Ecology of the Ogun River estuary,Nigeria

The distribution of benthonic communities (particularly Foraminifera) were studied from fourteen samples obtained from the Ogun River estuary and environs. Ten species of benthonic Foraminifera were identified; two of these constitute over 90% of the total foraminiferal population.Two broad biofacies are recognisable, namely the upper estuarine facies of Ammobaculites and the lower estuarine facies comprising arenaceous and calcereous forms with a preponderance of Ammonia beccarii (Linnaeus).Large populations of few species occur in the lower estuary, an area of weakly saline water with marked salinity fluctuations. The upper estuary on the other hand is sparsely populated and contains tests mainly of arenaeous Foraminifera. A few species are distinctive of particular facies but some are distributed throughout the estuary. Substrate is not a causal ecological factor, because sediments are similar in physical attributes throughout the estuary. Salinity and rate of sedimentation are among the more important factors affecting the distribution of all species. The low-energy nature of the environment is established by the abundance of faecal pellets and the fragility of the tests of the arenaceous Foraminifera.     

长江口邻近水域浮游动物群落特征及变动趋势

根据2000～2003年长江口邻近海域5月和8月8个航次的调查资料,对长江口浮游动物群落特征的变动趋势进行了研究。结果表明,桡足类、毛颚类和异足类在8月种数明显多于5月。8月暖流势力增强的同时淡水水团势力也增强,不同水团交汇处,浮游动物种类数和多样性指数等值线密集排列,外海暖水带来丰富的种类使该季节的种类数和多样性均明显高于5月。盐度是影响长江口浮游动物群落特征最主要的环境因子。     

Feeding activity and food habits of the shad, Ethmalosa fimbriata (Bowdich), in the coastal waters of Cape Coast, Ghana

The monthly feeding activity and food habits of populations of Ethmalosa fimbriata occurring in the sea and an estuary in Cape Coast, Ghana district were investigated during a 14-month period. The juvenile fish, whose total length (T.L.) ranged from 5.3 to 14.7 cm, occur in the estuary and appeared to be more active feeders than the marine samples which measured 15.0–30.4 cm. The peak feeding activity in the marine population coincided with the onset of'upwelling' in the sea, which period is characterized by high salinities, decreasing temperatures and high zooplankton production. The species is primarily a plankton feeder. The stomachs of the marine samples contained mainly protozoa, crustacea, molluscan larvae and a considerable amount of detritus while the stomachs of the estuarine fish contained mainly phytoplankton, protozoa, sand grains and organic detritus. These observations have been discussed in relation to other reports on populations occurring along the West African coast.     

Restoration flows for the Colorado River estuary, México: estimates from oxygen isotopes in the bivalve mollusk Mulinia coloradoensis (Mactridae: Bivalvia)

Because of competing demands for freshwater, restoration of estuaries requires estimates of inflows to sustain key species. In this study we estimated the pre-dam salinities of the Colorado River estuary by using oxygen isotopes in subfossil shells of the bivalve mollusk Mulinia coloradoensis. Since the construction of upstream dams and water diversions, average salinity in the estuary has increased to 38 practical salinity units (psu) and the population of M. coloradoensis has decreased by ~90%. In the pre-dam estuary, specimens grew when salinity ranged from 22 to 33?psu at the mouth of the river while populations 40?km distant grew at salinities from 30 to 38?psu. The river flow needed to reduce salinities at the mouth of the river to those recorded in the most distant localities (40?km from river??s mouth) ranges from 120 to 290?m³?s^?1. If these flows were sustained for a year, they would total 7?C16?% of the river??s annual average historical flow (~1.8?×?10¹⁰?m³).     

The effects of salinity,and calcium and potassium variations on the growth of two estuarine red algae

The effects of varying salinity and calcium and potassium concentrations on the growth of two species of estuarine Rhodophyta, Bostrychia radicans Montagne and Caloglossa lepricurii (Montagne) J. Agardh, were examined in unialgal culture. Inocula of settled tetraspores on glass coverslips were incubated in six concentrations of potassium (0. 100, 200, 300, 400 and 500 mg/l) at five salinities (0, 5, 15, 25, and 35%) in the presence of calcium. Growth responses of each alga were determined from the average cell number of 75 tetrasporelings after 4 days in Ott's synthetic sea-water medium. The concentrations of dissolved potassium and calcium in sea water along a salinity gradient in an estuary were determined with atomic absorption spectrophotometry. Four-day-old tetrasporeling of Bostrychia and Caloglossa demonstrated growth over wide ranges of potassium concentrations with growth maxima at 400 500 and 200 400 mg/l, at the optimal salinities for growth of 25 and 15%, respectively. These studies indicate also that the presence of calcium is essential for appreciable growth of both species at each salinity and the effects of variations in potassium are dependent upon the presence of calcium. The abundance of both species in the Mullica River estuary. New Jersey, appears to be a response to a total osmotic effect along the salinity gradient because sufficient levels of the major cations are present. However, the upper limit of both species towards the head of the Mullica River estuary may be determined by combinations of low salinity and low levels of dissolved calcium and potassium rather than by low salinity alone.     

