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Pelagic Zone (pelagic + zone)
Selected AbstractsGenetic diversity and distribution of periphytic Synechococcus spp. in biofilms and picoplankton of Lake ConstanceFEMS MICROBIOLOGY ECOLOGY, Issue 2 2004Sven Becker Abstract In various water depths of the littoral zone of Lake Constance (Bodensee) cyanobacteria of the Synechococcus -type were isolated from biofilms (periphyton) on three natural substrates and an artificial one (unglazed tiles). From one tile three strains of phycoerythrin (PE)-rich Synechococcus spp. were isolated, the first examples of these organisms in the epibenthos. Phylogenetic inference based on the 16S,23S rRNA intergenic spacer (ITS-1) assigned all periphytic isolates to two clusters of the picophytoplankton clade (evolutionary lineage VI of cyanobacteria). The sequence divergence in the ITS-1 was used to design specific PCR primers to allow direct, culture-independent detection and quantification of isolated Synechococcus strains in natural periphytic and pelagic samples. Denaturing gradient gel electrophoresis (DGGE) analysis revealed depth-related differences of Synechococcus spp. distribution on tiles placed in the littoral zone. Synechococcus genotypes were observed which occurred in both the periphyton (on tiles) and in the pelagic picoplankton. A strain with one of these genotypes, Synechococcus sp. BO 8805, was isolated from the pelagic zone in 1988. Its genotype was found on tiles that had been exposed at different water depths in the littoral zone in spring and autumn of the year 2000. Quantitative analysis with a genotype-specific TaqMan probe and real-time Taq nuclease assays (TNA) confirmed its presence in the pelagic zone, although appearance of this and related genotypes was highly irregular and exhibited strong differences between consecutive years. Our results show that the ability to form significant subpopulations in pelagic and periphytic communities exists in three out of four phylogenetic clusters of Synechococcus spp. in Lake Constance. This versatility may be a key feature in the ubiquity of the evolutionary lineage VI of cyanobacteria. [source] The marine copepod, Pseudocalanus elongatus, as a mediator between climate variability and fisheries in the Central Baltic SeaFISHERIES OCEANOGRAPHY, Issue 4-5 2003C. Möllmann Abstract Pseudocalanus elongatus is a key species in the pelagic zone of the deep basins of the Central Baltic Sea. The copepod serves as a major food organism for larval as well as for adult, pelagic planktivorous fish. Large interannual fluctuations in the standing stock of P. elongatus have been attributed to significant changes in the hydrographic environment over the last two decades. In particular, the decreasing salinity in the Baltic deep basins, a result of a change in atmospheric forcing leading to an increase in rainfall since the 1980s and of a lack of pulses of saline water intrusions from the North Sea, was found to affect reproduction and maturation of the copepod. In parallel, dramatic changes in the weight-at-age of herring, one of the most important commercial fishes of the Baltic Sea, have been observed since the late 1980s. Using time-series on herring stomach contents, as well as length and weight, we provide evidence for a chain of events relating variability in climate, salinity and P. elongatus abundance to changes in diet and condition of herring in the Central Baltic Sea. [source] Habitat selection and diel distribution of the crustacean zooplankton from a shallow Mediterranean lake during the turbid and clear water phasesFRESHWATER BIOLOGY, Issue 3 2007BRUNO B. CASTRO Summary 1. The fish fauna of many shallow Mediterranean Lakes is dominated by small-bodied exotic omnivores, with potential implications for fish,zooplankton interactions still largely unknown. Here we studied diel variation in the vertical and horizontal distribution of the crustacean plankton in Lake Vela, a shallow polymictic and eutrophic lake. Diel sampling was carried out on three consecutive days along a horizontal transect, including an open-water station and a macrophyte (Nymphaea alba) bed. Since transparency is a key determinant of the predation risk posed by fish, the zooplankton sampling campaigns were conducted in both the turbid (autumn) and clear water (spring) phases. 2. In the turbid phase, most taxa were homogeneously distributed along the vertical and horizontal axes in the three consecutive days. The only exception was for copepod nauplii, which showed vertical heterogeneity, possibly as a response to invertebrate predators. 3. In the clear water phase, most zooplankton taxa displayed habitat selection. Vertically, the general response consisted of a daily vertical migration (DVM), despite the limited depth (1.6 m). Horizontally, zooplankters showed an overall preference for the pelagic zone, independent of the time of the day. Such evidence is contrary to the postulated role of macrophytes as an anti-predator refuge for the zooplankton. 4. These vertical (DVM) and horizontal (macrophyte-avoidance) patterns were particularly conspicuous for large Daphnia, suggesting that predation risk from size-selective predators (fish) was the main factor behind the spatial heterogeneity of zooplankton in the spring. Thus, the difference in the zooplankton spatial distribution pattern and habitat selection among seasons (turbid and clear water phases) seems to be mediated the predation risk from fish, which is directly related to water transparency. 