Temporal changes and vertical distribution of macrophytes in Lake Kawaguchi

 The distribution of macrophytes in Lake Kawaguchi, Japan, was surveyed in August 1999 using a sampling anchor from a boat. The survey revealed that the present aquatic vegetation was composed of 17 submerged species, and no floating-leaved plants were present. The diversity of submerged plants and their vertical growth limits decreased progressively from the west to the east end of the lake. At the time of the survey, the dominant species was Elodea nuttallii (Planch.) St. John, which had once grown explosively in the mid-1980s in the lake, and except for Vallisneria asiatica Miki, all of the species commonly observed in the lake seem to have diminished their growth greatly. Among them, Potamogeton compressus L., which was the most dominant species in the lake before the invasion of Elodea nuttallii, had decreased most severely. It is suggested that the present state of aquatic vegetation in this lake was much influenced by the persistent growth of Elodea nuttallii as well as by environmental factors. Received: August 7, 2001 / Accepted: February 9, 2002     

Relationship between distribution and bottom sediment of submerged macrophytes in the Seta River,Shiga Prefecture,Japan

The purpose of this study was to survey the distribution and habitat of submerged macrophytes in the Seta River outflow from Lake Biwa, Shiga Prefecture, Japan. To accomplish this, I instituted a field survey with sampling on January 2009. I collected nine submerged macrophyte species during the diving operation. Sample collection showed that submerged macrophytes flourished on both sides of the river but did not flourish in the central portion of the river. Alien species (Egeria densa and Elodea nuttallii) were collected on all survey lines, while domestic species (Ceratophyllum demersum, Myriophyllum spicatum, Hydrilla verticillata, Vallisneria biwaensis, Vallisneria denseserrulata, Potamogeton maackianus, and Potamogeton malaianus) were collected in large amounts on the survey lines near Lake Biwa. The dominant species in cohesive soil or fine soil was Egeria densa, while the dominant species in sand gravel was Potamogeton maackianus. Although Egeria densa was collected in sand gravel too, Potamogeton maackianus was not collected in cohesive soil or fine soil, which indicates that Egeria densa has high fertility and can survive in an oxygen-poor environment, while Potamogeton maackianus cannot survive in an oxygen-poor environment.     

Echosounding observations of coverage,height, PVI,and biomass of submerged macrophytes in the southern basin of Lake Biwa,Japan

We have developed a procedure to process echosounding data to map the distribution of submerged aquatic macrophytes in the southern basin of Lake Biwa, a water body that has a surface area of 52 km² and a mean depth of 4 m. Echosounding observations were made along 27 transect lines spaced at 500-m intervals on August 4 and September 2 and 30, 2003. Quantitative vegetation data including percent coverage, mean vegetation height, and percent vegetation infestation were directly determined using image data from the echosounder recorded digitally on videotape. Based on the image data from an echosounder, a regression model was developed for estimating biomass of submerged macrophytes. The regression model using the total echo strength as the explanatory variable could reliably estimate macrophyte biomass up to 300 g m⁻². Distribution maps of macrophyte height and biomass suggest that the recent summer decline of submerged macrophytes started earlier in shallow areas (<3 m of depth) than deep areas (>4 m) in the southern basin of Lake Biwa.     

Effects of elevated turbidity on shallow lake fish communities

Synopsis We compared the fish communities of two shallow lakes in the lower Waikato River basin, North Island, New Zealand, to determine the effects of elevated suspended solids (SS) and collapse of submerged macrophytes. Lake Waahi was turbid (20–40 g m^-3 SS) and devoid of submerged macrophytes whereas Lake Whangape was clearer (5 g m^-3 SS) and dominated by submerged macrophytes. The lakes had similar fish species richness and had nine major species in common; representing eight families including Anguillidae, Retropinnidae, Galaxiidae, Eleotridae, Mugilidae, Ictaluridae, Poeciliidae, and Cyprinidae (two species). The only major fish that was absent from Lake Waahi was a lacustrine form of the common smelt, Retropinna retropinna, which disappeared after the lake became turbid in the late 1970s. CPUE, condition, and size of most species in Lake Waahi were similar to, or greater than, those in Lake Whangape. Lake Whangape clearly exceeded Lake Waahi only for CPUE of two species. Within Lake Whangape two species displayed significantly greater condition, and one species greater size, in a turbid arm of the lake than in the main basin. Apart from lacustrine Retropinna retropinna, the fish in these lakes appear well adapted to cope with, or to avoid, the direct toxic effects of suspended and settleable solids on sensitive early developmental stages. In Lake Waahi loss of cover and food provided by submerged macrophytes appears to have been compensated for by increased turbidity and an associated increase in the biomass of the mysid, Tenagomysis chiltoni (a major prey item).     

