Larval dispersion of the estuarine crab Neohelice granulata in coastal marine waters of the Southwest Atlantic

The estuarine brachyuran crab Neohelice granulata export their larvae from the parental intertidal population of the Mar Chiquita coastal lagoon, and probably other populations, to marine waters. The degree of larval dispersion or self-recruitment of populations is unknown. We evaluated the presence of all larval stages of N. granulata in coastal waters of Argentina between 37.9° and 35.8° S, at two different spatial scales: a broad scale of tens to hundreds of kilometers from the Río de la Plata estuary in the north, to Mar Chiquita lagoon in the south, and a small scale of hundreds of meters to some kilometers around the mouth of Mar Chiquita, during spring and summer. Additionally, we registered the larval composition and density at San Clemente creek population, in Samborombon Bay (Río de la Plata estuary), every 3 h along a 30-hour period. Evidence indicates that larval release of N. granulata is temporally synchronized with nocturnal ebb tides and all development from Zoea I to Zoea IV occur in areas close to the parental population, even with very different oceanographic characteristics. A possible mechanism based on salinity selection and wind-driven transport is proposed for such behavior, and some considerations related to the connectivity of present populations are made.     

Short time-scale wind forced variability in the Río de la Plata Estuary and its role on ichthyoplankton retention

The Río de la Plata Estuary presents a strong bottom salinity front located over a submerged shoal. Apparently favored by retention processes, it is a spawning ground for several coastal fishes. This estuary is very shallow and essentially wind driven and, moreover, in time scales relevant to biota, estuarine circulation is wind dominated and highly variable. Two intriguing questions are, therefore, how this system can favor retention and what the involved mechanisms are. This paper qualitatively explores mechanisms involved in the estuary where retention is favored applying numerical simulations in which neutral particles – simulating fish eggs and early larvae – are released along the bottom frontal zone and tracked for different wind conditions. Results suggest that retentive features can be a consequence of estuarine response to natural wind variability acting over bathymetric features. For winds from most directions, particles either remain trapped near their launching position or move northeastward to southwestward along the shoal. As alternation of winds that favor along-shoal motion is the dominant feature of wind variability in the region, a retentive scenario results from prevailing wind variability. Additionally, winds that tend to export particles with a poor chance of being restored to the front are neither frequent nor persistent. Results show, therefore, that physical forcing alone might generate a retentive scenario at the inner part of this estuary. The physical retention mechanism is more effective for bottom than for surface launched particles. Wind statistics indicate that the proposed mechanism has different implications for retention along the seasons. Spring is the most favorable season, followed by summer, when particles would have a larger propensity to reach the southern area of the estuary (Samborombón Bay). Fall and winter are increasingly less favorable. All these features are consistent with patterns observed in the region in organisms having different life history traits.     

Origin of resources and trophic pathways in a large SW Atlantic estuary: An evaluation using stable isotopes

The Río de la Plata (34° 36′ S, 55° 58′ W; Argentina and Uruguay) estuary, one of the most important South American estuarine environments, is characterized by weak seasonal freshwater discharge, low tidal amplitude (<1 m), a wide and permanent connection to the sea, and a salt-wedge regime. Using stable isotope analysis, we explored the relative importance of the different sources of primary production in the food web. Our results show that phytoplankton and macrodetritus from terrestrial salt and freshwater marshes both contribute to the food web of the Río de la Plata estuary. On the basis of the sampled species, we identified four trophic levels. The clam Mactra isabelleana, the calanoid copepod Acartia tonsa, and the opossum shrimp Neomysis americana are the primary consumers. The rays Atlantoraja castelnaui and Squatina guggenheim and the shark Galeorhinus galeus are the top predators. The Río de la Plata food web shows an important input of nutrients derived from phytoplankton. Rays, sharks, and predatory gastropods reveal an important contribution of C4 plants (likely Spartina spp.). However, production derived from C3 plants is also important for some species. The fishes Brazilian menhaden, Brevoortia aurea; the stripped weakfish Cynoscion guatucupa; and the whitemouth croaker, Micropogonias furnieri, showed differences in their isotopic signatures as juveniles and adults, indicating different food sources, and they were therefore treated as different components of the food web. Our data suggest that detritus from salt and freshwater marshes is reaching the Río de la Plata estuary and can be an important allocthonous source of energy to this environment.     

