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Surface area measurement is a common component of benthic research, especially in the quantification of chlorophyll. Multiple techniques are available and 10 are described: artificial substrates, area-specific sampling, geometric approximation, stone shape equations, foil wrapping, grids, stamps, wetted layer, particle layer, and planar area measurement. A literature search of 130 papers indicated the most common methods: using artificial substrates of known area, subsampling a specific area using a template or sampler, measuring stone dimensions and using an equation to derive area, and using the weight of foil wrapped on stones. Methods were compared using spheres of known area, smooth and rough granite stones, and plastic macrophytes. Most methods produced highly correlated measurements and accurately estimated surface area. The wetted layer method was sensitive to stone roughness and plant complexity, but may overestimate the area of complex surfaces. Replication of one method by 10 biologists indicated that individual differences in technique can affect surface area values. Factors to consider in choosing an appropriate method include ease of use, characteristics of the substrates (e.g., porosity and flexibility), fineness of scale in measuring area, and whether methods must be field-based or can include laboratory techniques. [ABSTRACT FROM AUTHOR]

Morphological taxonomy is a critical component of all aspects of aquatic biology. Hydrobiologia receives many manuscripts that focus on descriptions of new species of aquatic organisms. We offer suggestions for how these papers can better conform to the stated aims and scope of Hydrobiologia, which read, in part: ‘ Hydrobiologia publishes original articles of interest to a broad and international audience. Purely descriptive work will be considered if it is firmly embedded in a larger biological framework’. In our opinion, taxonomic studies that classify new species are more likely to meet these aims if they state the species concept being used, and include additional experimental, analytical or conceptual analyses. For example, we recommend that studies that use morphological taxonomy also include independent tests of species boundaries, such as multivariate analyses, molecular genetic analyses, and/or tests of reproductive isolation. Given the constraints under which many taxonomists operate, collaboration might be the most effective strategy for achieving these goals. [ABSTRACT FROM AUTHOR]

Examines the interactions between sediments and water. Recognition of the environmental influence of both sediment and sediment-associated chemical transfers and storage on aquatic ecosystems; Function of sediments as a pollutant in natural habitats; Environmental impact of physical catchment disturbances.

The magnitude and frequency of events leading to changes in turbidity have been studied in a large (61 km2), shallow (mean depth 3.4 m) wind-exposed lake basin at the western end of Lake Mälaren, Sweden. In this paper we couple changes in suspended particulate inorganic material (SPIM) resulting from wind driven sediment resuspension, and variations in the discharge and sediment load, to spectral variations in subsurface light and estimates of photosynthetically active radiation (PAR). To accomplish this we use a semi-analytical model which predicts the spectral variations in downwelling irradiance (E d(λ)) and the attenuation coefficient of downwelling irradiance (K d(λ)), as a function of the concentrations of chlorophyll, dissolved yellow substances, and suspended inorganic and organic particulate material. Unusually high river discharge, led to large inputs of yellow substances and large in lake yellow substance concentrations (a ys(420) ≈ 20 m-1), causing variations in yellow substance concentration to have the greatest role in influencing temporal trends in the attenuation of PAR and variations in the depth of the euphotic zone (Z eup). In spite of this, variations in SPIM could account for approximately 60% of the variation in Z eup attributed to changes in yellow substances alone. Our results show that changes in suspended sediment concentration leads to both long-term and short-term changes in the attenuation of PAR, even in the presence of high concentrations of dissolved yellow substances. [ABSTRACT FROM AUTHOR]

Rapid progress has been made recently in the understanding of heavy metal sorption and speciation on sediment and soils. One aspect that was overlooked in the previous studies was the process of pollutant transformation and transportation in hyper-concentrated solid-liquid systems. In this paper, batch experiments on copper sorption in association with loess at high sediment concentrations were conducted. However, some reaction mechanisms were difficult to determine experimentally due to the limitations of speciation extraction methods. In an additional study, the MINTEQA2 chemical equilibrium model was used to calculate the speciation and precipitation of copper sorption by loess to give quantitative predictions and detailed information about the reaction process. The experiments and the modeling simulation were made under the same sorption conditions, with sediment concentrations ranging from 50 to 200 kg/m3 and adsorbates of CuSO4 and Cu(NO3)2, in order to compare their results. The modeling results clearly supported the experimental results, fully explained the mechanisms of the effects of chemical form and sediment concentration on the copper sorption, and strengthened the dominant role of carbonates among the main components of loess in the process of copper sorption. [ABSTRACT FROM AUTHOR]

The Langmuir equation has been widely used for description of the adsorption characteristics in different solid–liquid systems, although it was originally advanced for adsorption of gas molecules on a planar surface. In this paper, the applicability of the Langmuir equation was discussed when it is modified or extended to describe sorption on heterogeneous surfaces such as soils or soil components. The sorption of Cu(II) by loess was investigated experimentally with sediment concentration ranging from 10 to 100 kg/m3, and copper concentration from 64.80 to 7499 mg/l. The measured results were found well fitted with the nonlinear Langmuir isotherm in form, but for the loess with high carbonate content, the Cu precipitation becomes the primary mechanism instead of the original adsorption in the ordinary cases with low carbonate content. Thus, the parameters identified from the same Langmuir form would be essentially different in their physical meanings comparing with those in the conventional Langmuir equation. Using the MINTEQA model, copper precipitation was calculated and the implications of parameters in Langmuir equation were interpreted. Both the `sorption coefficient' and the `sorption maximum' in the Langmuir equation for copper precipitation are very close to those for copper sorption, but the `sorption coefficient' for copper precipitation is greater than that for copper sorption and oppositely for the `sorption maximum', which explains why precipitation dominates the sorption process. [ABSTRACT FROM AUTHOR]

In a classical paper, Hutchinson (1961) argued that the large number of species in most plankton communities is remarkable in view of the competitive exclusion principle, which suggests that in homogeneous, well-mixed environments species that compete for the same resources cannot coexist. Few ideas in aquatic ecology have evoked more research than this `paradox of the plankton'. This review is an effort to put the main solutions to the paradox that have been proposed over the years into perspective. Hutchinson himself already suggested that the explanation could be that plankton communities are not in equilibrium at all due to weather-driven fluctuations. Subsequent research confirmed that such externally imposed variability can allow many species to coexist. Another important point is that in practice the homogeneous well-mixed conditions assumed in the competitive exclusion principle hardly exist. Even the open ocean, for instance, has a spatial complexity resulting from meso-scale vortices and fronts that can facilitate coexistence of species. Perhaps most excitingly, theoretical work on species interactions has given a counter-intuitive new dimension to the understanding of diversity. Various competition and predation models suggest that even in homogeneous and constant environments plankton will never settle to equilibrium. Instead, interactions between multiple species may give rise to oscillations and chaos, with a continuous wax and wane of species within the community. Long-term laboratory experiments support this view. This chaotic behavior implies among other things that plankton dynamics are intrinsically unpredictable in the long run when viewed in detail. Nonetheless, on a higher aggregation level, indicators such as total algal biomass may show quite regular patterns. [ABSTRACT FROM AUTHOR]

