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1.
During an ongoing study of the rotifer diversity in Thai peat swamps, several new or rare species were found. We here report on one new species, Lecane kunthuleensis n.sp., from a canal in Kun Thu Lee peat swamp, and on three rare species: Paracolurella aemula (Myers, 1934) and Lecane junkiKoste, 1975 from Kra Jood peat swamp (Suratthanee province), and Lepadella punctataWulfert, 1939 from To-Daeng peat swamp (Narathiwas province). 相似文献
2.
Kristen M. Reifel Brandon K. Swan Errel Olivo James M. Watts Charles C. Trees Stuart H. Hurlbert 《Hydrobiologia》2007,576(1):167-183
The influence of river inflows (2.5–5 g l−1) on phytoplankton and zooplankton was assessed with samples collected at 17 sites around the 50 km perimeter of the southern
basin of the Salton Sea (41–45 g l−1) along the 5 m isobath on 2 September and 11 December 2000. Phytoplankton generally increased in abundance downcurrent of
the points of inflow, but patterns in downcurrent abundance varied widely among species. Several diatom species showed large
increases; Chaetoceros muelleri var subsalsum, Cylindrotheca closterium and Thalassionema sp. increased up to 800-fold in abundance by ca. 20 km downcurrent from inflow points in September. In contrast, the dinoflagellates
Gyrodinium uncatenum and Prorocentrum minimum increased 6- and 4-fold, respectively, in December, and Gonyaulax grindleyi actually decreased downcurrent of the rivers in September. In September, patterns in downcurrent abundance were correlated
with the ratio of cell surface area to cell biovolume, with species with high ratios showing the largest increases. Zooplankton
abundances did not show regular trends downcurrent of river inflows except for the larvae of Balanus amphitrite, which increased in density ca. 100-fold. This increase most likely reflected the abundance of adult-colonized rocky substrates
near river inflow points. The strong upcurrent trends documented for some species seemed to have been due to the injection
of nutrient-rich water from central to nearshore areas and near-site mortality due to the presence of hydrogen sulfide. This
study gives a first glimpse of the complexity of the responses of nearshore plankton to river inflow and provides evidence
for how changes in factors such as current speed, nutrient supply and salinity stratification may influence plankton dynamics.
Guest Editor: John M. Melack
Saline Waters and their Biota 相似文献
3.
Based on materials from plankton surveys carried out in 2004–2009, the period of occurrence, density, and distribution of
larvae of three commercial species of crabs in the Peter the Great bay and adjacent areas of Sea of Japan were studied. The
larvae of the horsehair crab Erimacrus isenbeckii (Brandt, 1848) occurred in the plankton from mid-March to early June, within the range of water temperature from −1 to 10.8°C.
The larvae of the helmet crab Telmessus cheiragonus (Tilesius, 1812) appeared in the plankton in mid-April and occurred to the end of June within the temperature range from
2.8 to 13.0°C. The larvae of the snow crab Chionoecetes opilio (O. Fabricius, 1788) appeared in the plankton in mid-April as well, but some individuals sporadically occurred until early
August. All the species of crabs produced one generation of larvae for their reproduction season. The terms of larval stay
in plankton depended on water temperature and the duration of the pelagic period increased in colder years. In that area,
the larvae of C. opilio were the most abundant (up to 41 ind./m3) and the zoea density of horsehair and helmet crabs was significantly lower (no more than 2 ind./m3). The larvae of C. opilio occurred over the entire area of the Peter the Great bay; the greatest aggregations of their early stages were observed in
its southwestern open part. The maximum density of E. isenbeckii zoea was recorded in the south of the Amursky bay and in the Posyet bay. Individual larvae of T. cheiragonus occurred in the Posyet bay and in the southern part of the Amursky and Ussuriisky bays. The late-stage larvae of all crab
species were concentrated in areas of the coastal circulation. 相似文献
4.
