Germination of Teliospores of Tilletia bardayana, the Causal Agent of Kernel Smut of Rice, in Relation to Some Physical Factors

Teliospores of Tilletia harclayana germinated equally well on the surface of 2 % water agar, soil extract agar and in cavities made in water agar. Maximum germination occurred at 29 °C under 12 h photoperiod with artificial daylight (cool fluorescent light). There was marked increase in germination when the teliospores in bunted grains were pre-treated for 30 min at 60 °C. Seventeen-week-old tehospores did not germinate while 73 week-old-tehospores showed retention of good germinability. Teliospores buried at 2 mm depth showed no germination whereas those at the moist surface germinated to produce sporidia. Implications of these results in the disease development are discussed.     

Space and time distribution of zooplankton in a Mediterranean lagoon (Etang de Berre)

In the Berre lagoon, a large brackish and swallow area near Marseille, the environmental factors (temperature, salinity, oxygen, suspended particulate matter and chlorophyll) generally display strong space and time variations. The rotifer Brachionus plicatilis and the copepod Acartia tonsa constitute the bulk of the zooplankton population during all the year. Their space and time distributions were studied in 23 stations distributed all over the lagoon, during four seasonal cruises (February, June, October, November), at surface and bottom layers. There is no marked difference in the horizontal and vertical distribution of the two species, (except in November when rotifers were prevailing in surface and copepods at depth) and in their time occurence. When the four series of data are pooled, correlation analysis show that A.tonsa is positively correlated with temperature, salinity and seston and negatively to oxygen and chlorophyll. B. plicatilis is positively correlated with temperature and seston, but also with chlorophyll, while salinity has a negative effect. The specific eggs number of both species is chlorophyll dependent. Considering seasonal cruises separately, some differences appear in the sense or the significance of these different correlations. The respective distribution of the two species is only partly dependent on the variation of the environmental factors: most of the variance remains unexplained, as indicated by the result of a stepwise multiple regression analysis using the most significant factors (temperature, salinity and oxygen explain 33 to 42% of the variance in Acartia, while temperature and salinity explain 27 to 28% of the variance in Brachionus). Thus, internal behavioral factors could also play a role in the distribution of organisms, particularly in some cases of aggregations of organisms observed during this study. As the two species occupied the same space habitat most of the year, they are potentially in competition for food. A way to optimize the food utilization could be the time separation of their feeding activity, nocturnal in Acartia and diurnal in Brachionus. Another way could be selective feeding upon food particles depending on their size (Brachionus being able to use finer particles than Acartia) or their quality (Brachionus being more herbivorous than Acartia) as demonstrated in some grazing experiments carried out in parallel.     

Seasonal changes in the biochemical composition of the freshwater cat-fish,Wallagonia attu (Bloch.)

Summary Seasonal changes in the various biochemical constituents of muscle, liver and gonads were studied in the cat-fish, W. attu. Distinct phases of high and low fat accumulation occurred in each tissue. Moisture in different tissues showed marked seasonal variations which were related inversely to the changes in the amount of fat. Seasonal fluctuation in protein was less pronounced in muscle and liver while in ovaries these were fairly well defined. Protein values in all the tissues were generally low during the winter. Ash content showed little variations in the three tissues. The seasonal cycles of various constituents in each tissue were correlated with the cycle of maturation and depletion of gonads. Different phases of maturation were associated with marked quantitative fluctuations of each ingredient in different tissues.     

Geographical and seasonal differences in morphology and dynamics of the coccolithophore Calcidiscus leptoporus

Calcidiscus leptoporus is a cosmopolitan coccolithophore species, composed of three morphotypes characterised by differences in morphology and size. The seasonal dynamics of this species have been studied in four sediment trap and plankton time series covering different biogeographic settings. Investigated parameters were: variations in absolute and relative abundances of the three morphotypes, average size variations of the C. leptoporus assemblages, and intra-morphotype size variations. For each time series, and for the complete data set, the relationship between C. leptoporus dynamics and some environmental parameters was investigated. Seasonal variations can be recognised in the four time series, but the biogeographic pattern governing this seasonality is complex. The two best documented morphotypes show comparable seasonal fluctuations in absolute abundances, mainly co-varying with temperature and related factors such as water mixing. However, their relative abundances change with varying nutrient contents in the surface water masses, suggesting slight differences in their respective ecological preferences. Average size of the C. leptoporus assemblage provides information about the morphotype composition and allows a comparison of the seasonal variations observed in the present study and Holocene geographic patterns reported in the literature. Additionally, intra-morphotype size variations might be related to environmental changes.     

