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Volume 60, Issue 4
Displaying 1-12 of 12 articles from this issue
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Yu ISHITOBI, Hiroshi KAMIYA, Koji YOKOYAMA, Michio KUMAGAI, Setsuo OKU ...1999 Volume 60 Issue 4 Pages 439-452
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn a coastal lagoon, Lake Shinji, saline water intrusion frequently occurs from the lower Ohashi River. Continuous observation of current velocity, salinity and water level in the Ohashi River revealed that intermittent intrusions takes place when diurnal periods of astronomical tide coincide with the rising stage of meteorological tides during a low discharge from the influent Hii River.
The dynamics of tidal currents and saline transport in the Ohashi River were examined by numerical simulation with a simplified one-dimensional model using water level and salinity data from both river-channel ends. The calculated results reproduced well the observed time series of current velocity and salinity, though some disparity appeared under the two-layered structure. Related phenomena following the intrusion were described with respect to the formation of the stratified structure in Lake Shinji.View full abstractDownload PDF (752K) -
Osamu MITAMURA, Hiroto MAEDA, Munetsugu KAWASHIMA1999 Volume 60 Issue 4 Pages 453-467
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSSeasonal changes in the photosynthetic activity of pico phytoplankton and its contribution to total primary productivity in surface waters at eleven pelagic stations in the north and south basin were examined. Chlorophyll-α concentration of the pico phytoplankton was 0.3 to 5.7 mg chl.a m-3, and was two times higher in the south basin than in the north basin. High standing crops were observed from late July through August. The photosynthetic rate of the pico phytoplankton was 0.9 to 36 mg C m-3 hr-1 and changed seasonally according to a pattern. High values were obtained in the south basin and throughout the lake during summer. The seasonal changing pattern in photosynthetic rates of the larger phytoplankton showed quite a difference from that of the pico phytoplankton. The assimilation number of the pico phytoplankton was 1.8 to 7.3 mg C mg chl.α-1 hr-1 and changed seasonally with high values in summer. The percentage of the standing crop of the pico phytoplankton in the total phytoplankton was generally low, but an appreciable increase was observed from late July to early October. However, the contribution of the pico phytoplankton to primary productivity was lower. In summer, when a high standing crop and high assimilation number of pico phytoplankton were observed, however, the pico phytoplankton made a major contribution to the total primary productivity. The present results suggest that the photoautotrophic picoplankton, Synechococcus, is one of the principal primary producers and plays a significant role in the biogeochemical carbon cycle in the pelagic area of Lake Biwa.View full abstractDownload PDF (834K) -
Jordi CATALAN1999 Volume 60 Issue 4 Pages 469-494
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSSmall-scale water movements in pelagic systems constitute the proximal physical framework in which plankton has evolved. The size and displacement capacities of plankton (by swimming, floating or sinking) overlap with qualitative discontinuities in the small-scale motions of water, and the effects of these motions on diffusion of substances and particles. It is argued in this paper that this overlap-ping could be the basis for understanding different ecological behaviour and adaptive pathways in the diverse phylogenetic groups of plankton. The scales of turbulence relative to organism body size determine the "hydrodynamic weather" to which organisms are exposed. The espe-cially small organisms undergo laminar shear, larger ones can swim between different eddy sizes depending on their displacement capac-ities. This latter fact confers to some organisms great opportunities for behavioural adaptations, which increases the prey encounter taking advantage of the small-scale structure in the water column. Better understanding of the small-scale hydrodynamic environment, con-sidering intermittency, buoyancy-conditioned mixing, and coherent structures, and its description with statistics that are directly appli-cable to interactions between plankton organisms, may provide new clues, in the form of "hydrodynamic climates", for understanding the apparently paradoxically high diversity of plankton.View full abstractDownload PDF (1598K) -
Shin-ichi NAKANO, Takuo NAKAJIMA, Kazuhide HAYAKAWA, Michio KUMAGAI, C ...1999 Volume 60 Issue 4 Pages 495-505
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSBlooms of the dinoflagellate Ceratium hirundinella in large enclosures placed in Lake Biwa were followed from late July to mid September 1996 with special reference to the physico-chemical environment. We detected two blooms of C. hirundinella. The first occurred during a low dissolved inorganic nitrogen (DIN) period. C : N molar ratios of seston, however, indicated that phytoplankton were not limited by nitrogen during that period. The occurrence of the first bloom of C. hirundinella was attributable to the ability of the dinoflagellates to use scattered nutrient sources, since the literature has noted theoretically that large-sized, motile algae such as C. hirundinella are superior to other phytoplankters in exploiting the environmental heterogeneity of nutrient distribution. The second bloom commenced after a fresh supply of DIN due to rainfall when the abundance of C. hirundinella was still comparatively high among that of phytoplankton. Hence, it is likely that the flagellate advantageously utilized the supplied DIN, suggesting that the abundance of C. hirun-dinella in the present study was controlled by nitrogen availability.View full abstractDownload PDF (604K) -
Yuji TANAKA, Ryohei TSUDA, Minako MIZUTANI, Osamu MITAMURA1999 Volume 60 Issue 4 Pages 507-529
