Macrozoobenthic assemblages in littoral sediments in the enclosed Rhine-Meuse Delta

Littoral macrozoobenthos in the enclosed Rhine-Meuse Delta was investigated by taking 95 sediment samples from 17 sites between 1984 and 1990. In addition, a set of environmental parameters was determined. The aim was to identify the main assemblages and the environmental conditions under which they occur. By the use of TWINSPAN, three main littoral zoobenthic assemblages were distinguished, which were related to geographical zones and differences in sediment grain size distribution. The ‘litoral river sand’ assemblage was found in the most upstream part; it mainly consisted of ‘interstitial’ invertebrates, including the indicator speciesVejdovskiella comata, Propappus sp. andKloosia pusilla. The ‘littoral sedimentation area silt’ assemblage was dominated byGammarus tigrinus, Einfeldia dissidens andPisidium sp. It was found in several river sections and contained the indicator speciesEinfeldia dissidens, Potamopyrgus antipodarum andValvata piscinalis. The ‘littoral sandy basin’ assemblage was concentrated in the littoral fine sands of the Haringvliet and contained the indicator speciesPisidium henslowanum, P. moitessierianum, Cladotanytarsus sp. andLipiniella arenicola. These three assemblages are the reflection of an interaction between habitat, food and disturbance. Palaeoecological analysis of insect remains revealed that 14 out of the 24 insect taxa, that were formerly common in the river sand habitat, are now extinct from the Rhine. The river silt habitat seems less impoverished: two out of the 19 insect taxa found in palaeoecological analysis are now extinct from the Rhine and seven are rate. Exotic species (Corbicula fluminea, C. fluminalis andCorophium curvispinum) have recently colonized the Rhine-Meuse Delta, but their impact on the macrozoobenthos seems limited.Corbicula spp. have become abundant in the ‘littoral river sand’ assemblage only.     

Phytoplankton and Nutrients in Goat Island Bay,New Zealand

A quantitative study of the phytoplankton and nutrients in Goat Island Bay, northern New Zealand, was carried out at two stations of depths 7 m and 20 m in 1966-69. There were significant differences in the concentrations of the phytoplankton at the two stations, the deeper station having, in general, higher concentrations than the shallower. Low phytoplankton standing crops were found in winter when the increased run-off from the land resulted in lower salinities, higher turbidity, and higher dissolved silicate levels. The spring growth of diatoms was dominated by small diatoms (Cylindrotheca closterium, Leptocylindrus danicus, Nitzschia pseudoseriata, Phaeodactylum tricornutum, and Rhizosolenia delicatula). Occasionally it was dominated by a population of large centric diatoms (Chaetoceros spp., Coscinodiscus spp., Thalassiosira spp.), but these appeared to be found in a separate water mass which entered the bay and displaced the resident water mass. A third water mass entered the bay in spring and was characterised by the coccolithophore Emiliana huxleyi and a lower temperature. During the summer diatoms dominated the phytoplankton population, but were replaced by dinoflagellates for a short period in autumn.     

香溪河大型底栖动物群落结构季节动态

通过大型底栖动物的量化监测,对香溪河水系大型底栖动物季节动态进行研究.共采集大型底栖动物197种,隶属6纲68科,其中,四节蜉、高翔蜉、短尾石蝇为该水系优势类群,不同季节间大型底栖动物优势类群组成存在较大差异.大型底栖动物群落结构以冬季最为复杂,春、秋季次之,夏季相对简单.大型底栖动物功能摄食类群以集食者占优,其次为刮食者、捕食者和滤食者,撕食者丰度最小.典型对应分析表明,不同季节影响底栖动物群落结构的因子差异较大;夏季和秋季营养盐对底栖动物群落结构影响较大,水深对各季度大型底栖动物群落结构均有影响.     

Some factors affecting distribution of diatom assemblages in Pyrenean springs

SUMMARY.

