The impact of Temperature and other physical parameters on the size of planktonic organisms is widely known. The paper is focused on the impact of fish feeding habits on the phytoplankton and zooplankton body size in Lake Kinneret. The issue is comparatively considered with its implications in the marine environment. The study is relevant within the actual global trend of climate change of warming impact on freshwater and marine biota. Principal conclusion is that the planktonic organisms body size, in freshwater or marine ecosystems, is a dependant of complex interaction with significant impact of fish feeding habits. The most common species, the Bleaks, is a zooplanktivorous feeder through all its life cycle stages; Young stages (<5g) of Sarotherodon galilaeus are zooplanktivore whilst older stages are filter feeders which preferably utilize Peridinium if available but increased density of zooplankton prey was documented since late 1990’s after the decline of Peridinium availability. The complexity of the processes involved include chemical, physical and biological conditions which are prominently related to temperature and fish consumption.

Agmon is a small, shallow man-made lake (area: 1.1 km2; mean depth 0.45 m), excavated in the peat soils of the Hula Valley in northern Israel, that was filled with water in August 1994. We followed the seasonal variations in phytoplankton and metaphyton biomass, primary production and related environmental conditions between December 1995 and July 1997. Water temperature ranged between 9.5°C - 30.8°C; pH ranged between 7.2 - 8.6. The algae in Lake Agmon were characterized by seasonal alterations between summer-fall phytoplankton blooms and spring proliferation of benthic algal mats, with a winter clear-water phase. Chlorophyll a content in the water, as a measure of planktonic algal biomass, was low in winter (1.75 - 5 μg·L-1) and high in summer (>100 μg·L-1), when planktonic cyanobacteria (Microcystis spp.) bloomed. Metaphyton biomass varied between 3.5 and 970 g·dry·wt·m-2, with chlorophyll a content ranging from 5 - 701 mg·m-2. The dominant benthic algal genera were Spirogyra and Oedogonium in 1996 and Cladophora in 1997. Phytoplankton primary production was high in summer-fall, with a maximum of 1200 mg·O2·m-2·h-1. Benthic primary production was high from March till May, with a peak of 2173 mg·O2·m-2·h-1 in April 1997. The rate of benthic algal primary production was positively correlated to benthic chlorophyll a (r2 = 0.90). Diel measurements of water column dissolved oxygen (DO) concentration, conducted monthly from January to May 1997, revealed that DO concentration ranged from a nighttime minimum of 5.3 to a noon peak of 15.3 mg·L-1. Only during January to February, no significant changes in DO with depth were found, suggesting that at that time the water column was well mixed. The most salient feature of primary production in the lake was the seasonal partitioning between its benthic and planktonic components. This was most evident in the significant inverse relationship between benthic and planktonic primary productivity rates (r2 = 0.78).

An ecological project is proposed for the system of Lake Agmon (Hula Valley, Israel). The project indicates a change of the original concept of the Hula Project construction. Practically Lake Agmon system was found to remove negligible amounts of Nitrogen and Phosphorus from the Lake Kinneret budget. Moreover, Lake Kinneret ecosystem has undergone limnological changes. The P limited Kinneret system is currently N limited. Therefore reduction of P and enhancement of N from the Hula Valley outflow might be beneficial to the Kinneret ecosystem. Currently, the TN concentration in the Agmon outflow is lower than in its inflow and vice versa for P. Consequently, this paper recommends conveying peat soil drained waters, the Agmon inflow, directly to Lake Kinneret instead of letting the waters flow through Lake Agmon. Nitrogen reduction in Lake Agmon is due to de-nitrification and sedimentation and P increase is due to degradation of aquatic vegetation. Additional benefit of this change is the predicted improvement of the new infrastructure for the activity of aquatic birds aimed at eco-tourism improvement.

In this work, the thermal response of Mesocyclops ogunnus was experimentally studied. Temperature was the only one parameter that was tested. Other parameters, such as food quality and availability, light conditions, predation pressure, and water mass motions were not included in the study. Organisms were collected in Lake Kinneret and the experiments were carried out under diffused light, 12/12 hours light/dark conditions. In the experimental system, the organisms were exposed to different temperatures of 15℃, 25℃, 27℃, and 30℃ with open pathway to migrate according to temperature preference. The preference of upper thermal range (25℃, 27℃, 30℃) by copepodite and adult stages was documented.

Long term record (1933-2014) of Water Level (WL), nutrient concentrations, plankton densities, and temperatures in the epilimnion of Lake Kinneret was analyzed.The aim is to identify if water quality is deteriorated when the WL is low.It was found that water temperature increased and the composition and biomass of plankton communities were modified.Nitrogen and TDP decreased but TP slightly increased in the epilimnion during low WL conditions.The quality of epilimnetic water was not deteriorated and followed by a slight oligotrophism trend.