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSTo understand what factors govern the quantum yield for phytoplanktonic photosynthesis, field research was conducted in the northern basin of Lake Biwa in September of 1994 and 1995, when the water column was still thermally stratified. Vertical distributions of underwater spectral light energy, its absorption by phytoplankton, as well as photosynthesis and primary productivity were observed, together with temperature, chlorophyll a fluorescence, beam transmittance, and nutrient concentrations. The optical absorption coefficient, averaged over the wavelengths of photosynthesically active radiation (PAR), co-varied with sum of chlorophyll a and phaeopigment concentrations as has been reported in previous studies. The quantum yield of phytoplanktonic photosynthesis, φ, increased exponentially with decreasing radiation. This was clear in the high radiation region where scalar PAR exceeded 10 E m-2 day-1. Also, φ increased with decreasing specific absorption by phytoplankton, and especially with increasing dissolved inorganic nitrogen concentration under weak light. These results suggest that phytoplankton could efficiently utilize the absorbed light energy for photosynthesis under weak radiation in deep water.View full abstractDownload PDF (1093K) -
Kanako ISHIKAWA, Michio KUMAGAI, Shin-ichi NAKANO, Hiroyuki NAKAHARA1999 Volume 60 Issue 4 Pages 531-538
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn the summer of 1995, bloom-forming cyanobacteria were observed on the surface of Akanoi Bay in the South Basin of Lake Biwa. During that summer season, the horizontal distribution of chlorophyll a concentration was measured, and the cell density of phytoplankton was counted microscopically. Two different horizontal distributions of the dominant bloom-forming cyanobacteria were observed under moderate wind conditions. The colonial cyanobacteria with aggregated filaments, Anabaena of iinis, and mucilaginous clumps of Microcystis aeruginosa tended to be transported horizontally by wind, while Planktothrix agardhii with solitary filaments did not. This suggests that different cyanobacteria species may be affected by wind in different ways due to their varying physiology or morphology.View full abstractDownload PDF (401K) -
Machiko NISHINO, Akifumi OHTAKA, Tetsuya NARITA1999 Volume 60 Issue 4 Pages 539-558
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSForty oligocheate taxa were recorded from 133 sites of various depths and habitats of Lake Biwa from 1984 to 1998. They belong to 23 taxa of Naididae, 15 of Tubificidae, 1 each of Biwadrilidae and Lumbriculidae, which cover 75% of the known aquatic oligochaete fauna in Japan. Among 40 taxa, 37 were from the littoral, 17 from the sublittoral, and 15 species from the profundal habitat. In the mesotrophic northern basin 36 taxa were collected, 5 species of which were exclusive. In the eutrophic southern basin, 35 taxa were collected, 3 species being solely reported. The taxa were categorized into 4 groups of distributional patterns in the lake : (1) 23 taxa, including a lumbriculid, a biwadrilid, 17 naidids and 4 tubificids, distributed in the littoral habitat of both basins and in small inlets, (2) 2 naidids distributed in the littoral and sublittoral habitat of the northern basin, (3) 2 tubificids distributed in the sublittoral and profundal habitat of the northern basin, and (4) 4 naidids and 9 tubificids distributed widely over whole range of the lake. On the whole, tubificids are widely distributed in the lake, whereas a lumbriculid, a biwadrilid and two-thirds of the naidids were distributed exclusively in the littoral habitat of both basins.View full abstractDownload PDF (1028K) -
Keiji IWASAKI1999 Volume 60 Issue 4 Pages 559-568
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe distribution and life cycle of a water scorpion species, Laccotrephes japonensis SCOTT, were studied at 18 stations located at the river margins of the Yamato-gawa Water System in Nara Prefecture. The scorpions were collected only in the middle to lower part of the water system flowing through a rural area. No L. japonensis were found in mountain streams more than 200 m above sea level or in small streams in residential areas. They inhabited only the submerged parts of monocotyledonous hygrophytes (Glyceria sp., Phalaris arundinacea, Paspalum distichum var. indulum, and Isachne globosa) growing at the margins of main channels and in temporal pools formed on vegetated side bars, but were not collected within the stands of reeds, Phragmites japonica or P. communis. The larvae of the 2nd and 3rd instars were found only in June and July within small pools on vegetated side bars. The larvae of the 4th and 5th instars were collected from July to October both at channel margins and within pools on vegetated side bars. Adults were found from April to October both in pools and at channel margins. Neither adults nor larvae were collected from November to March. The significance of such river margin habitats for water insects inhabiting a primarily lentic environment was discussed with a view to the conservation and management of river biota.View full abstractDownload PDF (505K) -
Satoshi FUKUSHIMA, Shoji KANADA1999 Volume 60 Issue 4 Pages 569-583
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn a stream receiving only chlorine-treated sewage as maintenance water, the periphytic algal biomass and macroinvertebrate density were both low immediately below the entry of the effluent, but in-creased on passing downstream. However, at the most downstream site, the algal biomass again decreased, presumably due to the presence of many grazers. The species-richness of both groups of organisms also increased downstream, becoming obvious when the TRC concentration was <0.1 mg l-1. Choricystis chodatii (JAAG) FOTT was predominant in algal communities and Chironomus yoshimatsui MARTIN et SUBLETTE, or species of Tubificidae predominant in macroinvertebrate communities at all sites.
