The influence of macrophytes on the spatial distribution of littoral rotifers

1. The effect of macrophytes on the spatial distribution of littoral rotifers was examined in Lake Rotomanuka, New Zealand (37°55'S, 175°19'E). Total rotifer abundances and those of abundant species, were compared between three macrophyte species, Myriophyllum propinquum , Eleocharis sphacelata and Egeria densa , and spatially across a littoral transect in relation to these species.
2. The abundances of many species, for example Euchlanis dilatata, Lecane closterocerca and L. lunaris, differed significantly between macrophyte species. More planktonic forms, Ascomorpha saltans , Keratella cochlearis and Synchaeta oblonga, however, showed no significant preference for macrophyte species.
3. Differences in rotifer abundances were evident even when different species of macrophyte grew in close proximity to one another, indicating that variations in physical and chemical conditions, which occur in the littoral of Lake Rotomanuka, could be largely discounted for much of the variation between macrophyte species.
4. Variation in rotifers between macrophytes was probably the result of a number of factors, including differences in macrophyte morphology, macrophyte age, epiphytic algal growths and the differential effects of predation by invertebrates and fish between macrophytes.
5. Variability of rotifer abundances spatially across the ecotone was less marked than between macrophyte species. The species of macrophyte occurring, and therefore the community composition and distribution of macrophyte species in the littoral, appears to be a major influence in the spatial structuring of rotifer communities in the littoral region of lakes.     

Removal of settled sediments and periphyton from macrophytes by grazing invertebrates in the littoral zone of a large oligotrophic lake

• 1 The resistance and resilience of littoral zone communities to sedimentation will depend both on the extent to which sediment deposition affects productivity, and on interactions within the communities. A series of hypotheses were set up and tested to examine interactions and feedback mechanisms among deposited sediments, periphyton, macrophytes and grazers in a large oligotrophic lake subject to fluctuating sediment loadings.
• 2 Although sediments incorporated into periphyton reduced light availability to macrophytes, periphytic algae were generally the dominant light absorbing component under natural conditions. When grazers were absent, both sediments incorporated in the periphyton and periphytic algal densities increased, and both were then important in reducing light available to macrophytes.
• 3 Grazing rate and assimilation efficiency for the dominant grazer, the prosobranch gastropod Potamopyrgus antipodarum, increased with increasing sediment content under natural lake conditions to reach a maximum at 10 mg sediment cm^?2.
• 4 An increase in sediment incorporation into periphyton films resulted in an increased grazing rate and hence grooming of sediments from macrophytes.
• 5 Grazing invertebrates can play a major role in maintenance of littoral communities by continuously grooming macrophyte hosts of periphytic algae and settled sediments.

     

A comparison of algal periphyton composition on eleven species of submerged macrophytes

Summary The composition of algal periphyton was examined on eleven species of submerged macrophytes collected at a depth of 0.25 m in Sewell Lake, southwestern Manitoba, a shallow nitrogen and phosphorus rich lake. There were substantial differences in the periphyton on all macrophyte species. Diatom subcommunities were the most similar, while the green algal subcommunities were the most dissimilar on different plant hosts.Potamogeton zosteriformis differed the most from all other macrophytes with respect to the composition of its periphyton. These results and a comparison of the literature suggest that the composition and structure of periphyton communities on living substrates is a product of the interaction of many variables, determined by the characteristics of the host plant, the external environment and the algae themselves. Studies of periphyton at a given site must take into account the various substrates available.     