Until the late 1950s the Hula Valley, located between altitude of 170 masl in the northern part and 61 masl in the southern part, was covered by the old shallow Lake Hula (1.5 m mean depth; 1400 ha water surface); and 4500 ha of swamps partly or permanently were water covered. During 1950-1957 the old Lake Hula and the wetlands were drained and converted into agricultural usage. As a result of inappropriate agricultural management, a reclamation project (Hula Project, HP, 1990-1997) was implemented. A vertical plastic sheet (4.5 m deep) was placed along 2.8 km across the valley aimed at reduction of pollutants migration. This plastic barrier divided the valley into northern, organic, and southern mineral soil blocks. The HP was aimed at agricultural renovation together with prevention of water quality deterioration in the downstream Lake Kinneret. The chemical composition of the underground waters was monitored on a monthly basis in 14 drills and ground water table observation wells over the valley during 14 months. The Ground Water Table (GWT) in the northern part of the valley was shallower than in the south and seasonal fluctuation amplitudes were smaller in the north. Higher levels of TP, TDP, P-Ortho and particulate Phosphorus, TN and ammonium were documented in the southern underground waters. The level of nutrient concentrations in the south was probably enhanced by three factors: 1) accumulation by underground water migration; 2) eroded substances from the southern mineral soil; 3) intensive Evapo-Transpiration in the south. Due to the lower level of organic content in the south and in spite of possible underground accumulation no significant difference between southern and northern blocks was indicated for Nitrate (NO3) concentrations. Not like nitrates, the reduced nitrogen form of ammonium concentration in the undergrounds was higher in the south. It was suggested that the nutrient concentrations (dissolved and suspended) in the Southern underground waters were higher than those in the North as a result of water migration, which took over the plastic barrier underneath and/or aside while moving from north to south was resulted by the hydraulic gradient. This gradient was partly due to the topographic slope and partly to the intensive Evapo-Transpiration in this part of the valley, which also contributed to the decline of GWT.

ABSTRACT The food composition of Tristramella sacra (Gunther, 1864) in Lake Kinneret was studied. The gut contents of 126 specimens collected from all parts of the lake throughout a full year cycle were analyzed. It was found that organic detritus, zooplankton and phytoplankton are the major food sources. Seasonal changes of food composition and trophic adaptation of T. sacra to the conditions prevailing in the lake as well as the status of this fish in the Kinneret ecosystem are considered.

The feeding behaviour of the freshwater piscivore, Clarias gariepinus (C. lazera) (C & V 1840) was studied over two periods: 1973–1975 and 1981–1982, in Lake Kinneret (Israel). The total number of fish analysed was 264 and their sizes (SL) and weights varied between 238 and 830 mm (146 to 5728 g). More than fifty species of plants and animals from the plankton, benthos and nekton of Lake Kinneret were identified in the intestines of C. gariepinus. Preyed fish were the most abundant food component (81%) and constituted the highest biomass, with Mirogrex terraesanctae representing the majority (although other species were also found). The potential impact of piscivory in the Kinneret ecosystem is considered.

Long period analysis of Copepoda populations in Lake Kinneret indicated significant reductions in total biomass and production as well as densities of nauplii and adult stages, particularly females. The reduction of adult Mesocyclops sp. was statistically significant, but that of Thermocyclops sp. was not. Annual averages of eggs/female values and densities of copepodite stages did not show significant changes. Concentrations of adult Thermocyclops sp. became higher relative to the larger genus Mesocyclops sp. It is suggested that densities of large copepods were affected by intensification of predation pressure by particulate feeding fishes. The densities of nauplii were probably reduced by increased predation pressure of filter feeding fish.

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.

A method was initially suggested for the identification of zones where there are strong correlations between two distribution fields. The method was based on outlining areas where the gradients of the two fields are in the same or opposite directions. In the present study, correlation zones were optimized by varying the range of angles between gradients, simultaneously changing the correlation value and zone area. The major role was given to the correlation value: the zone area was maintained so that the optimized correlation zone was significant. The method was applied in an attempt to establish the interaction of spatial distribution of a grazer (Cladocera) and its food (nanophytoplankton) in Lake Kinneret (Israel), using data from multidisciplinary surveys carried out on 26 December 1991 and 13 May 1993. (C) 2003 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.

Zooplankton studies in Kinneret Limnological Laboratory started in 1968, and are still taking place. For 32 years the zooplankton communities have been routinely monitored by weekly and biweekly sampling at five to eight stations throughout the lake. In addition to long-term distribution monitoring, metabolic parameters and diurnal activities of woplankton were experimenrally measured. Routine monitoring revealed about five species of cyclopoid copepods and a calanoid copepod (a recent invader), seven cladoceran species and ca. 25 species of rotifers. The body size of all species was measured and incorporated into total biomass computation (Table 1). The food compositions (preferences) of herbivorous and predacious zooplankters were also studied (Tables 2 and 3). In this paper a comprehensive analysis of the trophic status of herbivorous woplankton communities in Lake Kinneret is presented, incorporating densities, biomass levels, food composition and metabolic activities. The analysis is part of cooperation between the Israel Oceanographic and Limnological

When a model can successfully predict, it is likely that it is based on a proper understanding of the system being modeled. Models are usually comprehensive and include a large variety of parameters. A small cornponent of freshwater ecosystern modeling the relationship between N and P availability and N,-fixing cyanobacteria bloorns, as illustrated using Lake Kinneret as an example is discussed below.

