Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area

1. We report on a long-term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.
2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long-term mean.
3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.
4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.
5. The dominant zooplankton species in spring shifted in recent years from the large-bodied Daphnia galeata to the smaller D. cucullata . Cyclops kolensis , previously the only invertebrate predator during winter, decreased in abundance while C. vicinus , usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.
6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.     

The impact of changing the season in which cereals are sown on the diversity of the weed flora in rotational fields in Denmark

1. Surveys have shown that there has been a dramatic decrease in the weed flora of fields under rotational cultivation during the last 30 years. This trend has been particularly noticeable in winter cereals, a crop of increasing importance in the landscape.
2. The weed flora of spring and winter cereals was compared in 19 unsprayed fields during a 5-year study to test the hypothesis that cereal type exerts no effect on the flora or on the absolute and relative abundance of single species.
3. Plant and species densities, and accumulated species richness, were lower in winter than in spring cereals.
4. Floristic similarity was greater among spring cereal fields and between spring and winter cereals within the same fields than among winter cereal fields.
5. Species that occurred with unequal density in spring and winter cereals occurred at higher densities in the spring cereals; these species germinated mainly in the spring. However, for a few species the relative plant abundance was highest in winter cereals; these species were able to germinate both in the spring and autumn.
6. Some species – on the relative scale – occurred indifferently of season of sowing; all but one of these species were able to germinate both in the spring and autumn.
7. Plant species and taxa that are important food resources for arthropod herbivores occurred at greater densities in spring than in winter cereals and, in addition, occurred with the highest relative abundance in spring cereals.
8. Change in land use from spring to winter cereals involves not only an immediate reduction of more than 25% in the density of plants and species, but also a change and increased uncertainty in the composition of the weed flora. These findings may have serious implications for the ecology of wildlife in the agricultural landscape.     

Plankton dynamics in the South of California Current]

We analyzed zooplankton biomass, micro- and nannophytoplankton abundance, Calanus pacificus Brodsky 1948 abundance, and sea surface temperature along the west coast of Baja California between February 1983 and September 1991. The zooplankton biovolume abundance decreased from spring to autumn. The average abundance of nannophytoplankton (< 20 microns) was generally higher than microphytoplankton (> 20 microns). Both increased 3.5 times in abundance after 1986. Seasonally, both fractions (NP and MP) were least abundant in winter and most abundant in summer and autumn. Calanus pacificus abundance was variable, but especially high in May of some years. Abundance was lowest in winter and highest in spring, dropping in summer and autumn. Sea surface temperatures averaged 21.5 degrees C, with highest in autumn (24.2 degrees C) and the lowest in spring (17.9 degrees C). C. pacificus abundance and sea surface temperature were inversely related by cruise, season, and latitude. The phytoplankton abundance and zooplankton biomass and C. pacificus abundance showed low and high abundance patterns coincident with warming and cooling events (El Ni?o-La Ni?a).     

黄河口邻近海域浮游动物群落时空变化特征

利用2012年12月—2013年9月4个季度的现场调查资料研究了黄河口邻近海域浮游动物群落的时空分布特征。研究表明,黄河口邻近海域共鉴定出浮游动物70种,包括浮游幼虫19类。浮游动物优势种主要由夜光虫(Noctiluca scintillans)、小拟哲水蚤(Paracalanus parvus)、双刺纺锤水蚤(Acartia bifilosa)、拟长腹剑水蚤(Oithona similis)、强额拟哲水蚤(Paracalanus crassirostris)、近缘大眼剑水蚤(Corycaeus affinis)、强壮箭虫(Sagitta crassa)、双壳类幼体(Bivalvia larvae)、多毛类幼体(Polychaeta larvae)等种类。黄河口邻近海域浮游动物丰度夏季最高(60620个/m~3),春季(31228个/m~3)和秋季(21540个/m~3)次之,冬季最低(7594个/m~3)。不同季节浮游动物丰度的空间分布具有差异性,春季浮游动物丰度呈现出从近岸到外海降低的趋势;夏季浮游动物形成两个高丰度区,分别位于河口邻近海区和河口东部海区;秋季和冬季浮游动物丰度高值区均位于河口东部海区。浮游动物生物多样性指数均呈现从河口到外海升高的趋势,低值区位于黄河口入海口附近海区。相关性分析显示,黄河口邻近海域浮游动物丰度与海水温度显著正相关(r=0.212,P0.05),表明温度为影响黄河口邻近海域浮游动物丰度变化的主要因素。     