Occurrence of the endangered species Nitellopsis obtusa (Charales,Charophyceae) in western Japan and the genetic differences within and among Japanese populations

Nitellopsis obtusa (Charales, Charophyceae) are widely distributed from Europe to Asia; however, this species has been recorded in only the five lakes in central Honshu in Japan. This species was thought to be extinct in Japan, but was rediscovered in limited areas of Lake Kawaguchi in central Honshu. More recently, we discovered more Japanese populations of N. obtusa in Lake Biwa in western Honshu, and it became clear that the species had a broader distribution in Japan than originally believed. In addition, although only male or female thalli have been collected at each lake, both male and female thalli were found from Lake Biwa. This is the first report of a potentially sexual population of N. obtusa in Japan. The DNA sequences of three chloroplast DNA markers, including both coding and non‐coding regions, were identical in all specimens from Lake Kawaguchi and Lake Nojiri (Central Honshu), and differed from those of Lake Biwa and German specimens. Although Japanese and German specimens were genetically similar, Japanese specimens displayed considerable genetic diversity according to locality.     

Plant community dynamics in a chain of lakes: principal factors in the decline of rooted macrophytes with eutrophication

Shoe Lake and East Graham Lake, part of a small chain of lakes in southeastern Michigan, USA, differ in nutrient loading and in the structure and productivity of their aquatic plant communities. A comparative study of species frequency and biomass distributions, nutrient contents, and responses to experimental nutrient enrichment and shading, was conducted to determine the principal factors controlling the macrophyte dynamics. A central objective was to address the question of why rooted macrophyte growth declines with eutrophication, and to test existing models designed to explain this phenomenon. In the more eutrophic Shoe Lake, diversity and productivity of rooted macrophytes were relatively low, restricted primarily by combined shading of phytoplankton, periphyton, and non-rooted macrophytes (principally Ceratophyllum demersum, along with Utricularia vulgaris and Cladophora fracta). In the less eutrophic East Graham Lake, lower nitrogen availability restricted the growth of all of these shading components, resulting in clearer water and higher productivity and diversity of rooted macrophytes. The macrophytes did not allelopathically suppress the phytoplankton in East Graham Lake. The results supported a direct relationship between nutrient loading, increasing growth of phytoplankton, periphyton and non-rooted macrophytes, and decline of rooted macrophytes.     

Utilizing stomach content and faecal DNA analysis techniques to assess the feeding behaviour of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus

In this study, the feeding behaviour of the non‐native invasive predatory fishes largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus was studied in the Ezura River, a northern tributary of Lake Biwa, Japan. Prey composition was estimated based on visual examination of stomach contents and faecal DNA analysis to determine feeding habits of these predatory fishes. Stomach content analysis showed that native fishes (e.g. ayu Plecoglossus altivelis and gobies Rhinogobius spp.) and shrimps (e.g. Palaemon paucidens) were the major prey items for M. salmoides, while snails, larval Chironomidae and submerged macrophytes were the dominant prey items of L. macrochirus. Micropterus salmoides tended to select larger fish in the case of crucian carp Carassius spp., but smaller fishes in the case of P. altivelis and Rhinogobius spp. Faecal DNA analyses revealed prey compositions similar to those identified in predator stomach contents, and identified additional prey species not detected in stomach content inspection. This study demonstrated that both stomach content inspection and DNA‐based analysis bear several inherent shortcomings and advantages. The former method is straightforward, although identification of species can be inaccurate or impossible, whereas the latter method allows for accurate species identification, but cannot distinguish prey size or stage. Hence, integration of morphology‐based and DNA‐based methods can provide more reliable estimates of foraging habits of predatory fishes.     

Can macrophytes be useful in biomanipulation of lakes? The Lake Zwemlust example

Lake Zwemlust (area 1.5 ha, Z_m 1.5 m) has been the object of an extensive limnological study since its biomanipulation involving removal of planktivorous fish (bream) in March 1987 and emptying of the lake. In the subsequent summer period of 1987 the Secchi depth increased to the lake bottom (2.5 m), compared withca 30 cm in the earlier summers. The reaction of submerged macrophytes to improving under-water light climate was rapid. In summer 1987, besides the introducedChara globularis, 5 species of submerged macrophytes occurred and colonized 10% of the lake area. In 1988 and 1989 only quantitative changes were observed; new species did not appear, but the area colonized by macrophytes increased by 7 and 10 times, respectively.Elodea nuttallii was dominant among the macrophytes andMougeotia sp. among the filamentous green algae. Their abundance, contributed to transient N-limination of phytoplankton causing a persistent clear water phase in 1988 and 1989, unlike in 1987 when zooplankton grazing contributed chiefly to the water clarity. Laboratory bioassays on macrophytes confirmed nitrogen limitation.     

