Analysis of Irrigation Pond Ecosystem. I. Population Dynamics of the Plankton and a Seasonal Succession of the Main Producers and Consumers

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(1)89. Analysis of Irrigation Pond Ecosystems. I. Population Dynamics of the Plankton and a Seasonal Succession of the Mam Producers and Consumers.. Osamu YAMAGUCHI* shu-ichi MORIMOTO, Noriko INOUYE Osamu IMANISHI , and Megumi KASAHARA (Received September 25 , 1987). Abstract Two irrigation pond ecosystems were analyzed over an one-year period. The monthly surveyed abiotic components were the temperature, transparency and pH of the surface water. The changes in the numbers of phytoplankton and zooplankton per 1 ml of the pond water were monitored in order to estimate the degrees of production and consumption in the ecosystems. In the Haibaraguchi pond, which was found to be ohgotrophic, the production was raised once during the period from May to June and once again during that from October to January. The maximum production occurred during this latter period from late autumn to early winter. The high production took place 〕ust after the water-circulation periods. The average number of plankton in 1 ml of the pond water was estimated to. be 85.8. The main producers of the pond were diatoms of Melosira distance, and the main consumers were the rotifers of Keratella cochlearis. The main zooplankton were the protozoans of a given species of the genus Trochelomonas- In the other pond, the Sara, which was found to be mesotrophic, the changes in plankton number were observed to be nearly parallel to those in the water temperature. A part of the reason for this comes from the shallowness of the pond and the big role of zooplankton due to the enrichment from human wastes. The average number of plankton in 1 ml of the pond water was estimated to be 6737.5. The. main producers rotated in the following succession: Melosira granulata. Euglena sp. and Coelastrum microsporum. The main zooplankton throughout the year were protozoans represented by several species of the genus Trochelomonas. In both of the ponds, the main decomposers were bacteria. We concluded that these two ponds had developed and evolved their own ecosystems independently although they are situated only 5 kilometers apart from one another.. To whom correspondence should be addressed. : Present address: Ashiya-Minami High School, Niihama, Ashiya, Hyogo 659. Department of Biology Hyogo University of Teacher Education Yashiro, Hy0g0 673-14-.

(2) 90. Intro ductio n A lacustrine ecosystem supplies one of the most suitable biotic communities to be analyzed biologically, particularly with respect to the simplicity of analysis afforded by the closed nature of such systems. In the southern part of Hyogo Prefecture, there are more than 2000 irrigation ponds (Imazu 1979) for the cultivation of rice since there is a comparatively small amount of the rainfall in this region. There exist 236 ponds, each having an area of more than 0.5 ha, in the town of Yashiro, where the average amount of annual rainfall is 951 mm (Hikime et al. 1986). Most of them were constructed artificially for irrigation use, and thus, the water level is higher than that of the surrounding rice fields. Each pond forms its own ecosystem independently of others even though the physical distance between the bodies is short. The amount of planktonic exchange between them due to water birds is not negligible; however, each pond would be expected to proceed in its own microevolution independently. The series of experiments described herein were designed with the following goals in mind: ( 1 ) To describe the present amounts of planktonic biomass in the given ponds and to determine their composition. These amounts are also used for assessing the present environmental conditions and for a standard to estimate the degree of environmental contamination in future. ( 2 ) To speculate on the floral and faunal successions and microevolution of fresh water ecosystems, and ( 3) To obtain some suitable experimental materials for studies on genetic divergence between discontinuous populations of planktonic species.. Materials and Methods Description of the water-sampled ponds: ( 1 ) Haibaraguchi pond is located at an altitude of 110 meters above sea level and is adjacent to the campus of the Hyogo University of Teacher Education, Yashiro, Hyogo, (Fig. 1 ). The pond was constructed for irrigation by the damming of a natural valley. It has no feeders upstream and is surrounded by a red pine forest. No aquatic higher plants grow there. Rainfall is the sole sourα of inflow of water. The pond is 1.5 ha in area and has a depth of 14.5 meters. (2) Sara pond is located in the town center of Yashiro, Hyogo (Fig. 1 ). The pond is situated at an.altitude of 60 meters and has an area of 0.84 ha and a depth of 2 meters. The pond has no inflow from the neighboring streams. No aquatic higher plants grow there. It is surrounded by houses and therefore has some inflow through drainage from kitchens. (3) Eibarahazama pond is located in Nagao, Kita-ku, Kobe, and is at an altitude of 110 meters (Fig. 1 ). It is 0.9 ha in area and has a depth of 1.4 meters. It has no inflow from nearby streams. Reeds (Phragmites communis) grow in one corner of the pond. The pond is adjacent to a ham-making factory. Sampling of the pond water: Periodic sampling of the water was done once a month at Haibaraguchi and Sara ponds for one year. Only two water samples,.

