Abundance, distribution and age structure offish populations in a Western Australian estuary

Beach seines, gill nets and otter trawls were used during 1979–81 to sample extensively the fish fauna of the Peel-Harvey estuarine system. Approximately 145,000 individuals were caught, representing 29 familes and 55 species. The Clupeidae, Teraponidae, Mugilidae, Apogonidae, Atherinidae and Gerreidae were the dominant families, each contributing at least 8.9% to the total catch and together contributing 86.2%. Seasonal catch data and length-frequency distributions were used to help clarify the way in which the estuary was utilised by fish. Nine of the 15 most abundant fish species were marine species which entered the estuary for variable periods while the other six were represented by populations in which the individuals were capable of passing through the whole of their life cycle within the estuary. In order of abundance, the nine marine species were Hyperlophus vittatus, Pelates sexlineatus, Aldrichetta forsteri, Mugil cephalus, Torquigener pleurogramma, Favonigobius lateralis, Pranesus ogilbyi, Gymnapistes marmoratus and Sillago schomburgkii , while the six species with estuarine populations were Apogon rueppellii, Atherinosoma elongata, Nematalosa vlaminghi. Atherinosoma wallacei, Cnidoglanis macrocephalus and Amniataba caudavittatus. The extent and seasonality of the distribution of the species within the estuary and associated river systems varied considerably. Evidence is also presented to show that fish tend to move further away from the shallow banks near the shore with increasing age and size. The fish fauna of the Peel-Harvey is compared with those of Cockburn Sound and the estuaries of the Swan-Avon and Blackwood rivers in Western Australia and with Botany Bay in eastern Australia.     

Abundance, distribution and feeding relations of root/fungal feeding nematodes in a Scots pine forest

In a 15–20 yr old forest of Pinus sylvestris, Tylenchus spp., Paratylemchus spp? and Malenchus tantulus were the most abundant stylet-bearing nematodes. Soil layers and ground cover affected the abundance. Mycophagy was observed for Tylenchus sp., M. tantulus, Aphelenchoides sp. and Tylencholaimus stecki. Feeding on roots of the forest grass, Deschampsia flexuosa was recorded for W. tantulus, Paratylenchus spp? and Rotylenchus sp. The latter fed also on pine roots. Connections occurred between feeding habits and field distribution. The facultative feeding habit of M. tantulus probably allowed this species to reach higher numbers under D. flexuosa. The importance, in the field, of the grass Calamagrostis arundinacea for Paratylenchus spp? was confirmed by laboratory experiments. As pine was a non-host, these nematodes were probably grass feeders. Paratylenchus spp? dominated the obligate root feeders with forest grass being a key-factor for the group abundance. Suspected high densities of Paratylenchus spp? on clearings should not affect the growth of pine seedlings and although Rotylenchus sp. to some extent reduced seedling growth its pathogenic status on P. sylvestris was doubtful.     

Abundance and distribution of Neomysis mercedis and a major predator, longfin smelt (Spirinchus thaleichthys) in Lake Washington

