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1.
Between 2003 and 2006, a severe drought occurred throughout the Mondego River catchment's area, inducing lower freshwater flows into the estuary. As a consequence, both 2004 and 2005 were considered as extreme drought events. From June 2003 to June 2006, the fish assemblage of the Mondego Estuary was sampled monthly in five stations during the night, using a 2 m beam trawl. Fish abundance was standardized as the number of individuals per 1000 m2 per season and the assemblage was analyzed based on ecological guilds: estuarine residents, marine juveniles, marine adventitious, freshwater, catadromous and marine species that use the estuary as a nursery area. A total of 42 species belonging to 23 families were identified, with estuarine residents and nursery species dominating the fish community. Variations in the fish community were assessed using non-metric MDS, being defined as three distinct periods: summer and autumn 2003, 2004/2005 and winter and summer 2006. The main drought-induced effects detected were the depletion of freshwater species and an increase in marine adventitious in 2004/2005, due to an extended intrusion of seawater inside the estuary and a significant reduction in abundance during the driest period of estuarine resident species. Nevertheless, from the management point of view, it could be stated that although some variations occurred due to environmental stress, the main core of the Mondego Estuary fish community remained relatively unchanged.  相似文献   

2.
The influence of climate variability on the diversity and distribution patterns of zooplankton communities was investigated in the Mondego estuary (Portugal) during four consecutive years characterized by highly variable precipitation and, consequently, river flow regime. Monthly samples were collected along the estuarine gradient at five sampling stations. Seasonal, inter-annual and spatial distributions were evaluated by multivariate analyses and three diversity indices were applied (Species number, Shannon Diversity and Average Taxonomic Distinctness). A two-year drought period presented significant differences in salinity values, especially in 2005 (extreme drought event). During the study period, copepoda was the main dominant group and Acartia tonsa the most abundant species, with the exception of autumn 2006, where high abundances of the cladoceran Penilia avirostris were noticed. Multivariate analysis indicated that zooplankton communities changed from a pre- to a post-drought period indicating the influence of hydrological parameters in communities' structure. The dry period was associated with an increase in zooplankton density, a reduction in seasonality and higher abundance and prevalence of marine species throughout the year. Seasonally, winter/spring communities were distinct from those in summer/autumn. Spatially, salinity-associated differences between upstream and downstream communities were reduced during the drought years, but during the post-drought year, these differences were detected again.  相似文献   

3.
The impact of biological, hydrodynamic and large scale climatic variables on the jellyfish community of Mondego estuary was evaluated from 2003 to 2010. Plankton samples were collected at the downstream part of the estuary. Siphonophora Muggiaea atlantica and Diphyes spp. were the main jellyfish species. Jellyfish density was generally higher in summer and since 2005 densities had increased. Summer community analysis pointed out Acartia clausi, estuarine temperature and salinity as the main driven forces for the assemblage's structure. Also, Chl a, estuarine salinity, runoff and SST were identified as the major environmental factors influencing the siphonophores summer interannual variability. Temperature influenced directly and indirectly the community and fluctuation of jellyfish blooms in the Mondego estuary. This study represents a contribution to a better knowledge of the gelatinous plankton communities in small temperate estuaries.  相似文献   

4.
The aim of this study was to examine spatial and temporal variability in zooplankton abundance and biomass, both during the closed (dry season) and open (wet season) phases of the Mpenjati Estuary, South Africa. On average, nighttime abundance values were 1–3 orders of magnitude higher than daytime values. A total of 51 and 36 zooplankton taxa were identified during the open and closed phases, respectively. The estuarine species Pseudodiaptomus hessei, Acartia natalensis and Gastrosaccus brevifissura dominated the assemblage during both phases. During the open phase marine zooplankton species entered the estuary and increased the zooplankton species diversity. At the same time, the biomass of the estuarine zooplankton species decreased substantially due to scouring of the sediment, increase in salinity and turbulence, and possibly also in grazing pressure. Conversely, during the closed phase the zooplankton diversity decreased, since no marine organisms entered the estuary, but the biomass of typical estuarine species increased due to the stability of the estuary. The fluctuations in the zooplankton community structure between the closed and the open phases suggest that the opening and the closing of the estuary are very important processes in determining the food web of the estuary.  相似文献   

