Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Phytoplankton structure and diversity in the eutrophic-hypereutrophic reservoir Paso de las Piedras, Argentina

This study aimed at analyzing the phytoplankton structure and dynamics in Paso de las Piedras Reservoir, Argentina, through the study of dominant species, diversity and similarity in relation with the abiotic environment. Samples were collected weekly or biweekly (January 2004–June 2005) at four sampling stations. The reservoir experienced a seasonal progression in phytoplankton composition that underlines six successional periods, each one characterized by the dominance of one or a few species. Cyanobacteria, green algae and diatoms were the most important constituents of the reservoir’s phytoplankton. Cyanobacteria dominated during summer and early autumn, green algae during late autumn and early winter, and diatoms during winter and spring. A high abundance of R. lacustris (Cryptophyceae) was observed during late September and early October. The general pattern of species succession is coherent with the general model of plankton seasonal succession described by the PEG model; however, the major discrepancy is the extremely short clear water phase observed. Successional periods were associated with changes in abiotic variables, and they showed differences in ecological traits. Cyanobacteria-Dictyosphaerium, Cyclotella, Stephanodiscus and Anabaena-diatom periods were characterized by a low number of cells, high diversity, with both dominance and specific richness low. On the contrary, during Cyanobacteria and Cyanobacteria II periods, the highest abundance was observed associated with low diversity and high dominance.     

Short-term changes in the mesozooplanktonic community in theSeine ROFI (Region of Freshwater Influence)(eastern English Channel)

Discrete-depth, hourly mesozooplankton samples were collectedover a 92 h period in May 1992 at an anchor station within theSeine Region of Freshwater Influence (ROFI) (English Channel).The mesozooplankton community defined as a euryhaline marineassemblage was dominated by the calanoid copepods Acartia spp.,Temora longicornis and Centropages hamatus, the cladoceran Evadnenordmanni and the appendicularian Oikopleura dioica. The semi-diurnaltidal current was the dominant factor in determining the short-termtemporal changes in the community in terms of density and speciescomposition so that zooplankton patches displayed oscillatingmotion in relation to tidal advection. Although a few species(e.g. Pleurobrachia pileus) exhibited higher densities aroundlow tide, maximum densities were observed for most species (e.g.T.longicornis and E.nordmanni) around high tide, according tosalinity variations. Diurnal changes were only reported forcyclopoid copepods (i.e. Halicyclops sp. and Cyclopina sp.)which wer$$$ mainly endobenthic during the day and moved intothe water column at night. Besides temporal changes in depth-averageddensities, most species exhibited vertical migrations at dieland/or tidal periods. Tidal vertical migrations were reportedonly for a few taxa and could be the result of passive mechanisms(e.g. vertical mixing) rather than of active behaviour. Dielvertical migrations were observed in most of the abundant taxa.While this migration pattern did not appear to be an adaptationto predator avoidance within the Seine ROFI, it could regulatehorizontal transport of organisms and promote their retention.The consequences of the short-term mesozooplankton fluctuationsfor sampling designs are discussed.     

Insect pollinators of the late winter flowering Rhamnus alaternus L., a candidate for honeybee-friendly scrubland spots in intensively managed agricultural areas

Insect pollinators of Rhamnus alaternus belong to 11 families, 17 genera and 20 species. The most abundant species is the honeybee followed by flies and bumblebees. Honeybee visits on R. alaternus decreased from late winter to early spring, highlighting the key role of this flowering in food paucity periods.     

Influence of the Agulhas Current on the distribution of lanternfish larvae off the southeast coast of Africa

Spatial and temporal distribution patterns of lanternfish larvaealong the southeast coast of Africa were analysed in relationto oceanographic conditions. Investigations werebased on theplankton collections made during winter, spring and summer monthsof 1990–1991. The warm southward-flowing Agulhas Currentis the dominant large-scale oceanographic feature in the area.The number of species of myctophid larvae collected per cruiseranged from 35 to 38. The most abundant species differed fromone season to the other.Afew species showed marked seasonalityin their occurrence, e.g. Scopelopsis multipunclatiis only appearedin winter and Hygophum hygomii showed the highest abundancesin winter. The majority of species occurred in relatively lowconcentrations during all three periods. Relatively large concentrationsof lanternfish larvae of most species sometimes occurred veryclose inshore (especially in the north of thestudy area) inwater depths of 50–100 m. This was related to shorewardintrusions ofAgulhas Current surface water. Low numbers of larvaeof few species appeared on the inshore shelf of the southernsector of the study area, where cold central Indian Ocean wateris forced onto the shelf by kinematic upwelling.     

