Algal epilithon and water quality of a stream receiving oil refinery effluent

Changes in epilithic algal communities colonizing introduced substrata were determined in a stream polluted with oil refinery effluent at Digboi (Assam, India). The number of algal taxa was reduced but the growth of blue-green algae, particularly two species ofOscillatoria, was encouraged. Epilithic biomass (as chlorophylla) also declined at polluted stations. The algal community of the upstream station was markedly different from the community occurring just after the confluence of effluent; however, the differences were gradually reduced downstream, indicating improvement in water quality. Of the various criteria tested for possible relationships with the level of pollutants, species richness, Shannon diversity and biomass showed significant relationships. The study demonstrates the usefulness of algal criteria for monitoring oil pollution in running waters.     

Introduction. Antarctic ecology: from genes to ecosystems. Part 2. Evolution, diversity and functional ecology

The Antarctic biota has evolved over the last 100 million years in increasingly isolated and cold conditions. As a result, Antarctic species, from micro-organisms to vertebrates, have adapted to life at extremely low temperatures, including changes in the genome, physiology and ecological traits such as life history. Coupled with cycles of glaciation that have promoted speciation in the Antarctic, this has led to a unique biota in terms of biogeography, patterns of species distribution and endemism. Specialization in the Antarctic biota has led to trade-offs in many ecologically important functions and Antarctic species may have a limited capacity to adapt to present climate change. These include the direct effects of changes in environmental parameters and indirect effects of increased competition and predation resulting from altered life histories of Antarctic species and the impacts of invasive species. Ultimately, climate change may alter the responses of Antarctic ecosystems to harvesting from humans. The unique adaptations of Antarctic species mean that they provide unique models of molecular evolution in natural populations. The simplicity of Antarctic communities, especially from terrestrial systems, makes them ideal to investigate the ecological implications of climate change, which are difficult to identify in more complex systems.     

南极磷虾行为与生理生态学研究进展

行为生态学和生理生态学是生态学领域的两个重要研究范畴,开展相关研究可以更好地理解海洋生物的生活习性及其对环境的适应能力.南极磷虾是南大洋生态系统中的关键物种,探究其行为和生理生态学可以了解磷虾类等海洋生物应对极端环境的能力.本文从行为生态和生理生态两方面总结了南极磷虾的典型生态学特征.行为生态学包括其集群(规模、行为)及游泳(游泳角度、附肢摆动)等;生理生态学包括呼吸、排泄与代谢以及蜕皮与生长等.目前关于南极磷虾的生理生态学和行为生态学的研究仍较为有限,且多数研究结果基于陆基实验室的暂养.鉴于陆基实验室暂养与自然的南极磷虾栖息环境差异较大,开展南极磷虾的现场实验生态学研究迫在眉睫.     

Aspects of algal ecology

Bicosoeca accreta sp. nov. is described by light and electron microscopy. This species is so far unique in the genus in accreting extraneous fragments of mainly inorganic material on the outside of its amorphous undifferentiated lorica.     

Antarctic ecology from genes to ecosystems: the impact of climate change and the importance of scale

Antarctica offers a unique natural laboratory for undertaking fundamental research on the relationship between climate, evolutionary processes and molecular adaptation. The fragmentation of Gondwana and the development of wide-scale glaciation have resulted in major episodes of extinction and vicariance, as well as driving adaptation to an extreme environment. On shorter time-scales, glacial cycles have resulted in shifts in distribution, range fragmentation and allopatric speciation, and the Antarctic Peninsula is currently experiencing among the most rapid climatic warming on the planet. The recent revolution in molecular techniques has provided a suite of innovative and powerful tools to explore the consequences of these changes, and these are now providing novel insights into evolutionary and ecological processes in Antarctica. In addition, the increasing use of remotely sensed data is providing a large-scale view of the system that allows these processes to be set in a wider spatial context. In these two volumes, we collect a wide range of papers exploring these themes, concentrating on recent advances and emphasizing the importance of spatial and temporal scale in understanding ecological and evolutionary processes in Antarctica.     