Seawater temperature measured at the surface and at two depths (7 and 12 m) in one coral reef at Culebra Bay, Gulf of Papagayo, Costa Rica

Superficial seawater temperature (SST) and at two depths (7 and 12 m) were measured non-continuously during the study of the corals and coral reefs of Culebra Bay (1993-1996). SST showed seasonal variations of approximately 4 degrees C. The highest average temperatures (27.0 +/- 0.1, range 23-29 degrees C) were during the rainy season from May to November and the lowest (22.9 +/- 0.3 degrees C, 15.5-29 degrees C) during the dry season from December to April. Cold fronts with 2-3 degrees C differences in SST frequently pass into the bay and remain there for several hours according to the tidal cycles. Differences of approximately 3 degrees C between SST and the bottom (5-10 m depth) were usually found, particularly at locations where bottom topography and tidal circulation produced tidal bores. The average temperatures recorded by data loggers placed at 7 and 12 m depth on a coral reef at the outer shores of Culebra Bay, were 27.1 +/- 0.02 degrees C (20.5-31.6 degrees C) and 25.8 +/- 0.04 (9.9-31.5 degrees C) respectively. The seasonal pattern of higher and lower temperatures corresponds respectively to the rainy and dry season of the northern Pacific coast of Costa Rica. Water temperature at 12 m was < 14 degrees C for some hours during an upwelling event whilst minimum temperatures at 7 m were > or = 22 degrees C. Negative temperature anomalies coincided with an increase of the NE-E winds intensity and there is a lunar and tidal component which influence diumal variations of temperature. These results suggest that coral reefs built by branching species (e.g. Pocillopora spp.) in Culebra Bay could be limited by both the influence of cold fronts and by seasonal upwellings which affect negatively those coral species, as reported for other locations in the tropical eastern Pacific.     

Some observations on the food of the gwyniad Coregonus clupeoides pennantii Valenciennes of Llyn Tegid (Lake Bala), North Wales

The seasonal variations in the diet of adult gwyniad Coregonus clupeoides pennantii=C. lavaretus from Llyn Tegid, North Wales were studied. Stomachs were examined to determine fullness, volume and identity of contents.
A clear seasonal cycle in food intake was found. Feeding rates were low from January to April but increased during the summer (May-June) and remained at a high level until December. The period of low feeding intensity coincided with the time of spawning and the time of annulus formation of both scales and otoliths. The diet showed seasonal changes and two main periods were distinguished : December to July, when the fish fed mainly on bottom fauna, and August to November, when the diet included both bottom fauna and midwater and surface foods.
The gwyniad were shown to be opportunistic in feeding, the composition of the diet reflecting availability of food items rather than selective feeding on the part of the fish.     

High resolution measurements of sediment resuspension above an accumulation bottom in a stratified lake

A detailed record of suspended particulate matter (SPM) concentrations in the benthic boundary layer (BBL) 1.5 m above an accumulation bottom and 13.5 m below the surface was obtained from frequent (30 min interval) beam attenuation measurements made with a Sea Tech transmissometer in the main basin of Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. Concentrations of SPM (g m^–3) were not as strongly correlated to the beam attenuation coefficient (c, [m^–1]), as were concentrations of the inorganic SPM fraction. Apparently, this was caused by large optically inactive organic particles which significantly affected the measurements of SPM, but had little effect on the attenuation of light.When the water column was thermally stratified, SPM concentrations in the BBL showed a seasonal increase which was related to an increase in the thermocline depth. As the epilimnion deepened, there was also a marked increase in the occurrence of rapid and large changes in SPM concentration. After the loss of stratification, the amount of SPM and the temporal variability in its concentration was reduced. Since surface waves could not influence sediment resuspension at the depth of measurement, these data show the importance of internal waves in promoting sediment resuspension in areas of sediment accumulation. The relatively short period in each summer, when the thermocline reaches a sufficient depth to allow for resuspension over accumulation bottoms, can have important consequences for both the redistribution of lake sediments and the internal loading of phosphorus.     