Macrophyte architecture affects the abundance and diversity of littoral microfauna

We tested the hypothesis that structural complexity is an important factor influencing the abundance and taxon richness of microfauna (e.g., rotifers, copepods, cladocerans) in littoral habitats. Research on littoral microfauna has to date focused mainly on field observations, which commonly show microfauna have preference for some macrophytes over others. However, while such studies commonly conclude that macrophyte architecture is a major determinant of these variations, independent factors may also be responsible (e.g., differences in macrophyte ages, differences in macrophyte bed densities and the depth of the respective macrophyte beds sampled). We used artificial macrophytes with three levels of complexity to keep the surface area and mass of the substrate sampled constant, and to control for confounding factors not related to the complexity of the plants. Our results support the hypothesis that structural complexity is an important factor influencing abundance and taxon richness, independent of other potential confounding factors. Microfaunal (mainly rotifer) abundance and richness were generally greater on more complex artificial macrophytes, likely a result of more complex substrates (1) providing a greater variety of habitat, (2) supporting a greater concentration or variety of food and/or (3) affording greater protection against predators. Less mobile surface-associated (i.e., benthic/periphytic) taxa were found to discriminate among substrates, whereas the abundance and richness of planktonic species were not affected by complexity level. Relatively low abundances and taxon richness of microfauna recorded in control samples, which did not contain artificial macrophytes, supports the contention that vegetated areas sustain a higher abundance and variety of species than non-vegetated areas.     

Seasonal dynamics of microcrustacean and rotifer communities in Malaysian rice fields used for rice-fish farming

The abundance, seasonal dynamics and species composition of microcrustacean and rotifer communities in rice fields used for rice-cum-fish culture were examined. The shallow littoral-like nature of rice fields resulted in the presence of cladoceran and rotifer species, but copepods were numerically more abundant. Abundance and seasonal dynamics were affected by factors such as pesticides and herbicide use, predator-prey relationships, presence of hydrophytes and interactions among microcrustaceans and rotifers. The implications of microcrustacean and rotifers abundance and seasonal dynamics on rice-fish farming are discussed.     

Establishing realistic restoration targets for nutrient-enriched shallow lakes: linking diatom ecology and palaeoecology at the Attenborough Ponds, U.K.

Eutrophication is a major problem for shallow lakes in the U.K. lowlands. Over the last few decades issues relating to the management and restoration of these lakes have come to the fore, including the need to develop methods for establishing realistic restoration targets. One group of lakes for which restoration is a key concern are the Attenborough Ponds in the English Midlands, an interconnected series of shallow, nutrient-enriched gravel-pit lakes. In November 1972, the highly polluted River Erewash was diverted into the Attenborough Ponds. To determine the ecological effects of this event and to establish restoration goals for this lake system, two complimentary studies were undertaken here; (i) monitoring of the ecology and sedimentary representation of diatom communities in a disturbed lake connected to the R. Erewash (Tween Pond: high nutrient concentrations, no submerged macrophytes) and a relatively undisturbed lake isolated from the R. Erewash (Clifton Pond: lower nutrient concentrations, abundant submerged macrophytes), and; (ii) examination of the sedimentary diatom record in a short sediment core collected from the chosen disturbed lake (Tween Pond). The species composition, seasonality, relative productivity and sedimentary representation of planktonic and periphytic diatom communities were very different in Tween and Clifton Ponds. In Tween Pond two major phases of planktonic diatom production/sedimentation were observed during March–May and July–September. By contrast, planktonic diatoms were restricted to a single spring peak in Clifton Pond and after May there was a switch to the dominance of periphytic diatoms associated with the development of submerged macrophytes. The 1972 diversion of the River Erewash was clearly reflected in the sedimentary diatom record from Tween Pond, by; (i) the abrupt shift to planktonic diatom dominance, and; (ii) increasing percentages of late summer–autumn associated planktonic diatom species. These changes suggest both significant nutrient enrichment and the switch from submerged macrophyte to phytoplankton dominance. Numerical matching of pre-1972 diatom assemblages with surface sediment assemblages in the gravel-pits using Principal Components Analysis (PCA) and a squared chord distance measure revealed no close analogues. Nevertheless, similarities between; (i) percentages of different diatom habitat and seasonality groups, and; (ii) pre-1972 and contemporary macrophyte survey data suggested that Clifton Pond is probably a good pre-diversion analogue for habitat structure (e.g. macrophyte biomass, composition and architecture) and phenology (e.g. diatom and macrophyte seasonality) in the Ponds. The practical value of combining space-for-time substitution and palaeoecological approaches in restoration ecology studies of shallow lakes is discussed.     