Several previous studies have attempted to correlate habitat complexity and reef fish species diversity. These studies have mostly examined natural reef systems, but results differed. To examine this relation, we built 1 m2 habitats with 20 replicates of five complexity levels from July to August 2001 in the northeastern Gulf of Mexico (n=100). In June and July 2002, we built new habitats using the 2001 design, but also added a sixth complexity level (n=120). In order of increasing complexity these included: cage, shell, cage-shell, block-shell, cage-block-shell, and shell-block-pyramid habitats. Most fish in both years were juveniles and included species common to reef structures in the northeastern Gulf of Mexico. In 2001, we identified 26 fish species, and the dominant species was red snapper, Lutjanus campechanus (41%), followed by rock sea bass, Centropristis philadelphica (23%), and sand perch, Diplectrum spp. (14%). In 2002 we identified 36 species, and the dominant species was tomtate, Haemulon aurolineatum (36%), followed by Diplectrum spp. (19%), and L. campechanus (13%). In 2001, species diversity and richness were significantly (P<0.05) higher on more complex habitats (H′=1.7, S=11–12) compared to less complex habitats (H′=0.8–1.0, S=4–9). In 2002, patterns among diversity, richness and reef complexity were less apparent with only the least complex habitats shell and cage showing significantly lower values. In both years, multidimensional scaling grouped by complexity levels with cage and shell habitats showing the clearest separation from other habitat types. Also, with few exceptions (only 8%) analysis of similarities showed significant (P<0.05) differences in fish communities across complexity levels. Although community composition varied between years, this study provided evidence to support the hypothesis that habitat complexity increased reef fish species diversity. 相似文献
5.
The zooplankton of freshwater systems has been recognized as an important energy resource for fish of small body size that,
in turn, provide energy to piscivorous fish consumers higher up the food web. This study evaluates the importance of zooplankton
to the diets of three species of fish living in floodplain waterholes of an Australian dryland river. The species selected
for study represent different trophic categories in waterhole food webs: Ambassis agassizii is a microcarnivore, Leiopotherapon unicolor is an omnivore, and Nematalosa erebi is a detritivore. Dietary differences among size classes of each species were also evaluated to understand possible ontogenetic
shifts in zooplankton consumption. Ambassis agassizii fed primarily on zooplankton (99.9%, made up mostly of 81.6% Calanoida and 17.4% Moinidae), regardless of the size of individual
fish. Leiopotherapon unicolor fed on zooplankton (47%, mostly Daphniidae and Moinidae) and aquatic insects (46.7%). Smaller individuals of Leiopotherapon unicolor (30–49 mm TL—total length) were responsible for 36.1% of the plankton consumed by the species. Nematalosa erebi fed on detritus (84.6%) with zooplankton (Calanoida, Moinidae, and Cyclopoida) contributing only 13.7% of the mean diet.
Smaller individuals (40–69 mm TL) were responsible for 98% of the plankton consumed by Nematalosa erebi, and individuals of 40–49 mm (TL) fed exclusively on zooplankton (53.8% Moinidae and 46.2% Calanoida). Although the three
fish species had different diets, reflecting differences in species-specific and ontogenetic morphological and behavioral
characteristics, zooplankton formed the basis of the diet of all species when young. These results confirm the importance
of zooplankton as a major food resource for three fish species and smaller size classes of these species in floodplain waterholes
of the Macintyre River, Australia.
Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira
Plankton Studies 相似文献
6.
Typically, the most abundant group of shrimp larvae in the German Bight is formed by representatives of the family Crangonidae.
Larvae of the remaining species have been largely ignored, and only scarce information concerning their ecology is available.