Landscape ecology as a bridge from ecosystems to human ecology

Landscape as a subject of (terrestrial) ecology can be interpreted: first, as a piece of land composed of different ecosystems; and second, as a holistic entity of aesthetic perception derived from landscape paintings and parks of the 18th and 19th century. Such entities display a characteristic arrangement of landscape elements regarded as a whole and taking them apart for specific investigation will break up and virtually destroy it (e.g. a symphony dissociated into single notes). Landscape as a holistic entity satisfies emotional human needs like identification with regions, and explains the attraction of tourists. Entity features are land-use and land cover combined with openness and a certain naturalness. A key question is whether you call a piece of the earths surface just land or landscape– and why. Such questions touch the interface between landscape ecology and human ecology. But human ecology must not dismiss landscape functions. The most beautiful landscape will be reduced to a mere picture if it does not also provide basic life-support. Therefore, energy and matter flows and transformations between the ecosystems of a landscape have to be determined along with its climate, geomorphology (relief), soils, hydrology, species and ecosystem diversity. These different approaches, however, may never be combined into a unified whole. There is no superscience, and incidentally, its complexity would by far exceed human brain capacity. What we can achieve is bridge-building by approximation of selected facts. A conscious spatial arrangement of diversified land-use units (ecotopes) will promote (bio)diversity and may be perceived as an integral landscape pattern. A spatially and temporally differentiated energy input into land-use units will result in a gradient of utilization intensity and allow more species to thrive, again enhancing both diversity and landscape beauty. Modern humans have deliberately chosen artificial surroundings to achieve complete environmental control, even in rural lifestyles. But as far as emotional needs are concerned, this artificiality seems to be neither human nor ecological. Something natural is lacking, and landscape in its holistic sense can provide it – be it a landscaped open space in a city, a rural scene, a seashore or a mountain range. Maintaining and managing such naturalness requires sound ecological knowledge – not as an aim in itself, but to provide a bridge for humans.     

Photosynthetic symbionts in Antarctic terrestrial ecosystems: the physiological response of lichen photobionts to drought and cold

Lichens form an important part of the biodiversity in terrestrial ecosystems of Antarctica where they represent the dominant vegetation. Previous studies on the genetic diversity of photobionts of lichens have indicated that clade S Trebouxia photobionts are the most widespread in continental Antarctica, predominantly in macrolichens. For the first time, a comparative study of the physiology of a variety of isolated Antarctic lichen photobionts (genus Trebouxia) was performed. Photosynthetic activity was examined by chlorophyll a fluorescence and correlated with freezing and desiccation under laboratory conditions and photosynthetic pigments were quantified in response to desiccation. Data were obtained from photobionts collected from the Antarctic regions of North Victoria Land, Coal Nunatak and Rothera Point, as well as from a European site (Gotland, Sweden). While the isolated algae reacted individually to stress treatments, they were highly susceptible to desiccation stress but could rapidly recover from freezing. Photobiont-specific physiological adaptations are considered to explain the dominance of clade S Trebouxia photobionts.     

Effects of microspatial complexity on a herbivore—epilithon interaction in an Australian upland stream

1. Increases in spatial heterogeneity may provide more food, create new resources or interfere with the foraging activities of a herbivore. 2. Three colonization experiments were performed in an upland stream to investigate the effects of one type of spatial heterogeneity (grooves on the substratum) on the relationship between an abundant herbivore, Agapetus monticolus (Banks, Trichoptera), and the epilithon on which it feeds. 3. The results indicate that grooves do not provide any different resources or interfere with the foraging activities of A. monticolus, but may increase food abundance, although the effect of grooves on food abundance appears to vary temporally. 4. Temporal variation in the effects of microspatial complexity raises the possibility that its importance to the community may be over- or underestimated unless experiments are designed to incorporate this temporal variation.     

Evolution of Antarctic lake ecosystems

Antarctic lakes present a wide variety of physical, chemical and biological conditions, and are not always the simplified systems imagined by earlier workers. The volume of data on lakes of various ages now allows informed speculation on the evolution of the Antarctic lake ecosystem.     

Metabolic stoichiometry and the ecology of fear in Trinidadian guppies: consequences for life histories and stream ecosystems

Consumer-driven nutrient recycling, the release of chemicals as byproducts and excesses of consumer physiology, can alter ecosystems by changing the availability of limiting nutrients at the base of the food web. The mere presence of predators can alter consumer physiology by restricting food intake and inducing stress. Predation risk, then, can influence ecosystem function by modifying the role of prey as nutrient recyclers, yet there are few empirical tests of how predation risk alters nutrient recycling by prey. Here, we present the results of a test for the effects of predation risk on the C and N budgets of Trinidadian guppies (Poecilia reticulata). We reared female guppies for 7 weeks on diets of varying quality, and we compared control individuals to those exposed continuously to chemical cues emitted by a guppy predator, Crenicichla alta. We measured food consumption, growth rate, tissue elemental stoichiometry and N excretion by guppies on all treatments. Guppies strongly reduced food intake in the presence of predator cues; however, cue-exposed guppies assimilated nutrients more efficiently than controls. Specifically, cue-exposed guppies strongly increased N retention efficiency while only moderately increasing C efficiency. Consequently, guppies reared with predator cues excreted 39 % less N than control guppies. We suggest that reduced foraging, enhanced nutrient efficiency, and decreased N excretion are adaptive responses to the extrinsic mortality threat posed by guppy predators. The resulting substantial reduction in N excretion by guppies may influence ecosystem function in natural streams by reducing the supply of a limiting nutrient.     

The moss ecology of a Lakeland stream

Abstract

The course of Torver Beck, a typical mountain stream of the English Lake District, is described, and its moss flora referred to four zones with well-marked altitudinal limits. The autecology of the four most important species and the main factors affecting the distribution of moss species are briefly discussed.     