Although evolutionary ecologists agree that proximate and ultimate aspects are two sides of one coin, they are seldom interested in studies on physiological and behavioural mechanisms at the base of ecological phenomena. Nevertheless, these mechanisms are objects of selection and evolved to realise adaptive significances. This paper is a plea to bring both fields closer together, and, by means of an example of Diel Vertical Migration of Daphnia, some proximate and ultimate aspects are discussed. It is argued that light changes, not fish kairomone, is the primary cause for an individual to swim downwards at dawn and upwards at dusk. However, what is called a causal factor might differ when ecosystems or individuals are studied. In addition, causality in ecology is not simple, and has the character of a `set of necessary conditions'. To illustrate the importance of proximate analyses in DVM, two basic response mechanisms are discussed: Photobehaviour system 1 and 2. The physiological character of these systems leads to a fixed type of migration or to a phenotypically induced DVM, respectively. The adaptive significance of the first might be a reduction of the hazardous effects of UV radiation and of the second a lowering of mortality due to visually hunting predators. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, control of Hopf bifurcation for a plankton population model with a non-integer exponent of closure is studied. For the plankton model with the closure term varies continuously between the commonly used linear and quadratic forms, washout filter aided feedback controllers are employed to control the stability of the Hopf bifurcation, and thus the chaos could be eliminated. By employing the stability theorems derived, the stability of a control system is investigated. Finally numerical simulations are provided to show the effectiveness and feasibility of the developed methods. [Copyright &y& Elsevier]

In Europe there is an extensive history of the derivation and use of benthic indicators which parallels similar developments in North America and elsewhere. Most recently, this has increased because major European Union Directives require that indicators of marine benthic change are used to confirm good ecological status quality (as in the Water Framework Directive) and favourable conservation status (as in the Habitats and Species Directive). Furthermore, these indicators have to fit within the current philosophy of the Ecosystem Approach requiring the development and use of Ecological Quality Objectives and Standards. Despite this, comparisons of families of indicators derived by differing methods have not been carried out such that the robust nature of the indicators on differing spatial scales and under differing benthic conditions has not been rigorously assessed. Using case studies from the Portuguese coasts and estuaries, this paper compares and contrasts univariate and multivariate macrobenthic indicators to quantify comparisons of change. The studies indicate the relative value of those indicators at contrasting spatial scales, e.g. in the transition from small areas around coastal submarine outfalls, to the local and regional estuarine and coastal scale. The analysis indicates the difficulties of deriving and using qualitative and quantitative indicators from benthic communities in stable, and in moderately and highly variable environmental conditions in estuarine, coastal and open sea habitats. In some areas, the variability in the indicators and indices within a station and site is as large as that between stations and sites. For those areas studied, there is an adequate quality and quantity of benthic data available for making management decisions but this is unlikely to be the case for all areas. Similarly, the interrogation of the methods shows that while their use and interpretation rely on a good understanding of the biology of the individual species and their responses to physical and polluting stress, that understanding is not yet available for many of the species. Most notably, while the indices and integrative indicators are becoming increasingly sophisticated, many are still dependent on the Pearson–Rosenberg model for organic enrichment hence they require to be validated for physical disturbance and for chemical pollution. Because of these features, the outcome of the analysis has repercussions for the management of coastal and estuarine areas. Although the present study indicates the value of indicators of benthic change for making management decisions at the various scales, further validation is required especially, for example, where one indicator over-estimates the ecological status for poor areas and underestimates it for good areas. [Copyright &y& Elsevier]

In this paper I review the three best-known aspects of community structure in the deep-sea benthos: depth gradients of species diversity, spatial dispersion, and faunal replacement with depth. Patterns of species diversity are documented for the megafaunal invertebrates and fishes and four macrofaunal taxa (bivalves, gastropods, cumaceans, and polychaetes). These trends and data on spatial dispersion provide the basis for evaluating theories of species diversity in the deep sea. I then compare rates of species replacement with depth in megafaunal and macrofaunal elements, and relate differences between the groups to life-history parameters and trophic roles. [ABSTRACT FROM AUTHOR]

1. Systematic conservation planning is a process widely used in terrestrial and marine environments. A principal goal is to establish a network of protected areas representing the full variety of species or ecosystems. We suggest considering three key attributes of a catchment when planning for aquatic conservation: irreplaceability, condition and vulnerability. 2. Based on observed and modelled distributions of 367 invertebrates in the Australian state of Victoria, conservation value was measured by calculating an irreplaceability coefficient for 1854 subcatchments. Irreplaceability indicates the likelihood of any subcatchment being needed to achieve conservation targets. We estimated it with a bootstrapped heuristic reserve design algorithm, which included upstream–downstream connectivity rules. The selection metric within the algorithm was total summed rarity, corrected for protected area. 3. Condition was estimated using a stressor gradient approach in which two classes of geographical information system Layers were summarised using principal components analysis. The first class was disturbance measures such as nutrient and sediment budgets, salinisation and weed cover. The second class was land use layers, including classes of forestry, agricultural and urban use. The main gradient, explaining 56% of the variation, could be characterised as agricultural disturbance. Seventy-five per cent of the study area was classified as disturbed. 4. Our definition of vulnerability was the likelihood of a catchment being exposed to a land use that degrades its condition. This was estimated by comparing land capability and current land use. If land was capable of supporting a land use that would have a more degrading effect on a river than its current tenure, it was classified vulnerable (66% of the study area). 79% of catchments contained more then 50% vulnerable land. 5. When integrating the three measures, two major groups of catchments requiring urgent conservation measures were identified. Seven per cent of catchments were highly irreplaceable, highly vulnerable but in degraded condition. These catchments were flagged for restoration. While most highly irreplaceable catchments in good condition were already protected, 2.5% of catchments in this category are on vulnerable land. These are priority areas for assigning river reserves. [ABSTRACT FROM AUTHOR]

1. Stream communities are structured by factors acting over multiple spatial and temporal scales. Identifying what factors are driving spatial patterns in stream communities is a central aim of ecology. 2. Here we used two large European data sets of fish, invertebrates, macrophytes, benthic diatoms and environmental data in two stream groups (lowland and mountain) to determine the importance of variables at different spatial scales (geographical, regional, local) on community structure. 3. Both geographical position and ecoregion were selected first in canonical correspondence analysis (CCA), clearly showing the broad spatial gradients covered in the data set. Secondary predictors (after accounting for spatial and/or ecoregion effects) were similar between stream groups and among the four organism groups. In particular, conductivity and N concentration were strong predictors reflecting catchment land use. 4. Using partial CCA, we assessed the individual importance of the three spatial scales on the community structure of the four organism groups in the two stream groups. The majority of among-site variability (22–29%) was accounted for by local scale variables (e.g. water chemistry and substratum type), with regional and spatial variables accounting 11–13% and 5–6%, respectively. Our findings indicate that the four organism groups are responding similarly to the different levels of spatial scale, implying much redundancy which should be consider when implementing studies of bioassessment. [ABSTRACT FROM AUTHOR]

1. Reference (i.e. least or minimally impaired) sites can provide important information about the expected range of biological metrics and can be used to establish impairment or non-impairment of a test site. A problem with using reference data is that biological metrics are affected by natural conditions. We present an approach that uses local information to adjust for natural conditions and a method for statistically evaluating condition at a test site using biological metrics. 2. Our method consists of four steps: selection of a distance measure to find neighbours of a test site, selecting natural variables to measure the distance, selection of the number of neighbours and calculating a scored metric. 3. We use a simulated example to illustrate when the nearest-neighbour approach improves classification of sites as reference or not reference. 4. Using a set of data from the Mid-Atlantic Highlands, we show that the nearest-neighbour method improved on the ability of a regression approach to correctly classify test sites known to be from a non-reference group without affecting the ability to correctly classify test sites known to be from the reference group. [ABSTRACT FROM AUTHOR]