Mechanisms regulating zooplankton populations in a high-mountain lake

SUMMARY 1. We studied the seasonal succession of phyto- and zooplankton and the potential impact of predation by salmonids on zooplankton population dynamics in a high-mountain Swiss lake.
2. A comparison of patterns in the abundance, body length, fecundity and age structure in the Daphnia galeata population strongly suggests that trout predation had little impact on the population and was not the cause for a decline in summer.
3. The dominance in the lake of adult trout that feed mainly on benthic prey may buffer the effect of predation on the larger zooplankton. Further, the relatively high amount of phytoplankton after spring thaw could be important for sustaining the Daphnia population under moderate fish predation.
4. Partial correlation analyses proved circumstantial evidence for both exploitative and interference competition between some zooplankton taxa. D. galeata depressed performance of other plankton species through exploitative competition.
5. Our study shows that the impact of fish on zooplankton in high-mountain lakes depends strongly on food web structure and trophic state of the lake. Where fish predation is weak, invertebrate predation combined with competition for food may be responsible for the dominance of large-bodied zooplankton species.     

福建中部近海浮游动物数量分布与水团变化的关系

根据2009—2010年在福建中部近海24°55'—25°13'N、119°11'—119°32'E水域冬、春、夏3个季节的调查资料,探讨了该水域浮游动物总丰度与生物量的平面分布、季节变化及其与台湾海峡水团变化的关系。结果表明,调查水域浮游动物的数量在冬、春之交变化较大,而在春、夏季变化较小。浮游动物冬、春两季的平均丰度分别为8.90 个/m³和245.65 个/m³,夏季为236.82 个/m³。冬、春两季,该水域浮游动物的分布特征相近。其数量在近岸较高,向外侧水域逐渐降低。冬季浮游动物的丰度最高为31.56 个/m³,春季最高达到831.67 个/m³。中华哲水蚤(Calanus sinicus)是冬、春季影响总丰度变化最主要的种类。与冬、春季不同,夏季浮游动物的数量在离岸水域较高,丰度最高达1053.13 个/m³,而在近岸较低,最低值仅19.17 个/m³。汉森莹虾(Lucifer hanseni)、双生水母(Diphyes chamissonis)是影响总丰度变化最主要的种类。浮游动物在各季的不同分布特征与台湾海峡的季节性水团变化有关。受季风转换影响,从冬季到夏季,海峡内沿岸流势力逐渐减弱,台湾暖流水势力逐渐增强,并影响到沿岸的水文环境。这导致调查水域内浮游动物的优势种类由暖温种向暖水种演替。由于冬、春季的重要优势种类中华哲水蚤与夏季的汉森莹虾、双生水母具有不同的温度适应性,受不同性质水团的影响,在近岸和离岸水域各自呈现出不同的数量高低。从而进一步影响到各季浮游动物总数量的分布。     

Seasonal variation in freezing tolerance of the New Zealand alpine cockroach Celatoblatta quinquemaculata