Thus, the purpose of the present study was to determine the species composition, distribution and abundance of noncrangonid
shrimp larvae in the German Bight in July 1990, after the mildest winter of the century. The material is based upon plankton
samples collected at 77 stations, covering the entire German Bight. Eight species were identified, as well as larvae of Palaemonidae
andProcessa-juveniles.Processa nouveli holthuisi (53.0%) andP. modica (31.3%) were predominant in the collection. The distribution of the two species was clearly separated: the main concentration
ofP. nouveli holthuisi (peak concentration of 1.94 larvae per m3) was confined to the northwest corner of the German Bight, while a majority ofP. modica larvae (peak concentration of 0.54 larvae per m3) occurred at the southwesterly stations. The spatial distribution ofCaridion steveni andEualus occultus around Helgoland indicates the presence of an adult population at the only rocky island in the study area. Other taxa, such
as larvae of Palaemonidae and juvenilePandalina brevirostris were collected exclusively in estuarine habitats. Based upon both the results of the present study and comparable data, we
conclude that developmental stages of ten non-crangonid species, as well as representatives of Palaemonidae, can be expected
to occur in the plankton of the German Bight. The extremely mild temperatures of the preceding winter may have been, in part,
responsible for the relatively high densities of some taxa encountered during our plankton survey. We assume that warm winter
temperatures favour the immigration, reproduction and survival of cold-sensitive species. 相似文献
7.
C. Paszko-Kolva M. Shahamat H. Yamamoto T. Sawyer J. Vives-Rego R. R. Colwell 《Microbial ecology》1991,22(1):75-83
Survival ofLegionella pneumophila SG 1 in seawater and river water was assessed using plate counts on buffered charcoal yeast extract agar amended with α-ketoglutarate
(BCYEα) and [3H]thymidine-labeling. The [3H]thymidine-labeling method for assessing survival ofL. pneumophila in aquatic environments was compared with viable counts, direct fluorescent microscopy (DFA), and acridine orange direct
counts (AODC). Protozoa were isolated from the samples employed in the study and identified by characteristic trophozite and
cyst morphology. Selective filtration employing 2.0 μm Nucleopore filters was used to determine the effect of grazing on survival
ofL. pneumophila in seawater and river water.Legionella viability as measured by plate counts (CFU/ml), declined to a greater extent than cell lysis, assessed by thymidine, DFA,
and AODC counts, suggesting thatL. pneumophila survives in aquatic habitats to a greater extent than revealed through culturable counts. 相似文献
8.
Recruitment courses of three amphidromous sleeper species, Eleotris acanthopoma, E. melanosoma, and E. fusca, were investigated at the surf zone adjacent to the river mouth and at five stations in the Teima River on Okinawa Island,
Japan. All three species occurred at the surf zone as pelagic larvae with transparent and compressed body, a conspicuous air
bladder, and an emarginated caudal fin. Eleotris fusca (16.0–19.6 mm in standard length: SL) sometimes possessed a vestige of the larval chin barbel and were larger than E. acanthopoma (9.7–13.2 mm SL) and E. melanosoma (11.2–12.8 mm SL). The pelagic larvae were also collected during full tide from the lower reaches of the tidally influenced
area of the river. The pelagic larvae may be carried in and out of the estuary with some tidal fluxes, and they may settle
when they reach the upper tidally influenced area where the salinity becomes extremely low. Body width and pigmentation of
newly settled larvae increased. E. fusca was considered to migrate upstream to the freshwater area against the flow of the river just after reaching the settled stage.
After settlement, all three species became completely pigmented, the caudal fin became round in shape, and the fin ray counts
became complete with growth. Also, E. acanthopoma dispersed widely to the lower part of the tidally influenced area or to the lower reaches of the freshwater area, E. melanosoma dispersed to the lower part of the tidally influenced area, and E. fusca dispersed upstream. 相似文献
9.