Snail–periphyton interactions in a prairie lacustrine wetland

This study examined the effects of nutrients and macrophytes on snail grazers and periphyton in a prairie wetland food web. Snails (Gyraulus circumstriatus) and periphyton in large enclosures in a lacustrine wetland, Delta Marsh, MB, Canada were subjected to two experimental treatments, nutrient addition (nitrogen, phosphorus) and macrophyte exclusion (using a porous geotextile carpet) during July and August. Snail biomass and periphyton biomass (on both artificial substrata and submerged macrophytes) increased over time in all treatments, representing seasonal growth. Snail biomass was three times higher on macrophytes than on artificial substrata. In response to nutrient addition, snail biomass was significantly elevated over time on macrophytes but not on artificial substrata. Conversely, periphyton biomass was higher on artificial substrata but not on macrophytes in response to nutrient addition. Snail biomass and periphyton biomass on artificial substrata showed no response to macrophyte exclusion. Snail biomass on all substrata was inversely correlated with turbidity, whereas periphyton biomass showed no relationship with turbidity. Timing of nutrient additions to wetlands may influence whether the response occurs primarily in phytoplankton or in periphyton and macrophytes.     

A COMPARISON OF PERIPHYTIC ALGAL BIOMASS AND COMMUNITY STRUCTURE ON SCIRPUS VALIDUS AND ON A MORPHOLOGICALLY SIMILAR ARTIFICIAL SUBSTRATUM1

Chemically inert, cylindrical rods positioned in the littoral of two eutrophic Alberta lakes supported higher periphytic algal biomass (measured as total chlorophyll a) than nearby morphologically similar culms of Scirpus validus Vahl. during most of the summer. Upon initiation of macrophyte senescence, biomass on the two substrata became more similar. Experiments were conducted to investigate the basis for these observations. Whole extracts of intact vegetative Scirpus culms had no effect on periphyton photosynthesis, suggesting that the natural substrata do not produce water-soluble allelochemicals. Various modifications of the rod surfaces (roughening, wax coating, wax color) were used to test whether surficial properties of Scirpus culms influenced periphyton accumulation. Roughened rods supported levels of biomass similar to those of smooth rods, and both substrata developed structurally complex periphyton communities. Rods covered with paraffin wax had periphyton communities that were lower in biomass and structurally more simple than those on un-coated rods or on Scirpus culms. Coloring of the wax coating had no consistent effect on periphyton accumulation. We hypothesize that the hydrophobic cuticle on actively growing Scirpus culms retards the development of precursors for attachment by periphytic algae. Upon senescence of the culm and loss of epidermal integrity, colonization of culm surfaces by periphytic algae may occur in a manner similar to that on artificial substrata.     

On relation to substrate in sessile rotifers

Information on the distribution of 45 sessile rotifers from diverse freshwaters in south and central Sweden was analyzed to reveal possible relationships to their substrates. Almost all of them showed an exclusively periphytic occurrence. The highest number of species was found on Utricularia, but otherwise it was not possible to correlate rotifer presence to any special macrophyte or category of plants (e.g., fine-leaved or floating-leaved species).     

Periphytic rotifer communities of an Australian seasonal floodplain pool

A seasonal, rainfill pool (Ryans 3) on the floodplain of the River Murray, near Albury, Australia was sampled in 1991 and 1993 for periphytic rotifer species and other microfauna. The main macrophytes present were species of Myriophyllum, Pseudoraphis and Triglochin, and, in 1993, there was an extensive covering of Azolla. Sampling methods included quantitative samples taken using a simple syringe. Rotifers numbered from about 10 to 150 per 100 ml and formed about 2 to 20% of the microfaunal community. Numbers of rotifers, and numbers of rotifer species, varied with different macrophytes (² tests, P<0.001 in each case), with the greatest numbers under Azolla. The two years showed marked differences in the macrophytes present and over half the rotifer species were also different (²test, P<0.001).     