1. The cold hardiness of the alpine cockroach Celatoblatta quinquemaculata was investigated. This species is found at 1360 m a.s.l. beneath schist slabs on the Rock and Pillar Range (Central Otago, New Zealand). Cockroaches were collected monthly from January to December 1996, and their LT₅₀ and supercooling points determined.
2. Celatoblatta quinquemaculata was freezing tolerant throughout the year, with a lower lethal temperature in winter of – 8.9 °C. Celatoblatta quinquemaculata was also found frozen under rocks in the field when the under-rock temperature was below – 3 °C, and could survive being frozen at – 5 °C for 4 days in the laboratory.
3. There was a marked decrease in LT₅₀ temperature from – 5.5 °C in April to – 7.5 °C in May. This coincides with decreasing temperatures from summer through autumn to winter, during which temperatures beneath snow-covered rocks may reach – 7.3 °C.
4. Supercooling points fluctuated during the year, with an increase from – 4.2 °C in autumn to – 3.4 °C in winter. Supercooling point was highest in spring, and changes in supercooling point do not appear to be related to changes in LT₅₀.
5. Recordings of environmental temperatures from the Rock and Pillar Range suggest that cockroaches may undergo up to twenty-three freeze–thaw cycles in the coldest month of the year, and that they may remain frozen for periods of up to 21 h. Maximum cooling rates recorded in the field (0.01 °C min^–1) were 100-fold slower than laboratory cooling rates, so survival estimates from laboratory experiments may be underestimates.     

The influence of year-to-year variations in winter weather on the dynamics of Daphnia and Eudiaptomus in Esthwaite Water, Cumbria

1. Micro-crustacea of the genus Daphnia and Eudiaptomus have evolved different physiological mechanisms for coping with life in a rapidly changing environment. In this paper, we analyse some of the physical and biological factors influencing the winter abundance of the two species in a small lake (Esthwaite Water in Cumbria).
2. The results demonstrate that much of the year-to-year variation in their relative abundance can be related to long-term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.
3. Year-to-year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring 'cohort'. The most important factor influencing the overwintering performance of the two species was the water temperature.
4. Winter air temperatures over much of Europe are influenced by the atmospheric pressure variation known as the North Atlantic Oscillation (NAO). Winter water temperatures in Esthwaite Water were strongly correlated with this empirical index and there was a significant positive correlation between the NAO and the number of overwintering Eudiaptomus.     

Seasonal spatial dynamics and causes of nest movement in colonies of the invasive Argentine ant (Linepithema humile)

Abstract.  1. Colony organisation and movement behaviour of the Argentine ant ( Linepithema humile ) was studied over 3 years in field populations in California and in captive colonies in the laboratory. This invasive species is highly polydomous and unicolonial; colonies consist of expansive and fluid networks of nests and trails. The spatial and temporal organisation of colonies may contribute to ecological dominance.
2. Argentine ant nests and inter-nest trails shift in size, abundance, and location, so that colony networks are spatially contracted in the winter and expanded spring to autumn. Colonies occupy permanent sites; ants migrated to and from the same winter nest locations year after year, and occupied 30% of the same nests repeatedly during seasonal migrations.
3. Nests were moved on average 2–3 m. Forty-two per cent were occupied less than 1 month, 4% the entire study, and the other 54% lasted 3.9 ± 2.3 months (mean ± SD).
4. Nests were located within 2–4 m of woody plants, in warm sites in the winter and cool sites in the summer. Both humidity and food availability influenced nest-site choice in laboratory colonies. However, when faced with a trade-off between factors, the ants chose humid nest boxes over nest boxes near food, and ants moved nests only in response to changes in humidity and not distance to food.
5. The results indicate that L. humile colonies are seasonally polydomous, and that nest movements are driven by changes in microclimate. Colony organisation maintains high local density and increases food supply, which may improve the competitive ability of L. humile colonies and reduce opportunities for species coexistence.     

Chlorella-bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis

1. Large mixotrophic ciliates ( Stentor araucanus , S. amethystinus and Ophrydium naumanni ) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1-year study, the abundance, biomass and primary production of these large Chlorella -bearing ciliates were compared with those of the total plankton community.
2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%).
3. Maximum cell-specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate^–1 h^–1 with high values during autumn and winter, and low values during summer. The depth-integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%).
4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high.
5. The mixotrophic ciliates represent an important 'link' between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.     

