Nitrogen Fixation by the Photosynthetic Sulfur Bacterium Chlorobium phaeobacteroides from Lake Kinneret

N₂ fixation by Chlorobium phaeobacteroides from Lake Kinneret was dependent on ammonia concentration and light intensity. In the thermocline of Lake Kinneret, N₂ fixation and photosynthesis were low. It was concluded that the bacteria do not contribute significantly to the organic nitrogen load of the lake.     

Seasonal Rotifer Dynamics in the Long-term (1969–2002) Record from Lake Kinneret (Israel)

Long-term (1969–2002) data record of biomass distribution of rotifers in Lake Kinneret is combined with previously published information on their metabolic activity and newly calculated population dynamics parameters to synthesize a model of their seasonal dynamics in Lake Kinneret. Nineteen rotifer species were recorded in routine samples collected in Lake Kinneret (Israel) in 7 offshore (deeper than 5 m), stations, at 12 discrete depths during 1969–2002. Organisms were sorted and counted (including external egg carrying females), biomass was measured and calculated for the entire lake stock (g_w.w m⁻²; mg l⁻¹). Rates of grazing, respiration and production were measured experimentally at three different temperature ranges. Results were extrapolated to the lake community for months with similar temperatures. Rotifera comprised 7% of total zooplankton biomass in Lake Kinneret whilst Cladocera and Copepoda 58 and 35% respectively. Rotifers were found to be more abundant during December–June and decline in summer months. Monthly (1969–2001) means indicated total grazing capacity of rotifers as 11%, respiration as 9% and production as 3.7% of the total zooplankton metabolic activity. Positive relations were indicated between rotifer and small bodied cladoceran numerical concentrations. Population growth models suggest that rotifers are not food limited in Lake Kinneret but that fish predation plays an important role in regulating abundance in spring-summer and fall.     

Denitrification in Lake Kinneret in the presence of oxygen*

SUMMARY. Denitrification experiments under anaerobic and aerated conditions were carried out in the laboratory with Lake Kinneret water and with pure cultures of the denitrifying bacteria Pseudomonas aeruginosa 2 Kin isolated from the lake. Although losses of nitrogen in Lake Kinneret due to denitrification have been found to occur during periods when dissolved oxygen exceeded 5 mg l^?1 it was found that under aerated conditions glucose as a carbon source must be added in order to get denitrification in the laboratory. Disappearance of nitrogen during the experiments was due to denitrification as shown by the nitrogen balance calculated for each sampling. The ATP content showed that no proliferation of cells took place during the experiment. The rate of denitrification was strongly influenced by and was directly proportional to nitrate concentrations. Temperature has a very slight effect on the denitrification rate. Q₁₀ for the range 15–30°C was 1.35. The role of denitrification in the nitrogen balance of Lake Kinneret is discussed.     

The structure and dynamics of the phytoplankton assemblages in Lake Kinneret, Israel

The phytoplankton of Lake Kinneret, a warm monomictic lake,is dominated by a Pyrrhophyta-Chlorophyta assemblage. Four stagesof succession of planktonic algae occur in the lake, startingwith thermal and chemical destratification and ending with stratification. The index of diversity of the phytoplankton communities is highduring the destratification and mixed periods. The index reachesminimal values during late summer, when the ecosystem is subjectto strong physical, chemical and biological stresses. The diversityin Lake Kinneret increases with the increase in nutrients andnot with the increase in temperature. During most of the year, the nanoplanktonic forms are in greaternumbers than the netplankton species. This fact is correlatedwith the amounts of available nutrients in the lake. The annual averages of the wet autotrophic biomass in Lake Kinneretare very high in comparison with other warm lakes. The contributionof the nanoplanktonic species to the total algal biomass isvery small during the Peridinium bloom, but represents approximatelyhalf of the total algal biomass during the rest of the year. The concentration of nutrients in the water, together with theadverse competitive effect of Peridinium on other algae, areto a large extent responsible for the composition, successionand abundance of the phytoplankton assemblages in Lake Kinneret.     

