phylum during the first study period was Chlorophyta highly dominate genera was Chlamydomonas sp. and Oocystis sp., respectively 92.87% and 4.65%and again similar with the study of Mohamed Z, et al. [24], between two small man-made lakes in Serdang, Selangor suggested that Chlorophyta was observed as most diverse phylum contributing 66.7% to total algal density (%) in Seri Serdang Lake and 63.6% in Engineering Faculty Lake. From phylum Bacillariophyta /diatom group is second dominant phylum during the first study period and among the identified genera of Bacillariophyta highly dominant genera were Nitzschia and Melisora respectively 67.17 % and 29.57%. As investigate that Bacillariophyta remained dominant in the lake during winter because of they are able to grow under the condition of weak light and low temperature which are less suitable for other algae and low concentration of nutrients (NO3-N AND PO4-P) in the winter [25]. This study agreed with reports of diatom diversity and distribution in shallow lakes of Wapusk National Park (Manitoba, Canada) it shows that the most abundant taxa of the above lake are Nitzschia which is not common in other Eco zones by Jacques O, et al. [26]. Therefore, the current findings are similar with that of Altaf H, et al. & Ganai AH, et al. [25, 27]. In the second study period the Bacillariophyta, Cyanophyta, Chlorophyta and Euglinophyta were dominant identified genera in Lake Abaya Siltie Zone. This shows that in the second period the nutrient which can used to make the bacillarophta’s shell such as silica is loaded to the lake by around vicinity community farm and vegetable production by irrigation with the adaptability of diatom with low condition, weak light and low temperature. In third study period Bacillariophyta, Chlorophyta, Cyanophyta, Euglenophyta and charophyta respectively. The pH values varied between 7.3-9.0 in the lake. As the pH values showed, the lake was medium alkaline. It had been determined that the pH values varied between 6-9 in unpolluted lakes [28].

In this period Euglenophyta was found. It has been defined that Euglenophyta members existed more abundantly in polluted water and water that is reach in the organic mass [28]. In third season Bacillariophyta is dominant and among Bacillariophyta phylum Navicula, Cyclotella, Aulocaseira and synedra were present all season. This is similar with the study of which suggests Species of Cyclotella and melosira were indicator species in transition to eutrophy [29]. Only one general from Charophyta was found (Closterium). This species was found in few numbers in one month’s (third months). The transparency of the lake water varies between 8cm- 27cm almost turbid throughout the year. Surroundings of the lake covered with forest in one side and the other side are covered with different vegetables and papyrus grass therefore this might pollute the lake and descend the diversity of microalgae seasonally. Species of Cyclotella, Anabaena flos-aquae, Microcystis and Euglena caused water bloom in certain months. According to these properties Lake Abaya has eutrophic characterizes.

Conclusions and Recommendations

Present study shows seasonal diversity of microalgae in dry, followed by post rainy season and rainy season respectively due to variation in PH, temperature and light intensity (transparency). In morphology there is great organization diversity from unicellular, colonial to filamentous. From this study, some information was gathered to determine the pollution levels based on the water properties and species diversities. Thus in a water body how this mechanic diversity occur is a matter of further study. There is a need to study the potential of robust microalgae in the future as the phytoplankton species diversity has a strong connection to the size of man-made freshwater lakes. Eco-restoration practices shall be the better solution to preserve nature of water organism biodiversity. Because of fluctuation of nitrogen and phosphorous ratios play significant parts as limiting growth factors to most microalgae species/ genera lake Abaya. Therefore, further study of Lake Abaya for nutrient availability is necessary.