The influence of biomanipulations (fish removal) on the structure of lake foodwebs, case studies using the LakeWeb-model

This paper presents results on how intensive fishing (fish removal) islikely to influence the structure of lake foodwebs. The work is based on acomprehensive dynamic lake ecosystem model, LakeWeb, which accounts forproduction, biomasses, predation and abiotic/biotic interactions of nine keyfunctional groups of organisms: phytoplankton, bacterioplankton, two types ofzooplankton (herbivorous and predatory), two types of fish (prey and predatory),zoobenthos, macrophytes and benthic algae. The model uses ordinary differentialequations, the ecosystem scale and gives seasonal variations (the calculationtime is 1 week). It is designed to account for all fundamental abiotic/bioticinteractions and feedbacks for lakes in general for the nine target groups. TheLakeWeb-model has been calibrated and critically tested using empirical data andregressions based on data from many lakes. It has been shown that the model canclosely capture typical functional and structural patterns in lakes, whichshould give credibility to the results presented in this work. Obtaining suchresults using traditional methods, i.e., extensive field studies in one or a fewlakes, would be very demanding (in terms of money, persons involved and time).In this paper, results are presented for two lakes, one Swedish and oneBelarussian. The intensive fishing operations carried out in LakeBlacksåstjärn, Sweden, to reduce Hg-concentrations in fish did notsucceed. A typical cost of an intensive fishing is about 10,000–30,000 USDper lake of this size ( 0.25 km²). The costs toremove fish would be about 40–120 USD per kg ww fish removed! Intensivefishing simulated for Lake Batorino, Belarus, to reduce the fish biomass willlikely increase the prey fish biomass as long as the predation pressure on preyfish is lower than during the prefishing stage. The biomass of predatory fishwill recover only slowly. However, this operation is not likely to succeed inlowering the algal volume in lakes with a high biomass of predatory zooplankton.This is easy to state qualitatively and the LakeWeb-model offers a practicallyuseful tool to quantify such changes and identify lakes where biomanipulationsare likely to fail or succeed.     

Zooplankton–phytoplankton relationships in shallow subtropical versus temperate lakes Apopka (Florida,USA) and Trasimeno (Umbria,Italy)

This study compares and contrasts the dynamics of phytoplankton, zooplankton, and nutrients in two of the largest shallow lakes in the USA (Lake Apopka, Florida) and Europe (Lago Trasimeno, Umbria, Italy) and considers particularly the biomass ratio of zooplankton to phytoplankton (BZ:BP) in relation to nutrient levels and in the context of data from other subtropical and temperate lakes. Lake Apopka is hypereutrophic with higher concentrations of total phosphorus (TP), nitrogen (TN), and nearly an order of magnitude higher BP than Lago Trasimeno. However, combined data from the two lakes can be fit to a single log–log regression model that explains 72% of the variability in BP based on TP. In contrast, BZ has a significant positive log–log relationship with TP only for Lago Trasimeno, and is much lower than expected based on the TP concentrations observed in Lake Apopka. Lake Apopka has a fish assemblage that includes high densities of gizzard shad (Dorosoma cepedianum) and threadfin shad (D. petenense), similar to other eutrophic Florida lakes that also have extreme low BZ. The ratio BZ:BP is below 0.01 in Lake Apopka, 10-fold lower than in Trasimeno and among the lowest values reported in the literature. Although stress of high water temperature and a greater proportion of inedible cyanobacteria may be contributing factors, the collective results support an emerging view that fish predation limits the biomass of crustacean zooplankton in subtropical lakes. Handling editor: S. I. Dodson     

Predation-driven dynamics of zooplankton and phytoplankton communities in a whole-lake experiment