Quantifying Ecological Stability: From Community to the Lake Ecosystem

We performed a methodological study aimed at extending our previously developed approach to quantify the ecological stability of biotic communities and an entire ecosystem, using Lake Kinneret as a case study. The ecological stability of the biotic communities (phytoplankton and zooplankton) of Lake Kinneret was estimated using two different aggregating schemes. The first scheme used the combined stability index, based on the combined indices of the individual phytoplankton (SI[Comb]_P) and zooplankton (SI[Comb]_Z) taxonomic groups. The total community stability index was calculated based on the total abundances of these communities. The stability of the entire ecosystem was estimated for two sets of ecosystem state variables, a lake “trophic state” set and a “water quality” set, which provided considerably different estimates of the lake ecosystem stability. Good agreement between the results of this study and qualitative estimates of Lake Kinneret stability validates the suitability of this approach to estimate the stability of different ecological units.     

Influence of temperature and body weight on mosquito predation by the dragonfly nymph Mesogomphus lineatus

Population densities, migrations and food composition of Echinogammarus veneris in Lake Kinneret were studied during march–September 1976. Migrations are affected by changes of water level and littoral currents. Peridinium was abundant in the gut content during its blooming period in the lake while cladocerans, benthic copepods, rotifers and other algae were abundantly found in other months. Metabolic parameters that were calculated for the gammarid population indicated that its contribution to the carbon-flow system in Lake Kinneret is negligible in comparison with nematodes, molluscans or planktonic copepods and cladocerans.     

Microbially — related redox changes in a subtropical lake 2. Simulation of metalinmetic conditions in a chemostat

The individual influence of sulfate reducing and brown phototrophic sulfur bacteria from Lake Kinneret on the metalimnetic redox conditions was investigated by simulating the hydrochemical and microbiological conditions in a specially designed chemostat. The results show a strong correlation between measured redox values and the prevailing hydrogen sulfide concentration leading to a linear relationship. Changes in this relationship allowed differentiation between the on-going microbial processes, sulfate reduction and sulfide oxidation. The comparison ofin vitro andin situ redox values shows that the results of the simulation experiments agree with the data previously measured in the metalimnion of Lake Kinneret.     

Food composition of Clarias gariepinus (= C. lazera) (Cypriniformes,Clariidae) in Lake Kinneret (Israel)

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.     

Food composition of the barbelTor canis (Cyprinidae) and its role in the Lake Kinneret ecosystem

Synopsis Gut contents of 294 individuals ofTor canis from Lake Kinneret (Israel), sampled throughout a full year indicated a wide trophic spectrum including 52 identified animal and plant species. Nevertheless a major part of ingested biomass (5.7 g per fish) was due to the Kinneret sardine (Mirogrex sp.). The biomass of other ingested organisms was relatively low (0.01–0.8 g per fish) consisting of planktonic organisms, zoobenthos, macrophytes and a few others. The role ofT. canis in the Kinneret ecosystem and management design is discussed.     

Holocene vegetation history of the southern Levant based on a pollen record from Lake Kinneret (Sea of Galilee), Israel

Lake Kinneret, also known as the Sea of Galilee and Lake Tiberias, is located in the northeast of Israel. At a lake level of 211 m b.s.l. (below mean sea level), the central basin is 43 m deep. The maximum length of the lake is 21 km (N–S) and its maximum width is 12 km (W–E). Lake Kinneret’s surface area is 166 km². A new 17.8 m long sedimentary core was drilled in 2010. Here, we present the entire palynological record from it, which covers the last?~?9,000 years. Special emphasis is given to the natural and human-influenced vegetation history of Galilee in comparison to that of the more southerly Dead Sea region. Significant signs of human impact are the first Olea (olive) increase during the beginning of the Chalcolithic period between 7,000 and 6,500 years ago, as well as the prominent Olea phase during the Hellenistic/Roman/Byzantine period between 2,300 and 1,500 years ago. Mediterranean macchia and bathas scrub vegetation, as known in the area today, has developed in the southern Levant under human impact since the last ca. 1,500 years.     