Dynamics of submerged macrophyte populations in response to biomanipulation

1. A 6‐year study (1992–97) of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjön, Southern Sweden. Ten sites around the lake were revisited each year. At each site five samples of above‐ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large fish were excluded was also conducted. 2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover increased from < 3 to 75% and above‐ground biomass from < 1 to 100 g DW m^–2. Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above‐ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997. 3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness. 4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or fish delay the re‐colonization of submerged macrophytes. 5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjön (11 km²). Species that spread by fragments will increase rapidly and probably outcompete other species. 6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear‐water state.     

The physical factor inducing spawning of the Biwa catfish, Silurus biwaensis

The physical factor inducing spawning of the Biwa catfish, Silurus biwaensis (Siluriformes: Siluridae), an endemic species of Lake Biwa, was investigated on the basis of field observations on 150 nights at the spawning site, the rocky shore of the Seta River, the lake's outlet, and environmental data from April to July in 1989–1994. The catfish gathered at the spawning site when the water level of the river rapidly rose and the rocky shoal became submerged, within a wide range of water temperature (15.0°–30.0°C); their spawning was induced in relation to increases in the submerged portion of the rocky shoal. This observation suggests that water level control operations in Lake Biwa might critically affect the spawning of this and other fish species. Received: December 17, 1999 / Revised: September 13, 2000 / Accepted: January 16, 2001     

Interactive effects of light and snail herbivory rather than nutrient loading determine early establishment of submerged macrophytes

Submerged macrophytes play a key role in maintaining a clear‐water phase and promoting biodiversity in shallow aquatic ecosystems. Since their abundance has declined globally due to anthropogenic activities, it is important to include them in aquatic ecosystem restoration programs. Macrophytes establishment in early spring is crucial for the subsequent growth of other warm‐adapted macrophytes. However, factors affecting this early establishment of submerged macrophytes have not been fully explored yet. Here, we conducted an outdoor experiment from winter to early spring using the submerged macrophytes Potamogeton crispus and Vallisneria spinulosa to study the effects of shading, nutrient loading, snail herbivory (Radix swinhoei), and their interactions on the early growth and stoichiometric characteristics of macrophytes. The results show that the effects strongly depend on macrophyte species. Biomass and number of shoots of P. crispus decreased, and internode length increased during low light conditions, but were not affected by nutrient loading. P. crispus shoot biomass and number showed hump‐shaped responses to increased snail biomass under full light. In contrast, the biomass of the plant linearly decreased with snail biomass under low light. This indicates an interaction of light with snail herbivory. Since snails prefer grazing on periphyton over macrophytes, a low density of snails promoted growth of P. crispus by removing periphyton competition, while herbivory on the macrophyte increased during a high density of snails. The growth of V. spinulosa was not affected by any of the factors, probably because of growth limitation by low temperature. Our study demonstrates that the interaction of light with snail herbivory may affect establishment and growth of submerged macrophytes in early spring. Macrophyte restoration projects may thus benefit from lowering water levels to increase light availability and making smart use of cold‐adapted herbivores to reduce light competition with periphyton.     

沉水植物化感作用对西湖湿地浮游植物群落的影响

通过微宇宙实验,在控制光照和营养盐浓度的条件下分别研究了苦草(Vallisneria spiralis)、金鱼藻(Ceratophyllum demersum)和穗花狐尾藻(Myriophyllum spicatum)的化感作用对采集于杭州西湖湖西湿地的藻类密度、叶绿素a浓度、群落结构、多样性指数等的影响。其结果表明,3种沉水植物对微宇宙系统中的藻类都具有明显影响,藻类密度与叶绿素a浓度受到显著抑制,3个草-藻研究系统中藻类群落结构都发生了变化。在实验末期苦草组、金鱼藻组和穗花狐尾藻组中藻类总生物量(以细胞密度计)分别较初始值降低了37.06%、78.37%和83.40%。栅藻对3种沉水植物的化感作用敏感性较弱。藻类生物多样性方面,穗花狐尾藻系统中最高,其次是金鱼藻组,最后是苦草组,其Shannon-Wiener指数(H)分别为2.76、2.06和0.72,穗花狐尾藻组中H的显著高于苦草组(P0.05)。     