In situ experiments showed that algal accumulation on artificial clay tiles exposed to chlorine was clearly less than at a reference site. When the reference site was also subjected to chlorine exposure, the algal community consisted of two species of green algae, as opposed to the many species of diatoms which were usually present.
Exposure of the algal biomass from the high TRC concentration site to three different TRC concentrations (1.0, 2.0 and 4.1 mg l-1) showed no significant differences from the control, whereas diatoms at the reference site showed significant differences from the control at all concentrations (P<0.01). The mortality of C. yoshimatsui MARTIN et SUBLETTE, collected from the sites exposed to chlorine and the reference site was always high in the presence of 4.1 mg l-1 TRC, but only significant differences were recognized in the control from the reference site (P <0.01) .View full abstractDownload PDF (785K) -
Hidetoshi NAGANAWA1999 Volume 60 Issue 4 Pages 585-606
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSA spinicaudatan branchiopod crustacean, Baikalolkhonia tatianae gen. et sp. nov., is described from the Baikal region in Russia. The genus is assigned to the family Cyzicidae STEBBING, 1910, based on the absence of a frontal organ on the head, the absence of triangular epipodal laminae on the thoracopods, and the presence of a pair of large frontal spines on the telson. The main distinguishing characteristic is that the epipodal upper corners of many anterior thoracopods (including even the first pair) are transformed into "sausage-like organs." Since such epipodal processes have been until now unknown in the Cyzicidae, the diagnosis of the family is emended, and 2 newly defined subfamilies, Baikalolkhoniinae and Cyzicinae, are proposed. Up to the present, 11 species belonging to 7 genera in 4 families of Spinicaudata (Cyclestheriidae, Cyzicidae, Leptestheriidae, and Limnadiidae) are known from the neighboring regions of East Asia, including the Russian Far East, Mongolia, China, Korea, and Japan. The list of species and the key to the species are provided. Their distribution defines 4 zoogeographical provinces, and the species diversity clearly shows a latitudinal gradient in a similar pattern to the European fauna.View full abstractDownload PDF (1213K) -
Osamu FUJINO, Kazuhiro ORIMI, Takeshi KOTANI, Isao NISHINO1999 Volume 60 Issue 4 Pages 607-617
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSMulti-elements (Ca, Mg, Sr, Ba, Na, K, Al, Mn, Fe, Cu, Zn) in the hard tissue (shell and pearl) of Ikecho-gai (Hyriopsis schlegeli), the mother shellfish inhabiting Lake Biwa were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Further-more, together with Akoya-gai (Pinctada fucata martensi), we examined whether ICP-AES signals for these elements were highly suppressed or increased by large amounts of calcium ions. Therefore, determination of these elements in the sample solution from shell and pearl samples was performed by a standard addition extrapolated method.
The contents were as follows, Ca > Na> Mn> Sr> Fe > Ba> K> Al > Mg> Cu> Zn in the shell of Ikecho-gai. The pearl showed a content tendency which was nearly the same as that of the shell. Relevance with the inhabiting environment water was suggested from Akoya-gai which contained high concentrations of sodium, strontium and magne-sium that also exists in the high concentrations in the sea water. However, the concentrations ratios of these three elements especialy showed high values in Ikecho-gai. Therefore, many elements can be considered as concentrated more often in Ikecho-gai than in Akoya-gai. Next, we examined the distribution of elements in 11 shell areas and the relationship between these elements of Ikecho-gai. Many elements were not uniformly distributed in the shell. A positive correlation coefficient of over 0.8 was found between alkali metals, alkaline earth metals and manganese in the shells. However, these elements showed a negative correlation toward iron and copper.View full abstractDownload PDF (467K) -
Kazumi TANIDA, Hiromune MITSUHASHI, Toshihito FUJITANI1999 Volume 60 Issue 4 Pages 619-624
Published: December 01, 1999
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSA simple method of measuring the amount of chlorophyll a in epilithic algae was newly developed. To scour the algae, we used a special acrylate fiber (Micro-cloth; Koyo Co. Ltd., Tokyo : by Shaleria of Asahi Chemical Co.) and a rubber plate with a hole 25 mm in diameter. The accuracy of the new method was tested in comparison with the traditional method of scrap-ing a rectangular area of 50 by 50 mm with a toothbrush, resulting in similar measured values between these two methods (R2=0.986 ; y=1.029x ; x : measured values by the toothbrush method, y : those by Micro-cloth method). This new simple method is appropriate for determining the micro-distribution of epilithic algae.View full abstractDownload PDF (300K)
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