(3) 91. Irrigation pond ecosystems. z - /. ) ￣・、ち.一一p. -・-、l GE ′4. !}ゝノ＼ノ. m i J ∼.ら・Haib蝣raatt°hi p°lld. Stnda ・Eibirihllllt. 0°nd. t I. ・ilka. Figure 1. A map of Hyogo Prefecture. Asterisks indicate the locations of the irrigation ponds from which the water samples were taken.. one in spring and one in summer, were taken from Eibarahazama pond. For all samplings two liters of the surface water was removed at a location near the floodgate at noon and put into a plastic tank. At the same time, the water temperature was measured with a thermometer. The transparency was measured with the use of a Secchi's white plastic disc having a diameter of 30 centimeters. The sampled water was immediately taken into our laboratory, and its pH measured with a pH meter. Soon after that, the samples were plat男d in a deep freezer at. -80C and kept for 24 hours in order to kill all the plankton. The sampling dates are shown in Table 1. Scoring of number of plankton perl milliliter of pond water. The melted sample solution was centrifuged at 3000 rpm for 5 minutes to concen-.

(4) 92. trate the organisms for counting purposes. The 2-liter samples were suspended as follows: 4 x 500 ml -4 x 50〟 for Haibaraguchi pond sample 4 x 500 ml -4 x 400iil for Sara pond sample. Table 1. Monthly changes in the temperature, transparency, and pH of the surface water in two irrigation ponds.. Pond. Haibaraguchi. pond. Sara. pond. Sampling Temp. Transparency pH Temp. Transparency pH date. Jun. 30, 1986 27.6. ) T j. 5.6. ' ^. 7.5. c O. May 21, 1987. 23.0. Jun. 17, 1987. 24.0. Jul. 4. 1987. 26.0. <. 17.5. '. Apr. 22, 1987. 3. ‖Hり. " o O C > -. of. well一mixed. sample. solution. was. placed. 279. microliters. C -' O. 0 m 1 3 ( 19 62. Mean 17.8 1 19.9 6.5 16.4 Stand, deviation 9.34 21.69 0.64 8.32. Several. OIWSQOIWS^1 tot-iflût-toaioit-t-c-. r. 6.2. 6. L. Mar. 17, 1987 7.5. 7.0. <. 1987 6.5. j. Feb. 18,. ^. 1987 7.1. ll.3. *. Jan. 7. ォ. 1986 7.2. '. Dec. 18,. 15.9. O. 1986 ll.3. i. Nov. 29,. 24.0. O. 1986 16.2. C. Oct. 30,. 29.2。C. '. 1986 24.0. j. Sep. 26,. T. Aug. 29, 1986 28.7. 10ootommn3IOIOIOOO. Jul. 24, 1986 33.8. COOCQCOOIMSOOCOH'a'O) サtDIOtOt-NtCtOLOI>^)tD. May 27, 1986 22.5. α. m o o o o o o o o o n 2 o l O u n tOOOi-ii-icoro^co^wtj l l l l l l l l l l l. Apr. 25, 1986 21.0。C. onto. an. EKDS. Thoma haemocytometer(No. 390, Kayagaki Med. Sci. Ins. CO.). All the plankton more than 5 〟m in length (microplankton and nannoplankton) included. in 0.1 !りof the concentrated sample solution were counted under a microscope and classified as to phylum. Representative photomicrographs of them are shown in Plate 1. For an identification of blue-green algal plankton (phylum Cyanophyta) and bacteria (prokaryotes), the organisms were stained with the DNA-specific dye ethidium. bromide. at. a. final. concentration. of. 50!上g. per. 1. ml. of. TE. buffer. so-. lution (pH 7.5). The observation was done by epifluorescence microscopy with an Olympus UV excitation filter set typed DMBG. Identification of diatoms (phylum Bacillariophyta) was made in the usual manner (Tumura 1961). A part of the sample solution was boiled in concentrated sulfunc acid solution for 20 minutes, then cleaned in potassium permanganate..