5.
《Journal of Sea Research》2007,57(2-3):209-217
The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but their occurrence differed among the estuaries. P. flesus only occurred in estuaries north of the Tejo estuary (39°N), S. solea was quite rare along the southern Portuguese coast (south of 37°30′N), S. senegalensis occurred in estuaries throughout the coast, but its abundance varied considerably, and the occurrence of M. hispidus was limited to the Sado estuary and Ria Formosa. A Correspondence Analysis was performed to evaluate the relationships between flatfish species abundance and geomorphologic and hydrologic characteristics of estuaries (latitude, freshwater flow, estuarine area, intertidal area, mean depth and residence time). Abiotic characteristics (depth, temperature, salinity, sediment type) of nursery grounds of each flatfish species were also evaluated. Results showed that some estuaries along the Portuguese coast have nursery grounds used by several flatfish species (e.g. Ria de Aveiro, Sado estuary), while in other systems a segregation was noticed, with juveniles of different species occurring in distinct estuarine areas (e.g. Minho and Mondego estuaries). This emphasizes the relevance of niche overlap, but the potential for competition may be considerably minimized by differences in resource use patterns and by an extremely high abundance of resources. Peak densities of flatfishes recorded in nurseries areas along the Portuguese coast were within the range of values reported for other geographical areas. Inter-annual abundance variability of all the species in the Tejo and Sado estuaries was extremely high, with a drastic decrease in P. flesus in the Tejo estuary, probably related to higher water temperature in recent years due to global climate change.  相似文献   

6.
The production of resident (Pomatoschistus minutus and Pomatoschistus microps) and marine juvenile fish species using the Mondego estuary (central Portugal) as nursery grounds (Dicentrarchus labrax, Platichthys flesus, Solea solea), was assessed in order to: (1) understand the potential of the estuary for fish production; (2) know the production of nursery fish species likely to be exported to the coastal stocks; and (3) how anthropogenic and natural stress could influence the estimated production. Sampling occurred from June 2003 to May 2006 and together the 5 species in study comprised around 70% of the whole fish community numbers and biomass. Increasing drought conditions were observed, starting with a normal hydrological year in 2003 until attaining a severe drought in 2005, which resulted in low river discharges (1/3 of the mean river discharges in 2003). Additionally, high water temperatures were observed in 2003 and 2005 (24 and 26 °C, night temperatures). The secondary production was estimated using the increment summation method, after recognition of the cohorts. Production was in general lower in the Mondego estuary when compared to other systems, which was associated to the estuary's small area (only 3.4 km2, less than 1/4 of area compared to other studied systems). Dicentrarchus labrax was among the most productive species. Production decreased in the drought year for all species, especially evident for D. labrax, P. minutus and P. flesus. No direct effects could be attributable to the salinity and temperature variations and to the low freshwater discharges (resulting from the drought and high temperatures), yet these were pointed as probable major reasons for the decreased production. A significant reduction (15–45% reduction in the estuarine production) was also concluded for the potential production to be exported for coastal areas by the nursery species in the drought conditions.  相似文献   

7.
This paper examines spatial and temporal variations of mesozooplankton abundance, biomass and community structure during three cruises of July 2002 (summer), January 2003 (winter), and April 2003 (spring) in the Pearl River estuary, China. Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the Pearl River estuary. A total of 154 species were identified during three surveys. The number of zooplankton species richness was strongly linked to salinity. Hierarchical cluster analysis identified three zooplankton groups during this study. Estuarine, neritic and pelagic groups corresponded to the upper, middle and lower reaches in the Pearl River estuary. The difference among groups could be mainly ascribed to changes in the relative contributions of the dominant species. The fluctuations in the zooplankton abundance, biomass and community structure were determined by the interactive effects of freshwater inflow, tidal and coastal currents, chlorophyll a, salinity and temperature. Significant spatial variability in the distribution of zooplankton species, abundance and biomass can be ascribed to the virtual presence of a horizontal gradient in salinity.  相似文献   