Summary 1. Species compositions of zooplankton and phytoplankton were followed in Tuesday Lake before and after experimental manipulation of its fish populations (addition of piscivorous largemouth bass, removal of planktivorous minnows). Plankton dynamics were compared to those of adjacent, unmanipulated Paul Lake, where piscivorous fish have been dominant historically. 2. Indices of similarity for the zooplankton communities in the two lakes in 1984 prior to the manipulation were low; however, following the manipulation in spring, 1985, similarity of the zooplankton in the two lakes rose considerably and remained high throughout 1986. This was the result of an increase in Tuesday Lake of previously rare large-bodied cladocerans (Daphnia pulex, Holopedium gibberum) which were the dominants in Paul Lake, and the disappearance in Tuesday Lake of the dominant small-bodied copepod Tropocyclops prasinus, a minor component of the Paul Lake zooplankton. These observations are consistent with prior observations of the effects of size-selective predation on zooplankton communities. 3. Phytoplankton communities also responded strongly to the manipulation, with similarity indices for the two lakes rising from low levels in 1984 to high levels of similarity in 1985 and 1986, reflecting the decrease of formerly dominant Tuesday Lake taxa which were unimportant in Paul Lake and the appearance or increase in Tuesday Lake of several taxa characteristic of the Paul Lake phytoplankton assemblage. these results clearly show that food web structure can have pronounced effects on community composition at all levels of the food web, and that, just as zooplankton communities are structured by sizeselective predation, phytoplankton communities are structured by herbivory. These observations may provide some insight into factors governing the complex distributions of phytoplankton species among various lakes.A contribution from the University of Notre Dame Environmental Research Center, funded by NSF grants BSR-83-08918 and BSR-86-06271     

Changes in the biota of Chany Lake along a salinity gradient

Relationships among salinity and diversity, abundance, biomass of major biological components of Chany Lake (western Siberia, Russia) are examined across a salinity gradient. As salinity increased from 0.8 to 6.4 g l⁻¹, the species richness of aquatic vascular plants decreased from 16 to 2 species, of phytoplankton from 98 to 52 species, and of zooplankton from 61 to 16 species, but changes in species diversity of zoobenthos were negligible. Guest Editor: John M. Melack Saline Waters and their Biota     

www.freshwaterecology.info – An online tool that unifies,standardises and codifies more than 20,000 European freshwater organisms and their ecological preferences

Species’ ecological preferences are progressively important for understanding distribution patterns, for conserving biodiversity or for assessing and evaluating the status of freshwater ecosystems. Comprehensive databases compiling species traits are already established in the terrestrial realm, but widely missing in freshwater science. We established a database for European taxa of five aquatic organism groups by compiling information on taxonomy, ecology and distribution based on extensive literature surveys, which were performed by experts for the targeted organism groups. The database includes fishes (654 taxa/21 ecological preferences), macro-invertebrates (8586/40), macrophytes (1083/5), diatoms (8868/36) and phytoplankton (1976/4). It is available online with various options and tools for finding information and has currently over 800 users. The reviewed literature as well as examples given in this paper, highlight the importance of the general availability of knowledge on ecological preferences for various aspects in ecological assessment. Freshwaterecology.info is considered a service for basic research, applied scientists, water managers or other stakeholders. It serves as base for bioassessment and monitoring.     

The role of solid waste materials as habitats for macroinvertebrates in a lowland dam reservoir

Eight hypereutrophic phytoplankton dominated ponds from the Brussels Capital Region (Belgium) were biomanipulated (emptied with fish removal) to restore their ecological quality and reduce the risk of cyanobacterial bloom formation. Continuous monitoring of the ponds before and after the biomanipulation allowed the effects of the management intervention on different compartments of pond ecosystems (phytoplankton, zooplankton, submerged vegetation and nutrients) to be assessed. Fish removal resulted in a drastic reduction in phytoplankton biomass and a shift to the clear-water state in seven out of eight biomanipulated ponds. The reduction in phytoplankton biomass was associated with a marked increase in density and size of large cladocerans in six ponds and a restoration of submerged macrophytes in five ponds. The phytoplankton biomass in the ponds with extensive stands of submerged macrophytes was less affected by planktivorous fish recolonisation of some of the ponds later in the summer. The two non-vegetated ponds as well as one pond with sparse submerged vegetation showed a marked increase in phytoplankton biomass associated with the appearance of fish. Phytoplankton biomass increase coincided with the decrease in large Cladocera density and size. One pond lacking submerged macrophytes could maintain very low phytoplankton biomass owing to large Cladocera grazing alone. The results of this study confirmed the importance of large zooplankton grazing and revegetation with submerged macrophytes for the maintenance of the clear-water state and restoration success in hypereutrophic ponds. They also showed that large Cladocera size is more important than their number for efficient phytoplankton control and when cladocerans are large enough, they can considerably restrain phytoplankton growth, including bloom-forming cyanobacteria, even when submerged vegetation is not restored. The positive result of fish removal in seven out of eight biomanipulated ponds clearly indicated that such management intervention can be used, at least, for the short-term restoration of ecological water quality and prevention of noxious cyanobacterial bloom formation. The negative result of biomanipulation in one pond seems to be related to the pollution by sewage water. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Asymmetrical food web responses in trophic-level richness, biomass, and function following lake acidification