5. The zooplankton in Lake Vela have anti-predator behaviour that minimises predation from fish. We hypothesise that, due to the distinct fish community of shallow Mediterranean lakes, aquatic macrophytes may not provide adequate refuge to zooplankters, as seen in northern temperate lakes. [source] ,15N of zooplankton species in subarctic lakes in northern Sweden: effects of diet and trophic fractionationFRESHWATER BIOLOGY, Issue 5 2004J. Karlsson Summary 1. To assess the use of stable nitrogen isotopes (,15N) for reconstructing trophic relationships in planktonic food webs, crustacean zooplankton species and pelagic dissolved and particulate matter were analysed in 14 subarctic lakes in northern Sweden. The lakes are situated along an altitudinal gradient and show a substantial variation in nutrient content and energy mobilization by bacterioplankton and phytoplankton. 2. The ,15N of dissolved and particulate matter was comparatively low, suggesting efficient N recycling and low losses of depleted N from the pelagic zone of these unproductive lakes. 3. Copepods had a systematically higher ,15N than cladocerans, with an average difference of 3.1,4.9, within lakes, implying different trophic positions of the two groups. Comparisons of nitrogen pools and energy fluxes suggest that the low cladoceran ,15N was a result of feeding on bacteria. 4. The difference in ,15N between copepods and cladocerans declined with decreasing bacterioplankton production among lakes, due either to increasing trophic isotope fractionation or decreasing relative importance of bacteria in the diet of cladocerans. [source] Food web topology and parasites in the pelagic zone of a subarctic lakeJOURNAL OF ANIMAL ECOLOGY, Issue 3 2009Per-Arne Amundsen Summary 1Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4For trophically transmitted parasites, the number of parasite,host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. [source] Intraspecific competition drives multiple species resource polymorphism in fish communitiesOIKOS, Issue 1 2008Richard Svanbäck It has been hypothesized that inter-specific competition will reduce species niche utilization and drive morphological evolution in character displacement. In the absence of a competitor, intra-specific competition may favor an expansion of the species niche and drive morphological evolution in character release. Despite of this theoretical framework, we sometimes find potential competitor species using the same niche range without any partitioning in niche. We used a database on test fishing in Sweden to evaluate the factors (inter- and intraspecific competition, predation, and abiotic factors) that could influence habitat choice of two competitor species. The pattern from the database shows that the occurrence of perch and roach occupying both littoral and pelagic habitats of lakes in Sweden is a general phenomenon. Furthermore, the results from the database suggest that this pattern is due to intra-specific competition rather than inter-specific competition or predation. In a field study, we estimated the morphological variation in perch and roach and found that, individuals of both species caught in the littoral zone were more deeper bodied compared to individuals caught in the pelagic zone. Pelagic perch fed more on zooplankton compared to littoral perch, independent of size, whereas the littoral perch had more macroinvertebrates and fish in their diet. Pelagic roach fed more on zooplankton compared to littoral roach, whereas littoral individuals fed more on plant material. Furthermore, we sampled littoral and pelagic fish from another lake to evaluate the generality of our first results and found the same habitat associated morphology in both perch and roach. The results show a consistent multi-species morphological separation in the littoral and pelagic habitats. This study suggests that intra-specific competition is possibly more important than inter-specific competition for the morphological pattern in the perch-roach system. [source] AN ECOLOGICAL REVIEW OF CLADOPHORA GLOMERATA (CHLOROPHYTA) IN THE LAURENTIAN GREAT LAKES,JOURNAL OF PHYCOLOGY, Issue 4 2008Scott N. Higgins Cladophora glomerata (L.) Kütz. is, potentially, the most widely distributed macroalga throughout the world's freshwater ecosystems. C. glomerata has been described throughout North America, Europe, the Atlantic Islands, the Caribbean Islands, Asia, Africa, Australia and New Zealand, and the Pacific Islands. Cladophora blooms were a common feature of the lower North American Great Lakes (Erie, Michigan, Ontario) from the 1950s through the early 1980s and were largely eradicated through the implementation of a multibillion-dollar phosphorus (P) abatement program. The return of widespread blooms in these lakes since the mid-1990s, however, was not associated with increases in P loading. Instead, current evidence indicates that the resurgence in blooms was directly related to ecosystem level changes in substratum availability, water clarity, and P recycling associated with the establishment of dense colonies of invasive dreissenid mussels. These results support the hypothesis that dreissenid mussel invasions may induce dramatic shifts in energy and nutrient flow from pelagic zones to the benthic zone. [source] | ||||||||||