(5) 93. Irrigation pond ecosystems. The debris was removed by centrifugation and permanent pr℃parations were made. by mounting in Mount media (Wako Chem.). Identification of planktonic species followed the criteria of Mizuno (1964) , Hustedt (1930), and Wakabayashi and Ichinose (1982). Results Seasonal succession in the ecosystem of Haibaraguchi pond: The abiotic conditions of the pond ecosystem were surveyed once a month for. one year (Table 1 ). The minimum temperature of the surface water was 6.5℃ in February; the maximum, 33.、8℃ in July. The mean value was 17.8℃. The transparency ranged from 63 cm in April to 145 cm in March with the mean value of 119.9 cm. The concentration of hydrogen inos (pH) ranged from 5.2 in June to 7.2 in September, and the mean value was 6.5. Thus the pH of this pond varied from weakly acidic to nearly neutral. The monthly changes in the above parameters are graphically represented in Fig. 2.. Haibaraguchi pond. ℃PHCl. ・ o o O. s s s 肝. o o 7 o o L o o. g. n 4. g. O o 3 O 0. 2. 9 l. 8. O 0 l. Q.-'IBC-**'OCサ/ーEー. Figure 2. Graphic representation of the monthly examined parameters of the water of Haibaraguchi pond. Figures above columns indicate the total number of plankton observed in 1 ml of the pond water.. The biotic components were surveyed to assess the dynamics of the planktonic population in this study. The plankton mass was described as the number of individual organisms in one milliliter of the pond water. When any plankton formed a colony covered with a jelly membrane or connected by protrusions from individual cells, they were counted as a single organism in this study.. Blue-green algal plankton were observed from August through March. Their maximum frequency was 5 plankton/ml in November, with a mean value of 1.4/ml for the year. The observed species was Oscillatoria sp. (Plate 2A), which predominated from autumn to spring. The monthly changes in plaktonic frequency.

(6) 94. are shown in Fig. 3. Diatoms are the dominant phytoplankton in this pond. The maximum number of organisms was 80/ml in November, and the minimum, 3/ ml in July. The mean value was 40.4/ml (Fig. 3 ). The identified diatomaαOuS. genera were Melosira, Cyclothella, Synedra, Navicula, and Nitzschia. The dominant species was M. distans (Plate 3A) throughout the year. The subdominant species was C. stelligera (Plate 3B). The nuclei of almost all the diatoms observed were stained with ethidium bromide; thus they were living forms. Green algal plankton were the second most predominant phytoplankton. They were observed from August through March. The maximum frequency was ll.0/ml in January, and the mean was 2.7/ml (Fig. 3 ). The main genera observed were Scenedesmus (Plate 3F) and Pediastrum. Haibaragnchi. pond. 岸腰上 HBMilliri軸N. Figure 3. Monthlychanges inthe numberofplanktonin 1 ml of surface water from Haibaraguchi pond. Phytoplankton were classified into the three constitutive phyla of Cyanophyta (blue-green algae), Bacillariophyta (diatoms), and Chlorophyta (green algae). Zooplankton were classified into the two main constitutive phyla of Protozoa (protozoans) and Trochelminthes (rotifers). Changes in the total plankton population are also shown..