Population ecology of Sinelobus stanfordi (Crustacea: Tanaidacea) in a temperate southern microtidal estuary

Sinelobus stanfordi is a tanaidacean of worldwide distribution of considerable significance within coastal ecosystems. The aim of this research was to provide essential information on the poorly-known population biology of this species. Benthic samples were taken seasonally from winter 2005 through summer 2007 along 155?km of shoreline within the Río de la Plata Estuary, Argentina. The density of this tanaidacean was higher in vegetated than in bare sediments. The smaller individuals flourished in spring and summer, whereas the larger mature members prevailed in the cooler seasons. Females were always twice as abundant as males. Copulatory females, with 18?±?8 eggs each, were collected during all the seasons. Five cohorts were distinguished by the von Bertalanffy growth function. This research represents a baseline investigation for future studies on the population dynamics of S. stanfordi both in this estuary and in other places where this species is found.     

Distribution of whitemouth croaker (Micropogonias furnieri, Desmarest 1823) larvae in the Río de la Plata estuarine front

Whitemouth croaker (Micropogonias furnieri) larvae obtained and hydrographic data collected in the Rio de la Plata estuary (35°S–56°W) between 1987 and 2000 were used to explore the early life stages spatial and temporal distribution patterns and their relation to oceanographic features. The spatial distribution, restricted to a band in the inner part of the estuary, coincided with the bottom salinity front and the maximum turbidity zone (MTZ, turbidity front). Larvae were present during the warmest months (October through May) within a range of 14–24.5 °C temperature and 0.9–33 salinity. A vertically stratified sampling performed in the region where the largest abundance was found (December 2005 and March 2006) was used to test the hypothesis that larvae retention occurs in the bottom salinity front.The vertically stratified sampling showed larvae throughout the water column with high predominance in the river–estuary transition zone. A positive correlation between abundance and the bottom salinity horizontal gradient was found. The size analysis showed that the largest individuals (>10 mm SL), probably undergoing the settlement process, inhabited near the bottom and that the smallest (<10 mm SL) were present in the whole water column. Length distribution along the front showed no trend.Results support the estuarine retention hypothesis of previous studies on whitemouth croaker gravid females, eggs distribution and outcomes from a numerical simulation model. Retention in the salinity front/MTZ would allow larvae to benefit from food accumulation in the region, the high turbidity level provide shelter against predators and retention in the estuary secure closeness to the main nursery ground.     

椒江河口高混浊水混合过程分析

根据１９９１年洪季的实测资料分析了高度浑浊的椒江河口的混合过程,并探讨了水动力学和沉积动力学因素对河口混合的重要作用,调查研究表明,椒江河口最大浑浊带下的高浑浊水－浮泥层厚达１ｍ,高浑浊水－浮泥层与上覆水之间是泥跃层,泥跃层与高混浊水－浮泥层对水体稳定的作用比同期观测到的盐跃层大１７倍以上,当高浑浊水－浮泥层被侵蚀时,在高浑浊水－浮泥层中的低盐水体又增加了水体的垂向混合能力。     

长江河口盐度锋

根据1988－1991年河口锋面现场调查、上海市海岸带调查及历次标准断面调查资料对长江盐度场及盐度锋进行了分析，提出了由口门至外海纵向上存在着三级锋面现象：内侧锋面即长江河口锋为长江河口水与长江冲淡水的界面；羽状锋是长江口羽状流水与口外混合水的界面，它是长江口最主要的盐度锋面，也是长江口一个重要的生物地球化学带，对河口沉积过程及水下三角洲发育具有重要的影响。外侧锋面即海洋锋，是长江冲淡水的最外边缘。     

Morphology, hydrography and sediment dynamics in a mangrove estuary: The Konkoure Estuary, Guinea

The Konkouré Estuary in the Republic of Guinea is a poorly understood atypical mangrove system. Sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge, morphology, salinity, erosion and deposition processes, the settling of mud, physico-chemical processes and mangrove swamps. Here we present a consistent set of data aimed at characterising the estuary and thus, increasing our understanding of tropical systems, as well as studying the impact of human intervention in the region. Water elevations, current measurements, salinity, suspended sediment concentrations, bathymetry and sediment cover are presented following a 3 year survey of the Konkouré Estuary. Here we provide conclusive evidence that the Lower Konkouré is a shallow, funnel shaped, mesotidal, mangrove-fringed, tide dominated estuary, well mixed during low river discharge. The estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides. The Konkouré Estuary has been described as hypersynchronous, and has three terminal outlets, two of which are landward-directed, attesting to a tidal pumping effect, while the third one is seaward-directed, and is controlled by the mangrove. The suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the Turbidity Maximum zone (TMZ). The location of the TMZ is river-controlled and is correlated with residual currents but not with salinity front. A dam, constructed 130 km upstream, impacts on the hydrodynamics, and reduces the salinity intrusion by about 25%. It causes an increased low river discharge whereas its efficiency over high river flows is unclear.     