• 1 The composition and abundance of diatom assemblages were studied together with physiographical and physicochemical variables in twenty-eight springs in the Central Pyrenees during the period 1987–88.
• 2 Characteristic groupings of diatom taxa are revealed by Principal Components Analysis. One group, made up of assemblages of the taxa Navicula cincta, Caloncis spp. and Niizschia elliptica, is characteristic of springs with waters of high ionic strength. Certain diatom taxa are characteristic of hard water springs, either in quiet waters (Denticula tenuis, Achnanthes minutissima, Eunotia spp.) or fast flowing ones (Fragilaria spp., Diatoma hiemale). Other taxa are representative of relatively quiet, softwater springs: Anomoeoneis bracfiysira, Tabellaria flocculosa, Aulacoseira distans and Fragilaria vaucheriae.
• 3 Five different spring types were identified, with respect to diatom assemblages, using discriminant analysis. The first consisted of high mountain springs with cold, fast waters and low ionic strength. The second group, distributed throughout the Pyrenees, had similar environmental characteristics to the first group but with intermediate water velocity and slightly higher mineral content. The third contained springs in calcareous regions of the Pyrenees, mainly slow-flowing and with hard waters. The fourth was composed of softwater springs, whilst the fifth consisted of two springs which were subject to stressful conditions (limitation of light, abundance of nitrates or high salinity).
• 4 Ionic strength and current velocity appeared to be the dominant environmental factors affecting diatom distribution in Pyrenean springs. These factors also seem to determine diatom communities in some other geographical areas. In some springs, however, peculiar environmental factors (dim light, salinity, and high temperature) affect the structure of diatom assemblages.

     

Longitudinal and seasonal distribution patterns of the benthic fauna of an alpine glacial stream (Val Roseg, Swiss Alps)

1. Seasonal changes in longitudinal patterns of environmental conditions and macroinvertebrate community distributions were examined in an alpine glacial stream (Roseg River, Switzerland). 2. Physico‐chemical parameters reflected seasonal changes in glacial influence via shifts in water sources and flowpaths (glacial meltwater versus ground water), and were best described by turbidity, particulate phosphorus and specific conductance. High nitrogen concentrations indicated snowmelt was the main water source in June. 3. Macroinvertebrate densities and taxon richness were highest during spring (4526 m^–2 and 16 taxa, all sites combined) and late autumn/early winter (8676–13 398 m^–2 with 16–18 taxa), indicating these periods may be more favourable for these animals than summer when glacial melting is maximal. Diamesa spp. (Chironomidae) dominated the fauna at the upper three sites (>95% of zoobenthos) and were abundant at all locations. Other common taxa at lower sites (1.2–10.6 km downstream of the glacier terminus) included other chironomids (Orthocladiinae, Tanytarsini), the mayflies Baetis alpinus and Rhithrogena spp., the stoneflies Leuctra spp. and Protonemura spp., blackflies (Simulium spp., Prosimulium spp.), and Oligochaeta. 4. Co‐inertia analysis revealed a strong relationship between environmental conditions and benthic macroinvertebrate assemblages. Furthermore, it elucidated temporal variability in longitudinal response patterns, as well as a similarity in temporal patterns among individual sites. 5. Our results suggest that zoobenthic gradients are not solely related to temperature and channel stability. Seasonal shifts in sources and pathways of water (i.e. extent of glacial influence), and periods of favourable environmental conditions (in spring and late autumn/early winter) also strongly influenced zoobenthic distributions.     

Seasonal variations of diatoms and dinoflagellates in a shallow,temperate estuary,with emphasis on neritic assemblages

Seasonal changes in the diatom and dinoflagellate assemblages were examined in the neritic zone of the Urdaibai estuary (north Spain) with regard to some major physical and chemical variables during an annual cycle. A total of 81 diatoms and 38 dinoflagellates were identified and quantified during the study period. Both groups displayed a distinctive pattern of seasonal succession. The seasonal distribution of the Shannon index showed a trend of increasing values from the upper estuary to the lower neritic segment. The diatom diversity maxima were observed in February, April and September, and dinoflagellate maxima in April–May, July and October. Diatoms dominated the assemblages, reaching 1×10⁶ cells l^–1 from April to September. A shift from large diatoms and dinoflagellates to small bloom-forming taxa was observed during winter–early spring. A spring diatom bloom composed of Rhizosolenia spp. was observed in April, while small chain-forming taxa (chiefly Chaetoceros spp.) dominated from June to September. Cell maxima for both groups in late summer were produced by the diatoms Chaetoceros salsugineum and Skeletonema costatum, and by the dinoflagellates Heterocapsa pygmaea and Peridinium quinquecorne. Silicate availability by river supply and strong tidal-mixing of the water column seem to determine the year-round dominance of diatoms over dinoflagellates.     