We tested for disproportional changes in annual and seasonal species richness and biomass among five trophic levels (phytoplankton, herbivorous, omnivorous, and carnivorous zooplankton, and fish) as well as altered trophic structure and ecosystem function following the 5-year experimental acidification of Little Rock Lake (Wisconsin, USA) from pH 6.1 to 4.7. Abiotic and biotic controls of trophic level response during acidification were also identified. Asymmetric reductions of species richness among trophic levels, separated by life stage and feeding type, were evident and changes in trophic structure were most pronounced by the end of the acidification period. Relative declines in richness of fish and zooplankton were greater than phytoplankton, which were generally unaffected, leading to a reduction of upper trophic level diversity. Each of the lower four trophic levels responded to a distinct combination of abiotic and biotic variables during acidification. pH was identified as a direct driver of change for only carnivorous zooplankton, while all other trophic levels were affected more by indirect interactions caused by acidification. Fluctuations in ecosystem function (zooplankton biomass and primary production) were also evident, with losses at all trophic levels only detected during the last year of acidification. The acidified basin displayed a tendency for greater variation in biomass for upper trophic levels relative to reference conditions implying greater unpredictability in ecosystem function. Together, these results suggest that trophic asymmetry may be an important and recurring feature of ecosystem response to anthropogenic stress.     

Relationships among nitrogen and total phosphorus,algal biomass and zooplankton density in the central Amazonia lakes

The relationship among concentrations of total nitrogen (TN), total phosphorus (TP), algal biomass (Chl) and the density and size of individuals of the zooplankton community were studied for the dry season (November 1999–January 2000) at 20 lakes of the Central Amazonia. The study was conducted along a productivity gradient to identify the existence of resource or predator-dependent patterns on the primary producers of the trophic web. A strong positive relationship was observed between the log Chl and TN (r ² = 0.88, P = 0.000) and to log Chl and log TP (r ² = 0.85, P = 0.000) in a simple linear regression. However, when both variables were running together in a multiple regression, TN alone explained every variation of algal biomass (r ² = 0.89, P _TN = 0.022, P _TP = 0.233). The total density of the zooplankton showed a positive correlation with log Chl (r ² = 0.53, P = 0.000) and the large zooplankton (>0.5 mm) was found to be a more positive function of the phytoplankton (r ² = 0.65) than the density of the small ones (<0.5 mm, r ² = 0.44). Results show that complex food web interactions could be responsible for patterns in tropical systems. We contend that Chl variation in tropical lake systems is controlled by TN and TP, but the predictor power of the TN increase the fit of the model in analysis and can be use alone to access the variability in algae biomass to Amazonian tropical lakes. We also agree that the density of large zooplankton individuals is regulated by the biomass of primary producers. Hence we concluded that the resource-dependent hypothesis is supported in these systems. Handling editor: J. Padisak     

Plankton community and the relationship with the environment in saline lakes of Onon-Torey plain,Northeastern Mongolia