The effects of oils and oil components on algae: A review

Plate structure analysis of the bloom-forming Peridinium of Lake Kinneret (previously identified as P. cinctum fa. westii) established its identity as P. gatunense. Peridinium cinctum was not observed. Material from different years and periods of the bloom, as well as specimens from cultures and P. gatunense from Lago Cristalino (Brazil), were studied using light and scanning electron microscopy. Peridinium gatunense from Lake Kinneret showed slight differences of the plate pattern as compared with specimens from other localities.     

The effect of environmental factors on the nesting and courtship behaviour ofTilapia zillii in Lake Kinneret (Israel)

Tilapia zillii is a polyphilic, guarding nest spawner which is widespread in west and north Africa and in the Middle East. A study of the nesting and courtship behaviour of this species in Lake Kinneret (Sea of Galilee), revealed that nesting and brood care differ according to the exposure of the nesting site to wave action and the nature of the substrate. The nests are simple and parental care is abbreviated in exposed, sandy sites whereas elaborate nests with brood chambers are excavated in sheltered areas with clayey substrates, and parental care is extensive. The implications of these findings to studies on cichlid breeding and the conservation ofT. zillii in Lake Kinneret are discussed.     

Distribution,growth, production,and ecological significance of the clam Unio terminalis in Lake Kinneret,Israel

The distribution, body composition, growth rate, and population structure of Unio terminalis were measured at different sites of Lake Kinneret (Israel). Maximum clam density was found on the muddy sand between 0.3–6 m depth. Clams were most abundant in the River Jordan inlet zone, where they showed the highest growth rate. This was probably related to both highest food availability and the highest density of fish hosting Unio glochidia in this area. U. terminalis in Lake Kinneret has a more massive shell and ash content as compared with the European Unio species. The annual P/B ratios of U. terminalis populations at different sites were similar and ranged within 0.17–0.18. The computated filtration capacity and energetic budget permit the assumption that the U. terminalis population plays a substantial role in removal of organic particles from the water in the Kinneret shallow inshore zone (up to 15 m depth), and in nutrient recycling.     

Food composition and feeding habits of Astatotilapia flaviijosephi (Lortet) in Lake Kinneret (Israel)

Food composition and feeding habits of 102 specimens of Astatotilapia (Haplochromis) flaviijosephi (Lortet, 1883), collected in Lake Kinneret during 1973–1975 and 1981–1982, was studied. A. flaviijosephi is relatively abundant in the littoral zone of the lake. Females feed mostly on chironomid larvae, oligochaetes and amphipods whilst males consume mostly gastropods. Small fry are rarely preyed upon or collected by both sexes. The adaptive relation between the teeth and the type of food and the ecological status of A. flaviijosephi in the Kinneret ecosystem is discussed.     

Present–absent: a chronicle of the dinoflagellate Peridinium gatunense from Lake Kinneret

A long-term record dating back to the 1960s indicates that Peridinium gatunense, an armored dinoflagellate, dominated the phytoplankton of Lake Kinneret (Sea of Galilee, Israel) until the mid-1990s, with a relatively stable spring bloom. However, since 1996, these blooms became irregular, failing to develop in 10 out of the past 16 years. During the later period, a significant correlation (R ² = 0.605, P = 0.013) was found between annual peak P. gatunense biomass and riverine inflow volume. In-lake surveys showed that patches of high P. gatunense densities were associated with water enriched with fresher inflowing Jordan River water. Supplementing laboratory cultures of P. gatunense with Hula Valley water stimulated its growth relative to un-enriched controls. A likely explanation to the recent irregular blooms of this dinoflagellate is a hydrological modification that was made in the catchment in the mid-1990s, preventing Hula Valley water from reaching Lake Kinneret in most years—except for exceptionally wet years. We propose that until the mid-1990s, the Jordan River water enriched Lake Kinneret with a growth factor (a microelement and/or organic compound) originating in the Hula Valley, which in recent years has arrived in sufficient quantities to support a bloom only in high-rainfall years.     