Comparison of attached algal communities on natural and artificial substrata along a thermal gradient

Colonization rate and community structure of periphyton assemblages was examined on aluminium and glass substrata and compared to populations on four submerged macrophyte species in three temperature zones in Cholla Lake, Arizona, U.S.A. Higher densities were achieved over shorter incubation intervals in the warmer zones (26–35° C). Representatives from the planktonic diatom community were first to colonize artificial substrata during the initial two hour incubation period in all temperature zones. Two periphyton diatom representatives, Amphora coffeiformis and Cocconeis placentula var. lineata were the numerical dominants after one week. Cocconeis placentula var. lineata was most competitive on natural substrata at temperatures <26°C, while Amphora coffeiformis dominated temperature zones >26°C with no significant preferences for artificial or natural substrata. The significance of temperature, specific conductance and availability of living hosts is discussed with respect to regulating populations of these two common periphytic diatom species in alkaline waters in southwestern U.S.A. Similarity indices (SIMI) were used to compare algal assemblages on various natural and artificial substrata pairs. Periphyton assemblages were very similar on all natural substrata within similar temperature zones, with little or no preference for macrophyte species displaying similar leaf morphology. Diatom assemblages were quite similar on aluminium and glass substrata throughout the incubation period in all temperature zones, while blue-green algal populations were significantly different, particularly in the higher temperature zones (>28°C). Natural periphyton communities were best represented after four weeks incubation with aluminium substrata in warmer temperature zones (>28°C) or where filamentous blue-green algae dominated. The selection of adequate incubation time when employing artificial substrata to evaluate natural assemblages for different environmental conditions and algal populations is discussed.     

Seasonal trophic dynamics affect zooplankton community variability

1. The degree to which communities are variable may be affected by the ecological conditions to which they are exposed and can affect their propensity to form alternative states. We examined the influence of two common ecological factors, predation and seasonal successional stage, on the variability in community composition of herbivorous pond plankton. In a highly replicated, two factor, mesocosm experiment we determined whether beta diversity was affected by seasonal successional stage of the community (two levels), by fish predation (presence/absence) or by their interaction. 2. Several significant changes were found in the composition of the rotifer, cladoceran and copepod assemblages. Most cladoceran abundances showed sharp declines in the presence of fish, while some rotifers, as well as their assemblage species richness, responded favourably to fish. The copepod assemblage was composed of omnivorous and carnivorous species, which added invertebrate predation to the experiment and which intensified as the season progressed. Copepods showed responses to fish predation that depended on seasonal successional stage of the initial community, because of changes in their stage structure and edibility as they grew from nauplii to adults. 3. Community variability was consistently high at the end of each month‐long experimental period for both cladoceran and rotifer assemblages, except under two conditions. In the early season treatments, the rotifer assemblages were more consistent (lower beta diversity) in the presence of fish. This was attributed to high population growth rates for rotifers under these ecological conditions because of reduced copepod predation on them through a trophic cascade from fish. Low community variability was also observed in the late season for rotifers when fish were excluded and, as a result, they were exposed to high invertebrate predation from cyclopoid copepods. 4. Results from the early season support theoretical predictions that when community size increases, variability in composition should decline because of an increase in competitive processes over stochastic ones. Late season results suggest that a second mechanism, specialist predation, can also reduce prey community variability. Our study demonstrates that plankton communities may be more predictable under certain trophic web configurations and challenges ecologists to find ways to incorporate such inherent variability into experiments and community theory.     