淮北煤矿区塌陷湖大型底栖动物群落结构及水质生物学评价

2013年对淮北采煤塌陷湖(乾隆湖和临涣湖)大型底栖动物群落结构进行了季节性调查。共采集到大型底栖动物26种, 隶属于3门5纲17科. 乾隆湖和临涣湖年平均密度分别为230.85和215.80 ind./m2, 年平均生物量分别为56.11和36.38 g/m2。两湖大型底栖动物以摇蚊幼虫、霍甫水丝蚓和苏氏尾鳃蚓为优势类群, 底栖动物最高密度均出现在夏季(乾隆湖为 278.0 ind./m2, 临涣湖为288.2 ind./m2); 生物量则主要以软体动物和水生昆虫为主, 夏季和秋季大型底栖动物生物量明显高于春季和冬季。运用Shannon多样性指数(H')、Margalef多样性指数(D)和Biotic Index生物学指数(BI)对乾隆湖和临涣湖进行水质生物评价研究, 结果显示Shannon多样性指数不适宜于该两湖的水质生物评价, BI的评价结果与水质状况基本相符。综合 Margalef多样性指数和BI生物指数评价的结果表明: 乾隆湖和临涣湖春季和冬季处于轻度污染状态, 夏季和秋季处于中度污染状态。     

Influence of the temperature regime on the composition of the macrozoobenthos community in a thermal brook in Serbia

In contrast to cold and eurythermal waters, benthic communities of warm brooks in temperate regions have been inadequately studied. In order to investigate the effects of water thermal regime on the benthic communities of warm waters and their relationships with those of cold and eurythermic ones, the macrozoobenthos was studied at eight sites in the Toplica River, and at four sites in its tributary, the Termalni brook. Investigations were carried out seasonally from April 2000 to January 2001. Warm waters of the Termalni brook were characterized by specific macrozoobenthos assemblages that exhibited significant differences to the populations of eurythermal and cold waters of the Toplica River. The dominant taxa in the macrozoobenthos community of warm waters were mainly Gastropoda species. Moreover, benthic communities of warm waters were characterized by lower diversity and greater biomass in comparison with those of cold and eurythermal waters. The gradient of average annual temperatures represented the main ecological factor influencing changes of diversity and biomass along the course of the investigated Termalni brook. Inflow of warm waters at site T₆ lead to a decrease in macrozoobenthos abundance and changes in qualitative and quantitative composition of the benthocoenosis of a highland stream, but did not significantly alter diversity.     

Effects of episodic acidification on macroinvertebrate assemblages in Swiss Alpine streams

1. Despite long‐standing ecotoxicological evidence that episodes of acidification in streams are important biologically, there is still uncertainty about their effects on invertebrate communities. We surveyed 20 streams in an acid sensitive Alpine area (Canton Ticino, Switzerland), where episodes are driven by snowmelt in spring and by rainstorms at other times of the year. Samples of water and macroinvertebrates were collected in pre‐event conditions (winter and summer) and during periods of high flow (spring and autumn). 2. Using pH, [Ca²⁺] and [Alⁿ⁺], streams were clustered into six acid–base groups that were either well buffered (groups 4–6), soft‐water with stable pH (group 3), or poorly buffered with low pH at high flow (groups 1 and 2). 3. Severe episodes occurred during snowmelt, when the group 1 streams became acidic with pH down to 5.0 and [Alⁿ⁺] up to 140 μg L^?1. pH declined to 6.2 in streams of group 2, but remained > 6.6 in groups 3–6. 4. Detrended canonical correspondence analysis showed that the streams sensitive to episodes (groups 1 and 2) had different invertebrate assemblages from well‐buffered sites (groups 4 and 5) or soft‐water stable streams (group 3), with faunal differences largest following spring snowmelt. Empididae, Isoperla rivulorum, Rhithrogena spp. and Baetis spp. were scarce in streams sensitive to episodes (groups 1 and 2). By contrast, Amphinemura sulcicollis was scarcer in hard‐water streams (groups 4–6). Taxonomic richness was lower in the episodic streams of group 1 than in other streams. 5. Together, these results indicate clear biological differences between acid‐sensitive streams with similar low‐flow chemistry but contrasting episode chemistry. Severe episodes of acidification appear to affect macroinvertebrate assemblages in streams in the southern Swiss Alps.     