福建北部近海浮游动物数量分布与水团季节变化的关系

根据2015—2016年在福建北部近海水域(120.10°E—120.65°E, 26.35°N—27.07°N)夏、秋、冬、春4个季节的海洋生态调查资料, 探讨了该水域浮游动物的数量分布、季节变化及其与水团变化的关系。结果表明, 调查水域浮游动物的平均生物量依次是: 夏季(479.51 mg/m3)>秋季(257.37 mg/m3)>春季(241.86 mg/m3)>冬季(84.05 mg/m3), 平均丰度依次是: 夏季(156.36 ind./m3)>春季(91.57 ind./m3)>秋季(40.34 ind./m3)>冬季(21.82 ind./m3), 生物量和丰度均值都呈现出夏季、秋季到冬季依次减少, 春季增多的趋势, 不同的是秋季生物量均值高于春季, 而丰度均值低于春季。在夏、冬和春三季, 浮游动物的总生物量和总丰度的分布总体较为一致; 而在秋季, 浮游动物的总生物量和总丰度的分布几乎相反。百陶箭虫(Sagitta bedoti)和微剌哲水蚤(Canthocalanus pauper)是影响夏季总丰度分布最主要的种类; 链钟水母(Desmophyes annectens)是影响秋季总丰度分布最主要的种类; 驼背隆哲水蚤(Acrocalanus gibber)、亚强真哲水蚤(Eucalanus subcrassus)和百陶箭虫对冬季总丰度的分布起到了重要影响; 五角水母(Muggiaea atlantica)和微剌哲水蚤是春季占总丰度比例较高的种类。浮游动物数量各季不同分布模式的根本原因是台湾暖流和浙闽沿岸流水团的季节性变化所致。研究结果不仅对了解与评价区域海洋生态系统动态和生物多样性变化具有重要的理论意义, 而且还可以丰富我国近海水域浮游动物的生态特征与水团变化之间的关系。     

Interactions between phytoplankton and zooplankton in a fertilized lake

The limnology of an oligotrophic lake, Langvatn, situated in Trøndelag county in Central Norway, has been studied for five years (1974–1978). In two years, 1975 and 1976, the lake was fertilized with a general fertilizer to change feeding conditions for the zooplankton. Mean phytoplankton biomass in the epilimnion and primary production for the years (1974–1978) were 417, 618, 1370, 607 and 779 mg m⁻³ and 10.6, 22.2, 49.0, 26.8 and 17.7 g C m⁻² yr⁻¹, respectively. Cladocerans were the dominant herbivore group in 1974 and 1975 and Rotifera in the next three years. The main difference in the interaction between phytoplankton and zooplankton occurred when cladoceran dominance gave way to rotifer dominance. Heavy phytoplankton grazing by cladocerans in 1974 and 1975 stabilized the biomass and maintained it at a low level, which also resulted in a relatively low primary production. The rotifer-dominated community during the years 1976–1978 did not possess the ability to maintain a stable level of algal biomass. Primary production was also relatively high during these years.     

Squid stock fluctuations and water temperature: temporal analysis of English Channel Loliginidae

1. Monthly series of abundance indexes for the English Channel squid stock, based on fishery statistics of the United Kingdom (1980–93) and France (1986–96), were compared with water temperature data. The two objectives of the study were to test empirical predictive models and to analyse the stock–environment relationship at various time scales; both correlation and time-series statistical techniques were applied. Sea surface temperature (SST) showed inter-annual fluctuations and month-to-month auto-correlation in addition to the annual cycle.
2. Trends in squid landings and temperature at the annual scale were found to be related, whatever the statistical method used (moving averages, cumulative functions or regression using averaged data).
3. Variable selection applied in a 'multi-month' model suggested that fishing season indexes could be predicted from temperatures observed in the previous winter. The link between mild winter conditions and cohort success in winter/spring spawning species suggested that early life survival (and/or growth) was involved. This empirical model is a first step in the development of environment-predicted recruitment indexes useful for management advice.
4. Seasonal decomposition was performed on both the squid resource data and SST data in search of short-term relationships. In spite of the flexibility of the loliginid life-cycle, no significant relationship was found between squid seasonally adjusted indexes and temperature anomalies in the previous months. This underlined the conclusion that temperature effect on cohort success was not constant throughout the year.     