Seasonal changes in the biochemical composition of the freshwater murrel,Ophicephalus punctatus Bloch

Summary Seasonal variations in various biochemical constituents in the tissues of Ophicephalus punctatus showed that. the fat content in the muscle was highest during November–January and lowest during June–October. Liver contained more fat than the muscle and its seasonal cycle was marked by two well defined peaks. Changes in the ovarian fat were also well defined seasonally. The moisture content in all the tissues varied inversely with the fat. Protein values in different tissues did not show as much fluctuations as fat. In muscle, protein remained high throughout the year except in January. In liver and gonads very low protein values were recorded during the winter months. Seasonal changes in the ash content were not very well marked in any of the three tissues.The seasonal variations in all the biochemical constituents seem related to the feeding intensity of the fish and the maturation of its gonads. Maximum and minimum values of fat fell in accordance with the high and low food intake. In the pre-spawning phase, more fat was stored in the muscle at first but subsequently the fat was mobilized in the liver and finally in the gonads. Peak ripeness was associated with an accumulation of greater protein and fat in the gonads (ovaries). During the spawning months the various constituents were depleted and the post-spawning phase of the fish was marked by minimal values of most of the biochemical constituents, excepting moisture and ash.     

Heavy metals in the Rosetta estuary of the Nile and the adjoining Mediterranean waters: evidence of removal of dissolved heavy metals from waters as a result of possible binding to suspended matter

The Rosetta estuary was partially separated from the Rosetta branch of the Nile by Edfina Barrage, which controls the Nile discharge into the Mediterranean Sea. The study area covers the Rosetta estuary (lotic environment) and the adjoining seawaters (lentic environment) to investigate the local and seasonal distribution of dissolved and particulate copper and zinc, as well as dissolved cadmium in this estuary and to illustrate its influence on the distribution of these metal forms in the inshore seawaters. Besides, emphasis on the removal of dissolved heavy metals from waters by their adsorption onto suspended matter (SM) was also considered. Contrary to particulate copper (PCu), the vertical values of dissolved copper (DCu) decreased generally with depth. Planktonic scavenging and regeneration processes might determine the vertical profiles of the copper forms. The copper data suggest that the surface sources of DCu exceeded the bottom sources, contrary to the sources of PCu. The markedly high and maximum seasonal averages of DCu in the estuary and inshore seawater in July inspite of the high uptake in summer possibly reflect higher amounts of humic materials. The lowest seasonal average value of DCu in the inshore seawater in January suggests removal of copper in presence of maximum value of SM during highest discharge. The highest regional average of DCu at the estuarine mouth coincided with desorption process during mixing of the fresh and salt waters. The vertical values of dissolved zinc (DZn) and particulate zinc (PZn) showed irregular variations and their high concentrations in the surface of the estuarine and inshore seawater indicate possible land-based sources. The high bottom DZn values, however, resulted from its contribution from the interstitial water of the sediments. The data suggest that the surface sources of DZn exceeded the bottom sources and PZn showed the opposite trend in the open sea area. In the estuary, the maximum seasonal average value of DZn accompanied by the lowest seasonal average of PZn in April inspite of the high uptake in spring suggest that desorption was the dominant process. The minimum regional averages of both zinc forms at the estuarine opening and the highest average of PZn near Edfina Barage are correlated with the amounts of SM, which decreased toward the estuarine mouth. The vertical values of dissolved cadmium (DCd) were much lower in the estuary than the other metals. They showed in both environments irregular variations with depth. The bottom maximum value of DCd can be attributed mainly to contamination from the sediments. There was a distinct seasonal variation of DCd. The minimum seasonal average value of DCd in the estuary in April seems to be caused by its specific binding to living plankton found in abundance. The minimum regional average of DCd value was found at the estuarine mouth. The decrease in Cd concentration due to removal from dissolved state is most pronounced in the early stage of mixing. The correlation coefficients of DCd were positive with salinity and negative with SM, indicating that Cd increased seaward. Statistical correlation between Cd and Zn concludes that the factors affecting their distribution are generally the same.     