Sea surface height variability in the Rio de la Plata estuary from synoptic to inter-annual scales: Results of numerical simulations

A long term simulation of the barotropic circulation in the Río de la Plata estuary was performed with the aim of identifying the characteristic patterns of sea surface height (SSH) variability from synoptic to inter-annual time scales and their forcing mechanisms. Hamburg Shelf Ocean Model (HamSOM), forced by tides, monthly mean runoffs and 4-daily 10 m winds and surface atmospheric pressure from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was run. The solution was analyzed for the period 1965–2004. Inter-annual variability accounts for almost 10% of the variance. The first EOF mode of SSH variability on this time scale is associated with a mean anomaly of approximately 0.25 m at the upper estuary forced by both runoff and winds, which seems to be strongly associated with the ENSO cycles. Other two modes, with periodicities around 2.5 and 10 years were also found. Even though they are linked to weaker SSH anomalies, they are consistent with inter-annual modes of wind variability reported by other authors. Those modes are important, particularly if they act in phase, because they can provide a background for stronger surges. In contrast with the salinity field, SSH variability on seasonal time scales accounts for a very small percentage of variance and it is the combination of an annual and a semi-annual signal forced by winds and runoff, respectively. Approximately 90% of the variance is due to wind driven variability on sub-annual time scales. The most significant SSH anomalies in this band are associated with cyclogenetic events in the atmosphere, occurring either over Uruguay or over the Patagonian Shelf, whereas the strengthening or weakening of the semi-permanent South Atlantic anticyclone displays a relatively smaller influence. In agreement with previous publications, the estuary's spatial patterns in response to short-scale wind variability seem to be determined by wind direction more than by wind speed.     

Spatiotemporal distribution of fish eggs and larvae in the Huanghe(Yellow) River estuary,China in 2005–2016

Decreasing fish resources in estuaries is a subject of anthropogenic activities. Studies of the spatiotemporal distribution of fish eggs and larvae can help identify the status and processes underlying recruitment in a fishery. As the fifth largest river estuary in the world, the Huanghe (Yellow) River estuary (HRE) is a typical estuary that has been seriously aff ected by human activities. Annual surveys on ichthyoplankton and environmental factors were conducted in the months of May of 2005 and 2009-2016 in the HRE to investigate the spatiotemporal distribution of fish eggs and larvae and the associated infl uencing factors. A total of 23 and 20 species of eggs and larvae, respectively, were collected. The dominant orders were Perciformes (51.2%) and Clupeiformes (25.6%). The average number of fish species eggs and larvae were 6.0 and 4.1 in average abundance of 0.91 and 0.13 ind./m^3 , respectively. The dominant species were mainly low-commercial-value small-sized fishes, such as Clupanodon punctatus , Harengula zunasi, and Acanthogobius, whereas certain traditional commercial fishes, such as Trichiurus lepturus , and Clupea pallasii, were not seen. Analysis of the fish egg and larval community revealed four temporal assemblages and two spatial assemblages. Salinity was the main factor on the spatial distribution of ichthyoplankton communities, the species number and Shannon-Weiner diversity index (H′) of the fish egg and larval community near the river mouth with lower salinity were signifi cantly lower than the community far away from the river mouth with higher salinity. In addition, increases of water temperature promoted the number and abundance of fish species eggs, and the areas of abundant prey tended to have a more diversified and abundant of ichthyoplankton species. In overall, overfishing, dam construction, and other human activities were the main drivers that led to the substantial decline in fishery resources in the HRE.     

Ichthyoplankton spatial pattern in the inner shelf off Bahía Blanca Estuary, SW Atlantic Ocean

This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m⁻³ (eggs) and 4000 per 10 m⁻³ (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it.     