Seasonal variations in the horizontal and depth distributions of Neomysis mercedis and longfin smelt (Spirinchus thaleichthys) were examined using night-time mid-water trawl and Bongo net samples collected in Lake Washington from July 1989 to February 1992. Mysid density varied spatially, seasonally and yearly. For example, during summer, and fall (odd years), mysid abundance was highest in the northern, and lowest in the southern sections of the lake, except in December 1991 when they were uniformly distributed. In fall (November 1990), mysid density was highest in the central basin of the lake. Furthermore, in winter of even years, highest mysid density occurred in the southern region of the lake, but in the central region in winter (February) of odd year. Longfin smelt horizontal distribution also varied seasonally. For example, density of the 1988 YC smelt (1+) was highest in the northern area of Lake Washington in summer but highest in the southern area in fall. During winter, distribution seemed random. The abundance of the 1990 YC smelt (YoY) was also highest in the northern section of the lake in summer, but highest in the southern section in fall; density remained high in the southern section in winter. But, by late spring when they were more than one year old, the distribution had changed such that highest abundance occurred in the northern and mid-section of the lake. By winter when they were about two years old and about to begin spawning, density had become highest again in the southern section. These suggest extensive movement of mysids and smelt from one area to another, perhaps driven by wind-induced water currents in the lake. Depth distribution patterns of mysids and smelt are discussed. Smelt were captured mainly in the shallow strata (8 m) of the lake during all seasons except during winter when they predominated at 50 m. Mysids were also mainly caught in the shallow strata of the lake during all seasons, although a significant proportion occurred at greater depths (> 30 m). The abundance of both species was positively correlated in spring and summer but negatively correlated in fall. A poor correlation was observed in winter. Negative correlation in fall was primarily due to the occurrence of mysids and smelt in different areas of the lake whereas poor correlation in winter was particularly due to their occurrence at different depths. Because of considerable overlap in the distribution of both species in the lake, mysids face a high risk of predation by smelt. This piece of information is consistent with the hypothesis that smelt control mysid abundance in Lake Washington. This revised version was published online in July 2006 with corrections to the Cover Date.     

长江口及邻近海域夏、冬季浮游病毒丰度分布

应用荧光显微计数法,对2006年夏季和2007年冬季长江口浮游病毒丰度(virus direct count,VDC)进行了检测.结果表明:夏季该海域VDC在2.22×106～9.97×107个·ml-1,高值分布在近海B区(122.5°-123.5°E)的表层海域;冬季VDC在1.99×106～2.66×107个·ml-1,高值分布在近岸A区(120.5°-122.5°E)海域,且由近岸向外海逐渐降低.夏季VDC与浮游细菌生物量、叶绿素含量关系密切,与营养盐相关性不显著(P＞0.05);冬季VDC与浮游细菌、营养盐含量关系密切,与叶绿素a含量相关性不显著(P＞0.05).夏季VDC显著高于冬季(P＜0.01),且两季的分布特征存在不同,此种差异主要与浮游细菌、浮游植物等病毒寄主的分布有关.冬季的营养盐含量也是影响其浮游病毒分布的重要因素.     

Abundance and feeding of microheterotrophic flagellates from a eutrophic lake

The growth of planktonic bacteria from a eutrophic lake was evaluated with microflagellate predators present and absent. Differential filtration (50 and 8 µm filters) was used to exclude ciliates and larger zoo-and phytoplankton from replicate experimental cultures. Additional filtration (1 µm filter) excluded heterotrophic microflagellates from a second set of experimental cultures, producing cultures that contained either bacteria and microflagellates or only bacteria. Growth of bacteria and microflagellates was evaluated by epifluorescent microscopy from repeated sampling over approximately 200 h. Bacterial numbers were reduced in the presence of microflagellates, and microflagellates were observed to contain bacterial prey. However, microflagellate numbers were high (about 10⁶ cells ml^-1) and were less than an order of magnitude lower than bacterial numbers. Bacteria growing in the presence of microflagellates did not show predator-prey population oscillations but had in-phase oscillations in numbers, suggesting that microflagellate predation in freshwater may not control numbers of planktonic bacteria. Clearance rates of heterotrophic microflagellates, estimated to be only 30 body volumes hr^-1, were insufficient to maintain flagellate growth, suggesting that other energy sources may be needed to maintain microflagellates in eutrophic freshwater ecosystems.     

Zooplankton distribution and dynamics in a temperate shallow estuary

The spatial, temporal and tidal dynamics of the zooplanktonic community of the Mondego estuary was studied from January 2003 to 2004. The monthly sampling procedure included the measurement of hydrological parameters (salinity, temperature, Secchi transparency, chlorophyll a and nutrients) and the collection of zooplankton with a Bongo net of 335 μm mesh size. Zooplankton composition, distribution, density, biomass and diversity were determined. The principal component analysis (PCA) revealed the existence of a spatial gradient with the upstream sampling stations, associated to high values of nutrients, in opposition to the downstream stations characterized by higher salinity and transparency values. The Copepoda was the main dominant group and Acartia tonsa revealed to be the more abundant taxon. The spatial and temporal dynamics of zooplanktonic communities analysed by non-metric MDS showed the existence of four assemblages of species-sites, reflecting differences in zooplankton composition between both branches of the estuary. The results suggest that abundance, biomass and diversity of the zooplanktonic community are strongly influenced by the hydrological circulation pattern and by direct or indirect human impacts that occur in each branch. The northern branch is dominated by the river flow suffering from regular dredging activities and the southern branch is dominated by tidal circulation suffering from an ongoing eutrophication process.     