Environmental influences on the spatial ecology of juvenile smalltooth sawfish (Pristis pectinata): results from acoustic monitoring

To aid recovery efforts of smalltooth sawfish (Pristis pectinata) populations in U.S. waters a research project was developed to assess how changes in environmental conditions within estuarine areas affected the presence, movements, and activity space of this endangered species. Forty juvenile P. pectinata were fitted with acoustic tags and monitored within the lower 27 km of the Caloosahatchee River estuary, Florida, between 2005 and 2007. Sawfish were monitored within the study site from 1 to 473 days, and the number of consecutive days present ranged from 1 to 125. Residency index values for individuals varied considerably, with annual means highest in 2005 (0.95) and lowest in 2007 (0.73) when several P. pectinata moved upriver beyond detection range during drier conditions. Mean daily activity space was 1.42 km of river distance. The distance between 30-minute centers of activity was typically <0.1 km, suggesting limited movement over short time scales. Salinity electivity analysis demonstrated an affinity for salinities between 18 and at least 24 psu, suggesting movements are likely made in part, to remain within this range. Thus, freshwater flow from Lake Okeechobee (and its effect on salinity) affects the location of individuals within the estuary, although it remains unclear whether or not these movements are threatening recovery.     

The estuarine phase in the spawning run of the River lamprey Lampetra fluviatilis

The biology of the very early stages in the upstream migration of the River lamprey has been studied using samples taken from the cooling water intake screens of the Oldbury Power Station in the Severn Estuary. Examination of the numbers of lampreys caught at different times indicate that an increase in freshwater discharge is the predominant environmental factor responsible for initiating the movement from the sea into the estuary, although temperature may also be a contributory factor. The migrants could be separated on the basis of size into typical and praecox forms whose mean lengths during peak abundance were approximately 300 and 240 mm respectively, the corresponding weights being about 53 and 22 g respectively. The typical forms were occasionally found in the estuary as early as July and as late as April, with peak abundance generally being reached in November, whereas the praecox forms were present mainly between January and March. The ratio of typical to praecox forms over the four years of sampling was estimated as 3.3 : 1. In both size categories, the gonadosomic and hepatosomic ratio was greater in females than males. Evidence was also found in the typical forms for a correlation between high numbers and an increased proportion of males. Measurement of a number of different characters, including lengths, weights and condition factors, as well as gonadosomic, hepatosomic and gut ratios, suggest that, although the typical forms enter the estuary over a long period of time, the onset of the changes leading to sexual maturity are more synchronous. A small number of the later typical migrants, however, exhibited different characteristics to those of the majority of the animals comprising this size category. Measurements made on typical animals from Oldbury in November indicate that they can regulate their plasma ions in salinities as high as 70% of full strength sea water.     

Kinetics of zooplankton in an aquatic continuum: from the Marne River and reservoir to the Seine estuary

A study was carried out within a 700-km river sector, including three types of ecosystems (a reservoir, a river and its estuary) to characterise the major features of zooplankton communities in the Seine Basin. In rivers, zooplankton biomass becomes significant only when the growth rate of the organisms is higher than the dilution rate (4-5th orders rivers, according to River Continuum Concept). Upstream, short residence times favour the development of small species (Rotifers) with low individual body weight and biomass. Conversely, larger species (microcrustaceans) develop more downstream, where increased residence time leads to autochthonous production (Riverine Productivity Model). Such a pattern is greatly modified by human impact. Zooplankton input from the Marne reservoir represents one type of disruption in the general upstream-downstream trend (according to the Serial Discontinuity Concept). This reservoir is a source of microcrustaceans; they rapidly disappear mainly through fish predation, and therefore have little impact on the river phytoplankton. Discontinuities, such as confluences, have a relatively small effect on the stock of zooplankton with regard to the water release from the reservoir, but they persist more downstream, because they have the same lotic origin. A few microhabitats with macrophytes play a small role for this canalised river, but they can modify locally the plankton community structure and composition. As a whole, the flux of zooplankton rises exponentially, whereas discharge increases linearly from upstream (4th order) to downstream (8th order). In the canalised sectors, Dreissena larvae build up an important biomass, adding to that of the zooplankton sensu stricto. Especially abundant in the downstream sector of the Marne and Seine Rivers, the larvae show a widespread colonisation of the benthic substrates by the adult Dreissena. One of the largest mussel colonies in the middle estuary can contribute to a rapid decrease of zooplankton. Estuary ecosystems form a transitional zone between freshwater and seawater, with zooplankton dynamics closely linked to the particular conditions on this part of the river system.     