The aim of this study is to assess the response of Trichoptera in a patchy tailwater stretch of the Drzewiczka River (Poland)
to dam removal as compared to the previous pulse discharge disturbance. The study was carried out in the river at the end
of a whitewater slalom canoeing track located downstream of the dam reservoir called Drzewieckie Lake (area 0.84 km2). Between February and April 2002, the dam reservoir was gradually emptied before its dredging, and the Drzewiczka River
recovered its natural discharge (1.7–4.5 m3 s−1) for several years (temporary renaturisation). Altogether, 120 monthly samples of macroinvertebrates and their environments
were collected in two sampling cycles, S1 in 2000–2001 during high discharge fluctuations (2.1–12.0 m3 s−1 daily) and S2 in 2002–2003 during renaturisation after emptying the reservoir, from the following five habitats: HP—pool habitat, HS—stagnant habitat, HM—macrophyte habitat, HB—bank habitat and HR—riffle habitat. On the basis of trichopteran abundance, the patterns in their assemblages were recognised with use of a self-organising
map that was a Kohonen artificial neural network. The obtained classification of trichopteran samples was found to be based
in general on the spatial criterion, i.e. dependent on habitats, irrespective of which sampling cycle the samples originated
from, which clearly showed that the habitat mosaic of the river bed was observed both in S1 and S2. In addition, a very important
function was noted for riparian and land plants, which developed intensively at the bottom of the Drzewieckie Reservoir immediately
after it was emptied. They restricted extensive transport of reservoir sediments to the downstream river reach, thus reducing
differences between S1 and S2 in the tailwater. It is also worth noting that in S1, in comparison to S2, Cyrnus trimaculatus, Mystacides azurea and Lype reducta flowing downstream from the reservoir were observed more frequently in the river, which confirmed that impoundments can be
conducive to the presence of certain species downstream of dams. Summing up, although artificial short-term flow fluctuations
usually diminish the quality and quantity of benthos, the article presents a case in which they were small and short enough
to allow the formation of a mosaic of bed patches and positively affected certain parameters of macrobenthic communities according
to the intermediate disturbance hypothesis.
Handling editor: David Dudgeon 相似文献
10.
Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural
carbon isotope ratio (δ
13C) and short-term carbon uptake rates (13C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates,
which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ
13C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction
(−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more
negativeδ
13C values (−22 to −18‰). Highδ
13C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the
increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the
nannoplankton fractions with higher POC values have relatively lowδ
13C values. 相似文献
11.
Abstract
Bacterial abundance and bacterivorous protist abundance and activity were examined in ice-brine and water column communities
of a cold temperate Japanese lagoon (Saroma-Ko Lagoon, Hokkaido, 44°N, 144°E), during the late winter phase of ice community
development (February–March 1992). Bacterial abundance averaged 6 and 1 × 105 cells ml−1 in the ice-brine and plankton samples, respectively, and generally decreased during the sampling period. Bacterivorous protists,
identified based on direct observation of short-term (<1 h) ingested fluorescently labeled bacteria (FLB) in their food vacuoles,
were largely dominated by flagellates, mainly cryothecomonad-type and chrysomonad-like cells and small dinoflagellates of
the genus Gymnodinium. Bacterivorous ciliates included mainly the prostomatid Urotricha sp., the scuticociliates Uronema and Cyclidium, the choreotrichs Lohmaniella oviformis and Strobilidium, and the hypotrich Euplotes sp. Protist abundance averaged 4 × 103 and 8.1 cells ml−1 in the ice-brine and 0.3 × 103 and 1.2 cells ml−1 in the plankton, for flagellates and ciliates, respectively. In contrast to bacteria, the abundance of protists generally
increased throughout the sampling period, indicating predator–prey interactions. Protistan bacterivory, measured from the
rate of FLB disappearance over 24 h, averaged 36% (ice) and 24% (plankton) of bacterial standing stock and exhibited the same
seasonal pattern as for protist abundance. The calculated specific clearance (range, 2–67 nl protozoa−1 h−1) and ingestion (<1–26 particles protozoa−1 h−1) rates were likely to be minimal estimates and grazing impact may have been higher on occasion. Indications for the dependence
of ``bacterivorous protists' on nonbacterial food items were also provided. Although alternative sources of bacterial loss
are likely to be of importance, this study provides evidence for the potential of protozoan assemblages as bacterial grazers
in both sea ice-brine biota and water column at the southern limit of sea ice in the northern hemisphere.