Abundance and distribution of Legionellaceae in Puerto Rican waters

Waters in marine and freshwater areas of Puerto Rico were analyzed for the presence of Legionella spp. by direct fluorescent antibody assay with guinea pig confirmation. Several species, including L. bozemanii, L. dumoffii, L. gormanii, L. longbeachae, L. micdadei, and L. pneumophila, were widely distributed among all sites. Legionellaceae, including L. pneumophila, were found in high densities in water collected in the rain forest from epiphytes in trees 30 ft. (about 9.25 m) above the ground. Both interspecific and intersite variations were significant. L. pneumophila was the most abundant species at all sites, with average densities of 10(4) cells ml-1, very close to the range which is potentially pathogenic for humans. Densities of L. pneumophila were highest in sewage-contaminated coastal waters. These are the highest densities of Legionella spp. ever reported for marine habitats. Densities of L. pneumophila were positively correlated with concentrations of sulfates, phosphates, and pH. A survey of 88 fatal atypical pneumonia cases at a Puerto Rico hospital showed that 15% of the patients had L. pneumophila infections. This study establishes L. pneumophila as a relatively common cause of atypical pneumonia in Puerto Rico and suggests natural aquatic habitats as possible sources or reservoirs of pathogenic Legionella spp. in the tropics.     

Abundance and movement patterns of age-0 juvenile lake sturgeon in the Peshtigo River,Wisconsin

In Great Lakes tributaries, age-0 juvenile lake sturgeon Acipenser fulvescens use riverine nursery habitats during their first summer of life and migrate to adjacent lakes after a seasonal decline in water temperature. We used mark-recapture data collected during this river-residency phase to monitor patterns in juvenile abundance and movement in the Peshtigo River, Wisconsin, during 2006 and 2007. Jolly-Seber and multistate models were used to estimate abundance and describe the probability of movement between river sections. Juvenile abundance was higher in 2007 than in 2006; however, in both years, abundance at the end of the sampling season was lower than at the beginning. Downstream movements were observed more frequently than upstream movements, and the probability of a downstream movement was higher than the probability of an upstream movement. The lower abundance later in the sampling season and propensity for downstream movements suggests that some age-0 juvenile lake sturgeon may leave the natal river before a seasonal decline in water temperature.     

长江口中华鲟幼鱼对底质的选择

采用单因子实验方法,研究了中华鲟幼鱼对沙(直径＜0.2 cm)、小砾石(直径1～2 cm)、中砾石(直径4～5 cm)、大砾石(直径13～15 cm)4种底质类型的选择.结果表明:单尾鱼实验时,中华鲟幼鱼(体长283.0 mm±18.6 mm,体质量86.2 g±17.8 g,n=30)在4种底质中的时间百分比分别为沙51.50%±21.20%、小砾石20.27%±9.70%、中砾石18.03%±6.17%、大砾石10.20%±11.20%,幼鱼在沙底质中时间明显长于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验时,中华鲟幼鱼(体长278.0 mm±14.3 mm,体质量79.2 g±19.6 g,n=30)在4种底质中的数量百分比分别为沙46.25%±8.06%、小砾石19.38%±7.72%、中砾石18.75%±7.19%、大砾石15.63%±8.92%,幼鱼在沙质底质中的数量明显高于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验中,活动鱼(在水层中游动,不贴底)在4种底质中的数量无显著差异(P＞0.05);非活动鱼(贴底游动或静止)在沙底质中的数量显著高于其它3种底质(P＜0.01).单尾鱼(从时间角度)和多尾鱼(从数量角度)实验均表明,中华鲟幼鱼明显选择沙底质.     