大陈岛礁海域甲壳类群落结构时空格局及其环境驱动

为探究局地尺度下近岸岛礁海域之多变水体环境、极高空间异质性对生物群落的影响,于2020—2021年4个季度在大陈岛礁海域底拖网采样,利用等级聚类(cluster)、非度量多维标度(NMDS)等多元统计方法分析甲壳类群落结构的时空格局,并整合温度、盐度、深度等环境因子进行冗余分析(RDA)以解析影响因素,同时利用丰度生物量曲线(ABC)及W统计量评估群落稳态。结果显示：全年共采集甲壳类53种,隶属2目13科29属,虾类占总种类数的56.60%,种类数秋季(43种)>冬季(41种)>春季(31种)>夏季(26种)。优势种的季节更替明显,夏秋季以哈氏仿对虾(Parapenaeopsis hardwickii)、中华管鞭虾(Solenocera crassicornis)和三疣梭子蟹(Portunus trituberculatus)为代表的中大型经济种为主,冬春季则以双斑蟳(Charybdis bimaculata)和细巧仿对虾(Parapenaeopsis tenella)为代表的小个体饵料种为主,口虾蛄(Oratosquilla oratotria)在各个季节皆为优势种...     

A SHORT-TERM DEMOGRAPHIC STUDY OF CYSTOSEIRA OSMUNDACEA (FUCALES: CYSTOSEIRACEAE) IN CENTRAL CALIFORNIA1

Several demographic features were examined in the field over a period of eleven months for the subtidal alga Cystoseira osmundacea (Turner) C. Agardh at two localities near Monterey, California. This species showed a restricted distribution with depth, with peak average numbers of 3–4 plants per m² occurring at 6–8 m and forming a dense canopy on the surface of the sea. Below 10 m depth, there was a decline in the abundance of plants and also in the proportion of plants which bore seasonal fronds and reproductive tissue. Macrocystis pyrifera (L.) C. Agardh plants were also common at both localities. There was a negative correlation between the presence of this species and C. osmundacea at a scale of 1 m², but no correlation at 4, 9, and 25 m². Cohorts of C. osmundacea were mapped and tagged at one locality. The plants had markedly seasonal growth, with the greatest elongation of fronds occurring between March and June. Dense surface canopies and reproductive tissue were present during the summer months of June–August. These seasonal fronds were shed during September, leaving small perennial holdfasts and fronds. Plants were strictly dioecious, and there was a one-to-one ratio of male to female plants at both localities. Length-dry weight relationships showed that the largest plants had over 80% of their weight invested in seasonal fronds (vegetative plus reproductive tissue). Recruits of C. osmundacea at one locality appeared during September–November only in areas cleared to bare substratum. There was 15% survival of recruits between November and the following May, while 98% of the original mapped cohort survived for the 11 months of the study.     

Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources

Distinct seasonal variations in the abundance of photosynthetic microbiota and limpet grazing intensity were recorded at Port St Mary, Isle of Man between January 1994 and June 1996. Microbial abundance was negatively correlated with insolation stress, while grazing intensity was positively correlated with sea and air temperature. These patterns result in a mis-match between the supply of and the demand for microbial resources with maximal grazing intensity during the summer and autumn, but maximal microbial standing stock during the winter and early spring. The importance of top-down control of microbial assemblages by grazing was demonstrated by experimental exclusion of limpets during autumn 1993. This resulted in a four-fold increase in the abundance of cyanobacteria within 6 days, followed by a more gradual proliferation of ephemeral algae during the next 4 weeks. The abundance of diatoms remained relatively constant and was not influenced by the removal of grazers at this time of year. The influence of microbial resource availability on the growth and mortality of limpets was examined using experimental enclosures of differing densities of either Patella vulgata or P. depressa. After 6 months, there were significant relationships between grazer density and both mortality and growth with increased mortality and reduced growth for P. vulgata at increased densities, and reduced growth for P. depressa at increased densities. Hence, the availability of microbial resources may also influence the biomass of grazers on rocky shores from the bottom upwards. A conceptual model is presented which describes seasonal and annual variations in microbial resources and grazing intensity and their potential consequences for other shore dwellers.     

The near-bottom zooplankton at the abyssal BIOTRANS site, northeast Atlantic: composition, abundance and variability

The near-bottom zooplankton of the abyssal BIOTRANS site (water depth 4500 m was studied at two stations 11 nautical miles (nm) apart. Stratified sampling was conducted by means of a double MOCNESS at three depth layers 20, 50 and 100 m above bottom. The composition of the zooplankton showed a predominance of copepods, making up >50% of the total zooplankton abundance. Ostracods and chaetognaths were the most important non-copepods, displaying a slight increase towards the bottom. The variability of abundance and biomass was analysed statistically at different scales. Logarithmic coefficients of variation ranged from 29 to 187% for various taxa. Sampling at the two stations added significantly to the total variance for some taxa. By contrast, vertical gradients were mostly weak. Possible reasons for the observed variability are discussed.      