The species diversity of phytoplankton is usually very high in wild aquatic systems, as seen in the paradox of plankton. Coexistence of many competitive phytoplankton species is extremely common in nature. However, experiments and mathematical theories show that interspecific competition often leads to the extinction of most inferior species. Here, we present a lattice version of a multi-species Lotka–Volterra competition model to demonstrate the importance of local interaction. Its mathematical equilibrium is the exclusion of all but one superior species. However, temporal coexistence of many competitive species is possible in an ecological time scale if interactions are local instead of global. This implies that the time scale is elongated many orders when interactions are local. Extremely high species diversity of phytoplankton in aquatic systems may be maintained by spatial coexistence in an ecological time scale. [ABSTRACT FROM AUTHOR]

Chironomid larvae were sampled sequentially from small experimental rice fields in southern New South Wales, Australia. Sampling was undertaken during the 1995, 1997, 1998 and 1999 crop establishment periods, starting 10 days after flooding (DAF) and continuing at 5 day intervals until 35 DAF. No agrochemical treatments were applied to the fields at any stage. Seventeen species were identified from 3429 recovered larvae. The most abundant species were Chironomus tepperi Skuse (0–91% of 35 day totals), Procladius paludicola Skuse (7–78%) and Polypedilum nubiferum (Skuse) (2–12%). No other taxon accounted for more than 8% of recovered larvae in any year. C. tepperi colonised fields more rapidly than other taxa and, when present, had only a single generation. The abundance of C. tepperi varied dramatically from year to year: from total absence in 1997 to a peak density exceeding 13 000 larvae m−2 in 1998. Significant differences between post-flood sampling times ( R = 0.407, p= 0.009) and between years ( R = 0.495, p = 0.001) were found using ANOSIM2 analysis. C. tepperi had a greater impact on community variability at 10 and 15 DAF (42–58%) than any other species, with P. paludicola exerting the most influence from 20 DAF onwards. Exceptionally high densities of C. tepperi in 1998 led to high levels of turbidity, which apparently prolonged the duration of the single C. tepperi cohort by suppressing water temperatures. Comparison of plant densities in the monitored bays to those in nearby bays receiving effective chemical protection shows that rice plant loss increased in response to higher C. tepperi densities. No plant loss occurred in 1997 when C. tepperi was absent, suggesting the other chironomid species present in the fields are not routinely involved in causing significant crop damage. [ABSTRACT FROM AUTHOR]

Biomass and breakdown of tree roots within streambed sediments were compared with leaf and wood detritus in three Coastal Plain headwater intermittent streams. Three separate riparian forest treatments were applied: thinned, clearcut, and reference. Biomass of roots (live and dead) and leaf/wood was significantly higher in stream banks than in the channel and declined with depth strata (0–10 > 10–20 > 20–30 cm). Riparian roots (live and dead combined) contributed on average 24 and 42% of coarse particulate organic matter (CPOM) biomass within the top 30 cm of channel and streambank sediments, respectively. Estimated mean surface area of live riparian roots within sediments was 1084 cm2 m−3. Streambed temperatures showed greater fluctuation at the clearcut site compared to thinned and reference treatments. However, breakdown rates among buried substrate types or riparian treatments did not differ after 1 y. Slow decay rates were associated initially with anaerobic conditions within sandy sediments and later with dry sediment conditions. Riparian roots represent a direct conduit between streamside vegetation and the hyporheic zone. In addition to contributing to organic matter storage, the abundance of riparian roots within streambed sediments suggests that roots play an important role in biogeochemical cycling within intermittent headwater streams of the Coastal Plain. [ABSTRACT FROM AUTHOR]

Coastal lagoons are usually subjected to several kinds of human impacts, especially eutrophication. The breaching of the sand bar, which separates the lagoon from the ocean, by human action, is a common process used to decrease the negative effects of eutrophication. The aims of this research were to evaluate the effects of the artificial sand bar breaching on the populations of the aquatic macrophyte Typha domingensis and the subsequent effects on nutrients concentration in a tropical coastal lagoon. Samplings were carried out monthly from February/01 to January/02 in a monospecific stand of T. domingensis at Imboassica lagoon (Rio de Janeiro/Brazil). Two sampling sites, in the middle and in the border of the stand, were marked in three different transects. Water depth was measured and the aerial biomass sampled with a 0.25 m2 quadrat. The macrophyte samples were separated into live and dead material and the shoot length, shoot density and number of leaves were analyzed. All plant material was oven dried till constant weight and net primary production, dead stand crop production and the nutrients release through decomposition were estimated at each site. The decrease in water level due to sand bar opening affected negatively T. domingensis populations, but the most intense effects were observed in the middle of the stand. The shoot mortality was highly enhanced after the sand bar breaching and the nutrients were released through decomposition to the water column. It reflected on an input of 11.5 kg C m−2, 0.22 kg N m−2 and 0.13 kg P m−2 into the lagoon, which represent from 22.5 to 44.8 ton P and 35.9 to 71.8 ton N to the lagoon. The decrease of nutrients concentration after the sand bar breaching was not successfully accomplished. The decay of T. domingensis stands due to the sand bar breaching neutralized the exportation of nutrients to the ocean, and contributed to the phosphorous increase in the water column. Thus, to a better management of aquatic ecosystems subjected to human eutrophication, the role of aquatic macrophytes decomposition on internal fertilization of aquatic ecosystems should be accounted. [ABSTRACT FROM AUTHOR]

Climatic and hydrological variability is usually high in the Pampa Plain (Argentina). However it has not studied yet how this variability may affect the phytoplankton and zooplankton biomass and community structure in aquatic systems of this region. The main purpose of this study was to assess flushing effects on nutrient and plankton dynamics in two interconnected very shallow lakes of the Pampa Plain. In order to study the impact of hydrology on the plankton biomass and community structure, we compared the summer plankton community among three consecutive years with contrasting hydrological characteristics. Water residence time varied an order of magnitude among years and this variability was correlated to strong changes in physicochemical and biological lake characteristics. Depending on the water discharge level, the hydrological regime within the lakes ranged from lentic to more lotic conditions. Nutrient and phytoplankton biomass were positively related to water discharges. During high flushing periods, nutrients import from intensive agriculture lands leads to a dramatic increase in trophic conditions. On the other hand, macrozooplankton biomass was positively related to water residence time and showed a dramatic decrease during high flushing years. Rotifers biomass was not affected by interannual water discharge variability during the study period. Our results support that in case of lakes with high flushing rates, zooplankton development is dependent on water residence time and that hydrology may have stronger effects on macrozooplankton biomass than top-down control by planktivores. [ABSTRACT FROM AUTHOR]