Abundance and tissue distribution of selenocysteine-containing proteins in the rat

The form and distribution of selenium (Se) in proteins from selected tissues of the rat were studied by measuring 75Se radioactivity in animals provided for 5 months with [75Se]selenite as the main dietary source of Se. Equilibration of the animals to a constant specific activity of 75Se allowed the measurement of 75Se to be used as a specific elemental assay for Se. Skeletal muscle, liver and blood accounted for 73% of the whole-body Se and 95% of the total Se-dependent glutathione peroxidase activity. Over 80% of the whole-body Se was in protein in the form of the selenoamino acid, selenocysteine. All other forms of Se that were measured accounted for less than 3% of the whole-body Se. The Se in protein was distributed in seven subunit sizes and nine chromatographic forms. The Se in glutathione peroxidase accounted for one-third of the whole-body Se. These results show that the main use of dietary Se, as selenite, in rats is for the synthesis of selenocysteine-containing proteins. Furthermore, the presence of two-thirds of the whole-body Se in nonglutathione peroxidase, selenocysteine-containing proteins suggests that there may be other important mammalian selenoenzymes besides glutathione peroxidase.     

Tidally driven distribution of phytoplankton blooms in a shallow, macrotidal estuary

The influence of the ebb tide on the abundance and distributionof bloom-forming species, as well as the mechanisms for theselection of those species which remain, were investigated inthe shallow, tidal-flushed Urdaibai estuary, north Spain. Phytoplanktonwas collected monthly from May to September 1998 during differenttidal conditions (neap-spring) at five stations along the salinitygradient of the estuary. During the neap tides of May, Leptocylindrusdanicus dominated in the lower estuary, together with Thalassiosiraguillardii and Peridinium foliaceum in the upper segment; T.guillardiiexperienced the broadest displacement along the estuary. Duringthe June and July cruises, coinciding with mid-tidal amplitudesand high temperatures, Peridinium quinquecorne densely aggregatedin the upper estuary at the slack high tide, whereas Chaetocerossalsugineum bloomed at the intermediate stations. Cyclotellaatomus and Protoperidinium achromaticum reached high concentrationsin the upper zone only during the late stages of the ebb. Duringthe spring tides of September, Prorocentrum minimum, Heterocapsapygmaea and Heterocapsa rotundata appeared in the lower marineestuary, being washed out at low tide. By contrast, the diatomsSkeletonema costatum, Thalassiosira guillardii and Cyclotellaatomus were the most abundant species in the upper reaches,peaking during the ebb. Physical trapping and high water residencetimes served to retain blooming species in the upper estuary.The intense growth of the estuarine diatoms may compensate forthe advective seaward losses of cells during the ebb, thus allowingthe development of stable populations in the estuary. Only Peridiniumquinquecorne seems to combine an endogenous tidal rhythm witha photic response to remain in the tidal area of the estuary.     

Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m2/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m2/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m2/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m2/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km² over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.     

Abundance and distribution of elephants in the Luangwa Valley, Zambia

Elephant density over 40 000 km² of the Luangwa Valley was estimated as 2–17 km^-2 to give a population size of around 86 000 in that area, a tally that would probably top 100 000 if unsurveyed areas within the drainage had been included. Seasonal movement is largely restricted to a migration on to the riverine strip during the wet season and reciprocal dispersal across the valley thereafter. The mean annual range of movement is about 25 km.     