Laboratory experiments on the impact of biofilms on the plankton of a large river

1. Benthic organisms can have a strong effect on the plankton in rivers, although normally only members of the macrofauna are considered as important consumers. In the present study we conducted experiments on four different dates (in December, March, June and September) to assess the potential role of periphytic heterotrophic flagellates (HF), ciliates and rotifers in the control of potamoplankton (bacteria, algae, HF and ciliates). 2. Natural periphyton was established on the walls of circular flow channels by exposing them to river water (River Rhine, Germany). The experimental channels (with periphyton) and control channels (without periphyton) were filled with riverine water and the increase rates of planktonic bacteria, algae, HF and oligotrich ciliates were determined for the two treatments. 3. The abundance of periphytic ciliates and rotifers at the beginning of the four experiments showed large differences with low values in December and March, and high values in June and September. Dominant potential consumers of plankton were the heterotrich ciliate Stentor sp. and bdelloid rotifers. 4. The rates of increase of planktonic algae, HF and ciliates were significantly smaller in the presence of periphyton compared with those in their absence. Significant interactions between the treatment (with and without periphyton) and the time of experiment were found for the planktonic HF and algae, indicating that the impact of the periphyton varied temporarily. The planktonic groups responded differently to the periphyton with the planktonic HF showing the highest loss rate. Significant differences were also found among the loss rates of different HF groups and different diatom size classes. 5. These laboratory experiments demonstrate that periphytic ciliates and rotifers are potentially important consumers of different planktonic groups. The quantitative impact of periphyton on plankton with respect to the selective feeding needs further attention.     

Periphyton in Lake Vechten,with emphasis on biomass and production of epiphytic algae

Summary Characteristics of the periphyton associated with the submerged macrophytesCeratophyllum, Elodea andMyriophyllum were similar. During the whole growing season the periphyton dry weight often exceeded that of the macrophyte. The periphyton contained much detritus and carbonates, and the epiphytic algae were accompanied by large numbers of bacteria, protozoans and rotifers. Attached algae were scarce, but motile diatoms were abundant throughout the year. Thus the periphyton showed the features of a benthic community. Consequently, the role of the macrophytes would be rather the extension of the bottom area instead of actively promoting the growth of microorganisms by providing minerals or excreting organic substances.During the peak of the littoral development the epiphytic algae expressed a high photosynthetic capacity, while at the same time the periphyton dark respiration was intense. After measurements of the depth distribution of biomass and light in aCeratophyllum stand, it was concluded that the contribution of the epiphytic algae to the production in the lake's littoral zone was substantial. Furthermore, on a daily basis, the total association of macrophytes and periphyton would be oxygen consuming due to heterotrophic activity, notably mineralization of the detritus.     

Environmental Predictors of Rotifer Community Structure in Two Types of Small Water Bodies

The species diversity and distribution of rotifers between different habitats (elodeids, helophytes and open water) of 34 field and 31 forest ponds, differing in regard to origin, size, depth, macrophyte cover, overshading and the presence of fish were examined (N = 381). 197 taxa were found in both types of ponds with 32 species being rare, endangered or new to Polish fauna. The species composition and Shannon‐Wiener index distribution reflected heterogeinity of the habitats, while rotifer mean densities revealed a reverse pattern in both types of water bodies. The great variability of limnological features contributed to a lack of significant differences in rotifer abundance between both types of water bodies. Although some rotifers preferred one specific type of water body (forest vs. field), the type of habitat was a much stronger predictor of their distribution, which reflects a necessity to examine ponds in relation to their microhabitats created by various macrophytes. Rotifers revealed a strict division into two groups – of pelagic origin (e.g., Polyarthra vulgaris), which were attributed to the open water and helophytes, and of littoral origin (e.g., Lepadella patella), which were associated with elodeids, biomass of a plant habitat and a lack of fish. The selective choice of the most complex habitat (elodeids) by only littoral species suggests the weak impact of fish in the studied ponds and the most advantageous conditions for littoral rotifers among such a habitat. The first group comprised species characteristic of field ponds, while the second was characteristic of forest ponds. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Influence of Biotic and Abiotic Factors on Psammic Rotifers in Artificial and Natural Lakes