Phytoplankton composition in the Weddell-Scotia Confluence area during austral spring in relation to hydrography

During the EPOS leg 2 cruise of the RV Polarstern, carried out in late austral spring of 1988–1989, the composition of phytoplankton in relation to the distribution of hydrographic parameters was studied in four successive transects carried out along 49°W and 47°W, across the Weddell-Scotia Confluence (WSC) and the marginal ice zone (which overlapped in part). In all transects, a maximum of phytoplankton biomass was found in the WSC, in surface waters stabilized by ice melting. Different phytoplankton assemblages could be distinguished. North of the Scotia Front (the northern limit of the WSC) diatoms with Chaetoceros neglectus, Nitzschia spp. and (Thalassiosira gravida) dominated the phytoplankton community. This assemblage appeared to have seeded a biomass maximum which occupied, during the first transect, an area of the WSC, south of the Scotia Front. The southernmost stations of the first transect and all the stations to the south of the Scotia Front in the other transects were populated by a flagellate assemblage (with a cryptomonad, Pyramimonas spp. and Phaeocystis sp.) and an assemblage of diatoms (Corethron criophilum and Tropidoneis vanheurkii among others) associated to the presence of ice. During the last three transects, the flagellate assemblage formed a bloom in the low salinity surface layers of the WSC zone. The bulk of the biomass maximum was formed by the cryptomonad which reached concentrations up to 4×10⁶ cells l^–1 towards the end of the cruise. Multivariate analysis is used to summarize phytoplankton composition variation. The relationships between the distribution of the different assemblages and the hydrographic conditions indicate that the change of dominance from diatoms to flagellates in the WSC zone was related to the presence of water masses from different origin.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Catastrophic mass extinction and assemblage evolution in planktic foraminifera across the Cretaceous/Paleogene (K/Pg) boundary at Bidart (SW France)

A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition.Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species.The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation.Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids (Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls (Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids (Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery.     

西江大型底栖动物群落特征研究

河流担负着水源供给、食物生产、旅游、航运等功能。近年来, 人类活动的加剧导致河流生态系统受到威胁。底栖动物常被作为环境指示生物, 研究其群落特征为河流保护及管理有着重要意义。为了航运需求,西江开展了航道整治工程, 由此引起河道生物栖息生境条件的改变, 从而影响河流的生态健康。为了西江的保护和管理, 研究于2009 年枯水期和2010 年丰水期对西江的底栖动物开展了系统调查。调查期间共鉴定底栖动物70 种, 隶属于30 科59 属。其中环节动物7 科12 属16 种, 软体动物11 科14 属21 种, 节肢动物11科32 属32 种, 其他动物1 科1 属1 种。底栖动物的密度和生物量分别为140 ind/m2、0.23 g dry weight/m2。统计分析表明河床底质在底栖动物丰度和分布上起着尤为重要的作用。稳定性越高的底质越有利于底栖动物生存。软泥底质以直接收集者(主要包括颤蚓科寡毛类和摇蚊亚科昆虫)占优, 而各类石质底质则以刮食者(主要是短沟蜷Semisulcospira spp.)或过滤收集者(主要是淡水壳菜Limnoperna lacustris)占优。西江航道整治工程的开展降低了生境条件质量甚至使得原有生物栖息地丧失, 由此会对底栖动物的生存产生不利影响。       

Structure of the diatom community of the River Adige (North-Eastern Italy) along a hydrological gradient