The plankton community of sixteen saline lakes located on Onon-Torey plain (Northeastern Mongolia) during the filling phase and the raising of the water level was investigated in July 2011. Thirty-five taxa of phytoplankton and thirty-one species of zooplankton were found. For phytoplankton, blue-green algae (Merismopedia elegans, Anabaenopsis elenkinii, Arthrospora fusiformis, Spirulina major, Lyngbya sp., Oscillatoria sp.) and green algae (Monoraphidium minutum, Tetrastrum komarekii, Ankyra ocellata, Oocystis sp.) were dominant. For zooplankton, Filinia longiseta, Brachionus plicatilis, B. variabilis, Hexarthra mira (Rotifera), Daphnia magna, Moina brachiata, M. mongolica (Cladocera), Arctodiaptomus bacillifer, Mixodiaptomus incrassatus, Metadiaptomus asiaticus (Copepoda) dominated. Mineralization, active hydrogen ratio, dissolved oxygen and water temperature were the main factors influencing the diversity, structure and distribution of plankton organisms in the steppe lakes during low water level. The RDA analysis for phytoplankton and zooplankton from different lakes was carried out for selected two groups which included lakes and a subset related species. The first group is of oligohaline and mesohaline lakes in which mostly green algae, rotifers and copepods inhabit. The second group is of mesohaline and polyhaline lakes with mainly blue-green algae, some crustaceans and rotifers inhabiting. High abundance and biomass of Spirulina major, Oscillatoria sp. and Brachionus variabilis were observed in lakes with high mineralization, pH and temperature.     

Study of biocomplexity in an aquatic ecosystem through ascendency

The ascendancy concept aims at quantitatively describing the growth and development of an ecosystem as whole. Growth is an increase in the total system throughflow, while development is taken to be a rise in the average mutual information inherent in the network flow structure. As an ecosystem matures and goes through a series of successional stages, its ascendancy exhibits a propensity to increase. In any ecosystem the equilibrium condition may gradually turn into a chaotic situation for different reasons. In this paper a model is proposed of an aquatic ecosystem comprising of three groups, viz., phytoplankton, zooplankton and fish. Rate parameters are changed according to the change of the size of the organisms. The model is run in different conditions with gradual decrement of the body sizes of zooplankton. Allometric principle of the relationship of body size of zooplankton and two rate parameters (growth rate and half saturation constant) are incorporated in this model. According to allometric principle gradual decrement of body sizes of zooplankton consequently increases the grazing rate and decreases the half-saturation constant of this organisms. The system exhibits different states (equilibrium point--stable limit cycle--doubling and ultimately chaos) by gradual increase of zooplankton grazing rate and decrease of half-saturation constant. This paper tests the high level of ascendancy of the systems at the edge of oscillation before starting of the chaos. This high level of throughflow and mutual information, i.e. Ascendency supports the hypothesis that the system can coordinate the most complex behavior and shows maximum biocomplexity in this situation.     

有害赤潮藻对浮游动物影响的研究进展

有害赤潮藻对浮游动物的影响在赤潮危害的研究中越来越受到关注,本文综述了有害赤潮藻对浮游动物的毒害作用,主要表现为影响浮游动物的存活和生长,降低母体的产卵力、卵的受精率或受精卵的孵化率以及减慢胚胎发育或造成畸形,影响幼体的正常发育,抑制浮游动物的摄食和改变其正常行为等;这些毒害作用主要是由赤潮藻产生的藻毒素或其它一些胞外渗出物通过降低浮游动物对食物的利用率、造成生理损伤、破坏细胞膜、降低亲体产生的配子质量、抑制有丝分裂和胚胎发育等造成的．某些赤潮藻营养成分单一如缺乏多不饱和脂肪酸,也会对浮游动物的生长繁殖产生影响．     

Impacts of environmental scenarios on chlorophyll-a in the management of shallow, eutrophic lakes following biomanipulation: An application of a numerical model