Taxonomic composition and distribution of Euphausiacea and Decapoda (Crustacea) in the neuston of the Bay of Fundy, Canada

The taxonomic composition and geographic distribution of Euphausiaceaand Decapoda occurring in the neu.ston were examined in spring,summer and autumn surveys of a 2.4x10⁴ km² area of the Bay ofFundy. Adult Meganyctiphanes norvegica and Thysanoessa inermis(Euphausiacea) were present in every survey and were most abundantin autumn. Larval euphausiids were most abundant in summer butwere also present in spring and autumn. Adults of three natantiandecapod species were rarely collected; however, larval Natantiawere common in summer and autumn. Larvae representing sevengenera of reptantian decapods were collected in summer and autumn;the most abundant was Cancer sp., which was numerically dominantin summer samples. Distributional patterns divide the taxa intoinner and outer bay components at a line drawn between Digby,Nova Scotia and St John, New Brunswick, corresponding to theboundary of the major counterclockwise gyre in the Bay of Fundy.     

A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

Long-term dynamics of main mesozooplankton species in the central Baltic Sea

Long-term dynamics (1959–1997) of the copepod speciesPseudocalanus elongatus, Temora longicornis, Acartia spp. andCentropages hamatus, as well as the taxonomic group of cladocerans,are described for the open sea areas of the central Baltic Sea.Differences between areas, i.e. Bornholm Basin, Gdansk Deepand Gotland Basin, as well as between 5 year periods, were investigatedby means of Analysis of Variance (ANOVA). No significant differencesin mesozooplankton biomass between areas were found. On theother hand, clear time-trends could be demonstrated and relatedto salinity and temperature, with P.elongatus biomass mainlydependent on salinity and T.longicornis, Acartia spp. and cladoceransbiomasses dependent, to a large extent, on thermal conditions.Decreasing salinities since the early 1980s due to a lack ofmajor inflows of highly saline water from the North Sea andincreased river run-off, both triggered by meteorological conditions,obviously caused a decrease in biomass of P.elongatus. Contrarily,the standing stocks of the other abundant copepod species andcladocerans followed, to a large degree, the temperature developmentand showed, in general, an increase. The shift in species compositionduring this period is considered to be a reason for decreasinggrowth rates of Baltic herring (Clupea harengus) since the early1980s, and for sprat (Sprattus sprattus) since the early 1990s.Generally, it is suggested that low mesozooplankton biomassesin the 1990s were caused, at least partially, by amplified predationby clupeid fish stocks.     

Successional dynamics of the phytoplankton in the lower part of the river Ebro

The temporal and spatial dynamics of phytoplankton have beenstudied in four sites located along the last 60 km of the riverEbro, over a period of 1 year. Diatoms and green algae werethe most abundant groups; blue-green algae were frequent onlyin autumn. Asterionella formosa dominated the winter phytoplanktonassemblages. In autumn, spring and early summer centric diatomswere dominant: Aulacoseira granulata (Ehr.) Simonsen in autunm;Cyclotella sp. p1., Skeletonema potamos (Weber) Hasle and StephanodisciLssp. p1. in spring. A great abundance of green algae was observedduring the summer, mainly in the lower sites. In the sites closerto the mouth, the spring maximum of centric diatoms extendedto the summer. Mainly in the downstream sites, a remarkablegrowth of Acrinocyclus normanii f. subsalsa (Juhl.-Daunf.) Hustedtand Stephanodiscus hantzschii f tenuis (Hust.) Hak. & Stoerm.was added to green algae in the late summer. As has been investigatedthrough a principal component analysis, the phytoplankton temporalsuccession and longitudinal differences between the sites maybe affected by the variations in flow and the increase of waterconductivity downstream; both factors seem to act together.The river is rather homogeneous with respect to the phytoplanktonassemblages during the winter and spring months, and from latespring to the following autumn, differences greatly increaseboth in time and downstream.     