Release of dissolved organic matter by photosynthesizing algae in Lake Kinneret,Israel*

The incorporation of inorganic carbon in particulate and dissolved organic matter by natural populations of photosynthesizing algae has been studied in Lake Kinneret, Israel, from August 1972 to December 1973. The release of dissolved organic material was directly related to the rates of particulate productivity. However, the percentage of extracellular release (PER) of dissolved organic compounds showed an inverse relationship with chlorophyll a concentrations. Mean PER values (for the trophogenic layer) over the experimental period were 3·7%, and were lowest during the exponential growth phase of the annual dinoflagellate bloom (mean PER = 1·9%). Highest PER were measured in deep, light-limited samples (mean = 31·7%; s.d.· 21·9%). In a dense metalimnic layer of photosynthetic sulphur bacteria (Chlorobium phaeobacterioides), PER was not as extremely high as has been reported for a similar layer in Lake Wadolek, Poland. Although the amounts of dissolved organic matter released by phytoplankton in Lake Kinneret were low, they may have significance as growth modulators and as substrates for heterotrophic organism.     

Food and feeding habits of Mirogrex fingerlings in Lake Kinneret (Israel)

The food composition of the fingerlings (13–41 mm TL) of Mirogrex terraesanctae terraesanctae was studied on specimen collected at four stations in Lake Kinneret. The fingerling feed mostly on pelagic zooplankters and zoobenthic forms whereas algae were found in the intestines in low biomass. The number of zooplankton organisms in the guts of the fingerling that were sampled during June–August was higher by 234% than in fingerlings that were sampled during March–April. The role of sardines fry in the Kinneret ecosystem is discussed.     

Visual versus non-visual selection of shell colour in an Israeli freshwater snail

Summary The Israeli freshwater snail Theodoxus jordani exhibits high variability both in shell colour and shell pattern.In most localities in Israel, more than 80% of the snails are black regardless of the colour of their background. Within Lake Kinneret, however, there is a significant association between the relative frequency of dark patterned shells and the distribution of a black (basalt) background.Predators of jordani include the fishes Barbus longiceps, Blennius fluviatilis, and the crab Potamon potamon. In Israel, the former two are limited in their distribution to the Kinneret. Thus, the distribution of cryptic variants of the snail is positively correlated to the distribution of some of its predators.Beyond the Kinneret, shells are black probably as a result of selection by the injurious effects of ultraviolet radiation. Within the Kinneret, snails can manage without an anti-radiation shield probably because the penetration of UV light into the water is considerably reduced, due to the daily summer storms and to the seasonal bloom of unicellular algae.Apparently, then, outside the Kinneret selective forces for crypsis are partly relaxed and their effects overidden by selective pressures for solar radiation devices; within the Kinnertt, selective pressures for anti-radiation devices are partly reduced and their effects overridden by selective pressures for crypsis.     

Characteristics of the introduced fish fauna of Israel

Fishes have been introduced worldwide with deleterious effects on various native ecosystems. To gain insight into this phenomenon in Israel, we studied the introduced ichthyofauna. There are 27 species of introduced fishes in the freshwater habitats of Israel, a large number for a nation this size. Ten of these species reproduce in the wild. Most of these fishes were introduced for aquaculture; some are constantly restocked. The proportion of restocked versus established species in Israel is high compared to other regions. New fish introductions continue in recent decades, unlike the global trend. In Israel these species are found in the Jordan Basin, Lake Kinneret (Sea of Galilee), and the coastal plain rivers. A few species are widespread, and most are found in Lake Kinneret. Harmful effects of introduced fishes have been suspected and in several cases demonstrated. We encourage further caution when new introductions are contemplated; in some regions eradication should be attempted.