Seasonal and decadal patterns in Discostella (Bacillariophyceae) species from bi‐weekly records of two boreal lakes (Experimental Lakes Area,Ontario, Canada)

A recent rise in the relative abundance of Discostella species (D. stelligera and D. pseudostelligera) has been well documented from sedimentary diatom assemblages across the Northern Hemisphere. This unprecedented change over the last ~150 years has been linked to rises in atmospheric temperatures, changes in ice cover, and/or increases in thermal stability, among other factors. The bi‐weekly monitoring data from two boreal lakes at the Experimental Lakes Area (ELA) in northwestern Ontario were analyzed across seasons (spring, summer, and fall) and decades (1970s–2000s). We found that Discostella species are primarily spring/early summer bloomers (i.e., late April to June) in these lakes and changes in concentrations of Discostella over time were most pronounced in the spring or early summer months. Increases in Discostella abundance over time may be linked to earlier ice‐off and a longer period of spring turnover, resulting from increased winter and spring temperatures. It is also possible that a trophic mismatch between the spring diatom bloom and zooplankton is occurring, thus reducing diatom loss rates, and resulting in greater overall abundance. Moreover, the spring dominance of Discostella in our study lakes occurred at a time of the year when nutrient concentrations were at their highest seasonally, suggesting that these taxa are neither limited directly by nutrients, nor responding to enhanced stratification during the summer months in these lakes.     

兴化湾浮游动物群落季节变化和水平分布

兴化湾为福建北部最大的海湾,于2006年对该海湾浮游动物群落进行了四季9个站位的调查。共检出浮游动物及幼虫124种,其中春季42种,夏季89种,秋季71种,冬季20种;分属近岸暖温、近岸暖水和广布外海3个生态类群;优势种15种,春季以水母和桡足类占优势,夏季以水母占优势,秋季以水母、桡足类和箭虫占优势,冬季则以桡足类占优势。不同季节兴化湾浮游动物生物量湿重和丰度水平分布特征变化明显,并与温度和盐度呈显著相关。聚类分析显示兴化湾浮游动物群落夏季类群和秋季类群相似度较高;各季节水平分布基本可分为湾口区和湾内区两大类群。与20世纪80年代相比,尽管本次调查浮游动物群落没有表现出显著差异,但随着电厂等大规模工程的投产,兴化湾海域生态系统健康面临着极大威胁,其环境压力需引起持续关注。     

Overwintering survivorship of pupae of the mimosa web worm, Homadaula anisocentra (Lepidoptera: Plutellidae), in an urban landscape

ABSTRACT. 1. Overwintering survivorship of pupae of the mimosa webworm, Homadaula anisocentra Meyrick (Lepidoptera: Plutellidae), was examined in several urban habitats in central Iowa during the winters of 1981–82, 1982–83 and 1983–84.
2. Survivorship and supercooling point temperatures were determined throughout the winters. Corroborative laboratory studies were conducted during the winter of 1982–83.
3. Minimum ambient temperatures that equalled or were below the supercooling point of the insect, at any time, were lethal.
4. Prolonged cold exposure below 0°C and above the supercooling point resulted in high mortality levels. To quantify this relationship, a concept of minimum-temperature exposure was developed by tabulating the number of degrees that the daily minimum temperature was below 0°C for a given sampling period.
5. Some mimosa webworm pupae were found to overwinter in highly protected sites (2.5–5.0°C warmer than the ambient air temperatures) in the urban environment, resulting in less minimum-temperature exposure and reducing the probability of reaching the lethal supercooling point temperature.     