The oceanography around Mauritius (in the Western Indian Ocean) remains largely unstudied, hence there is an acute scarcity of marine environmental data for management purposes. Rigorous water depth and current measurements were made on a system of grids inside Le Morne lagoon (in the south western part of Mauritius) in March–April 2000 to generate semi-quantitative models of general flow pattern in the form of contour maps using SURFER 6 computer programme. A simultaneous survey on composition of bottom cover was conducted to examine possible relationships with current speed. A separate investigation recorded surface and bottom currents prevailing amongst various habitat types to demonstrate the nature of the resulting damping effect on surface current speed. Significant correlations generated from data analysis were discussed as a basis for real biophysical relationships. Some of the limitations in the current analysis and some of the seemingly contradictory results are acknowledged and addressed in the light of the general assumption that the structure of the lagoon is conditioned by current speeds. Much stronger current speeds just outside the reef (e.g. >0.5 m s−1) than inside the lagoon (e.g. <0.32 m s−1) indicated a substantial slow-down of water current by the reef barrier. Inshore bottom currents were weaker than at the surface and current speed correlated well with water depth. Bottom and surface current directions were generally similar, i.e. going northward during flood tide and southward during ebb. The lagoon would be classified as ‘restricted’, exhibiting well-defined tidal circulation, which is modified by wind forcing. Dense fields of branching Acropora corals slowed down surface current speed by as much as 87%, but the relationship between current speed and bottom cover appears to be variable, depending on the specific location within the lagoon under consideration. The contour plots of the flow pattern model generated reasonably high qualitative modelling of spatial current speed pattern in the lagoon, with stronger currents generally along the reef areas, at the reef passes and in the deeper zones. However, these plots did not match closely those displaying distribution of bottom cover, thus confirming results obtained from pair-wise correlation tests, namely the lack of a significant relationship between current speed and bottom cover. Most of the correlations would appear to represent biological relationships, with different types of communities enabling or excluding other types. Thus, the biophysical structure of the lagoon would be driven a priori by the distribution and abundance of corals rather than current speeds, which contradicts the above hypothesis. Recurrent natural hazards subject the benthic communities to a state of ‘perpetual knock-down and recovery’. Recovery, however, can be seriously impaired by the chronic ongoing degradation of the coastal marine environment of Mauritius. An urgent review of its coastal zone management and protection strategy would be desirable for the island. [ABSTRACT FROM AUTHOR]

The Mary River, in the Australian wet/dry tropics, flows seasonally. When the river ceases flowing in the dry season, a series of isolated lakes remain along the river’s main floodplain channel. The limnology of a channel lake, which is 14 km long and 6-9 m deep in the dry season, was examined between April and December 2000. Four hydraulic phases were identified, these being (1) riverine (April), (2) riverine to lake transition (May), (3) lake (June–late-November), and (4) lake to riverine transition (late-November–December). These phases differ with respect to their duration and flow direction from lakes located on tropical floodplains of perennially flowing rivers. Despite the variable hydraulic conditions, the main channel remained thermally stratified, with only infrequent and short-lived deep mixing events, and sufficient light for photosynthesis in the diurnal mixed layer. During the period of isolation and in contrast to floodplain lakes in tropical South America, the depth of the Mary River channel lake always exceeded, by at least 2-fold, the depth of the diurnal mixed layer. The water quality (conductivity, dissolved oxygen, pH, Si and water clarity) and phytoplankton assemblage of the channel lake was primarily driven by its hydraulics, though this was not evident for the channel’s nutrient concentrations. Dissolved oxygen concentrations during lentic conditions were double values during the riverine and transition phases. This was attributed to the cessation of inflowing waters with a high biological oxygen demand, and enhanced photosynthetic activity of higher concentrations of phytoplankton retained under lentic conditions. The channel’s phytoplankton assemblage reflected the channel’s hydraulics, with the most common phytoplankton throughout the study period belonging to functional groups Lo( Peridinium inconspicuum), W1 (euglenoids), W2 ( Trachelmonas) and Y ( Cryptopmonas, Rhodomonas), with groups A ( Acanthoceras) and D ( Nitzschia agnita, Synedra alna) prominent during the lentic phase. Despite persistent stratification under lentic conditions, there was no clear evidence of autogenic succession or domination by any single phytoplankton functional group. [ABSTRACT FROM AUTHOR]

Highly regulated salinity gradients in solar salt pond concentrating sequences provide an opportunity to investigate in situ salinity impacts on aquatic flora and fauna. The Shark Bay Salt solar ponds at Useless Inlet in Western Australia vary in salinity from seawater to four times seawater over the pond sequence. We observed a shift from planktonic to benthic primary productivity as salinity increased. Water column photosynthesis and biomass decreased markedly with increasing salinity, while benthic productivity increased as cyanobacterial mats developed. Correspondingly, productivity shifted from autotrophy to heterotrophy in the water column and from heterotrophy to autotrophy in the benthos. Both shifts occurred at intermediate salinity (S = 110 g kg−1, ρ = 1.087 g cm−3) in the pond sequence, where there was little production by either. Within individual ponds, productivity, algal biomass and physico-chemical conditions were relatively constant over one year, with only water column photosynthesis significantly different between seasons, mostly due to greater winter production. Transitions between benthic and planktonic production and their relative magnitudes appear to be driven mostly by direct responses to salinity stress, but also by changes in nutrient availability and grazing, which are also influenced by salinity. [ABSTRACT FROM AUTHOR]

Estuarine benthic organisms are frequently subjected to disturbance events caused by hydrodynamic processes that disrupt and move the sediment in which the animals reside, however the mechanisms by which physical disturbance processes affect infaunal and epifaunal populations and communities remain poorly resolved. The responses of three infaunal and two epifaunal estuarine benthic species to sediment disturbance (burial) were compared in laboratory experiments. Overburden stress (kPa) was calculated to quantify the force exerted on organisms by sediment burial for 6 d. At the levels tested (0–16 kPa), increasing overburden stress did not significantly decrease survival or growth of juvenile burrowing bivalves, Macoma balthica (Linnaeus). Survival of juveniles and adults of the tubiculous polychaete Streblospio benedicti (Webster) and neonates of the burrow-forming amphipod Leptocheirus plumulosus (Shoemaker) declined exponentially with increasing overburden stress. The mean S. benedicti survival rate was 4% of the control at an overburden stress of ≈4 kPa, while an overburden stress of 12 kPa was necessary to comparably reduce survival of L. plumulosus. At the low levels of overburden stress used in the experiments with epifauna (≤0.2 kPa), juvenile oyster Crassostrea virginica (Gmelin) did not suffer significant mortality at an overburden stress of 0.1 kPa. In contrast, the epifaunal tunicate Molgula manhattensis (DeKay) exhibited significant mortality when partially (one or two siphons exposed) or completely buried under sediment with an overburden stress of 0.2 kPa. Species-specific response to burial varied as a function of motility, living position, and inferred physiological tolerance of anoxic conditions while buried. We conclude that some benthic species exhibit mechanical and possibly physiological adaptations that may allow them to survive deposition events of the magnitude commonly encountered in estuarine environments. [ABSTRACT FROM AUTHOR]

Small freshwater systems often depend on allochthonous organic subsidies to sustain productivity. Benthic invertebrates consuming coarse detritus maintain the energy flow by conveying dead organic matter into prey items and increase the food availability for other consumers. Compared to lotic systems, the dynamics of coarse detritus decomposition has not received much attention in lakes. The objectives of this study were to investigate the seasonality of leaf litter turnover and the timing of abundance of potential shredder species in a typical oligotrophic boreal lake. Leaf litter was experimentally exposed in litterbags in the littoral zone in Lake Välen from autumn to late spring two consecutive years. The weight loss rate of leaf litter initially followed the same pattern during both winter periods, but was markedly influenced by freezing in late winter the second year. Further, the seasonal variation patterns in abundance in litterbags were quite different among the potential shredder species. Only the limnephilid caddis larvae showed a density variation pattern possible to connect to the weight loss of leaf litter in litterbags. Otherwise frequent detritivores such as Asellus aquaticus and Leptophlebia marginata displayed lowest density in litterbags during the main weight loss period. However, after the long ice period the second winter the remaining leaf litter seemed to be consumed by A. aquaticus. With increasing knowledge of the initial leaf breakdown process and the guild of shredders in lakes, the decomposition rate may also in this habitat become a useful instrument when evaluating the impact from perturbations on ecosystem function. [ABSTRACT FROM AUTHOR]