Community collocation of four submerged macrophytes on two kinds of sediments in Lake Taihu, China

To explore a method for rapid restoration and artificial regulation of submerged macrophytes in large-scale restoration of eutrophic lakes, the succession and the biodiversity changes of four communities composed of four native, common submerged macrophytes, Hydrilla verticillata, Potamogeton malaianus, Vallisneria spiralis and Najas marina, on two kinds of sediments were investigated. Under low light intensity (reduced by 99%), the plant biomass changed with seasonal changes, plant competition, and environmental stress. The competitive capability for light differed in the four species due to different shoot height and tiller number. After 405 days of transplantation, H. verticillata became dominant in all communities. The biomass of H. verticillata, with strong ability to endure low water light environment, accounted for more than 90% of the total community biomass, and P. malaianus had only weak growth, while V. spiralis and N. marina almost disappeared. Based on livability and biomass of submerged macrophytes on two sediment types, brown clay sediment appeared to be more favorable for the settlement of the plants, while fertile sludge sediment was suitable for vegetative growth. In conclusion, the improvement of habitats and the selection of appropriate plant species are of the greatest importance for ecological restoration of the aquatic ecosystem.     

Reproductive ecology of the Far Eastern catfish, Silurus asotus (Siluridae), with a comparison to its two congeners in Lake Biwa, Japan

Spawning activity of the catfish, Silurus asotus, takes place in temporary water (rice fields) from early evening to midnight, generally in connection with rainfall, from late April to late August. Spawning of the catfish was correlated with hydrographic parameters dependent on rainfall: daily precipitation, turbidity, water depth, and water temperature. The spawning habits of the catfish, and in particular the use of temporary waters such as rice fields that become submerged after rainfall or by irrigation, are presumed to be adaptations to the Asian monsoon climate with a pronounced rainy season. The apparent sex ratio of the catfish was extremely biased toward females. Intraspecific variation in the reproductive ecology, particularly mating behavior, of this species is observed among local populations. Factors that may have caused this variation are discussed in the context of a comparison of mating behavior, reproductive environment, and sex ratio between the Lake Biwa population of S. asotus and other conspecific populations, as well as two other species of silurid catfish that occur in the Lake Biwa drainage, S. biwaensis and S. lithophilus.     

Community Structure of Bacteria Associated with Sheaths of Freshwater and Brackish Thioploca Species

Bacterial communities associated with sheaths of Thioploca spp. from two freshwater lakes (Lake Biwa, Japan, and Lake Constance, Germany) and one brackish lake (Lake Ogawara, Japan) were analyzed with denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. The comparison between the DGGE band patterns of bulk sediment and Thioploca filaments of Lake Biwa suggested the presence of specific bacterial communities associated with Thioploca sheaths. As members of sheath-associated communities, bacteria belonging to Bacteroidetes were detected from the samples of both freshwater lakes. A DGGE band from Thioploca of Lake Biwa, belonging to candidate division OP8, was quite closely related to another DGGE band detected from that of Lake Constance. In contrast to the case of freshwater lakes, no bacterium of Bacteroidetes or OP8 was detected from Thioploca of Lake Ogawara. However, two DGGE bands from Lake Ogawara, belonging to Chloroflexi, were quite closely related to a DGGE band from Lake Constance. Two DGGE bands obtained from Lake Biwa were closely related to phylogenetically distant dissimilatory Fe(III)-reducing bacteria. Cloning analyses for a dissimilatory sulfite reductase gene were performed on the same samples used for DGGE analysis. The results of the analyses suggest that sheaths of freshwater/brackish Thioploca have little ecological significance for the majority of sulfate reducers.     

Adaptation of submerged macrophytes to both water depth and flood intensity as revealed by their mechanical resistance

Little is known about the mechanical resistance response of submerged macrophytes to floods. An experiment was conducted to investigate the plant growth, root anchorage strength, and stem tensile properties of five submerged macrophytes under three initial water levels (1.0, 2.5, and 4.0 m) with four water level fluctuation speeds (0, 5, 15, and 25 cm d⁻¹). Our results demonstrate that the biomass, relative growth rate, root anchorage strength, and stem tensile properties of the five species decreased with increasing initial water level, suggesting that deep water can inhibit plant growth and decrease their mechanical resistance. Floods weakened the stem tensile properties and strengthened the root performances of Myriophyllum spicatum, Hydrilla verticillata, and Potamogeton malaianus in shallow water. However, floods induced opposite mechanical resistance responses from plants in deep water, indicating a possible trade-off between stem breakage and uprooting under flooding conditions. M. spicatum, Ceratophyllum demersum, and P. malaianus were more tolerant of deep water and flood intensity than Potamogeton maackianus and H. verticillata, as indicated by their larger biomass, plant heights, stem tensile properties, and root anchorage strength. This is the first article that mechanically explains the competitive capability and survival potential of submerged macrophytes to water depth and flood intensity.     