Accurate prediction of species changes in lake ecosystems following biomanipulation measures is of paramount importance in view of water quality management. The temporal variation of phytoplankton biomass as chlorophyll-a and transparency as Secchi depth measurements are studied in the Lake Bleiswijkse Zoom, The Netherlands, with a comprehensive structural dynamic model. In the formulation of the biological model, phytoplankton as several species, zooplankton, detritus, planktivores and benthivores, and piscivores are considered to be major contributing state variables for the model. The primary goal of this paper is to describe the possible impacts of several environmental scenarios on chlorophyll-a biomass qualitatively as it would help lake and environmental managers and relevant authorities elucidate the processes of eutrophication and biomanipulation in a broad way. Some of the scenarios that have been studied by this model are: (1) The effect of fixed stoichiometry in terms of internal nitrogen and phosphorus that are tied up within algal cells; (2) the effects of external phosphorus limitation; (3) light limitation and external nitrogen limitation on algal growth; (4) probable consequences that have taken place within the chlorophyll-a biomass due to change in biomasses of various aquatic organisms; and (5) possible changes of chlorophyll-a biomass due to higher temperatures caused by global warming.     

Origin and trophic importance of detritus-evidence from stable isotopes in the benthos of a small,temperate estuary

Ratios of ¹³C/¹²C and ¹⁵N/¹⁴N were measured in dissolved inorganic carbon (DIC), marginal vegetation, benthic macrodetritus (diameter > 1 mm) and selected invertebrate consumers in the Gamtoos estuary, South Africa to: (1) trace the provenance of benthic detrital deposits, and (2) determine the extent to which three abundant species of macroinvertebrates utilise this resource. DIC was strongly depleted in ¹³C with average ¹³C values (–9.5±0.5) being typical of limnetic waters. Benthic detrital particles (¹³C–24.1±0.3) originated mainly from marginal vegetation (¹³C–25.7±0.3), but their slightly elevated carbon ratio suggests additional input from ¹³C-rich sources-possibly C₄ plants cultivated on the floodplain. Populations of the fossorial ghost shrimp Callianassa kraussi, the bentho-pelagic amphipod Grandidierella lignorum and the epifaunal crab Hymenosoma robiculare together account for 96% of total benthic biomass in the upper regions of this estuary. Marked differences in trophic niches were evident among these three consumer species. Ghost shrimp (¹³C –32.5±0.3) foraged by filter-feeding on fine suspended particulate organic matter (¹³C–31.2±0.5). Amphipods (¹³C–28.0±0.6) utilised some benthic detritus but fed mainly on suspended material. Only the relatively rare crabs (¹³C–23.8±1.5) appeared to utilise benthic detrital particles to any significant extent. In the benthic consumer community of the upper Gamtoos estuary, suspension feeders make up 98% of biomass and thus clearly dominate over deposit feeders. This can be traced to the low contribution of higher plants (c. 13%) to overall carbon production, and detritus originating from macrophytes is consequently relatively unimportant in supporting invertebrate secondary production in this particular system.     

Effects of an artificial protection structure on the sandy shore macrofaunal community: the special case of Lido di Dante (Northern Adriatic Sea)

Biomanipulation of eutropicated peaty lakes has rarely been successful; clear water with dense macrophyte stands fails to develop in most cases. It was unclear whether (1) high turbidity due to resuspension by benthivorous fish or wind is the major cause of low macrophyte density or whether (2) the establishment of submerged macrophyte stands is prevented by a lack of propagules, low cohesive strength of the lake sediment, high concentrations of phytotoxics, grazing by waterfowl and/or shading by periphyton growth. These hypotheses were tested in an experiment in a shallow peat lake in the Netherlands (Terra Nova). Removal of fish from a 0.5 ha experimental site resulted in clear water and the development of a dense (90% coverage) and species-rich (10 species) submerged vegetation. At a fish-stocked site and a control site the water remained turbid and dense macrophyte stands did not develop. The establishment of submerged macrophytes appeared not to be limited by a lack of propagules. Introduced plants grew poorly in turbid water, but very well in clear water. Exclosures showed that bird grazing reduced the plant biomass. In clear water grazing seemed to enhance the vegetation diversity. Periphyton development did not prevent plant growth in clear water. After the experiment, the fish stock was greatly reduced in the whole lake (85 ha), to test if (3) in a large lake, submerged macrophyte stands will not develop after biomanipulation. In the first season after fish reduction, transparency increased and species-rich submerged macrophyte stands developed, covering 60% of the shallow parts of the lake. Most of the species known to have occurred in the past re-established. The results indicate that high turbidity caused by benthivorous fish in combination with bird grazing were the major causes of the absence of submerged macrophyte stands in this lake. Abiotic conditions after the clearing of the lake were suitable for the growth of macrophytes. We infer that the restoration potential of submerged macrophyte stands in eutrophicated peaty lakes can be high, and results can be obtained quickly.     