The Kinneret ecosystem has undergone significant man-made modifications. These include, among others: construction of the south dam (1932); drying of Hula Lake and swamps (1950s); salty springs diversion (1964); lake water salinity decline from 395 (1961) to 210 ppm chlorid; deepening of the Jordan River near Bnot-Yaacov bridge (1971) with consequent high loads of suspended matter; National Water Carrier (NWC) operation (1964); sewage removal and fishpond restriction in the catchment; implementation of the Hula Project (1994–1998); introduction of native and exotic fishes; an amplitude of water level fluctuations of 4.8 m. Natural fluctuations occurred as well: heavy floods with high nutrient loads in 1968/69 and 1991/92 and droughts in 1973, 1989–1991 and 1998–1999; 4.6 m water level fluctuations; low temperatures (12.3°C) and fish kill in 1971/72 and 1991/92; no mixing period in 1984; low (1975, 1996–1997) and high biomass of Peridinium (1994, 1998); N2-fixing cyanobacterium bloom (1994, 1995); high stock of Lavnun (Acanthobrama) fishes (1990s); zooplankton biomass decline (1969–1993) and increase afterwards. Although man made changes and natural environmental changes were significant, the lake ecosystem did not deviate from the level of resilient fluctuations and the classification of long-term instability in Lake Kinneret is probably an overestimation. In this paper I use long-term (31 years) distribution data of plankton, nutrients, and water level in Lake Kinneret to distinguish between resiliency and instability.

The hypothesis of the study states that two fluxes of bottom sediments, with opposite direction (to the shore and from it), are formed under the influence of hydrodynamic factors, first of all, the wave flow turbulence and energy of the waves. Under conditions of high hydrodynamic activity, this can cause redistribution of different size fractions of bottom sediments along the bottom slope. One can suppose that the effect may be proven for both nonliving particles and sessile living organisms. Experimental studies were carried out in the littoral zone of Lake Kinneret (Israel). The major factors affecting the benthic community (i.e. bottom sediments balance, variability of their granulometric size-composition in space and time, bottom turbulence, structure of waves and currents) were analyzed. The theoretical description and experimental evidence demonstrated that several parameters controlling sedimentation and resuspension had an effect on bottom community composition, and a consequent conceptual model was developed. The model describes the size fractionation of particles along the bottom slope, in connection with the slope steepness and height of the waves. The model forecasts are in a good agreement with the empirically evidenced distributions of both gravel sediments and inhabiting them molluscs. The results obtained provide an insight into the size structure and diversity of the benthic communities in Lake Kinneret, and their relationship to several components of the aquatic system.

1. Daphnia lumholtzi is a subtropical, Old World species which is rapidly spreading throughout reservoirs in the southern U.S.A. It was first recorded in Lake Texoma (Oklahoma–Texas) in September 1991.2. Southern U.S. reservoirs typically have strong spatial and temporal gradients in temperature, conductivity, turbidity and in the distribution of organisms. Therefore, the present experiments examined the reproductive and moulting rates, and survival of D. lumholtzi in relation to extremes of food concentration, temperature, conductivity and turbidity.3. Increases in temperature (range = 15–29 °C) and decreases in turbidity (range = 0.6–470 NTU) increased reproductive and moulting rates, whereas food concentration only affected the rate of reproduction, while conductivity had no effects. Survival was affected only by temperature.4. Daphnia lumholtzi tolerates high temperatures (27–30 °C) at which other cladocerans in Lake Texoma disappear. Therefore, D. lumholtzi may exploit resources in midsummer, when there are few potential competitors.

Kinneret, the only natural freshwater lake in Israel is operated like a mac-made reservoir since 1964. Top priority of lake utilization is given to water supply. The water budget of the lake is mostly controlled by the south dam and pumping through the National Water Carrier and by local consumers and regional utilization of water from rivers before entering the lake. The fishery is aimed at planktivorous species and stocking program include native and exotic fishes. Water quality improvement is achieved by creating high pressure of fish grazing on phytoplankton and low pressure on zooplankton together with fair income to the fishermen. Zooplankton decline and water quality deterioration were indicated during 1970-1993. Removal of zooplanktivorous noncommercial Lavnun (bleak) enhanced an increase Of zooplankton biomass which was accompanied by water quality improvement.