Pacific salmon effects on stream ecosystems: a quantitative synthesis

Pacific salmon (Oncorhynchus spp.) disturb sediments and fertilize streams with marine-derived nutrients during their annual spawning runs, leading researchers to classify these fish as ecosystem engineers and providers of resource subsidies. While these processes strongly influence the structure and function of salmon streams, the magnitude of salmon influence varies widely across studies. Here, we use meta-analysis to evaluate potential sources of variability among studies in stream ecosystem responses to salmon. Results obtained from 37 publications that collectively included 79 streams revealed positive, but highly inconsistent, overall effects of salmon on dissolved nutrients, sediment biofilm, macroinvertebrates, resident fish, and isotopic enrichment. Variation in these response variables was commonly influenced by salmon biomass, stream discharge, sediment size, and whether studies used artificial carcass treatments or observed a natural spawning run. Dissolved nutrients were positively related to salmon biomass per unit discharge, and the slope of the relationship for natural runs was five to ten times higher than for carcass additions. Mean effects on ammonium and phosphorus were also greater for natural runs than carcass additions, an effect attributable to excretion by live salmon. In contrast, we observed larger positive effects on benthic macroinvertebrates for carcass additions than for natural runs, likely because disturbance by live salmon was absent. Furthermore, benthic macroinvertebrates and biofilm associated with small sediments (<32 mm) displayed a negative response to salmon while those associated with large sediments (>32 mm) showed a positive response. This comprehensive analysis is the first to quantitatively identify environmental and methodological variables that influence the observed effects of salmon. Identifying sources of variation in salmon–stream interactions is a critical step toward understanding why engineering and subsidy effects vary so dramatically over space and time, and toward developing management strategies that will preserve the ecological integrity of salmon streams. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Marine pelagic ecosystems: the west Antarctic Peninsula

The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba. Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2 degrees C increase in the annual mean temperature and a 6 degrees C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6 degrees C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in icedependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along the WAP and the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response.     

The physiology of some blue-green algal isolates from peat

An investigation of the physiology of a number of blue-green algae isolated from peat sites in Glenamoy, Co. Mayo, is reported. Physical and nutritional parameters were studied and correlated to the conditions prevailing in the natural environment of the algae. The occurrence of blue-green algae in peat was found to be controlled by the pH level and the presence of phosphorus in the environment.     

Grazing insects reduce algal biomass in a neotropical stream

The Darwinulidae are the only surviving post-Palaeozoic darwinulocopine family of an extensive radiation that reached its maximum in the Permian. Whereas at least some Palaeozoic darwinulids are known from sexual populations, the surviving lineages after the end-Permian mass extinction have abandoned sex since 200 million years ago. This makes the extant family Darwinulidae one of the few putative ancient asexual groups. Only about 30 species in 5 genera are presently known. The phylogeny of these taxa is here analysed using both morphological characters and molecular data. Twelve characters on valve morphology and 17 characters pertaining to appendages are used to construct the most parsimonious (unrooted) cladogram of 12 species in 5 genera. DNA sequences of one nuclear (ITS1) and a mitochondrial (COI) gene of 6 species in 5 genera are used to construct rooted maximum parsimony trees. Both molecular and morphological trees show a high degree of congruence, indicating that Alicenula and Vestalenula mostly cluster closely together, while Penthesilenula and Microdarwinula constitute a robust group. The position of the monospecific genus Darwinulais more variable, but is mostly closer to the two former genera. Congeneric species always cluster together in the morphological cladograms, and these results thus confirm that the five genera recognised by Rossetti & Martens (1998) are good phyletic units. An approximate molecular clock (calibrated with fossil data) indicates that the extant darwinulids share a common ancestor, which lived at least 100 million years ago.     

Hierarchical structure of stream ecosystems: consequences for bioassessment

It has long been recognized that communities and their ecosystems are structured at several, nested spatial scales. But identifying the appropriate scale(s) to collect, analyse and interpret data to answer specific questions about ecosystems has been a vexing problem for ecologists. We collected observations of the benthic invertebrate community and its environment in 10 primarily agricultural tributary streams of the Thames River in southwestern Ontario, Canada. Within each stream we sampled two reaches, in each reach we sampled three riffles, and in each riffle we took three kick samples of invertebrates and characterized the substrate environment. We also characterized the habitat at each of the 20 reaches (10 streams × 2 reaches/stream). Most of the variability in the stream invertebrate community structure (as described with taxonomic richness and the biotic index of tolerance, as well as by the Bray-Curtis distance of the community composition from the mean at a spatial scale) was at larger spatial scales of among streams and between riffles. Much of the substrate and habitat variation was also at the larger spatial scales, as were correlations between the biota and the environment of the benthic invertebrate community. We concluded that for the purposes of bioassessment, characterization of one reach per stream is sufficient, at least in this context, for describing a stream and evaluating its health. Handling editor: R. Norris