Mitochondrial phylogeny reveals the artificial introduction of the pale chub Zacco platypus (Cyprinidae) in Taiwan

The presence of the pale chub Zacco platypus (Japanese name, Oikawa) in Taiwan has been suggested to be a result of its inadvertent introduction from Lake Biwa in Japan in the 1980s in conjunction with the Japanese Ayu, Plecoglossus altivelis altivelis, which was released several times into the Tamsui River to restock the extinct Ayu population of Taiwan. However, it is also possible that Z. platypus is native to Taiwan and has not been previously described for reasons of its narrow range. Knowledge of the colonizing history of Z. platypus is of considerable importance because it provides insight into the evolutionary process and, hence, impacts management decisions regarding this species in Taiwan. A portion of the mitochondrial D-loop was sequenced for 77 specimens from five populations of Z. platypus from Japan and Taiwan. A total of 22 haplotypes were identified, and nucleotide divergence among haplotypes ranged from 0.20% to 2.82%. Haplotype diversity was high in all populations examined, with a range from 0.718 in the Tagiri River population to 0.909 in the Lake Biwa population. Phylogenetic and statistical parsimony analyses of the molecular data revealed a close genetic relationship between Taiwanese and Japanese Z. platypus and supported the previous report that the Taiwanese Z. platypus originated in Lake Biwa in Japan.     

Effects of Spirogyra arcta on biomass and structure of submerged macrophyte communities

The presence of algae can greatly reduce the amount of light that reaches submerged macrophytes, but few experimental studies have been conducted to examine the effects of algae on biomass and structure of submerged macrophyte communities. We constructed communities with four submerged macrophytes (Hydrilla verticillata, Egeria densa, Ceratophyllum demersum, and Chara vulgaris) in three environments in which 0 (control), 50 and 100% of the water surface was covered by Spirogyra arcta. Compared to the control treatment, the 100% spirogyra treatment decreased biomass of the submerged macrophyte communities and of all the four macrophytes except C. demersum. Compared to the control and 50% treatments, the 100% treatment significantly increased relative abundance of C. demersum and decreased that of E. densa. Therefore, the presence of S. arcta can greatly affect the productivity and alter the structure of submerged macrophyte communities. To restore submerged macrophyte communities in conditions with abundant algae, assembling communities consisting of C. demersum or similar species may be a good practice.     

A Century of Change in Macrophyte Abundance and Composition in Response to Agricultural Eutrophication

Clear Lake, Iowa, USA is a shallow, agriculturally eutrophic lake that has changed drastically over the past century. Eight macrophyte surveys since 1896 were pooled and examined to characterize long-term impacts of eutrophication on macrophyte community composition and relative abundance. Surveys in 1981 and 2000 revealed few submergent and floating-leaved species and a dominance in emergent species (Scirpus, Typha). Over the past century, however, species richness has declined from a high of 30 species in 1951 to 12 found today, while the community composition has shifted from submergent-(99%) to emergent-dominated floras (84%). Potamogeton praelongus was the first emergent species to disappear but was followed by several other clear water Potamogeton species. Several floating leaved and emergent genera increased in relative abundance with eutrophication, notably Nuphar, Nymphaea, Phragmites, Polygonum, Sagittaria, Scirpus, and Typha. P. pectinatus was present over the entire century due to its tolerance of eutrophic conditions. Macrophyte growth was generally light-limited, with 93% of the variance in relative abundance of submergent species explained by changes in water transparency. Clear Lake exhibits signs of alternative stable states, oscillating between clear and turbid water, coupled with high and low submerged species relative abundance. The maximum macrophyte richness occurred as the lake oscillated between submergent- and emergent-dominated states. Changes in the water level have also impacted macrophyte growth since the area of the lake occupied by emergent macrophytes was negatively correlated with water level. Strongest correlations indicated that macrophytes respond to water level variations with a 2-year time-lag.