(7) 95. Irrigation pond ecosystems. Protozoan plankton were the dominant zooplankton in this pond. As according to Mizuno (1964) , any flagellate algal plankton (e. g., Eugler,W and Eudorina) were classified as protozoans in this article. They were observed throughout the year with the maximum frequency of l訂.I/ml in March (Fig. 3 ). Their mean value was 37.7/ml. The most frequently appearing one was Peridi柁mm sp.. in the spring, and Trochelomohas sp. was found in the other seasons. Rotifers (phylum Trochelminthes) were observed at the frequency of 6.0/ml in September. Keratella cochlearis (Plate 4D) was most frequently observed. We also observed water fleas (phylum Arthropoda) in water samples from this pond; however, we could not quantitate their number due to their big bodies which would not easily pass into the haemocytometer for counting. The water fleas observed were Alona (Plate 4E) sp. and Cyclops sp. (Plate 4F). The seasonal dynamics of planktonic population of this pond are graphically represented in Figs. 2 and 3 using a quantity of a total of planktonic individuals in 1 ml of the pond water, together with the changes of the magnitudes of the abiotic parameters. Seasonal succession in the ecosystem of Sara pond:. In the Sara pond the temperature of the surface water changed from 5.6℃ as the minimum in February to 29.2℃ as the maximum in August. The mean was l6.4℃ Thus, no freezing of the pond water took plaα durinig the observation period. The transparency changed from 35 cm as the minimum in April to 145 cm as the maximum in May, with the mean value of 61.3 cm. The values of pH ranged from 5.9 in December to 9.1 in April, the mean being 7.2. The monthly changes in the abiotic conditions are shown in Table 1 and graphically in Fig. 4. 100000. Sara pond. 90000. ▲ f. 70000. 00000000. 6. 80000. < N. 60000. O. 50000 C O. ▲0000 ( O. 30000. * サ. 20000. 蝣ォ. 10000 0. Figure 4. Graphic representation of the monthly examined parameters of the water of Sara pond. Figures above columns indicate the total number of plankton observed in 1 ml of the pond water..

(8) 96. Blue-green algal plankton were observed mainly in the autumn and winter (Fig.. 5 ). Their overall mean frequency was 69.5/ ml. Most of them were the algae of Oscillatoria sp. (Plate 2A) and Microcystis aeruginosa (Plate 2B) The former was dominant over the latter over the entire observation period. Diatoms appeared in every sample for the year, and were the dominant phytoplankton in the pond. Their frequency distribution was bimodal, having two peaks. in April and September (Fig. 5). The mean value was 666.8/ml. The diatomaceous genera identified in this study were Melosira, Cyclothella, Synedra, Navicula, and Nitzschia. Among them, M. granulata (Plate 3C ) was the most dominant species especially in the summer and autumn. C. meneghiniana (Plate 3D) was the subdominant species. Green algal plankton were seen in abundance in the summer. The frequency distribution was unimodal with the single peak in July (Fig. 5 ). Coelastrum microporum (Plate 3E) was the. Sara. pond. UVJ-jBS貞仁二二. ﹁ ^￨chlorophyU ￨J 3-". - T仇m¥ Plai付加. i---. 1■-. 實」. Figure 5. Monthly changes in the numberofplankton in 1 ml of surface water of Sara pond. See legends to Fig. 3..

(9) Irrigation pond ecosystems. 97. dominant green algal plankton at that time. In the remaining seasons, Pediastrum duplex and some species of the genus Scenedesmus (Plate 3F) were observed rather consistently except during February and March. Protozoan plankton appeared repeatedly in all the monthly samples. The frequency distribution seemed to be somewhat bimodal (Fig. 5 ). The mean value was 4346.4/ml. The most frequently appearing protozoans were of species of the genus EuglerW in the winter and spring and of species of the genus Trochelomonas (Plate 4B) in all the seasons. Rotifers were observed in March and August with the frequency of 12.0/ml in both of these months. The most of them were species of the genera Keratella(Plate 4D) , Brachionus(Plate 4C) and Asplanchna. Water fleas, such as Alona sp. (Plate 4E), were also observed as arthropoda zooplankton, but quantitation of their frequency could not be done. The population dynamics of the total number of plankton in 1 ml of the pond water are shown in every month in Fig. 4. The magnitudes changed drastically. from 39.5 in May to 27771.0 in July. The mean value of this pond was 6737.5 /ml, which is approximately 80 times greater than that of Haibaraguchi pond (-85.8/ml). The physical distance between the two ponds is 5 kilometers. Planktonic flora and fauna of Eibarahazama pond: The sampling of the water was made only twice from Eibarahazama pond, once in May and once in August of 1987. SO, quantitative analysis was not undertaken. The so-called "water-bloom" formed by the blue-green algal plankton of. Anabaena spiroides (Plate 2C) and Microcystis aeruginosa (Plate 2B) were found in these samples. They usually fragmented into small pieces after oentrifugation. Some species of ciliated protozoans and water fleas of the genus Cyclops were also observed frequently.. Discussion Population dynamics of the irrigation pond ecosystems: A lacustrine ecosystem is composed of both abiotic and biotic components. The former comprise the amount of sunlight, water circulation, temperature, inorganic ions, transparency, pH, and other parameters. The latter are composed of three functional units, namely, producer, consumer, and reducer. In this study, the population dynamics was surveyed monthly by quantitation of the numl光r Of plankton found in 1 ml of pond water. Therefore, the quantities determined represent the sum of producers and main consumers, and do not involve macro- and microconsumers and reducers. In Haibaraguchi pond, the total population grows twice a year, once during the period of March to June and once again during that of Octol光r to January (Fig. 2 ). During these periods, every 1 ml of the surface water contains more than 60 individual plankton. Both of the periods come 〕ust after a time when the water temperature changes rapidly. This phenomenon corresponds to the circulation period (c. f. Hogetsu 1974). In autumn, the chilled water comes down.