Zooplankton Communities of a Dammed Estuary in the Bay of Fundy,Canada

The upper estuary of the macrotidal Petitcodiac River, New Brunswick, Canada, was converted to a freshwater impoundment by construction of a causeway in 1968. Thirty years later, zooplankton community structure in the impoundment was characteristic of a disturbed ecosystem. The depauperate zooplankton consisted of a mixture of freshwater and marine/brackish taxa, but was not typical of regional estuaries or lakes. The causeway dam was an obstacle to fish migration, and several anadromous species that would formerly have been represented in the ichthyoplankton were absent. The invertebrate plankton community was dominated by rotifers, likely as a result of frequent water level fluctuations, and highly suspended sediment levels in the water column. Estuarine/marine calanoids (Eurytemora affinis, Temora longicornis, Centropages typicus, Tortanus discaudatus), the mysid Neomysis americana, and Cancer crab zoeae were collected in fresh water up to 14 km upstream of the causeway.     

The Dual Origin of the Black Sea Foraminifera

Evidence is given supporting the possibility of survival in the modern Black Sea of descendents of Miocene Pontic foraminiferal populations. This evidence includes the present existence of Foraminifera in the Aral and Caspian Seas, the existence of pockets of species in the Paratethys area in waters long isolated from any seas, the existence in the Golovitza Lagoon of Foraminifera living at salinities lower than those that are thought to have existed in the Pontic Basin during its lacustrine period, and evidence from zoogeography. It is shown that there are morphological, ecological and physiological modifications in these aboriginal populations as compared to populations of the same species living in the Mediterranean. In addition to these aboriginal populations, evidence is given for three invasions of Foraminifera from the Mediterranean during geological periods when the Black and Mediterranean Seas were merged.     

Phases in the development of riverine plankton: Examples from the rivers Rhine and Meuse

Observations on phyto and zooplankton in two hydrographically different rivers were compared in order to discriminate phases in plankton development. Along the longitudinal axis of the River Rhine a gradual increase in the development of phytoplankton was observed, which reached its maximumca. 100 km before the river flows into its artificial sedimentation area. The development of rotifer populations was slightly retarded as compared with that of phytoplankton and highest population densities were only reached in the sedimentation area. Crustaceans developed in significant numbers, not until the river water had entered the sedimentation area. Development of zooplankton coincided here with a strong decrease in the density of phytoplankton. A similar trend in plankton development was observed in the River Meuse, although in this river the highest densities of phyto and zooplankton already occurred in its middle reaches. The differences in the timing of plankton growth in the two rivers are probably caused by differences in flow regime between both rivers. The River Rhine, which is fed by rainwater and melting of glaciers in the Alps, has a relatively constant discharge. On the other hand, the low discharge of the rain-fed River Meuse combined with an increased residence time of the water as a consequence of large numbers of weirs, allows a full cycle of plankton development long before its discharge into the sea. This phenomenon was also reflected in the silicate cycle in the Meuse, where the consumption by planktonic diatoms and the regeneration of silicate of deposits seem to be important. In contrast, in the main branches of the River Rhine only the effects of silicate consumption were detectable.     

Movements of Atlantic salmon, Salmo salar L., in an estuary in south-west England

In the years 1985–1987, salmon were tracked in the estuary of the River Fowey, Cornwall using the 'sonar buoy' system developed at the M.A.F.F. Fisheries laboratory and described by Solomon & Potter (1988). Sixty-one salmon were caught and tagged in the estuary, 25 with radio and 36 with combined radio and acoustic transmitters. About half these fish were not recorded entering the freshwater reaches of the R. Fowey, and from tag recoveries it seems likely that about 27% were returning to other rivers. For fish returning to the R. Fowey the time between tagging and entry into fresh water varied between 9 h and 130 days. In the estuary the fish largely moved in the same direction as the tidal currents, although movements over the ground against the current were more common in the bottom 2 km and the top 2 km. During periods of low river-flow in summer all salmon tracked in the estuary dropped back out to sea where they stayed for varying periods: some of these made several sorties past the estuary mouth and on occasions well up the estuary before finally entering fresh water. During periods of higher river discharge, in both the summer and the autumn, some fish remained in the estuary for longer periods, sometimes holding position in deep, sheltered water. Most fish entered fresh water at night during periods of increased freshwater discharge, although at very high flows fish also entered in daylight.     