The effect of sand grain size, porosity and the abundance of algae on the community structure of psammic rotifers was tested in three anthropogenic lakes (Upper Silesia) and compared with three natural ones (West Pomerania). The structure of grain size in the studied beaches of artificial and natural lakes was similar but differences were found in the abundance of algae. The structure of the psammic rotifer community in Upper Silesian lakes was different from natural lakes in West Pomerania. The structure of psammic rotifer communities in anthropogenic reservoirs and lakes (West Pomerania) differed in numbers of species and numbers of psammobiont species, and also diversity index. The most altered structure of rotifer assemblages was observed in the psammon rotifers of the strongly contaminated Dzierżno Duże Lake.     

Plant community dynamics in a chain of lakes: principal factors in the decline of rooted macrophytes with eutrophication

Shoe Lake and East Graham Lake, part of a small chain of lakes in southeastern Michigan, USA, differ in nutrient loading and in the structure and productivity of their aquatic plant communities. A comparative study of species frequency and biomass distributions, nutrient contents, and responses to experimental nutrient enrichment and shading, was conducted to determine the principal factors controlling the macrophyte dynamics. A central objective was to address the question of why rooted macrophyte growth declines with eutrophication, and to test existing models designed to explain this phenomenon. In the more eutrophic Shoe Lake, diversity and productivity of rooted macrophytes were relatively low, restricted primarily by combined shading of phytoplankton, periphyton, and non-rooted macrophytes (principally Ceratophyllum demersum, along with Utricularia vulgaris and Cladophora fracta). In the less eutrophic East Graham Lake, lower nitrogen availability restricted the growth of all of these shading components, resulting in clearer water and higher productivity and diversity of rooted macrophytes. The macrophytes did not allelopathically suppress the phytoplankton in East Graham Lake. The results supported a direct relationship between nutrient loading, increasing growth of phytoplankton, periphyton and non-rooted macrophytes, and decline of rooted macrophytes.     

Macrophytes moderate the taxonomic and functional composition of phytoplankton assemblages during a nutrient loading experiment

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THE INFLUENCE OF SUBMERGED MACROPHYTES ON SEDIMENTARY DIATOM ASSEMBLAGES1

Submerged macrophytes are a central component of lake ecosystems; however, little is known regarding their long‐term response to environmental change. We have examined the potential of diatoms as indicators of past macrophyte biomass. We first sampled periphyton to determine whether habitat was a predictor of diatom assemblage. We then sampled 41 lakes in Quebec, Canada, to evaluate whether whole‐lake submerged macrophyte biomass (BiomEpiV) influenced surface sediment diatom assemblages. A multivariate regression tree (MRT) was used to construct a semiquantitative model to reconstruct past macrophyte biomass. We determined that periphytic diatom assemblages on macrophytes were significantly different from those on wood and rocks (ANOSIM R = 0.63, P < 0.01). A redundancy analysis (RDA) of the 41‐lake data set identified BiomEpiV as a significant (P < 0.05) variable in structuring sedimentary diatom assemblages. The MRT analysis classified the lakes into three groups. These groups were (A) high‐macrophyte, nutrient‐limited lakes (BiomEpiV ≥525 μg · L^?1; total phosphorus [TP] <35 μg · L^?1; 23 lakes); (B) low‐macrophyte, nutrient‐limited lakes (BiomEpiV <525 μg · L^?1; TP <35 μg · L^?1; 12 lakes); and (C) eutrophic lakes (TP ≥35 μg · L^?1; six lakes). A semiquantitative model correctly predicted the MRT group of the lake 71% of the time (P < 0.001). These results suggest that submerged macrophytes have a significant influence on diatom community structure and that sedimentary diatom assemblages can be used to infer past macrophyte abundance.