We used mesocosms to analyze predation impacts on the prey populations and prey community structures by two cyclopoid copepod species, the larger Mesocyclops pehpeiensis and the smaller Thermocyclops taihokuensis, who coexist with small-sized herbivorous zooplankton species in a fish-abundant lake. The overall predation impact on the prey populations was stronger for Mesocyclops than for Thermocyclops. Mesocyclops had a strong and less selective impact on the rotifer community but a selective impact on the crustaceans. In contrast, Thermocyclops had a selective predation impact on rotifers but a weak and less selective impact on the crustacean community. As a result, the former predator reduced the diversity of the crustacean community but not the rotifer community, while the latter had an opposite impact on the diversities of the two communities. It has been suggested that fish induce development of a zooplankton community dominated by the small-sized zooplankton species in fish-abundant lakes. Our results demonstrated that cyclopoid copepods altered species composition and diversity of the small-sized zooplankton community in such lakes. Thus, the results have given an important suggestion on the role of the invertebrate predator cyclopoid copepods, which often coexist with fish, that they determine population dynamics and community structures of small-sized zooplankton in fish-abundant lakes. [ABSTRACT FROM AUTHOR]

Seedling survival and growth of two common Vallisneria species in China, Vallisneria natans and Vallisneria spinulosa were quantified experimentally for current velocities from 0 to 40 mm/s. At the same time, changes in the concentrations of three hormones (IAA, ZR, and GA3) in the leaves were compared to identify how current velocity influenced the two Vallisneria seedlings growth discrepantly. All plants survived in all treatments and showed positive growth. The most rapid growth for both species was found at the velocity of 10 mm/s. Although V. spinulosa showed faster growth than V. natans at the beginning of the experiment, there was no significant difference on final biomass. Higher IAA and ZR contents were measured in seedlings of both species grown under low current velocity. The time reaching the maximum for IAA and ZR was just around the time of a maximum seedling growth rate. IAA and ZR contents were positively correlated with growth rate. However, GA3 was negatively associated with growth rate and more GA3 in V. natans seedlings was induced by high current velocity. [ABSTRACT FROM AUTHOR]

Non-point-sources of nitrogen (N) and phosphorus (P) are recognized as major causes of eutrophication of surface waters. Adoption of policies to reduce pollution in the former German Democratic Republic following re-unification of Germany in 1990 provided an opportunity to examine how taking agricultural land out of production affected nutrient loads and aquatic biota in a small rural watershed. Between 1994 and 1996, soluble reactive phosphorus (SRP) and dissolved inorganic nitrogen (DIN) loads in a first-order agricultural stream decreased by >90% while instream concentrations decreased by 89% for DIN and 40% for SRP. This reduction in nutrients coincided with a decrease in precipitation (from 760 to 440 mm between 1994 and 1996) and an increase in the area of land set aside from agricultural production (from 0.3% in 1990 to a maximum of 8% in 1994). The biomass of primary producers (episammic algae) showed no clear response to this decrease in nutrient concentrations. However, benthic invertebrate composition shifted from a chironomid–amphipod to an oligochaete–gastropod dominated community in response to the decrease in DIN and changes in episammic algal abundance and sediment organic carbon concentrations. Results from our 4-year study showed reductions in soil nutrient losses combined with less precipitation resulted in less P and N in a rural stream and a change in benthic invertebrate community composition and abundance. [ABSTRACT FROM AUTHOR]

A specific landfill leachate that contained 1.036 mgl−1of 2-chlorobiphenyl was used in the study (255 mg l−1 COD and 133 mg l−1 BOD5). Three, 2-l semi-continuous batch reactors (SBRs) were used to simulate the treatment potential of this method on a small scale. Aerobic digestion effectively reduced the leachates COD concentration. Regardless of dilution, the leachates COD reached a <20 mg l−1 equilibrium after 96 h exposure to aerobic digestion, however, increasing the level of dilution accelerated the process. In untreated leachate, the LC50 for Asellus aquaticus was 57% v/v leachate in deionised water and 5% for Gammarus pulex (96 h, static LC50 tests without nutrition and oxygen depleting conditions). After being exposed to aerobic digestion, these values rose to 95% and 40%, respectively. Prolonged exposure to a 1:20 sub-lethal dilution of the aforementioned leachate has been previously shown to affect the breeding colony size of Asellus aquaticus and a 1:66 dilution influenced the fecundity of a Gammarus pulex population. After remediation by aerobic digestion, however, the population dynamics of both test species remained unaltered. [ABSTRACT FROM AUTHOR]

As part of a habitat restoration experiment wood substrates (red gum) were introduced to two lowland streams of SE Australia in which habitat has been severely degraded by deposition of sand eroded from higher in the catchment. We monitored net primary production (NPP) and community respiration (CR), nutrient concentrations and the succession of algae and invertebrates (abundance and species richness), sampling at 2, 4, 8, 12, 16 and 20 weeks. Colonisation by algae was rapid, and there were distinct changes in the assemblages over the first 4 weeks. Thereafter, changes were much less marked. There were also differences in nutrient concentrations and some measures of algal abundance between the two creeks. As with the algae, invertebrates colonised these substrates extremely rapidly, peaking in abundance and richness in week 8. Invertebrate abundances closely tracked changes in the abundance of algae. By the end of the study both algal and invertebrate communities were in apparent decline, with sharp decreases in invertebrate and algal abundance and invertebrate species richness. Rates of GPP also declined toward the end of the experiment, and this coincided with the detachment of large mats of filamentous algae and the recession of flows over the summer months. However, in both streams the added timber quickly created habitat with high levels of primary production in an otherwise strongly heterotrophic stream system. These hotspots of autotrophic production were quickly colonised by high numbers of macroinvertebrates indicating timber addition may provide an effective means of augmenting habitat for algae and invertebrates in sanded streams. [ABSTRACT FROM AUTHOR]

The River Nile is one of the world’s major rivers. Its’ catchment in Egypt has a population of 75,000,000. River flow is highly regulated and there are known discharges of pollutants. 1035 km of the river downstream of the Aswan high dam was studied to test the hypothesis that representative qualitative samples can be used to estimate macroinvertebrate biodiversity. Benthic macroinvertebrates are difficult to sample in large rivers and a reliable sampling strategy is required to evaluate their ecological status. Three methods for sampling have been investigated. Ekman Grab, macrophyte sweep netting and Artificial Substrate Samplers (ASS) were used to sample 15 sites from Aswan to Cairo between September 2001 and June 2002. Organisms were identified to species level where possible. Taxon accretion curves indicated that the all taxa present at a site should be collected using either 15 grab samples, 10 macrophyte samples or 5 ASS. The best time to sample was May–June. The biodiversity of macroinvertebrates in the Nile was recorded as 50 taxa with values of 7–31 at individual bank-side sites. Mid-stream biodiversity was much lower (0–19). Lowest biodiversity occurred at sites with known pollution inputs whilst highest occurred at sites with high levels of sedimentation. A regular programme for biomonitoring is recommended which will allow current status to be confirmed and future changes detected. [ABSTRACT FROM AUTHOR]