8.
Distribution patterns and trophic contributions of rotifers from freshwater through polyhaline estuarine waters were examined in the southern Chesapeake Bay and its major tributaries for a two-year period. Trichocerca marina and Synchaeta spp. were the major taxa in abundance, followed by Polyarthra vulgaris, Keratella cochlearis and Brachionus spp. There was a significant negative correlation between salinity and rotifer density, biomass, and number of species. Rotifers were a component of the microzooplankton biomass during specific periods and at particular sites, dominating summer assemblages in tidal freshwater and river–estuary transition sites, plus the winter communities in estuarine waters. This observation indicates that rotifers may play an important trophic role by seasonally replacing metazoan nauplii as a biomass source in both tidal freshwater and estuarine ecosystems. The annual contribution of rotifers to the total microzooplankton biomass exclusive of heterotrophic dinoflagellates was brief but intensive, achieving over 50% of annual biomass during a 2–3 month period. Despite the small annual mean contribution of rotifers to the total microzooplankton biomass, rotifers may have a limited, but significant impact on the trophic dynamics of the zooplankton community in Chesapeake Bay and its major tidal tributaries.  相似文献   

9.
The recruitment variability of the marine fish species Dicentrarchus labrax, Platichthys flesus and Solea solea was evaluated in the Mondego estuary (Portugal) from 2003 to 2007. The relationships between sea surface temperature, NAO index, coastal wind speed and direction, precipitation and river runoff prior to the estuarine colonization and the abundance of 0-group fish were evaluated using gamma-based Generalized Linear Models. Dicentrarchus labrax and P. flesus 0-group decreased in abundance towards the end of the study period, while S. solea, despite low abundance in 2004, increased in abundance in 2007. For D. labrax, river runoff, precipitation and east–west wind were significant; for P. flesus, precipitation, river runoff and both north–south and east–west wind components were significant parameters, while for S. solea only river runoff was important. Results were compared with recent projections for climate change scenarios, to evaluate their effects on future recruitment levels.  相似文献   

10.
珠江口浮游动物的群落动态及数量变化   总被引：15，自引：0，他引：15  
根据2002年4月至2003年6月珠江口10个航次的调查资料,分析了丰水期(4—9月)和枯水期(10—3月)浮游动物的种类组成、优势种、群落结构、丰度和生物量的时空变化。经鉴定共有终生浮游动物71种和阶段性浮游幼虫7个类群。刺尾纺锤水蚤Acartia spinicauda是丰水期和枯水期皆出现的优势种。调查区的浮游动物可划分为河口类群、近岸类群、广布外海类群和广温广盐类群。丰水期浮游动物的平均丰度(1 131 ind.m-3)高于枯水期(700 ind.m-3),枯水期浮游动物的平均生物量(382 mg.m-3)高于丰水期(203 mg.m-3),浮游动物的丰度和生物量呈明显的斑块状分布。盐度是影响浮游动物种类、丰度和生物量分布的主要因素。  相似文献   

11.
Recent variations in the precipitation regime across southern Europe have led to changes in river fluxes and salinity gradients affecting biological communities in most rivers and estuaries. A sampling programme was developed in the Mondego estuary, Portugal, from January 2003 to December 2008 at five distinct sampling stations to evaluate spatial, seasonal and inter-annual distributions of fish larvae. Gobiidae was the most abundant family representing 80% of total catch and Pomatoschistus spp. was the most important taxon. The fish larval community presented a clear seasonality with higher abundances and diversities during spring and summer seasons. Multivariate analysis reinforced differences among seasons but not between years or sampling stations. The taxa Atherina presbyter, Solea solea, Syngnathus abaster, Crystallogobius linearis and Platichthys flesus were more abundant during spring/summer period while Ammodytes tobianus, Callionymus sp., Echiichthys vipera and Liza ramada were more abundant in autumn/winter. Temperature, chlorophyll a and river flow were the main variation drivers observed although extreme drought events (year 2005) seemed not to affect ichthyoplankton community structure. Main changes were related to a spatial displacement of salinity gradient along the estuarine system which produced changes in marine species distribution.  相似文献   