Received: 30 July 1998; Accepted: 18 November 1998 相似文献
12.
灞河城市段浮游生物群落结构时空变化及其与环境因子的关系 总被引:4,自引:0,他引:4
为了解灞河城市段浮游生物群落结构及其与环境因子之间的关系,于2016年9月至2017年7月每2个月进行一次采样分析。调查期间共鉴定出浮游植物7门63属,其中绿藻门种类数最多(34.9%),其次为硅藻门(30.2%);浮游动物4类45种,以轮虫(48.9%)和原生动物(24.4%)为主。浮游植物和浮游动物的丰度分别为0.73×10~4—98.5×10~4个/L和20—1084个/L,在时空分布上均呈现下游高于上游的趋势,峰值均出现在夏季。根据水体透明度、溶解氧、总磷、总氮、高锰酸盐指数和重金属等理化指标、浮游生物丰度、Shannon-Wiener多样性指数和Margalef丰富度指数对灞河城市段水质状况进行综合评价,结果显示,所研究流域总体为中污状态,上游景观河道内的水生植物对水体具有一定的修复能力。典范对应分析表明,水温、总氮、pH、溶解氧和汞是浮游植物群落分布的主要影响因子;影响浮游动物群落分布的主要因子为水温、总氮、总磷、叶绿素a和汞。 相似文献
13.
Enikő Krasznai Gizella Fehér Gábor Borics Gábor Várbíró István Grigorszky Béla Tóthmérész 《Biologia》2008,63(6):928-935
A method recently proposed by Coesel that uses the desmid flora to assess the conservation value of aquatic habitats was applied
to an alkaline and hypertrophic oxbow of the Upper Tisza river (NE Hungary). According to the macrophyte community the oxbow
contains two distinct habitats, both of which provide suitable conditions for the development of a rich desmid flora. High
temporal and spatial differences in the algal flora were observed in periphyton and plankton samples taken in June and August
2004. The sample of Utricularia vulgaris periphyton collected in August was characterised by the most species-rich desmid flora. The conservation value of this sample
was the maximum according to Coesel’s method. The latter also proved to be useful for the assessment of the conservation value
of plankton net samples taken from among the macrophytes. The use of modified rarity value calculations as recently proposed
by Fehér did not significantly affect the conservation value, but different enumeration methods to quantify the floristic
diversity did result in different conservation values. We found that Coesel’s desmid based method is a useful tool for assessing
the conservation value of the studied oxbow. Based our results the Coesel method’s applicability and usefulness depended on
(i) the sampling location (open water or macrophytic region) samples were taken from open water or from macrophytic region;
and (ii) species enumeration procedures (up to 400 specimens counted, or whole droplets counted).
Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. 相似文献
14.
We examined feeding of blue catfish, Ictalurus furcatus, and flathead catfish, Pylodictis olivaris, collected from floodplain lake, secondary (side) river channel, and main river channel habitats in the lower Mississippi
River (LMR), U.S.A. We described the feeding ecology of two large river catfish species within the context of whether off-channel
habitats in the LMR (i.e., floodplain lakes and secondary channels) potentially provided energetic benefits to these fishes
as purported in contemporary theory on the ecology of large rivers. We used diet composition and associated caloric densities
of prey consumed as indicators of energetic benefit to catfishes. Differences in diet among habitats were strong for blue
catfish, but weak for flathead catfish; consumed foods generally differed among habitats in caloric (energy) content. Caloric
densities of consumed foods were generally greatest in floodplain lakes, least in the main river channel, and intermediate
in secondary river channels. Strong between-year variation in diet was observed, but only for blue catfish. Blue catfish fed
disproportionately on lower-energy zebra mussels in the main river channel during 1997, and higher-energy chironomids and
oligochaetes in floodplain lakes during 1998. Results suggested that although off-channel habitats potentially provided greater
energetic return to catfishes in terms of foods consumed, patterns of feeding and subsequent energy intake may vary annually.