Feeding strategies are typical traits reflecting the adaptation of species to environmental conditions. This concept is currently developed in some water quality systems (e.g. Index of Trophic completeness) and the structure of functional feeding groups (FFGs) could form part of a unified measure across communities differing in taxonomic composition. However, in South America, information about the FFG classification of invertebrates in streams is almost absent and existing studies using FFG structure follows classification from North America. But even taxonomically related species may have different diets in tropical and temperate areas and therefore, studies about FFG structure in neotropics could be biased. For this reason, we determined diet composition, trophic level and FFGs, using gut contents analysis and mouthpart observations of 49 macroinvertebrate taxa (mostly at genus level) from neotropical streams. We observed that practically all macroinvertebrates fed upon fine detritus which indicates the importance of this food resource in neotropical streams. As the assignment to a single FFG does not accurately reflect the functional profile of taxa, we transcribed the affinity of taxa to each FFG using fuzzy codes. Finally, we published the coding of diet composition and FFG of the taxa examined, which could be used in future community analyses of lotic ecosystems in the Neotropical zone. [ABSTRACT FROM AUTHOR]

Small ponds ( ≤ 2 ha) are often a common landscape feature, but their ecology has been less well studied than that of lakes. Studies of some lakes and reservoirs show among-year repeatability in the seasonal abundance of different zooplankton (i.e., succession). For small ponds the seasonal dynamics of zooplankton community structure are relatively unstudied, as are any mechanisms underlying these dynamics. We took a community-level approach to studying the spring–summer abundance of zooplankton in two small Ohio ponds. In particular we wanted to know if repeatable patterns exist for zooplankton community structure in these ponds. We surveyed the spring–summer zooplankton communities in the ponds from 2001 to 2003 and used community-level ordination techniques (i.e., non-metric multidimensional scaling, NMDS) to characterize the assemblages. For both ponds the seasonal pattern of total zooplankton abundance differed significantly among years. We found that the proportional abundance of taxa across the season also varied among years. Elements of the zooplankton community, as described by the NMDS dimensions, showed among-year variation in the spring–summer trajectories that developed. Some of the variation in these zooplankton communities was associated with seasonal changes in water temperature. This among-year variation in the seasonal pattern of zooplankton community structure suggests that community dynamics in these small ponds may not be very repeatable. These complex dynamics of zooplankton thus challenges us to improve our characterization of zooplankton communities in small ponds such that we can better understand the factors that drive the patterns we observe. [ABSTRACT FROM AUTHOR]

Body density measurements were carried out on larval Artemia franciscana that had been held for 24 h at either 33 or 100‰ after hatching. Body density was low (1.0308–1.0342 g ml−1) by comparison with marine crustacean zooplankters or benthic freshwater crustaceans, and very stable, being only 0.3% higher in 100‰ than in 33‰. Vertical and horizontal swimming in 2nd instar larvae was studied at 8.5, 17, 34, 50, 100, 150 and 250‰ at 23 °C. At 8.5–50‰ downwards swimming was always significantly faster than upwards swimming, but in 100‰ downwards swimming was much slower than upwards swimming, indicating substantial positive buoyancy. At 150 and 250‰ downwards swimming was impossible. Horizontal swimming speed was unaffected by salinity over the range 8.5–100‰, but could not be studied at 150 and 250‰ as larvae could not leave the surface film. An asymptotic relationship between salinity and viscosity was found over the range 8.5–250‰. Calculations indicate a rise from 1.197 to 1.513 cp between 8.5 and 100‰, but this does not significantly impede horizontal locomotion. It appears that water column use by early stage Artemia larvae, that use a pair of 2nd antennae for rowing-type locomotion, is constrained by the increasing positive buoyancy associated with living at salinities above that corresponding to neutral buoyancy (approximately 48‰). [ABSTRACT FROM AUTHOR]

Substantial in situ measurements on clear days in a variety of marine environments at depths in the water down to 200 m have demonstrated the ubiquitous daytime presence of sun-related e-vector (= plane of polarization) patterns. In most lines of sight the e-vectors tilt from horizontal towards the sun at angles equal to the apparent underwater refracted zenith angle of the sun. A maximum tilt-angle of approximately 48.5°, is reached in horizontal lines of sight at 90° to the sun's bearing (the plane of incidence). This tilt limit is set by Snell's window, when the sun is on the horizon. The biological literature since the 1980s has been pervaded with assumptions that daytime aquatic e-vectors are mainly horizontal. This review attempts to set the record straight concerning the potential use of underwater e-vectors as a visual compass and to reopen the field to productive research on aquatic animals' orientation and navigation. [ABSTRACT FROM AUTHOR]

The planktonic period of planktotrophic veliger larvae from the nudibranch Dendronotus frondosus was characterized by laboratory culture methods. Larvae in culture successfully metamorphosed at 73–86 days after hatching. These veligers have Type 2 (Thompson) larval shells that significantly increased in length over the first 7–14 days after hatching. Direct observations of the development of nudibranch larvae with Type 2 protoconchs are limited, and these data help clarify previous attempts to correlate shell type and growth with minimum planktonic periods. Although these are not absolute values for the planktonic period of D. frondosus larvae, these data show the potential for extended larval dispersal and may help explain reports of an extensive geographic range in north-temperate waters for this species. [ABSTRACT FROM AUTHOR]

We assessed the role of macroconsumers (e.g. fishes and shrimps) in affecting the response of insect assemblages to a natural phosphorus gradient formed by six streams with different phosphorus levels (range 12–350 μg/l). We hypothesized that insect responses to the phosphorus gradient would be strongest in the absence of macroconsumers. Within each stream, macroconsumers were allowed access to, or were excluded from, leaf packs using electric `fences'. Macroconsumers did not have significant effects on insects, but there was a significant phosphorus effect. Insect assemblages in high-phosphorus streams had 3–12-fold greater biomass and 3–11-fold greater abundance than assemblages in low-phosphorus streams. We also found that insect responses to phosphorus were more variable when assessed on the natural benthic substrate (e.g. mixed detritus) than in standardized leaf packs. In both substrates, the relationship between insects and phosphorus was not linear: abundance and biomass increased with phosphorus concentration to an asymptote. This suggests that insects were responding to a food resource gradient (e.g. fungi and bacteria). The Michaelis–Menten model provided a good fit for the relationship between insects and phosphorus concentrations, with half-saturation constants ranging from 12 to 60 μg SRP/l. The asymptotic relationship observed between phosphorus and insects suggests that phosphorus saturation occurred above a threshold of ca. 100 μg SRP/l. Our results provide support for the hypothesis that detritus-based food webs are mainly controlled by bottom-up forces. [ABSTRACT FROM AUTHOR]

Benthic community data from eight stations around Pulau Semakau, an island south of Singapore, were collected during three surveys and analysed to determine changes in community structure under different sediment regimes resulting from construction activity at the eastern part of Pulau Semakau. Multidimensional Scaling (MDS) Configurations indicated distinct changes in the abundance, family number and diversity of benthic invertebrate fauna, which corresponded to sedimentation rate. SIMPER analysis suggested that polychaetes tolerate increased sedimentation better than crustaceans and molluscs. Sedimentation rate and other physico-chemical parameters were also investigated to determine the relationship between environmental factors and benthic community structure. Results from Principal Component Analysis (PCA) showed that sedimentation rate, sediment composition and ammonia concentration were the most important factors impacting the benthic community. [ABSTRACT FROM AUTHOR]