Physical constrains such as water discharge, suspended solids and turbidity act as dominant factors in driving the planktonic diatom assemblages of the River Adige (North-Eastern Italy). Two sampling stations, characterised by different hydromorphological features (Cortina all’Adige and Boara Pisani, with torrential and more potamal characteristics, respectively) were sampled fortnightly following an integrated approach encompassing physical, chemical and biological measurements and aiming at identifying the dominant factors controlling the temporal development of the community. A morpho-functional approach was used to classify the diatom assemblages where Morpho-Functional Diatom Groups (MFDG) were defined for diatom genera, according to their morphology, habitat selection and modality of adhesion to river substrate. In the two sampling points, algal growth was never limited by nutrients or zooplankton. The irregular development of MFDG was determined by the stochastic hydrological events and changes in variables related to water discharge (suspended solids and light attenuation). Tychoplanktonic, benthic and drifted taxa (such as Diatoma spp., Encyonema spp., Navicula spp. and Nitzschia spp.) were dominant in the torrential station (Cortina all’Adige), while the contribution of euplanktonic unicellular centric taxa (such as Cyclotella spp., and Stephanodiscus spp.) was higher in the potamal station (Boara Pisani).     

Dinoflagellate cysts as indicators of water quality and productivity in British Columbia estuarine environments

Palynological analyses of 60 surface sediment samples from estuarine environments near Vancouver Island, including the Georgia Strait (GS), the Effingham (EFF) and the Seymour–Belize (SB) Inlets were performed in order to document the distribution of dinoflagellate cyst assemblages and their relationship to hydrographic conditions, productivity and nutrient concentrations. We tested transfer functions using the analogue method, and suggest that dinoflagellate cyst assemblages can be used to reconstruct primary productivity, temperature and salinity. The EFF and SB Inlets are characterized by a dominance of autotrophic taxa, particularly Operculodinium centrocarpum, whereas the Protoperidinioid and gymnodinial heterotrophic taxa such as Quinquecuspis concreta and Brigantedinium spp. dominate the assemblages of the GS. Multivariate analysis shows that this distribution is closely linked to primary productivity, sea-surface temperature (SST) and spring silica concentration. The abundance of autotrophic taxa in the EFF and SB Inlets is associated with high primary productivity and low summer SST, indicating summer upwelling of coastal British Columbia, whereas the heterotrophic taxa that characterizes the GS assemblages are related to low productivity, high summer SST and high silica concentration during spring. Multivariate analysis shows that the most important environmental parameters related to dinocyst distribution in the restricted embayment of the GS, are distance to the shore, distance to Vancouver Harbor, spring sea surface salinity (SSS), spring phosphate concentration and spring productivity. The autotrophic taxa are generally more common in coastal and shallow waters, but Spiniferites ramosus and Pentapharsodinium dalei show an opposite correlation to spring productivity and salinity. P. dalei is particularly abundant around Vancouver Harbor, near highly urbanized shores and within the Fraser River plume, where salinity is low and spring productivity and continental runoff are high. S. ramosus shows its highest abundance on the western coast of GS. Protoperidinioid and gymnodinial cysts characterize distal zones within the central and southern GS that are associated with a mixture of brackish waters coming from the Fraser River and deep upwelling waters entering the GS via Juan de Fuca Strait. The relationship between dinoflagellate cyst assemblages and primary productivity in these estuarine systems differs from that in oceanic and outer neritic zones, where the abundance of heterotrophic taxa is commonly associated with upwelling and high productivity.     

Identification,enrichment, and isolation ofThiothrix spp. from environmental samples

We have developed a method to enrich, isolate, and identifyThiothrix spp. in environmental samples. This procedure employs low concentrations of organic compounds, the addition of reduced sulfur compounds (sulfide or thiosulfate), and preparation with spring water that containsThiothrix spp. The enrichment enhanced identification ofThiothrix spp. by promoting deposition of intracellular sulfur granules and inhibiting overgrowth by other bacteria. The relatively high calcium content of the spring water contributed to the culture procedure. With this technique,Thiothrix spp. were observed in two activated sludge systems, a municipal water storage tank, three springs, and four underground freshwater caves in the phreatic zone of the Floridan aquifer. Two differentThiothrix cultures have been isolated from a freshwater cave and a water storage tank by this procedure. It appears that media prepared with spring water known to supportThiothrix spp. can be designed to provide highly selective methods for isolation ofThiothrix spp. from a wide range of environments.Florida Agricultural Experimentation Station, Journal Series Number R-03446.     

Physical and chemical differences in karst springs of Cantabria, northern Spain: do invertebrate communities correspond?