东海赤潮高发区春季浮游动物生态特征的研究

根据2002年4～5月东海122°～123°30′E、29°～32°N水域海洋综合调查资料,对东海赤潮高发区浮游动物的数量分布、群落特征、种类组成及优势种等进行了分析．结果表明,在调查区共鉴定出饵料浮游动物128种[不含16种浮游幼虫(体)和仔鱼],分5门12大类,以桡足类占优势(40种,31．25％)．浮游动物群落以广温广盐生态类群为主．中华哲水蚤(Calanus sinicus)为最主要优势种(142．10ind·m-3,68．09％)．总生物量均值为243．80mg-m3(55．53～773．92mg·m-3),最高密集区(>500mg·m-3)位于长江口30°45′～31°15′N、122°45′～123°15′E水域．饵料生物量均值为195．96mg·m13(55．53～496．09mg·m。),呈长江口(30°30′N以北)水域高于舟山岛东南水域、长江口外海(122°45′E以东)高于近海水域的分布趋势．多样性指数(H′)均值为2．12(1．09～3．73)．长江口水域多样度、均匀度和丰富度低,优势度大,反映出浮游动物群落结构不够稳定．采用逐步回归分析得知,影响本区春季浮游动物生态特征值分布的主要因子是水温、硅藻和甲藻．     

Trophic structure and avian communities across a salinity gradient in evaporation ponds of the San Francisco Bay estuary

Commercial salt evaporation ponds comprise a large proportion of baylands adjacent to the San Francisco Bay, a highly urbanized estuary. In the past two centuries, more than 79% of the historic tidal wetlands in this estuary have been lost. Resource management agencies have acquired more than 10 000 ha of commercial salt ponds with plans to undertake one of the largest wetland restoration projects in North America. However, these plans have created debate about the ecological importance of salt ponds for migratory bird communities in western North America. Salt ponds are unique mesohaline (5–18 g l⁻¹) to hyperhaline (> 40 g l⁻¹) wetlands, but little is known of their ecological structure or value. Thus, we studied decommissioned salt ponds in the North Bay of the San Francisco Bay estuary from January 1999 through November 2001. We measured water quality parameters (salinity, DO, pH, temperature), nutrient concentrations, primary productivity, zooplankton, macroinvertebrates, fish, and birds across a range of salinities from 24 to 264 g l⁻¹. Our studies documented how unique limnological characteristics of salt ponds were related to nutrient levels, primary productivity rates, invertebrate biomass and taxa richness, prey fish, and avian predator numbers. Salt ponds were shown to have unique trophic and physical attributes that supported large numbers of migratory birds. Therefore, managers should carefully weigh the benefits of increasing habitat for native tidal marsh species with the costs of losing these unique hypersaline systems.     

Instability of the turbidity maximum in the macrotidal Geum River estuary, western Korea

In the low-salinity area of many macrotidal estuaries, through the combination of tidal pumping and estuarine circulation, an estuarine turbidity maximum (ETM) develops providing favorable conditions for various organisms. To investigate ecological roles of the ETM in East Asian estuaries, we conducted seasonal observations in the Geum (or Keum) River estuary, one of the representative macrotidal estuaries flowing into the Yellow Sea, from 2007 to 2008. The estuary was frequently filled with high-salinity (>10 PSU) and low-turbidity (<100 NTU) water under small or no freshwater discharge from a dam (ca. 8 km upstream from the river mouth). Brackish water was, however, completely pushed out of the estuary within a few hours after an intensive discharge in summer. Chlorophyll a (up to 50 μg l⁻¹) and pheophytin (up to 80 μg l⁻¹) were concentrated in a low-salinity (<1 PSU) and high-turbidity (up to 1000 NTU) area, indicating that the intensive discharge transported both living phytoplankton and resuspended detritus into the area. In contrast, a phytoplankton bloom (chlorophyll a, up to 100 μg l⁻¹) was observed at low salinities under little discharge in winter. The present study demonstrated an absence of the ETM suitable for estuarine-dependent organisms from the present Geum River estuary, indicating potential importance of adequate control of freshwater discharge for the formation and maintenance of the ETM.     