Energetic benefits associated with off-channel habitats as purported under contemporary theory (e.g., the ‘flood-pulse concept’)
may not be accrued by catfishes every year in the LMR. 相似文献
15.
Siphonophores are exclusively marine cnidaria and their predatory role in plankton food-webs is well recognised. In this study,
we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows
and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of
149 samples were collected using a 505 μm multiple closing net at 1–6 levels (0–100 m) of the water column, depending on the
bathymetry. Data on siphonophore species biovolumes (ml 100 m−3) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the ‘inner’
and the ‘outer’ assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore
species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical
distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger
than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially,
the lowest diversity and mean siphonophore biovolumes values were registered in the ‘inner assemblage’, where the highest
and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore
populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity,
since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps,
their prey. All the 23 species here registered were found in the ‘outer assemblage’; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the ‘outer’ group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the ‘inner assemblage’ during both seasons and, supporting previous
observations, this species might be considered as an indicator of nearshore waters.
Handling editor: K. Martens 相似文献
16.
Meso- and bathypelagic distribution and abundance of chaetognaths in the Atlantic sector of the Southern Ocean 总被引:1,自引:0,他引:1
We conducted multinet sampling during winter and summer in the Southern Ocean (Atlantic sector) to investigate the effect
of water mass, season and water depth on abundance and species composition of meso- and bathypelagic chaetognaths. Eukrohnia hamata (mean 115 ind. 1,000 m−3) and Sagitta marri (mean 51 ind. 1,000 m−3) were dominant, complemented by E. bathypelagica (mean 19 ind. 1,000 m−3) and E. bathyantarctica (mean 19 ind. 1,000 m−3) below 1,000 m. A further six species were identified, among them the rare bathypelagic species Heterokrohnia fragilis and the subtropical Eukrohnia macroneura that is new to the Antarctic. Water depth and season were the principal determinants of abundance and species composition
patterns, indicating vertical seasonal migration and vertical segregation of species. The life cycles of E. hamata and S. marri were studied additionally. Their maturity stages were vertically segregated and prolonged reproductive periods are suggested
for both species. 相似文献
17.
Cyanobacteria were a major constituent of phototrophic communities in the lakes, ponds and streams of Bylot Island, in the
Canadian high Arctic. The waters spanned a range of temperatures (1.8–16.8°C in late July), pH regimes (6.2–9.2) and conductivities
(1.5–1700 μS cm−1) but nutrient concentrations were consistently low (< 1 μg dissolved reactive P l−1 at all sites; < 10 μg NO3-N l−1 at most sites). Picoplanktonic species (Synechococcus spp.) were often the numerical dominants in the plankton, and periphytic filamentous species (Oscillatoriaceae) commonly
formed thick (5–50 mm) benthic mats. Bloom-forming species of cyanobacteria were either absent or poorly represented even
in Chla-rich ponds. The total community biomass ranged from 0.1 to 29.8 μg Chla l−1 in the plankton and from 1.1 to 34.8 μg Chla cm−2 in the benthos. The in vivo absorbance characteristics of isolates from these environments indicated a genetically diverse
range of species in each group of Arctic cyanobacteria. Growth versus irradiance relationships were determined for each of
the isolates and similarly revealed large genetic differences (maximum growth rates from 0.17 to 0.61 day−1), even between morphologically identical taxa. A comparison of nutrients, pigment concentrations and species composition
underscores the strong similarities between freshwater ecosystems in the north and south polar zones.
Received: 3 June 1996 / Accepted: 3 November 1996 相似文献
18.