Benthic macroinvertebrate communities were studied and environmental variables were measured in six rheocrene springs in Cantabria, northern Spain. Principal component analysis revealed two different spring types according to their physical and chemical characteristics. Springs from group A (GA) had higher temperature and conductivity, while springs in group B (GB) had higher values of pH, altitude, mean water velocity, percentage of boulders and coarse particulate organic matter. Total number of invertebrate taxa and individuals were not different between GA and GB springs. However, Shannon diversity index was significantly higher for GB springs. Analysis of similarities (ANOSIM) and non-metric multidimensional scaling (NMDS) analysis indicated that invertebrate assemblages from GA and GB springs were different. The snails Theodoxus fluviatilis and Bythinella sp., and the amphipod Echinogammarus spp. had higher densities in GA springs, whereas ephemeropterans, plecopterans, trichopterans and chironomids were more important in GB springs. Higher water velocities in GB springs interacting with predation by Echinogammarus tarraconensis may be responsible for the observed patterns on invertebrate community structure and composition. The taxonomic resolution limited our ability to detect crenobiontic taxa. Sampling aquatic, semi-aquatic and semi-terrestrial habitats are needed to account for the biodiversity patterns of spring habitats.     

Annual trend of fish assemblages associated with FADs in the southern Tyrrhenian Sea

A study on fish assemblage associated with fish aggregating devices (FADs) in Sicily was carried out between January 2000 and January 2001. With a fortnightly periodicity, 156 experimental hauls were carried out by means of a purse seine in a FAD‐containing marine section banned to commercial fishing. A total of 14 229 fish specimens belonging to six families and 10 species was found. These species were Balistes carolinensis, Caranx crysos, Naucrates ductor, Seriola dumerili, Seriola fasciata, Tachurus picturatus, Coryphaena hippurus, Schedophilus ovalis, Thunnus thynnus, Polyprion americanus and showed all young‐of‐the‐year undergoing a rapid growth. The applied ordination technique highlighted the existence of four assemblage periods describing the annual trend. The results confirm that fish assemblages associated with FADs are related to season, following a fish colonization tied to natural recruitment. Comparison of the ecological indices across the four periods showed that the assemblages in the periods from summer to winter were more structured than those in spring. The quantity of individuals also showed a strong variation peaking in the summer period. The results of this study reveal that FADs represent a particular nursery area for the associated species that could influence their survival.     

Effect of cattail (<Emphasis Type="Italic">Typha</Emphasis> spp<Emphasis Type="Italic">.</Emphasis>) mowing on water beetle assemblages: changes of environmental factors and the aerial colonization of aquatic habitats

Some studies found no, or weak evidence that dense monotypic cattail (Typha spp.) stands exclude water beetle species from aquatic habitats, or modify aquatic beetle assemblages. Other studies suggest that cattail may reduce the chance of aerial water beetle colonization, and decreases water temperature; negatively affecting these insects. We examined the response of aquatic beetle assemblages to the mowing of cattail (Typha angustifolia L., T. latifolia L.) in a freshwater marsh. Following removal of cattail at the water level in experimental plots, aquatic beetles were sampled both in mowed and intact (control) plots weekly, through a month in the spring of 2008. Aquatic beetles were more abundant in mowed plots. Species richness was the same, but it showed different patterns in mowed and intact plots. Shannon’s diversity was similar between treatments, while evenness was lower in mowed plots. 29% of the aquatic beetles showed a strong preference for mowed plots, and 15% preferred the control plots. Water temperature was an important factor, with mowed plots having higher water temperatures because of increased solar radiation. Polarization visibility of the water surface was also a factor, since aerially colonizing (flying) aquatic beetles use horizontally polarized light reflected from the water surface to seek potential locations. Using imaging polarimetry, we showed that mowing strongly enhanced the water-reflected polarized light signal, because it reduced the screening effect of cattail leaves, which made the visual detection of water easier. Our results suggest that cattail mowing is a useful method in aquatic beetle conservation: it increases the chance of aerial colonization due to the enhanced polarization visibility of the water surface, and creates a habitat for more abundant assemblages otherwise excluded by the monodominant dense cattail stands. Thus, sustaining hemi-marsh conditions with vegetated and mowed areas is advisable to maximize overall aquatic beetle diversity.     