鸭绿江口近岸海域水质环境对冬季浮游动物群落结构的影响

定量分析滨海湿地近岸海域水质环境与浮游动物群落结构之间的关系对揭示海水水质环境健康状态具有重要意义。2019年12月在鸭绿江口湿地国家级自然保护区近岸海域开展了浮游动物和水环境因子调查,运用冗余分析和结构方程模型等方法探讨了水质环境对冬季浮游动物群落结构的影响。研究区共鉴定出浮游动物14种以及浮游幼虫5大类,桡足类最多占比52.63%;保护区不同功能分区间浮游动物群落结构总体差异不大,多样性指数、均匀度指数和丰富度指数平均值分别为1.34、0.51和0.59;浮游动物的种群分布与海水化学需氧量、溶解性无机氮、浮游植物群落多样性指数和铜元素含量关系显著;结构方程模型模拟结果表明,海水富营养化水平对浮游动物丰富度的效应系数为-0.26,具有显著的直接影响(P=0.01),重金属污染水平通过影响浮游植物丰富度(效应系数为-0.41,P<0.001)间接对浮游动物丰富度产生作用(间接效应系数为-0.2)。研究结果将有助于深化对海水环境和浮游动物群落结构协同演变过程的认识,为滨海湿地近岸海洋生态系统科学管理提供理论支撑。     

Seasonal colonisation and effects of salinity and temperature on species richness and abundance of fish of some brackish and estuarine shallow waters in Sweden

In this study two questions concerning the structure and organisation of shallow brackish and estuarine fish assemblages are: (1) Does the species number decline with lower salinity as found for the macrofauna invertebrates? (2) Does the water temperature during the year influence the abundance of fishes along the Swedish coast? In a west coast estuary salinities were higher but fluctuated more than in the Bothnian Sea. Days with temperatures exceeding 15°C were up to twice as many in the west coast estuary as in the Bothnian Sea. In spring the species number increased, but later on in summer it declined to increase again in autumn, but declined once again as winter approached. Fish density in the west coast estuary increased gradually to a maximum in late summer and then declined, while in the Bothnian Sea there was often a decline during summer. Positive correlations were found between observed minimum salinities and average species number, and between number of days with temperatures exceeding +15°C and both yearly average and maximum fish densities. Juveniles (0+) were present for longer periods in the west coast estuary than in the Bothnian Sea and reproduction of the common species started earlier in the former area. In winter the shallow areas are devoid of fish because of ice and so are re-colonised each spring. The study demonstrates that water salinity limited the species number, and water temperature the abundance of fish.     

珠江口浮游桡足类的生态研究

根据2002～2003年珠江口12个航次的调查资料,分析了浮游桡足类种类组成、优势种演替和丰度的时空变化,探讨其影响因素。以表层盐度(S)变化将调查海域划分三个区域:I区(S<25)、Ⅱ区(2530)。结果表明:调查海域共出现桡足类65种,Ⅱ区和Ⅲ区的种类多于I区;桡足类的平均丰度为118ind·m^-3,三个区域之间的比较为Ⅱ区(165ind·m^-3)>I区(129ind·m^-3)>Ⅲ区(62ind·m^-3),春、夏季的丰度高于冬季;优势种有明显的时间和区域上的变化。I区9个航次的研究结果表明:I区桡足类种类较少;各月份之间的平均丰度差别大,由河口内往外呈增加趋势。盐度是影响珠江口桡足类种类组成和数量变化的主要因素。     

Archival tags reveal that Arctic charr Salvelinus alpinus and brown trout Salmo trutta can use estuarine and marine waters during winter

By tagging north-Norwegian anadromous riverine Arctic charr Salvelinus alpinus and brown trout Salmo trutta with simple archival tags that measured ambient water temperature and relating the recordings to the temperature in the surrounding environments, it was demonstrated that 91% of the S. trutta and 80% of the S. alpinus utilized the estuarine and marine environment during the winter. There was large individual variation in migratory behaviour. Salvelinus alpinus on average entered the estuary on 12 January and the marine environment on 26 February, had continuous marine migrations lasting up to 55 days, and spent on average 40 days in the estuary and 25 days in the sea during the winter. The corresponding numbers for S. trutta were 15 December and 4 January for first entry in the estuary and sea, maximum 39 days in the marine environment and average number of days in the estuary and sea were 34 and 50. Most individuals of both species frequently shifted between the three habitats. These findings thus contradict previous studies conducted on lake-dwelling populations, which suggested that northern populations of both species solely overwinter in fresh water. The use of inexpensive temperature recording archival tags gave detailed continuous information on seasonal migrations between habitats with different thermal characteristics.