We report on the γ- diversity of Rotifera in freshwater habitats of the River Mun floodplain, Northeast Thailand. Qualitative samples were collected during the pre-monsoon (April) and post-monsoon (October) periods of 2000, from 70 habitats spanning a diverse array of freshwater habitat types. Of the 184 species identified, most belong to Lecane (31.0%), followed by Trichocerca (12.0%), Lepadella (11.4%) and Brachionus (8.2%). Oriental, Australasian, and Eastern hemisphere taxa account for 4.3%, 3.3% and 7.1%, respectively, of the total rotifer fauna, and 8.8%, 1.7% and 10.5%, respectively, of Lecane. Although comparison between studies is difficult, these numbers conform to previous reports on the diversity and composition of the rotifer fauna of Thai freshwater habitats, and of tropical floodplain ecosystems. Diversity is lowest during the post-monsoon period, which may result from disturbance by monsoon conditions. Two morphospecies, Brachionus srisumonaen. sp., and Lecane niwati n. sp., are described as new to science. Additional noteworthy occurrences are, Lecane robertsonae Segers, previously considered a Neotropical endemic, and L. subtilis Harring & Myers, a tropicopolitan species new to Thailand and the Oriental region. 相似文献
19.
Invasive Asian carps Hypophthalmichthys spp. are an ecological threat to non-native aquatic ecosystems throughout the world, and are poised to enter the Laurentian
Great Lakes. Little is known about how these filter-feeding planktivores grow and impact zooplankton communities in mesotrophic
to oligotrophic systems like the Great Lakes. Our purpose was to determine how different plankton densities affect bighead
carp H. nobilis biomass and how bighead carp affect zooplankton species composition. We conducted a 37-day indoor mesocosm experiment (volume = 678 l)
with high and low plankton treatments (zooplankton dry mass ≈ 1,900 and 700 μg l−1; chlorophyll a = 25 and 14 μg l−1, respectively) in the presence and absence of juvenile bighead carp (mean = 5.0 g, 8.5 cm). Carp lost weight in the low plankton
treatment and gained weight in the high plankton treatment, suggesting that food availability may be a limiting factor to
bighead carp growth in regions of low plankton densities. In the presence of carp, zooplankton shifted from Daphnia to copepod dominance, while in the absence of carp, Daphnia remained dominant. Chydorids and ostracods increased in the presence of carp, but only in the low plankton treatment, suggesting
that the impact of bighead carp on zooplankton species composition may vary with zooplankton density. Chlorophyll was higher
in the absence of carp than in the presence. Chlorophyll and zooplankton densities in many Great Lakes ecosystems are substantially
lower than our low treatment conditions, and thus our results suggest that Asian carp establishment in these regions may be
unlikely.
Handling editor: S. Declerck 相似文献
20.
The purpose of this work is to increase ecological understanding of Avicennia germinans L. and Laguncularia racemosa (L.) Gaertn. F. growing in hypersaline habitats with a seasonal climate. The area has a dry season (DS) with low temperature and vapour pressure deficit (vpd), and a wet season (WS) with high temperature and slightly higher vpd. Seasonal patterns in interstitial soil water salinity suggested a lack of tidal flushing in this area to remove salt along the soil profile. The soil solution sodium/potassium (Na+/K+) ratio differed slightly along the soil profile during the DS, but during the WS it was significantly higher at the soil surface. Diurnal changes in xylem osmolality between predawn (higher) and midday (lower) were observed in both species. However, A. germinans had higher xylem osmolality compared to L. racemosa. Xylem Na+/K+ suggested higher selectivity of K+ over Na+ in both species and seasons. The water relations parameters derived from pressure–volume P–V curves were relatively stable between seasons for each species. The range of water potentials (Ψ), measured in the field, was within estimated values for turgor maintenance from P–V curves. Thus the leaves of both species were osmotically adapted to maintain continued water uptake in this hypersaline mangrove environment. 相似文献