Long-term response of a shallow, moderately flushed lake to reduced external phosphorus and nitrogen loading

1. The responses of nutrient concentrations, plankton, macrophytes and macrozoobenthos to a reduction in external nutrient loading and to contemporary climatic change were studied in the shallow, moderately flushed Lake Müggelsee (Berlin, Germany). Weekly to biweekly data from 1979 to 2003 were compared with less frequently collected historical data. 2. A reduction of more than 50% in both total phosphorus (TP) and total nitrogen (TN) loading from the hypertrophic (1979–90) to the eutrophic period (1997–2003) was followed by an immediate decline in TN concentrations in the lake. TP concentrations only declined during winter and spring. During summer, phosphorus (P) release from the sediments was favoured by a drastic reduction in nitrate import. Therefore, Müggelsee acted as a net P source for 6 years after the external load reduction despite a mean water retention time of only 0.1–0.16 years. 3. Because of the likely limitation by P in spring and nitrogen (N) in summer, phytoplankton biovolume declined immediately after nutrient loading was reduced. The formerly dominant cyanobacteria (Oscillatoriales) Limnothrix redekei and Planktothrix agardhii disappeared, but the mean biovolume of the N₂‐fixing species Aphanizomenon flos‐aquae remained constant. 4. The abundance of Daphnia spp. in summer decreased by half, while that of cyclopoid copepod species increased. Abundances of benthic macroinvertebrates (mainly chironomids) decreased by about 80%. A resource control of both phytoplankton and zooplankton is indicated by significant positive correlations between nutrient concentrations and phytoplankton biovolume and between phytoplankton and zooplankton biomass. 5. Water transparency in spring increased after nutrient reduction and resulted in re‐colonisation of the lake by Potamogeton pectinatus. However, this process was severely hampered by periphyton shading and grazing by waterfowl and fish. 6. Water temperatures in Müggelsee have increased in winter, early spring and summer since 1979. The earlier development of the phytoplankton spring bloom was associated with shorter periods with ice cover, while direct temperature effects were responsible for the earlier development of the daphnid maximum in spring.     

Spatial distribution of Late Pliensbachian (Early Jurassic) calcareous nannofossils within the Lusitanian basin (Portugal)

Quantitative analyses of Pliensbachian calcareous nannofossils have been carried out on a proximal-distal transect in the Lusitanian Basin (Portugal). The studied sections Vale Venteiro near Tomar and Peniche represent proximal and distal environments with respect to the emerged land of the Iberian Meseta (to the East). The upper portion of the Vale das Fontes Fm (Davoei and Margaritatus ammonite Zones) is studied in both sections and correlated by means of ammonite and nannofossil integrated biostratigraphy. A careful analysis of the preservation state of nannofossils is performed. Preservation state is moderate to good in the two settings; changes in nannofossil assemblages are therefore considered as primary. Samples were analysed for nannofossil absolute and relative abundances, species diversity and wt%CaCO₃. The analysis of calcareous nannofossils (absolute abundance, percentage, average abundance) shows changes in the community structure in space (i.e., from proximal to distal), and vertically within the water column. This pattern suggests a partitioning of habitats within the photic zone, and with respect to emerged lands. Proximal environments within the Lusitanian Basin were probably more eutrophic, because of the proximity of emerged lands to the East (Iberian Meseta). This was the source area for nutrients delivered into the basin by river transport. Distal environments were likely characterized by a greater water depth and by a deeper light penetration leading to a relatively more expanded photic zone. The assemblages recorded in the proximal setting exhibit high mean relative abundance of placolith-bearing coccolithophorids (Lotharingius spp., Biscutum spp. and Similiscutum spp.) and of Schizosphaerella spp., while distal assemblages are dominated by Crepidolithus crassus and Schizospharella spp. Crepidolithus crassus is interpreted as a deep-dweller coccolithophorid, inhabiting preferentially distal and deeper settings in the Lusitanian Basin. Placolith-bearing coccolithophorids were more abundant in proximal settings with respect to emerged lands, under relatively elevated trophic conditions. The probable calcareous dinocyst Schizospharella spp. proliferated in surface waters of both proximal and distal environments.