Changes in diatom assemblages in the profundal sediments of two large oligohumic lakes in eastern Finland

Sedimentary diatom assemblages in two large oligotrophic clear-water lakes were analysed, to assess their present ecological state and possible eutrophication due to diffuse nutrient loading. The lakes Pyhäjärvi and Puruvesi (Finnish lake district) are proportionally large for their catchment areas which accounts for their long retention times (ca 7 and 11 yr) and oligohumic character. Pyhäjärvi was studied by pairwise comparison of surface sediment diatom assemblages collected in 1985 and 1990 at 12 sites from different parts of the lake. In Puruvesi, the stratigraphy of diatoms was analysed in two short cores from 8 m and 32 m depths.The diatom assemblages of the two lakes are rather similar, and quite distinct from the assemblages of the mesohumic large lakes of the area. Cyclotella kuetzingiana is the most common planktonic dia- tom, but Aulacoseira ambigua abounds in Pyhäjärvi at sites with local sources of eutrophication. A diverse assemblage of benthic forms, especially Fragilaria and Achnanthes spp. characterizes the shallow bottoms in both lakes.There was little change within the short-core diatom profiles of Puruvesi, but the floral composition of the 8-m and 32-m sites differed markedly. The 8-m site, with 60–70% of benthic forms, represents illuminated bottom, on which much of the buried algae have lived in situ, while the deeper site is true profundal, dominated by sedimented planktonic algae.In Pyhäjärvi there was a slight increase in the benthic diatoms from 1985 to 1990, coinciding with increased phosphorus and chlorophyll concentrations as well as Secchi depth lowering. We interprete this observation as a very early step of eutrophication, of which first the sessile algal communities of the illuminated bottom areas have benefited.     

The depth distribution of Oligochaeta in an Irish quaking marsh

The depth distribution of oligochaetes was studied in a quaking marsh at Tinure, Co. Louth, Ireland. The dominant plants were grasses which formed a fibrous mat floating on semi-liquid peat. The water level remained near the surface except for a few weeks in winter and early spring when up to 50% surface cover of water was seen. Depth profiles of pH and redox potential showed seasonal variations with the anaerobic layer approaching the surface in summer. Oligochaetes were the most important group of invertebrates and were represented by 7 species of Naididae, 7 Tubificidae, 2 Lumbriculidae, 13 Enchytraeidae and 1 Lumbricidae. Lumbricids and most species of Enchytraeidae were concentrated at the surface but the enchytraeids Marionina riparia, Cernosvitoviella spp. and Cognettia glandulosa were frequent in the anaerobic layer. Aquatic oligochaetes were most numerous below the surface. Tubificids penetrated further than other groups and reached a peak at 4–6 cm. The effects of lowering the water level were studied in pot cultures where water was maintained at 4 different levels. Enchytraeids always remained near the surface, while aquatic oligochaetes concentrated nearer the water level. It is concluded that enchytraeids are prevented from colonizing most freshwater habitats by their inability to tolerate extended periods of anoxia.     

Observations on the effect of visual and olfactory ablation on the swimming behavior of migrating adult chum salmon,Oncorhynchus keta

The behavior of chum slamon,Oncorhynchus keta, was studied using ultrasonic telemetry in the waters off the Okhotsk coast of Hokkaido from 1979 to 1981. Thirty-six adult fish were outfitted with a 50 KHz ultrasonic transmitter provided with either a depth sensor, depth/illumination sensors, or depth/ temperature sensors. Twenty-one of the experimental fish were used as controls and left intact. Of the remaining fish, six had their sight destroyed, seven had their olfactory nerves severed or their nares filled with wax, one had both senses destroyed, and one had a sham operation, but had only a shallow transverse cut made in the skin over the olfactory nerves. Control fish and the fish with the sham operation initially swam in a horizontal zigzag pattern while fish with an obliterated sense swam in a similar pattern but to a reduced extent. The horizontal and vertical speeds of the intact fish were faster than those of the fish with a destroyed sense. Amplitude of vertical movements of the intact fish stretched from surface to bottom, while fish with destroyed vision tended towards midwater. Fish without an olfactory sense tended to be at the surface or near the bottom. Regular vertical movement would be effective in refreshing olfactory epithelia which might become acclimated when exposed to one odor. The vertical movements can be found in the horizontal zigzag movements in coastal and near shore migrations, as well as in the stream phase of homing. The zigzag movements, both horizontal and vertical, allow the fish to sense the water masses and locate the correct tributary.     