广东典型小型供水水——-契爷石水库浮游生物与富营养化特征分析

于2000年丰、枯水期对契爷石水库的理化因子,浮游生物种类组成,细胞密度等进行了调查研究,并利用有关评价指数对该水库水体的营养水平进行了评价。结果表明,契爷石水库目前已进入富营养化状态,且枯水期较丰水期富营养化程度更为严重,另外,全年有机污染也比较严重。浮游植物丰水期以蓝藻、绿藻为主,枯水期以蓝藻、硅藻为主,该水库属于典型的蓝藻-绿藻-硅藻型水库,且有较高丰度的耐有机污染的裸藻所在。浮游动物以轮虫和桡足类为主,轮虫主要以耐有机、喜富营养的萼花臂尾轮虫（Rrachionus calyciflorus）、前节晶囊轮虫（Asplanchna priodonta）、螺形龟甲轮虫（Keratella cochearis）为主,挠足类主要以无节幼体,桡足幼体为主,成体很少,且主要以剑水蚤为主,喜寡营养的哲水蚤在该水库中没有出现,枝角类种类,数量都很少,多为广温型、嗜暖型种类,其中长额象鼻蚤（Bosmina longirostris）和微型裸腹蚤（Moina micrura）习居于富营养型水体中。     

A hitchhiker's guide to European lake ecological assessment and intercalibration

The Water Framework Directive is the first international legislation to require European countries to establish comparable ecological assessment schemes for their freshwaters. A key element in harmonising quality classification within and between Europe's river basins is an “Intercalibration” exercise, stipulated by the WFD, to ensure that the good status boundaries in all of the biological assessment methods correspond to similar levels of anthropogenic pressure. In this article, we provide a comprehensive overview of this international comparison, focusing on the assessment schemes developed for freshwater lakes. Out of 82 lake ecological assessment methods reported for the comparison, 62 were successfully intercalibrated and included in the EC Decision on intercalibration, with a high proportion of phytoplankton (18), macrophyte (17) and benthic fauna (13) assessment methods. All the lake assessment methods are reviewed in this article, including the results of intercalibration. Furthermore, the current gaps and way forward to reach consistent management objectives for European lakes are discussed.     

Above- and belowground competition between two submersed macrophytes

Several studies have shown that submerged macrophytes provide a refuge for zooplankton against fish predation, whereas the role of emergent and floating-leaved species, which are often dominant in eutrophic turbid lakes, is far less investigated. Zooplankton density in open water and amongst emergent and floating-leaved vegetation was monitored in a small, eutrophic lake (Frederiksborg Slotssø) in Denmark during July–October 2006. Emergent and floating-leaved macrophytes harboured significantly higher densities of pelagic as well as plant-associated zooplankton species, compared to the open water, even during periods where the predation pressure was presumably high (during the recruitment of 0+ fish fry). Zooplankton abundance in open water and among vegetation exhibited low values in July and peaked in August. Bosmina and Ceriodaphnia dominated the zooplankton community in the littoral vegetated areas (up to 4,400 ind l^?1 among Phragmites australis and 11,000 ind l^?1 between Polygonum amphibium stands), whereas the dominant species in the pelagic were Daphnia (up to 67 ind l^?1) and Cyclops (41 ind l^?1). The zooplankton density pattern observed was probably a consequence of concomitant modifications in the predation pressure, refuge availability and concentration of cyanobacteria in the lake. It is suggested that emergent and floating-leaved macrophytes may play an important role in enhancing water clarity due to increased grazing pressure by zooplankton migrating into the plant stands. As a consequence, especially in turbid lakes, the ecological role of these functional types of vegetation, and not merely that of submerged macrophyte species, should be taken into consideration.