Factors affecting distribution and abundance of jellyfish medusae in a temperate estuary: a multi-decadal study

Three hydrozoan species, reputedly from the Black Sea (Maeotias marginata, Blackfordia virginica, Moerisia lyonsi), are now found throughout the San Francisco Estuary, California, but long-term and seasonal patterns of distribution and abundance have been poorly documented. We evaluated trends from 35 years of monthly otter trawl data and from a 2-year macrozooplankton survey in Suisun Marsh, a brackish region with extensive tidal sloughs and channels that is part of the San Francisco Estuary. Medusae of all three hydrozoans occurred primarily during the dry season (summer–fall). Abundance of M. marginata medusae significantly increased since the 1980s. Moerisia lyonsi was the most abundant hydrozoan in the macrozooplankton medusa survey followed by M. marginata and B. virginica. Salinity and temperature were strongly positively associated with medusa abundance. Maeotias marginata occurred in the lowest salinity range (2.3–9.1 ppt), while M. lyonsi (2.8–9.9 ppt) and B. virginica (5.6–10.3 ppt) occupied slightly higher salinities. Overall, abundance and distribution of medusae of these three hydrozoans in Suisun Marsh depended on seasonal stability of environmental conditions that favored blooms. While harmful effects have yet to be demonstrated, they could become more of a problem as both sea level and water temperatures rise, especially given the combined range of environmental conditions at which the three species occur.     

Abundance and distribution of mammals in Katavi National Park, Tanzania

Ground transects were used to determine densities of 24 larger mammals in Katavi National Park. The Park consists of miombo woodland habitat and two seasonal lakes. Mammalian biomass was extremely high due primarily to large numbers of buffalo. The highest mammal densities were found around Lake Chada to the south-east of the Park. Contrary to earlier reports, species' densities did not differ significantly between dry, wet and intermediate seasons, suggesting that, aside from elephant and warthog, mammals did not enter or leave the Park in large numbers. Similarly, aside from zebra and waterbuck, sightings of species in different vegetation types did not change markedly between seasons. Thus, seasonal lakes in Katavi National Park support very high local concentrations rather than acting as dry season refuges for mammals outside the Park.     

Movements of green sturgeon, Acipenser medirostris, in the San Francisco Bay estuary, California

Synopsis The green sturgeon, Acipenser medirostris, is a long-lived, iteroparous, anadromous acipenserid that is native to the San Francisco Bay Estuary, California. Sub-adult and adult fish are oceanic, but enter the estuary during the spring and remain through autumn. Little is known about green sturgeon distribution within the estuary or what, if any, physical parameters influence their movements. We report the results of a telemetry study conducted between September 2001 and November 2002. Five sub-adult and one adult green sturgeon were captured by trammel net in the San Pablo Bay region of the estuary. We implanted depth-sensing, ultrasonic transmitters within the peritoneum of individuals and tracked them from a boat for 1 – 15 h per day over periods ranging from 1 to 12 days. Salinity, temperature, and dissolved oxygen profiles of the water column were measured hourly. Observed movements were categorized as either non-directional or directional. Non-directional movements, accounting for 63.4% of observations, were closely associated with the bottom, with individuals moving slowly while making frequent changes in direction and swim speed, or not moving at all. Directional movements consisted of continuous swimming in the top 20% of the water column while holding a steady course for extended periods. Four of the five sub-adult fish remained within the confines of San Pablo Bay for the duration of their tracking period. The remaining sub-adult moved over 45 km up-river into Suisun Bay before contact was lost. The adult fish exited the bay and entered the ocean 6 h after release near Tiburon, CA, a movement of approximately 10 km. The sub-adult fish typically remained at the shallower depths (<10 m) of the estuary, but there were no apparent preferences for temperature, salinity, or dissolved oxygen, with the fish moving widely and rapidly across the range of these physical parameters. Activity is believed to be independent of light level with no discernable crepuscular, nocturnal, or diurnal peaks in activity.     

蜜蜂全基因组中微卫星的丰度及其分布

查找出蜜蜂基因组中由1～6个碱基重复单元组成的简单序列重复,分析蜜蜂基因组中微卫星的分布频率,并比较其在各染色体中的分布频率。微卫星在蜜蜂基因组中的分布频率为1/0·804kb,其中二碱基重复序列占26·86%,是最丰富的重复单元,而六、一、三、四、五碱基重复单元序列分别占24·74%,22·19%,13·65%,10·98%,2·59%。同时发现富含A和T碱基的微卫星占主导地位,富含G和C碱基的微卫星数量较少。第4,1,3条染色体微卫星分布频率较高,而第11,14,12条染色体微卫星分布频率较低。