El Niño effects on soil seed bank dynamics in north-central Chile

The soil seed bank was monitored in four 75×75 m plots over 6 years (1990–1995) in an arid thorn scrub community in north-central Chile. Sixty-six species were identified. Total seed densities ranged from 2,000 to 42,000/m². Average mass of shrub seeds was significantly greater than that of other growth-forms. Between 70 and 90% of the seeds were less than 1 mg, with those in the 0.51–1.00 mg size class being most numerous. Seed densities were highly variable between years as well as within years, but were also closely associated with plant cover patterns and rainfall regime. Higher seed densities were found in wet years, and in samples taken in early summer and early autumn (i.e., after seed set); the lowest seed densities were in late winter (i.e., after annual plant germination). The annual plant species with the highest cover were also the most abundant in the soil seed bank and exhibited the largest seed density fluctuations. In general, seed densities were 5- to 10-fold higher during the 1991–1992 El Niño/southern oscillation (ENSO) years than non-ENSO years, showing the importance of this phenomenon for seed bank replenishment in the arid region of Chile.     

Comparison of mesozooplankton assemblages across quasi-synoptic oceanographic features on the north-western Iberian shelf break

The mesozooplankton community at the north-western Iberian shelf break was studied among adjacent oceanographic regimes (including upwelling, stratification and anticyclonic eddies) during 17 days in autumn 2009. Zooplankton sampling locations were determined in situ, after identifying the oceanographic regimes from CTD profiles performed over the continental shelf and upper slope. Zooplankton samples were sorted indentifying taxonomically the main zooplankton groups, from phylum to subclass. Copepods were the most abundant group (ind m^?3) in all stations, followed by appendicularians, doliolids and siphonophores. The mesozooplankton community was significantly different amongst oceanographic conditions. Meroplankton abundance was higher in upwelling stations; particularly lamellibranchia, polychaeta and bryozoan larvae abundance, and decreased from early to late upwelling conditions. Medusae and chaetognata were found exclusively under the latter oceanographic regime. However, dissimilarity between the oceanographic conditions was mostly based on the varying contribution of the four most common groups.     

Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site

Kelp forests are highly productive and species‐rich benthic ecosystems in temperate regions that provide biogenic habitat for numerous associated species. Diverse epifaunal communities inhabit kelp sporophytes and are subject to variations in the physical environment and to changes experienced by the kelp habitat itself. We assessed seasonal variations in epifaunal invertebrate communities inhabiting giant kelps, Macrocystis pyrifera, and their effects on this seaweed. Six seasonal samplings were conducted over a year at an upwelling‐dominated site in northern‐central Chile where physical conditions are known to fluctuate temporally. More than 30 taxa were identified, among which peracarid crustaceans stood out in both diversity and abundance. Species richness and abundance differed among sporophyte sections (holdfast and fronds) and throughout the year. The frond community was dominated by two grazers (the amphipod Peramphithoe femorata and the isopod Amphoroidea typa), while suspension feeders, grazers, and omnivores (the amphipod Aora typica, the isopod Limnoria quadripunctata, and polychaetes) dominated the holdfasts. Abundances of the dominant species fluctuated throughout the year but patterns of variation differed among species. The most abundant grazer (P. femorata) had highest densities in summer, while the less abundant grazer (A. typa) reached its peak densities in winter. Interestingly, the area of kelp damaged by grazers was highest in autumn and early winter, suggesting that grazing impacts accumulate during periods of low kelp growth, which can thus be considered as ‘vestiges of herbivory past.’ Among the factors determining the observed seasonal patterns, strong variability of environmental conditions, reproductive cycles of associated fauna, and predation by fishes vary in importance. Our results suggest that during spring and early summer, bottom‐up processes shape the community structure of organisms inhabiting large perennial seaweeds, whereas during late summer and autumn, top‐down processes are more important.     