Seasonal distribution,composition and abundance of the planktonic Ciliata and Testacea of Cayuga Lake

The planktonic protozoans (Ciliata and Testacea) of Cayuga Lake were studied from September 1974 through July 1975. Monthly collections were taken at four depths (surface, 15,31 and 92 m) at each of seven stations along the 125 m depth contour. All samples were collected with a 6-liter Van Dorn bottle sampler. Densities and biomass were determined for total protozoans and total zooplankton at each depth on each sampling date. Temperature profiles at one-meter intervals were also determined on or within a few days of the zooplankton sampling.The vertical distribution of the total protozoans was directly related to temperature; maximum densities corresponded to high summer surface temperatures. Dominant protozoan taxa included Didinium nasutum, Stokesia vernalis, Codonella cratera, Strobilidium gyrans, Strobilidium sp., Strombidium viride, Paradileptus canellai, Difflugia limnetica, and unidentified ciliates belonging to the families Halteriidae, Holophryidae, Epistylidae, and Vorticellidae. Protozoans composed 69% or more of the total zooplankton density on nine of eleven dates. Protozoan dominance was most evident during winter and spring, corresponding to the near absence of rotifers and microcrustaceans. Protozoans accounted for 30% or more of the zooplankton biomass from April through June, reaching 47% in May.     

Interactive effects of temperature and predation on an estuarine zooplankton community

The winter planktonic copepod community of the estuaries near Beaufort N.C. underwent a consistent transition from dominance by Acartia tonsa Dana to dominance by Centropages spp., which was associated with unpredictable decreases in water temperature and increases in abundance of predatory mysids. Centropages subsequently remained dominant until spring. Experimental manipulations of water temperature and mysid abundance in enclosures showed that copepod species composition was determined by an interaction of direct temperature effects with predatory interactions among copepods and mysids. Low temperatures stimulated recruitment of Centropages spp. and inhibited recruitment of Acartia tonsa. Temperature decreases also apparently stimulated migration of mysids into the study area. While A. tonsa was dominant, selective predation by mysids reduced the relative abundance of A. tonsa, but after Centropages became dominant mysid predation had no effect on copepod species composition. Predation by Centropages on the nauplii of other species probably contributed to its persistent dominance in the estuary. Rising temperatures in the spring favored recruitment of Acartia tonsa and inhibited Centropages recruitment. Selective predation by fish entering the estuary in spring may have contributed to the decline in abundance of Centropages spp. and mysids.     

太平湖浮游动物动态演替与环境因子的相关性研究

2012年11月至2014年10月, 对太平湖浮游动物群落进行了为期两年的调查研究。共鉴定出浮游动物45属89种, 其中轮虫 29属69种、枝角类5属7种、桡足类2属4种和原生动物9属9种; 优势种主要来自于轮虫异尾轮虫属(Trichocereca)和龟甲轮虫属(Keratella)。浮游动物的丰度值存在明显的季节变化, 表现为夏季最大, 平均达1326 ind./L, 秋季春季次之, 分别为608和605 ind./L, 冬季最小为216 ind./L; 垂直分布表现为春夏季太平湖表层浮游动物丰度最高, 中间层次之, 底层最小, 秋冬季则表现为中间层最高。浮游动物群落Shannon-Wiener多样性指数和Margalef丰富度指数中间层普遍高于表层和底层, Pielou均匀度指数表现为底层要高于表层和中间层, 季节变化表现为夏秋季显著高于冬春季的现象, 水质评价表明夏秋季水质好于春冬季。聚类和多维尺度分析表明: 太平湖浮游动物可分为夏秋季类群与春冬季类群, 两类群均表现为湖心与上下游区域群落结构差异较大, 其中春冬季类群差异较明显; 相关和逐步回归分析表明: 透明度和水温为太平湖浮游动物群落结构变化的主要环境影响因子; 依据结构方程模型(SEM)和冗余分析(RDA)的结果显示, 在溶解氧和水温较高的水环境中浮游动物丰度值表现为较大, 其中水温对轮虫的影响高于对枝角类和桡足类的影响。     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.