(10) 98. from the surface to the pond bottom, and the bottom water goes up. The nutrient salts found in bottom deposits follow this water movement. The photosynthesis is accelerated at the surface layer. The reverse condition takes place in spring. Thus, a non- or rather negative correlation is expected I姫tween the temperature of the surface water and the number of plankton therein. The correlation coefficient (r) was estimated to t光-0.60 (Table 2 ). When plankton grow well, they consume nutritious compounds and carbon dioxide, and should cause the transparency and pH to increase. Such expected correlations were not obtained; however, a tendency toward a parallel between plankton number and these two parameters were recognizable in the analysis (Table 2 ).. Table2. Relationships between the number of plankton in 1 ml of pond water and each of the abiotic components of the irrigation pond ecosystems.. P on d. S a ra p o n d. H a ib a ra g u ch i po n d t. C o rre la tio n. C orrela tio n. C O rrela tion. b etw een N o . o f. co efficien t. co efficien t. p la n kto n an d. (r). (r ). tem p , o f. r = - 0 .600. 2.3699. d .f.. 10. P < 0 .05. r = + 0 .455. t. d .f.. 1.6 144. 10. tra n sp a ren cy. pH. N S (0.05 < P < 0 .1). surf, w ater r = 十0 .462 r = - 0 .128. 1.64 69 0.4065. 10 10. NS (0 .05< P < 0.1). r = 一0 .089. N S. r = + 0.54 1. 0 .2835. 10. NS (P > 0 .5 ). 2.0321. 10. P < 0 .05. (P > 0.5 ). In Sara pond, the situation is different in two ways from that of Haibaraguchi pond. First, the pond is too shallow to have its own water circulation sinα the depth is only 2 meters. Instead, the wind has a greater influence on water circulation. Secondly, the pond is located in the town center of Yashiro and is contaminated with kitchen refuse. Organic compounds ai℃ constantly supplied into the pond. Zooplankton seem more adapted for growth under such conditions. The overall mean of the number of plankton (6737.5/ml), was 80 times greater than that of the former pond (85.8/ml). The number of plankton is parallel to the water temperature. A respiration product of the zooplankton, Carbon dioxide, enhances the growth of phytoplankton. This growth then influences the concentration of hydrogen ions. A positive correlation was detected t光tween these two quantities (Table 2 ). The magnitude of transparency (T) is an indicator of the depth of the trophogenie layer (D) of a given pond. There exists a relationship D-2.5T (see Hogetsu 1974). Thus, it seems that Haibaraguchi pond has a trophogenic layer of2.5 x 120 cm or 3 meters,andthat Sara pond has one of2.5 x61 cm or 1.5 meters.. 良asonal succession of the main producers and consumers:.