Classification of highly turbid Jiaojiang Estuary

ThisstudywassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49276274,theZhejiangProvinceNaturalScienceFoundationundercontractNo.490013,theChina-Australiabilateralscienceandtechnologyprogram,theAustralianInstituteofMarineScience,theModellingLaboratoryoftheMarineScienceintheSecondInstituteofOceanographyoftheStateOceanicAdministration.INTRODUCTIONTheJiaojiangEstuaryis1ocatedintheeasterncoastofChina,2OokmfromthesouthoftheChangjiangRiver(YangtzeRiver),linkedin…     

闽江冲淡水扩展范围的季节变化特征

利用2006～2007年春、夏、冬季3个航次的CTD资料分析闽江冲淡水扩展范围季节变化特征.通过分析闽江口及邻近海域温度、盐度的平面、垂直分布特征,结果表明:闽江冲淡水的扩展范围具有明显的季节变化.春季由于闽江口附近受到闽浙沿岸流的影响,冲淡水的扩展范围难以确定,但从盐度分布情况不难看到闽江口表层被盐度低于25的具有明显冲淡水特征的水体覆盖.夏季闽江口被温度高于27℃、盐度低于25的冲淡水覆盖,冲淡水前沿向东北扩展至罗源湾、三沙湾.冬季闽江径流减弱,闽江口主要受到闽浙沿岸水的影响,基本看不到闽江冲淡水的痕迹.春季、夏季闽江冲淡水明显的影响闽江口时,闽江口附近海域被25盐度等值线包围,25盐度等值线可作为闽江口明显受冲淡水影响的指征.     

Species composition, distribution, and invertebrate prey of fish assemblages in the Columbia River Estuary

The fish community of the Columbia River Estuary was sampled with trawl, beach seine, and purse seine over an 18 month period during 1980–1981. Seasonality of abundance and species richness in the estuary reflect the timing of migrations and the reproductive cycles of marine and anadromous species. Composition of the fish community and dominant species in the Columbia River estuary are similar to many smaller estuaries in the Pacific Northwest. These similarities reflect the influence of the nearshore marine environment on fish community structure throughout the West Coast as well as the wide geographic distribution and considerable physiological tolerance of many dominant euryhaline species. The distribution of fish assemblages within the Columbia River estuary is influenced by large seasonal variation in river discharge and salinity. Within large areas or salinity zones, species assemblages use different habitats and invertebrate prey. The distribution of abundance and the stomach fullness of fishes vary directly with the density of potential prey. We hypothesize that fish production may be limited by dynamic physical processes that control prey availability or the feeding efficiencies of predators in the highly turbid estuary.     

Environmental control on early life stages of flatfishes in the Lima Estuary (NW Portugal)

Several flatfishes spawn in oceanic waters and pelagic larvae are transported inshore to settle in the nursery areas, usually estuaries, where they remain during their juvenile life. Nursery areas appear as extremely important habitats, not only for juveniles but also for the earlier planktonic larval fish. Yet, the majority of nursery studies tend to focus only on one development stage, missing an integrative approach of the entire early life that fishes spent within a nursery ground. Thus, the present study assessed the influence of environmental parameters on the dynamics of the larval and juvenile flatfishes, throughout their nursery life in the Lima Estuary. Between April 2002 and April 2004, fortnightly subsurface ichthyoplankton samples were collected and juveniles were collected from October 2003 until September 2005. Larval assemblages comprised nine flatfish species, while only six were observed among the juvenile assemblages. Solea senegalensis and Platichthys flesus were the most abundant species of both fractions of the Lima Estuary flatfishes. Larval flatfish assemblages varied seasonally, without relevant differences between lower and middle estuary. Platichthys flesus dominated the spring samples and summer and autumn periods were characterized by an increase of overall abundance and diversity of larval flatfishes, mainly S. senegalensis, associated with temperature increase and reduced river flow. On the contrary, during the winter abundance sharply decreased, as a consequence of higher river run-off that might compromised the immigration of incompetent marine larvae. Juvenile flatfishes were more abundant in the middle and upper areas of the estuary, but the species richness was higher near the river mouth. Sediment type, distance from the river mouth, salinity, temperature and dissolved oxygen were identified as the main environmental factors structuring the juvenile flatfish assemblages. Juveniles were spatially discrete, with the most abundant species S. senegalensis and P. flesus associated with the middle and upper estuary, while the remaining species were associated with the lower estuarine areas. The larval fraction exhibited distinct dynamics from the juvenile estuarine flatfish community. Larval flatfishes showed a strong seasonal structure mainly regulated by biological features as the spawning season and also by seasonal variations of water characteristics. On the other hand, juvenile flatfishes were markedly controlled by site specific characteristics such as sediments structure, distance from the river mouth and salinity regime. The present study emphasized the idea that the environmental control varies throughout the ontogenetic development, stressing the importance of integrating all the early life of a species in flatfish nursery studies.     