The spatial population structure of a harpacticoid copepod community in spring

The spatial population patterns of an assemblage of meiobenthic harpacticoid copepod species were analysed for two sets of samples resulting from a systematic survey of an intertidal, estuarine, sandy beach in spring. The fauna was characterised by mesopsammic species, the 6 most abundant of which showed a great degree of interassociation, such that they could not be considered to distribute themselves independently. Populations of each of the 6 species were overdispersed, such that a negative binomial distribution adequately fitted all population samples. Spatial segregation of closely related species was indicated during the late spring sample, so leading to a patchy population distribution. It is proposed that during early spring, during periods of extreme disturbance in the seasonal r-selecting environment, the species populations do not interact, but that during periods of less extreme perturbation an interactive community evolves.     

Flowering and fruiting phenology in the coastal shrublands of Doñana,south Spain

Flowering and fruiting phenological patterns at the individual-, population-, and community level were studied in a southern Spanish scrub community composed of 30 shrub species. Few individuals of any species produced a high number of flowers. Intrapopulation deviation in the peak time of flowering showed a strong and positive skewness. Relative flowering duration, however, displayed a virtually normal distribution. Generally, species flowering in spring have a short flowering time, while species flowering earlier or later in the year show significantly longer flowering periods. Species were in bloom throughout the year, but there was a major peak during spring and two lesser ones in autumn and early summer. Shallow rooting taxa in typically mediterranean genera displayed a strategy of spring flowering and summer fruiting. Summer and autumn flowering occurred among heath-like shrubs of relatively wet places, and forest-associated, vertebrate-dispersed species which commonly have underground storage organs. Species with ripe fruits presented two peaks, the major one during the summer including the majority of taxa with seeds dispersed by non-vertebrate agents. There was a minor fruiting peak in autumn dominated by taxa that rely on vertebrates for dispersal. The complex seasonal patterns observed are interpreted in relation to environmental conditions and physiological constraints on species living in a highly seasonal climate.     

Annual cyclic changes and self-organization processes in the marine sea-bottom organisms

The dynamics of marine microbenthos species structure shows clear annual cycle. From late winter till early autumn community changes towards increasing complexity and orderliness. The sharp increase in available energy (light and heat) in the beginning of the winter acts as trigger of these processes. The further development of the community is connected with system fluctuations arising as a result of interactions or organisms between each other and their environment (feeding, competition, predation). In the end of summer these processes are terminated by the state of high species diversity, maximum species coordination, expansion of inhabited zone within the sediments, and the distinct segregation of space and nutrient resources among species (i.e., achievement of ecological complementarity). Decrease in light and temperature causes the reverse process--weakening of organism coordination and significant simplification of the community structure. In general, these changes correspond to the theory of self-organization in nonequilibrium systems (Prigogine, Stengers, 2001). The most important distinction of observed processes from the classical self-organization is their cyclic dynamics, i.e. the annual return of community to its most simple state at the end of winter.     

Nitrogen Fixation in Wild Legumes

Isolations of the rhizobia from nodules of field plants of Ulexeuropaeus and Medicago lupulina have been examined for effectivenessin fixation of nitrogen by inoculating them into host plantsgrowing in a medium free of combined nitrogen. The results indicatethat vigorous fixation may be presumed to occur in associationwith field plants of the Ulex species, but that fixation inMedicago is probably decreased by the presence of ineffectiverhizobia in some nodules. The general importance of fixationin wild legumes is discussed, and it is pointed out that dueattention must be paid to non-legume genera with root nodules.These genera are locally abundant, and in former periods werestill more prominent in some regions of the world.     

'St Martin's Summer': the case of an autumn phytoplankton bloom in the Gulf of Naples (Mediterranean Sea)

Phytopiankton abundance. species composition and primary productionof the Gulf of Naples were investigated during an autumn bloomin November 1985. Hydrographic data and surface phytoplanktonsamples were collected during a 3 day cruise, whereas investigationson in situ primary production and phytoplankton vertical distributionwere conducted from a second boat on three different dates.A coast-offshore gradient was recorded for most of the chemicaland biological parameters analysed. At stations closer to thecoast, which were affected by land run-off, phytoplankton populationsattained concentrations of 2.5 10⁶ cells l^–1 with amarked dominance of diatoms belonging to the genera Thalassiosiraand Chaetoceros. The most striking character of the system wasa remarkably high carbon assimilation rate (up to 1.04 g C m^–2day^–2) at stations closer to the coast. The causativemechanism for this bloom appeared to be land-derived nutrientenrichment, possibly enhanced by autumn rains, followed by aperiod of favourable meteorological conditions, which occursrecurrently in the region for a brief period around November,known locally as ‘St Martin's Summer’. We hypothesizethat a similar mechanism can stimulate phytoplankton growthmore than once every year. since high-stability penods followingmeteoro logical perturbations can occur several times in temperateregions of the northern hemisphere in autumn.     