Terrestrial sediments transported off disturbed watersheds can threaten downstream estuarine and coastal environments. Practitioners in the field of environmental management need to be able to assess how activities that disturb the land are likely to impact on downstream estuarine and coastal receiving waters. Such assessments usually take the form of estimating risk, which has two components: the extent of undesirable consequences and the probability of occurrence of those consequences. The consequence in this case is primarily the ecological damage. In order to estimate risk, a methodology was developed around the use of a deterministic computational model of watershed/estuarine sediment transport. Model simulations are run which cover the physically realistic range of the controlling variables (e.g., wind speed, wind direction, sediment runoff). The model results are related to estuary damage and combined with the probability of occurrence for each scenario, providing a means of quantifying risk. In addition, answers to `long-term average', `most likely' and `worse case' type questions can be made. The procedure has the advantages of being easily implemented, transparent and repeatable. It is also more efficient than a standard Monte-Carlo procedure. The risk associated with changes in landuse can be examined without repeating model simulations. The example used to illustrate the method is that of a developing watershed in which proposed building activities are expected to alter the sediment yield to the downstream estuary during floods, which in turn is expected to smother shellfish beds. By elucidating risk associated with each development scenario, the management debate can be focused on choice of an acceptable risk level. [ABSTRACT FROM AUTHOR]

A review of the sediment budget concept, a brief history, cognate mass balances and the significance of the storage term. Questions of temporal and spatial scales, errors and uncertainties and the nature of system response. Management implications include natural hazards, climatic change and land use disturbance. [ABSTRACT FROM AUTHOR]

Twenty-nine Danish streams were investigated in September 1998. The streams drained catchments of varying hydrology, topography, soil type and land use. In each stream, the newly accumulated streambed sediment was sampled and subsequently analysed for pesticides. In each stream, five replicate macroinvertebrate samples were taken in the same sediments as the pesticide samples. In addition, five samples were taken in riffles to provide a complete picture of macroinvertebrate community composition. The number of detected pesticides reflected soil type and land use: in agricultural catchments on clay soils the average number of pesticides were 4.3±2.2; on sandy soils 2.6±1.0, while only 1.5±0.6 pesticides were found in streams without agricultural activities. The macroinvertebrate composition showed clear changes along this gradient of sediment pesticide concentrations. The number of the amphipod Gammarus pulex was negatively correlated with sediment pesticide concentration, while the number of Oligochaeta and Hirudinae was positively correlated. The findings indicate that pesticides have a potential to structure macroinvertebrate communities in Danish streams. However, agricultural impact is more than pesticides, and several other factors, such as channelisation, affect the macroinvertebrate community and these are not easily separated. [ABSTRACT FROM AUTHOR]

Cores of overbank deposits were collected from locations along the Rivers Swale and Aire in Yorkshire, U.K. The middle and lower reaches of the River Aire drain heavily industrialized and urbanized areas, whereas the River Swale drains a predominantly rural catchment, although Pb and Zn mining in the headwater areas in the 19th century introduced contaminated sediment. Downcore changes in the heavy and trace metal (Al, Cr, Cu, K, Pb, Sr and Zn) and phosphorus (P) content of the floodplain sediment were used to provide evidence of temporal changes in the contaminant content of the fine-grained sediment transported by the study rivers over the last ca. 100 years. The core collected from the downstream site on the River Aire shows upcore increases in P content, which reflects the expansion of the urban area during this period. Variations in the metal content of the deposited sediment over the period represented by the core reflect changes in the extent and type of industrial activity in the catchment. For the cores from the River Swale, there are no major upcore changes in the P content of the sediment, but there was a period characterized by increased levels of Pb and Zn which can be linked to metal mining activities. [ABSTRACT FROM AUTHOR]

A sampling programme was undertaken to monitor the total carbon (C) and total nitrogen (N) content of suspended matter in a small undisturbed upland drainage basin in the New Territories of Hong Kong. Mean C and N contents were 12.9% and 1.0%, respectively, for 132 samples. Samples collected under stable flow conditions had mean C and N contents of 12.8% and 1.1%, respectively. Stormflow samples had mean C and N values of 12.9% and 1.0%, respectively, which were very similar to the levels observed under stable flow conditions. The mean C: N ratios of 12.5 and 13.4 for stable flow and stormflow also reveal little variation with hydrologic conditions. When all the data is considered, little seasonal variation was observed in C and N. However, in winter there is a significant difference in C and N content between stable and stormflow samples. When C and N are plotted against water level, the scattergraphs suggest that as stage increases the percentage of C and N in the suspended matter declines. Scattergraphs of C and N against suspended sediment concentration reveal a negative association. This may reflect the dominance of inorganic sediments produced by erosion processes during rainfall. [ABSTRACT FROM AUTHOR]

Over a period of three years, the flux of particulate phosphorus to the sediment–water interface of Lake Kinneret was monitored by using seston traps deployed near the bottom of both accumulation and resuspension zones. The trap material was subjected to sequential phosphorus extraction. The obtained data set was compared to the phosphorus distribution in the surface layer of bottom sediments. Due to the sequence of drought years less allochtoneous phosphorous is reaching the lake resulting in a continuous decline of total particulate phosphorus (TPP) in the upper sediment layer. The observed decline in sedimentary TPP in spite of increased TPP sedimentation can be seen as a dilution effect due to the sedimentation of material with a relatively lower P content. The change in sedimentation can be seen as the result of increased resuspension at low lake levels. With sedimentary P in the littoral zone being unaffected by the drop in the external P load, the changes observed in the profundal zone appear to be driven by internal wave activity. [ABSTRACT FROM AUTHOR]

A model is presented, which describes the daily variations in suspended particulate inorganic matter (SPIM) in a large (61 km2), shallow (mean depth 3.4 m) wind-exposed lake basin at the western end of Lake Mälaren, Sweden. Field studies have shown that wind speed and river inflow are the two major factors leading to changes in SPIM. Wind speed and beam attenuation were measured at high (10 min) frequency, while river inflow were monitored at daily frequency to develop the model. From these field measurements, model-coefficients were determined for the SPIM transport, settling and resuspension. Large-scale variations in SPIM lasting many weeks could be explained by events of high river inflow with a correspondingly high particle load. The threshold for river transported SPIM to have effect on lake concentration was 150 m3 s-1, while wind induced resuspended SPIM was related to the square root of wind speed. [ABSTRACT FROM AUTHOR]

A survey on phytoplankton:zooplankton biomass ratios was performed in 342 Norwegian lakes, covering a wide range in lake size and productivity (total phosphorus: 3–246 μg l-1), but with most localities being oligo- to mesotrophic. Mean phytoplankton biomass was 88 μg C l-1, yet with the majority below 50 μg C l-1and a median of 25 μg C l-1. Total zooplankton biomass displayed a mean and median of 37 and 26 μg C l-1, respectively. Cladocerans were by far the dominant group, making up a median of almost 60% of total zooplankton biomass. Total zooplankton biomass as well as that of major aggregated metazoan taxa (cladocerans, calanoid copepods, cyclopoid copepods and rotifers) all showed a positive, but weak correlation with total phytoplankton biomass. These weak correlations suggest that algal biomass per se is a poor predictor of zooplankton biomass. An average phyto-:zooplankton biomass ratio (C:C) of 2.8 (SD±4.7) was found. 30% of the lakes had a phyto-:zooplankton biomass ratio below unity. While there was no correlation between the phyto-:zooplankton biomass ratio with increasing productivity in terms of P concentration, there was a higher biomass ratio in lakes with high fish predation pressure. The low ratio of phyto-:zooplankton biomass suggest major requirements from non-algal sources of C in the zooplankton diet. The need for dietary subsidizing is also supported by the fact that more than 75% of the lakes had algal biomass less than the estimated threshold for net positive growth of zooplankton, although it should be kept in mind that a high share of picoplankton would imply an underestimation of autotroph biomass in these lakes. Since the C-deficiency apparently is most pronounced in oligotrophic systems, it contradicts the view that the detritus pathways plays a predominant role in highly productive systems only, but while the source of detritus probably is mostly of autochthonous origin in eutrophic lakes, allochthonous detritus will be more important in oligotrophic systems. [ABSTRACT FROM AUTHOR]