(11) 99. Irrigation pond ecosystems. Monthly replacement of the dominant producers and consumers has a sharp contrast between the above two ponds. In Haibaraguchi pond, the main producer throughout the year was the common unicellular diatomaceous alga Melosira distans. The main consumers or zooplankton were the rotifers of Keratella cochlearis and unicellular protozoans, a species of the genus Peridinium and some species of the genus Trochelomonas (Plate 1 and Table 3 ). This profile of planktomc distribution indicates that this pond should be classified as an oligotrophic. type of ponds (Mizuno 1964). In the Sara pond, the main producers rotate season to season. A species of genus Euglena was dominant in the low thermal seasons. Then a species of green alga, Coelastrum microsporum, replaced it. A species of diatom, Melosira granulata, was dominant in the high thermal seasons. The main consumers were the rotifers of Brachioltus sp. Protozoans of some species of the genus Trochelomonas appeared throughout the year ( Plate 1 ). The planktonic profile indicates that the Sara pond is to be classified as mesotrophic (Imazu 1979 and 1981). Eibarahazama pond was characterized by its. forming. of. a. "water. bloom". by. blue一green. algae. in. the. summer.. Thus,. this. pond seems to be eutrophic. Table 3. Seasonal succession of the main producers and consumers in the irrigation pond ecosystems. Pond. Haibaraguchi. pond. Sara. pond. Date Main producer Main consumer Main producer Main consumer. Apr. 1986 Melosira distans Keratella cochlearis May 1986 Melosira distans Keratella cochlearis Jun. 1986 Melosira distans Keratella cochleans Jul. 1986 Melosira distans Keratella cochlearis Aug. 1986 Melosira distans Keratella cochlearis Sep. 1986 Melosira distans Keratella cochlearis. Melosira granulata. Brachionus sp.. Melosira granulata. Brachwnus sp.. Melosira granulate. Brachionus sp.. Nov. 1986 Melosira distans Keratella cochlearis Dec. 1986 Melosira distans Keratella cochleans. Melosira granulata. Brachionus sp.. Euglena sp.. Brachionus sp.. Jan. 1987 Melosira distans Keratella cochleans Feb. 1987 Melosira distans Keratella cochleans Mar. 1987 Melosira distans Keratella cochlearis. Euglena sp.. Brachionus sp.. Euglena sp.. Brachionus sp.. Euglena sp.. Brachionus sp.. Apr. 1987. Euglena sp.. Brachionus sp.. Eugiena sp.. Brachionus sp.. nct.. 1986. Melosira. distans. Keratella. cochlear乙S. Coelastrum microsporum Brachionus sp. Coelastrum microsporum Brachionus sp.. Throughout this study, decomposers or reducers were not considered so much since they are too small to be classified, although they have an important role in ecosystems. However, several types of bacteria were recognized in the water samples from all of the pond. Photomicrographs obtained by epifluorescence microscopy profile their existence beautifully ( Plate 5 )- Prokaryotic bacteria and eukaryotic fungi play a role in the circulation of nutritious substances in pond ecosystems..

(12) 100. Haibaraguchi pond. t. /. '. 蝣. '. A _. J. T*. .. _・{. <. I. -. サ.". ・. -. Tv㌧pY竜パ﹁7 --サ. .・サ・>、. r.. ォ#. 瞥'l,-プでー曳。滅「/蝣蝣錘磨∈. /... :∴∴ 嬢針、きr4、..嶺ro '(増. Plate 1.. 箪冊蔚山中. q- ,」、iJ 粁1Dec. 1686. ・、・∴∴. Iも、﹂∴㌦心. 蝣. 、. ・. * ! ,. _. / I F. '. ∴ 、 . ∴∵. '. {%<.IL・. 白^^Êsi^K^HS^Î震)田. .こ・ L、. 、、r'、. 塊へ<S. ∴∴. II・,1・-・-・T∼--I-・'-・1--. " ,: ? '. o. ﹁匝_-.し訟ノiφ ふ I.・㍉ _Irrk﹁、--..^-. -;-_蝣?義 8-′∵論定詔㍉'i*蝣'"蝣サ∴ -" ∼= II I・ I; eI -s -1'. 9: r=蝣 * I,J・1. /喝H3﹂. ut. x昭KQE. I_φ Jfl、.

(13) Irrigation pond ecosystems. 、ヰ・. Plate 2.. 101.

(14) 102. Plate 3..

(15) Irrigation pond ecosystems. Plate 4.. 103.

(16) 104. Plate 5..