Characteristics of the distribution of birds infected with hemosporidians (Sporozoa, Haemosporidia) during the fall migration in flight waves

Chaffinches, infected with hemoproteids (Haemoproteidae) and leucocytozoids (Leucocytozoidae), are uniformly distributed in the ranges of each nonequivalent from the point of view of bioenergetics migratory wave. Extensiveness of infection of birds with leucocytozoids in autumn increases reliably at the time of late migratory waves as compared to early ones. The last flight wave, which is observed in the Kurskaya Kosa in the second half of October, consists, in general, of chaffinches which have already gone through the leucocytozoonosis. Concentration of infected birds at the end of the species migration flow can be regarded as a peculiar parasitic filter delaying the birds, which have been seriously ill, from flying away to wintering places at the most favourable periods. The thesis on different influence of hemosporidians on energetic balance of birds during spring and autumn migrations is substantiated. Hypothesis has been advanced on the causal relationship between high bird mortality during spring migration and the most high extensiveness and intensity of their infection with hemosporidians.     

Life histories, microdistribution and drift of two mayfly (Ephemeroptera) species in the Pembina River, Alberta, Canada

Ephemerella inermis Eaton is a univoltine species that emerges in July. Eggs hatch in August and larvae grow rapidly in autumn and spring, but not during winter. Baetis tricaudatus Dodds produces three cohorts per year. Emergence periods occur in early June, July and early September. Only one cohort overwinters as larvae.
Microdistribution of both species is controlled largely by the discharge pattern of the river. During 1978, a year of frequent floods, animals were equally distributed among slow and fast water portions of the river. Nocturnal drift densities of both species were much greater in slow than in fast water areas. During 1979, a year of relatively stable flow, benthic larval densities were significantly greater in fast water than in slow water.
Early instar E. inermis larvae are most abundant in nearshore areas, but move to deeper water in late autumn. Baetis tricaudatus larvae are seldom numerous in near-shore areas.
Densities of both species were positively associated with concentrations of detritus and of other invertebrates, but only when relationships were considered in areas of similar current velocity independently of season.     

大兴安岭地区兴安落叶松林步甲群落多样性时间动态分析

兴安落叶松林是大兴安岭地区代表性的植被类型,其生物多样性具有独特性。步甲是森林生态系统环境和多样性的指示性物种,以及认识环境变化和生物多样性特征的关键物种。为研究大兴安岭地区兴安落叶松林步甲群落多样性的时间动态,分析步甲群落对时间变化的响应规律,于2019年5月下旬-8月下旬步甲活跃期,利用陷阱诱捕法在兴安落叶松林5个样地中采集步甲标本共15属34种1149头,其中大兴安岭地区地理新纪录物种7种,中国地理新纪录物种6种。研究结果表明,通缘步甲属（Pterostichus）和大步甲属（Carabus）物种丰富度最高;通缘步甲属未定种5（Pterostichus eximius）为极优势物种,对时间变化最敏感。兴安落叶松林小生境类型的多样化和步甲休眠期的选择是步甲群落个体数和物种数随时间变化呈双峰模式的主要因素,最高峰均出现在6月下旬;多样性与均匀度指数均在7月上旬达高峰期,8月下旬多样性下降而均匀度上升,各指数之间相关性较低。步甲群落在6月下旬到7月下旬对环境具有较高的适应度;群落结构在环境条件相对稳定的6月下旬到7月下旬和8月上旬到8月下旬均表现为极相似（I>0.75）。物种取食特征和生活史策略的多样化使步甲群落各指数随时间变化具有显著差异,而物种取食特征和生活史策略受环境因子的综合影响较大。稳定的森林环境条件下,步甲活跃期更长,群落结构相似度更高。该结果为步甲群落时间动态研究奠定了一定的理论基础,为大兴安岭地区地下生物多样性的保护和管理策略制定提供了一定的理论和数据依据。