Trophic relationships and seasonal utilization of salt-marsh creeks by zooplanktivorous fishes

Synopsis In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result.     

The Water Relations of Pinus sylvestris III. Diurnal and Seasonal Patterns of Water Potential

The water potential (ψ) in twigs from four clones of Scots pine (Pinus sylvestris L.) growing in close proximity to each other was measured in a pressure chamber during five selected periods between May 1972 and March 1973. Diurnal and seasonal patterns of ψ are presented in relation to irradiance, air temperature and vapour pressure deficit (VPD) for one cloudy and one clear day in each experimental period. Significant differences in ψ were found amongst most of the clones. Larger amplitudes and earlier day-time minima in ψ were found during the summer than during the winter. Noon values of ψ of less than ?12 bars were regularly found during the summer months. Plots of ψ against irradiance or VPD during a day, showed marked hysteresis as the result of the simultaneous influence on ψ of several environmental factors. Close linear relations resulted when ψ was plotted against potential evaporation rate (calculated from the Penman-Monteith formula). The slopes of these regression lines, essentially the flow resistance, showed marked seasonal variations. At both high and low evaporation rates, the clone that grew the fastest had the lowest values of ψ, and the clone that grew the slowest had the highest values of ψ, while the other two clones had intermediate values. Differences in solute potential or in stomatal, plant or soil resistance are discussed as possible explanations of the more or less constant differences between the clones during the year of observations.     

Limnological investigations on the Rosetta branch of the Nile. I. Environmental conditions

SUMMARY.

• 1 Seasonal and local variations of some environmental conditions in the Rosetta branch of the River Nile are reported. The lowest air and water temperatures were recorded in January (winter) and the highest in July (summer). Slight decrease in water temperatures with depth is related to solar heating and mixing processes. The pH values, averaging between pH 7.5 and 8.2, showed seasonal changes which, in the main, may be related to photosynthesis.
• 2 The seasonal average chlorosity values showed very wide variation, due to fluctuations in the discharge rate of the River Nile and its effect on the estuarine sea water. Sharp increase in chlorosity values with depth at the estuarine stations was produced by the less dense river water, flowing over denser tongues of sea water. In January, however, the maximum discharge flushed out the sea water.
• 3 Minimum oxygen saturation values occurred in January and the highest values of dissolved organic matter were obtained in July. Both of these will be shown in a later publication to be related to phytoplankton abundance. Increase in dissolved organic matter near the bottom was common and is interpreted as due to the more complete decomposition of descending dead organisms and the release of organic matter from the bottom deposits.

     

Vertical Distribution of Archaea and Bacteria in a Meromictic Lake as Determined by Fluorescent In Situ Hybridization

The prokaryotic cells distribution in the water column of the coastal saline meromictic Lake Faro (Messina, Italy) was investigated by microscopic counting techniques. Water samples were collected at a central station from the surface to the bottom, when waters were characterized by a marked stratification. A “red-water” layer, caused by a dense growth of photosynthetic sulfur bacteria, was present at a depth of 15 m, defining a transition area between oxic (mixolimnion) and anoxic (monimolimnion) layers. Fluorescently labeled 16S rRNA oligonucleotide, group-specific probes were used to determine the abundance of Bacteria and Archaea, and their subgroups, Green Sulfur Bacteria (GSB), Sulfate Reducing Bacteria (SRB), Cyanobacteria and Chromatium okenii, and Crenarchaeota and Euryarchaeota, as key elements of the microbial community. Bacteria decreased from surface to bottom, while Archaea increased with depth and reached the maximum value at 30 m, where they outnumbered the Bacteria. Bacteria and picophytoplankton prevailed in the mixolimnion. At the chemocline high numbers of prokaryotic cells were present, mainly represented by Cyanobacteria, Chromatium okenii and Euryarchaeota. GSB, SRB, and Crenarchaeota prevailed below the chemocline. Although Archaea constitute a minor fraction of microbial community, they could represent active contributors to the meromictic Lake Faro ecosystem.