12.
Data obtained from 14 years of monthly samplings (1996–2009) were used to investigate the response of the crustacean zooplankton community to improving water quality in the Scheldt estuary. A strong reduction of poor water quality indicators, such as NH4+ and BOD5, as well as an increase in oxygen and in chlorophyll a concentrations were observed during the study period. During the study period, important changes were observed in the zooplankton community composition and spatial distribution. From 2007 onwards, most of the calanoid population, previously mainly found in the brackish water reach of the estuary, moved to the freshwater, where they reached higher abundances than previously observed. Simultaneously, cyclopoids populations strongly decreased in freshwater while cladocerans did not change their abundance, except during years with high chlorophyll a concentrations. Redundancy analyses (RDA) showed that the variability within the calanoid population can be explained by the improvement in water quality. Variability within the cyclopoids and cladoceran community is mainly explained by chlorinity and chlorophyll a concentrations. Their presence in the most polluted upstream area until 2007 suggests they are more tolerant to poor water quality than calanoids. Several hypotheses to explain the disappearance of cyclopoids after the move of calanoids to the freshwater are presented and discussed.  相似文献   

13.
根据珠江口枯水期(2013年11月)和丰水期(2014年8月) 24个站位调查资料,对中小型浮游动物种类组成、丰度分布、群落结构及其主要影响因子进行了研究.结果表明,枯水期和丰水期分别鉴定浮游动物成体91种和70种,以桡足类最为丰富.浮游动物种类从河口上游向外围逐渐增加.浮游动物丰度时空分布差异显著,丰水期平均值高达11 619. 78 ind/m~3,显著高于枯水期的1 707. 13 ind/m~3.桡足类在珠江口中小型浮游动物中占绝对优势,枯水期和丰水期分别占总丰度的80. 3%和93. 0%,对浮游动物的丰度分布起关键作用.强额孔雀哲水蚤(Parvocalanus crassirostris)、中华异水蚤(Acartiella sinensis)和刺尾纺锤水蚤(Acartia spinicauda)在两个水期均为主要优势种,小拟哲水蚤(Paracalanus parvus)和厦门矮隆哲水蚤(Bestiolina amoyensis)则分别在枯水期和丰水期具有较高的优势度.聚类分析的结果显示,枯水期和丰水期该水域浮游动物均可划分为3个群落.相关性分析表明,珠江口中小型浮游动物群落结构受多个环境因子的影响,但盐度是其中最为关键的非生物因子.  相似文献   

14.
The St Lucia Estuarine System, South Africa, has been under pressure due to recent drought conditions, which have led to closure of the mouth, extremely low lake levels and hypersaline conditions. The estuary mouth closed in June 2002 and remained so for almost 5 years before being breached by Cyclone Gamede in May 2007. After mouth closure in August 2007, salinities in South and North Lake gradually increased to reach highs of 68 at the end of 2008, while salinities in the Narrows gradually declined during the study. Fish were sampled biannually during 2006–2008 with seine and gill-nets at six sites throughout the system. A total of 20,422 fish from 72 species were recorded, with the number of species and CPUE gradually decreasing from the Narrows throughout the system to Hells Gate in the upper parts of the system. The fish community was dominated by the freshwater species Oreochromis mossambicus, and two estuarine species, Ambassis ambassis and Hyporamphus capensis. The fish community was dominated in terms of species numbers by marine spawning species, but in terms of fish abundance by freshwater and estuarine breeding species. Recruitment of post-larvae of 20 marine species into the system occurred following opening of the mouth in March 2007, highlighting the importance of the system as a nursery area for marine species. The fish community was structured by spatial differences between sampling areas and between the three main compartments of the system, and not by temporal changes during the study period.  相似文献   