Three short-term laboratory experiments were conducted to investigate allelopathic effects of a mixture of Chara globularis var. globularis Thuillier and Chara contraria var. contraria A. Braun ex Kützing on three different green algae. Single phytoplankton species were exposed to filtered water originating from charophyte cultures. Phytoplankton growth was monitored by determination of chlorophyll concentrations in batch cultures. The change in chlorophyll concentration during the experiments was analysed with a logistic growth model, resulting in an estimate of the exponential growth rate and the duration of the lag phase of the single green algae. The results indicate allelopathic effects of Chara on the growth of the green algae Selenastrum capricornutum Printz and Chlorella minutissima Fott et Nováková, whereas Scenedesmus obliquus (Turpin) Kützing did not seem to be affected. The exponential growth rate of S. capricornutum decreased 7% in the presence of water from a charophyte culture, while the growth rate of C. minutissima decreased with 3%. The allelopathic effect of Chara did not increase when the green alga C. minutissima was P-limited. The effect of Chara was different when young sprouts were used. With young sprouts the duration of the lag phase of C. minutissima was extended (25%), whilst for old plants the growth rate of this green alga decreased. Although the inhibiting effect of charophytes on specific phytoplankton species is rather small, the differential sensitivity of the species to Chara might influence the composition and biomass of phytoplankton communities in the field. [ABSTRACT FROM AUTHOR]

Thirty-six enclosures, surface area 4 m2, were placed in Little Mere, a shallow fertile lake in Cheshire, U.K. The effects of different fish species (common carp, common bream, tench and roach) of zooplanktivorous size, and their biomass (0, 200 and 700 kg ha-1) on water chemistry, zooplankton and phytoplankton communities were investigated. Fish biomass had a strong effect on mean zooplankton size and abundance. When fish biomass rose, larger zooplankters were replaced by more numerous smaller zooplankters. Consequently phytoplankton abundance rose in the presence of higher densities of zooplanktivorous fish, as zooplankton grazing was reduced. Fish species were also significant in determining zooplankton community size structure. In enclosures with bream there were significantly greater densities of small zooplankters than in enclosures stocked with either carp, tench and, in part, roach. When carp or roach were present, the phytoplankton had a greater abundance of Cyanophyta than when bream or tench were present. Whilst top-down effects of fish predation controlled the size partitioning of the zooplankton community, this, in turn apparently controlled the bottom-up regeneration of nutrients for the phytoplankton community. At the zooplankton–phytoplankton interface, both top-down and bottom-up processes were entwined in a reciprocal feedback mechanism with the extent and direction of that relationship altered by changes in fish species. This has consequences for the way that top-down and bottom-up processes are generalised. [ABSTRACT FROM AUTHOR]

Planktonic organisms exhibit diverse morphological, behavioural and life-history responses to the chemical presence of potential predators. Prey organisms have been found to sense such predators via predator-derived kairomones. The induced reactions are assumed to reduce predation risk and thus to be adaptive. Numerous studies have investigated various aspects of inducible defences in different crustaceans, in rotifers, planktonic ciliates and algae. As a first step, we summarise recent work on chemically induced anti-predator defences in morphology, life history and behaviour. Morphological defences have been found in a wide range of different plankton organisms and recent studies on predator-induced morphologies mainly addressed the question of costs for these changes. Life-history responses were mainly studied in cladocerans and several studies have recently addressed some novel topics, such as diapause induction and the influence of predator kairomones on hatching of resting stages. Behavioural anti-predator defences also have been found for several plankton species and are characterised by relatively fast induction times. We further identified four research directions in which substantial progress has been made recently: (I) The effects of simultaneous exposure to infochemicals from different predators and the consequences of a complex chemical environment. Some environmental contaminants, such as synthetic chemicals or heavy metals, have been found to potentially disturb natural chemical communication in aquatic predator-prey systems. (II) The influence of genetic variation on the reaction to infochemicals and its implications. Clonal differences have not only been found for the presence or absence of a certain trait but also with respect to the type of response. (III) The degree to which different types of responses to a specific kairomone are coupled. Recent studies underline the uncoupling of different anti-predator responses of which some have been considered to be coupled. (IV) Studies on the chemical properties and on the metabolic origin of predator kairomones. Substantial progress has been made recently, especially with respect to the identification of predator kairomones that are important for planktonic ciliates. The identification and isolation of kairomones are an important step towards studies addressing the consequences of predator-induced defences on the level of populations, communities and ecosystems. So far most studies have considered effects and consequences on the level of individual prey organisms and studies taking the consequences at higher ecological levels into account are rare. [ABSTRACT FROM AUTHOR]

In recent years, some studies addressing the modification of phenotypically plastic traits of Daphnia in the presence of chemical cues (kairomones) from invertebrate predators have reported a lack of trade-off among resource allocation of traditional life history traits (growth and reproduction) (Spitze, 1991; Black, 1993; Weber & Declerck, 1997). In this study, we term this finding the `Chaoborus paradox'. The Chaoborus paradox contrasts with the generally accepted theory that facultative changes in life history traits are associated with costs or a modification in resource allocation. In order to unravel the Chaoborus paradox, we have tested four groups of traits that may explain resource allocation. These were (1) the trade-off between present and future reproduction, (2) reduced growth of morphological features (body length, helmet length, spine length, carapace width) prior to maturity (pre-maturity) or (3) during the first adult instar (at maturity), and (4) an increase in feeding and assimilation rates to fuel the amount of resources available to the organism. As experimental animal we used Daphnia galeata (Cladocera) and to simulate invertebrate predation we used the Chaoborus (phantom midge larvae) kairomone. A clear trade-off existed between present and future reproduction. Survival was less in the presence of Chaoborus kairomone and therefore more resources could be channelled into growth and reproduction early in life at the cost of dying younger when compared to control animals. The other groups of traits (reduced growth of morphological features and an increase the amount of resources) offer partial solutions to the Chaoborus paradox for single clones only and not for the whole population. [ABSTRACT FROM AUTHOR]

Various approaches to modeling the population dynamics and demography of Daphnia have been published. These methods range from the simple egg-ratio method, to mathematically complex models based on partial differential equations and numerically complex individual-based Daphnia population models. The usefulness of these models in unraveling the population dynamics and demography of Daphnia under natural conditions is discussed. Next to this, an extended version of an existing individual-based Daphnia model is documented (Cladosim) and its application to a typical field data set collected in 1995 in Lake Volkerak is shown. To answer the question which factor was limiting Daphnia numbers during the course of the season food level and temperature in the model were varied and results were compared with those obtained for the observed food level and temperature. These analysis showed that in April temperature was limiting while during May–July and September–October food was limiting. In August neither temperature nor food was limiting. Analysis with a set of size-selective mortality scenarios showed that on average the Daphnia population in Lake Volkerak experienced a mild positive size-selective mortality during the year that was analyzed. Birth rates derived with the detailed individual-based model were compared with those derived with the much simpler egg-ratio method. For the conditions as observed in Lake Volkerak in 1995, both methods gave very comparable results, despite sampling intervals of up to four weeks. The same holds under the environmental scenarios. Using the size-selective mortality scenarios it could be shown, however, that under strong mortality of the smaller daphnids, the egg-ratio method severely underestimates the birth rate. The vices and virtues of the new model and potential extensions are discussed. [ABSTRACT FROM AUTHOR]