(17) Irrigation pond ecosystems. 105. Acknowledgements We thank Dr. Frye for reading the manuscript.. References Hikime, S-, Y. Onoue, I. Naka and T. Ozeki (1986) Studies of the seasonary changes of water of the irrigation ponds in Ureshmo Height, (in Japanese). Hyogo Univ. Teacher Edu. Jour., 6 : 49-73. Hikime, S., H. Fujita and T. Ozeki (1987) Studies on the correlation between the growth of aquatic plants and the changes of water of the irrigation ponds in Ureshino Height, (in Japanese). Hyogo Univ. Teacher Edu. Jour., 7 : 43-60. Hogetsu, K. (1974) Aquatic ecosystems, (in Japanese). Kyoritsu Shuppan, Tokyo. Hustedt, F. (1930) Bacillariophyta. In Pascher, A. (ed.) Die Susswasser-Flora Mitteleurops, 10. (in German). Gustav Fisher, Jena. Imazu, T. (1979) Phytoplankton in small irrigation ponds of Kanzaki district, Hyogo prefecture, (in Japanese). Jap. J. Limnol., 40 : 93-101. Imazu, T. (1981) The succession of phytoplankton communities in the Sara-ike irrigation pond in the Akashi district of Hyogo prefecture, (in Japanese). Jap. J. Phycol., 29 : 135-141. Mizuno, T. (1964) Illustrations of the freshwater planktons of Japan, (in Japanese). Hoikusha Publ. C, Osaka. Tumura, K. C1961) Notes on cleaning methods of diatoms, (in Japanese). Jap. J. Phycol. 9 : 33-36ー Wakabayashi, T. and S. Ichinose (1982) The planktons of Lake Biwa. (in Japanese). Shiga Pref. Inst. Pub. Health and Env. sci., Shiga.. E叩Ianation of the Plates Plate 1. Seasonalsuccession of the plankton in the irrigation pond ecosystems. Photographs on the left are of organisms found in Haibaraguchi pond; and those on the right in Sara pond. The density of plankton was eight times higher in Haibaraguchi pond than in Sara pond. Each quadrat is 50 Mra x. 50um. Plate 2. Three main species of blue-green algae found in the irrigation ponds. A. A light microscopic view of Oscillatoria tenuis. B. A light photomicrograph of Microcystis aeruginosa. The round-shaped organism in the center is a ciliated protozoan. C. A light photomicrograph of a colony of Anabaena spiroides. D. An epifluorescent photomicrograph of Oscillatoria tenuis (rod-shaped) stained with ethidium bromide. Cytoplasms were stained entirely, and no nucleus could be differentiated. E. An epifluorescent photomicrograph of Microcystis aemginosa. No nuclei are observable. F. An epifluorescent photomicrograph of Anabaena spiroides. The round-shaped organism is a colony of Eudorina elegans, whose nuclei are recognizable since the cells are eukayotic. Plate 3. Dominant and subdominant phytoplankton of the irrigation pond eco-.

(18) 106. systems. A. Melosira distans, a diatom, is the dominant phytoplankton in Haibaraguchi pond. B. Cyclothella stelligera, a diatom, is the subdominant phytoplankton in Haibaraguchi pond. C. Melosira granulata, a diatom, is the dominant phytoplankton in Sara pond in hot seasons. D. Cyclothella meneghiniana is the subdominant diatom in Sara pond. E. Coelastrum microporum (indicated by arrows), a green alga, is one of the dominant phytoplankton in Sara pond. F. Scenedesmus quadricauda is the one of subdominant green algae in Sara pond. Plate 4. Dominant and subdominant zooplankton of the irrigation pond ecosystems. A. A species of Peridinium sp. (P. volzii? ), a dinoflagellate, is the dominant zooplankton in spring in Haibaraguchi pond. B. A species of Euglena (E. proximo.? indicated by the plain arrow), a flagellate, is the dominant zooplankton in winter in Sara pond. A species of Trochelomonas (T. volvocina? , indicated by open arrows) is dominant in hot seasons. Phacus logicauda (indicated by the broken arrow) is one of the subdominant zooplankton. C. Brachionus rubens is one of main rotifers in Sara pond. D. Keratella cochlearis, a rotifer, is rarely seen in Sara pond but often in Haibaraguchi pond. E. A species of Alona (A. guttatal), a water flea, is frequently observed in Sara pond. F. Cyclops vicinus, another water flea, is also found often in Sara pond and also in Eibarahazama pond. Plate 5- Epifluorescent photomicrographs of bacteria stained with ethidium bromid. Since they have no nuclei, the cells were stained entirely. A. They are attached to a colony of Microcystis aerugmosa. B. The bacteria are attached to a colony of Anabaena spiroides..

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