15.
徐兆礼 《海洋与湖沼》2009,40(6):793-798
根据1959年和2002年在长江口海域28°00'—32°00'N,122°00'—123°30'E海域4个季节8个航次海洋调查资料,分析长江口夜光藻丰度的平面分布和季节变化特征。并结合同步的温度资料进行曲线拟合,构造数学模型,计算最适温度。结合夜光藻分布特征、生态类群,比较不同年间夜光藻丰度变化趋势,分析长江口富营养化趋势对夜光藻丰度的影响。结果表明,夜光藻出现率和平均丰度均表现为春季丰度极高而其它季节较低。例如春季长江口夜光藻的最高丰度可以达到48576.00ind/m3,出现率为96.30%。该种在春季有明显的集群性,其它季节聚集强度指标值较低。盐度是影响夜光藻的平面分布的主要因素。长江口夜光藻适温范围较窄。仅仅在15—20℃之间有较高的数量。通过曲线拟合计算,其丰度和温度的函数关系符合YieldDensity模型。进一步通过极值计算得出,夜光藻最适温度为17.53℃。在长江口,夜光藻往往生活在在长江径流和外海水形成的河口锋水域。因而是暖温性近海种。近年来在春季,长江口夜光藻数量明显增多,夜光藻数量的年间变化特征可能与长江口富营养化相关。夜光藻赤潮的爆发就是长江口海域富营养化的结果之一。  相似文献   

16.
《Oceanologica Acta》2002,25(1):13-22
This paper is the first to describe the spatio-temporal changes of mesozooplankton in the Seine estuary. Monthly samples were collected along the estuary in 1996 in order to analyse the seasonal changes of the mesozooplankton community and to identify the major environmental parameters that may influence the spatial distribution of zooplankton in this megatidal estuary. Statistical analysis (canonical correspondence analysis) showed that salinity was the main factor correlated with the longitudinal distribution of zooplankton. Marine species (Temora longicornis, barnacle larvae…) were located in the outer part of the estuary, while more oligohaline species (Eurytemora affinis) were recorded in the inner part of the estuary. A mixed zone was characterised by the presence of the neritic copepods Acartia spp. and Eurytemora affinis. The marine species (e.g. T. longicornis, Oikopleura dioica, Barnacle larvae) showed maximum abundance at the end of spring (June) while the most abundant estuarine species, E. affinis, peaked in late winter-spring and declined with the onset of summer. This copepod dominated the estuarine zooplankton throughout the year, and found in the Seine estuary very high favourable conditions to exhibit ultimate abundances (> 190 000 ind m–3) which is one order of magnitude higher than those found in other European estuaries. It represented the main prey for major planktonivorous species such as suprabenthic and fish species located living in the upstream zone of the Seine estuary.  相似文献   

17.
春季我国不同纬度河口浮游动物群落变化趋势   总被引：2，自引：0，他引：2  
根据2010-2012年春季由南向北河口海域:北仑河口、九龙江口、瓯江口、长江口和灌河口的浮游动物调查资料;通过比较不同纬度河口浮游动物群落的生物多样性指数（H'）、物种更替率（R）和群落相似系数（S）;探讨了河口浮游动物群落特征沿着不同纬度变化的趋势。结果表明;自南向北5个河口可以划分为3个不同的浮游动物区系。北仑河口和九龙江口为南部亚热带区系;位于亚热带海域;以亚热带种为主;H'分别为1.01和2.18;两河口之间R值为65.52%;S值为51.28%;瓯江口和长江口为中部过渡区系;位于亚热带和温带过渡海域;亚热带种和暖温带种是主要出现的种类;H'分别为1.31和1.86;两河口之间R值为58.33%;S值为58.82%;灌河口单独为北部温带区系;位于温带海域;暖温带种是主要出现的种类;H'值为1.19;与其余河口物种更替率均高于80.00%;群落相似系数均低于32.00%;表明群落结构由南到北的变化非常显著。线性回归结果表明:我国不同河口之间浮游动物的物种更替率与纬度差（两河口所处纬度的差值;δN）呈正相关关系（R=0.026ΔN+0.608;p=0.002）;群落相似系数与纬度差呈负相关关系（S=0.034ΔN+0.578;p=0.001）。春季;我国不同纬度河口浮游动物群落结构的变化;主要是因为影响各河口的水温和水团存在较大差别所致。  相似文献   

18.
An analysis of the structural and functional characteristics of zooplankton community and their coupling with the synoptic situation was carried out for the spring period in the northern Sea of Okhotsk. The years of 2000 and 2001 may be referred to as “cold” type due to the significant extent of the ice-covered area. Based on the ice cover extent, the years of 2004 and 2005 may be referred to as “warm” years due to the decreased extent of the ice-covered area. The “cold” and “warm” years did not significantly differ from each other in terms of the total zooplankton biomass. In the northeast Sea of Okhotsk, the zooplankton abundance increased during the “cold” years, while, in its northwestern part, the zooplankton abundance increased during the “warm” years. The different types of years significantly differ in the species structure of the macrozooplankton community. The abundance of copepods was higher in the “warm” years, whereas the chaetognath abundance increased in the “cold” ones. These features of the dynamics and distribution of zooplankton in the northern part of the Sea of Okhotsk also affected its productivity. The higher production of the elements of the zooplankton community that was revealed in the “warm” years was caused by the increase in the seasonal P/B ratio of both nonpredatory and predatory species. In the “warm” years, the production of nonpredatory zooplankton was higher in the northwest, while, in the “cold” years, it was higher in the northeast of the area.  相似文献   

19.
Estuaries are used as nursery grounds by numerous marine species despite being usually subject to strong anthropogenic disturbances. Abundances of marine recruits (fish and crustacean decapods) and their main prey (mysids) were monitored by monthly sampling, from June 1997 to February 2009, in the lower reaches of the Guadalquivir estuary (SW Spain). During that period, unusually high and persistent turbidity events (HPTEs) were observed twice. Both HPTEs started with strong and sudden freshwater discharges after relatively long periods of very low freshwater inflow. Data from this time-series were used to test the hypothesis that HPTEs may negatively impact the nursery function of estuaries either by decreasing prey availability or by decreasing survival/arrival of marine recruits. During HPTEs, the commonest mysid (Mesopodopsis slabberi), a key species in the estuarine food web, showed a significant decrease in abundance. Likewise, some marine recruits that prey on M. slabberi and whose peaks of abundance within the estuary occur in summer–autumn (Engraulis encrasicolus and Pomadasys incisus) were less abundant during HPTEs. It is also suggested that HPTEs might have triggered a shift in the distribution of the most euryhaline prey (Neomysis integer) and predator (Dicentrarchus punctatus and Crangon crangon) species, towards more saline waters. This could have contributed to an increase in the inter-specific competition (for food/habitat) within the estuarine nursery area. The results discussed in this study call attention to the need to reduce as much as possible the anthropogenic pressures that may stimulate the occurrence of high and persistent turbidity events (HPTEs) in order to preserve the nursery function of temperate estuaries.  相似文献   

20.
Knowledge of estuarine hydrodynamics and water quality comes mostly from studies of large estuarine systems. The processes affecting algae, nutrients, and dissolved oxygen (DO) in small and shallow subtropical estuaries are relatively less studied. This paper documents the development, calibration, and verification of a three dimensional (3D) water quality model for the St. Lucie Estuary (SLE), a small and shallow estuary located on the east coast of south Florida. The water quality model is calibrated and verified using two years of measured data. Statistical analyses indicate that the model is capable of reproducing key water quality characteristics of the estuary within an acceptable range of accuracy. The calibrated model is further applied to study hydrodynamic and eutrophication processes in the estuary. Modeling results reveal that high algae concentrations in the estuary are likely caused by excessive nutrient and algae supplies in freshwater inflows. While algal blooms may lead to reduced DO concentrations near the bottom of the waterbody, this study indicates that stratification and circulation induced by freshwater inflows may also contribute significantly to bottom water hypoxia in the estuary. It is also found that high freshwater inflows from one of the tributaries can change the circulation pattern and nutrient loading, thereby impacting water quality conditions of the entire estuary. Restoration plans for the SLE ecosystem need to consider both a reduction of nutrient loading and regulation of the freshwater discharge pattern.  相似文献   

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