Loggerhead turtles Caretta caretta (Linnaeus) preying on the invading gastropod Rapana venosa (Valenciennes) in the Río de la Plata Estuary

Here we report the first observations of loggerhead turtles Caretta caretta preying on a conspicuous molluscan invader, the rapa whelk Rapana venosa. An average number of 136 opercula were found in stomach contents of five turtles, the curved carapace length ranging in from 51 to 112 cm. No other alimentary items were found in the turtles analyzed. We suggest that the rapa whelk may constitute up to 100% of the diet for immature and mature loggerheads in the Río de la Plata estuary (Uruguay), highlighting the plastic nature of the foraging behavior of loggerheads.     

三峡工程蓄水前后秋季长江口鱼类浮游生物群落结构的动态变化初探

对长江口及其邻近海域2002年秋季与2003年秋季鱼类浮游生物的调查资料进行比较,分析三峡工程蓄水前后秋季长江口鱼类浮游生物群落结构特征变化.结果发现,蓄水后鱼类浮游生物种类和数量比蓄水前有所增加,群落结构和时空分布特征发生了明显的改变,一些分布在黄渤海的种类如方氏云ND022等开始在东海出现,并且部分鱼类的生殖时间上也发生了改变.利用相对重要性指数（IRI）对长江口鱼类浮游生物进行优势度检验,其优势种成分也发生了很大的变化,虽仍是以小型种类为主,但原占绝对优势的日本ND023优势度开始逐渐下降,成为常见种,而康氏小公鱼的数量急剧上升.阐明了长江口鱼类资源的补充及群落结构和多样性变化规律及其与环境的关系,为动态监测三峡工程对河口生态环境的影响提供科学依据.     

Diatom assemblages from surface sediments of the Río de la Plata estuary,Uruguay

The Río de la Plata estuary (RdlP) exhibits environmental gradients associated with the freshwater input and oceanic water intrusion. The aim of this study was to assess diatom species distribution in surface sediment samples related to such environmental gradients. The internal section of RdlP was dominated by Aulacoseira spp., Eunotia spp., Staurosirella martyi, Actinocyclus normanii and Thalassiosira baltica, indicatives of low salinity levels and high trophic conditions, associated with the riverine and estuarine regimes. The external section was dominated by Coscinodiscus radiatus, Thalassiosira spp., Paralia sulcata, Cyclotella striata, among other marine taxa, indicatives of high salinity and low trophic conditions, associated with the influence of the Southwestern Atlantic Ocean. Furthermore, the intermediate section presents a mixture of both diatom groups representing mixing conditions. The observed diatom species groups capture fairly well the RdlP environmental variability and can be reliably used for paleoenvironmental studies in this and other similar estuarine systems.     

Effects of substratum type on fish assemblages in shallow areas of a tropical estuary

While there is already a comprehensive understanding of the effects of environmental variables, such as dissolved oxygen, temperature and salinity, on the structure, biomass and metabolism of aquatic biota in estuarine habitats, the effect of sedimentation, a harmful underlying factor, remains unclear. The aim of this study was to assess the differences in fish assemblages along the freshwater to salt water gradient of a large tropical estuary, and to evaluate the effects on them of habitat disturbance associated with shallow water sedimentation in the intertidal areas. Fish and environmental variables were recorded in the upper, middle and lower salinity zones of the estuary at ebb tide in both the dry and wet seasons. Sediment samples associated with different levels of habitat disturbance were analysed using granulometry, and their organic content and dissolved oxygen levels were quantified. Water temperature, salinity, pH and dissolved oxygen levels were also measured. Habitat disturbance was found to be correlated with the density, biomass and richness of fish assemblages. A total of 77 species were recorded, forming two distinct fish assemblages, with the Eleotridae family dominating in the upper zone, and Gerreidae, Gobiidae and Tetraodontidae the most common in the middle and lower estuary. Changes in the structure of fish assemblages, including reductions in density, biomass and richness, were associated with disturbance to natural features, where muddy sediment was replaced by sandy sediment and the quantity of organic matter fell. Atherinella brasiliensis was the species which showed a preference for the disturbed areas in the middle and lower zones, while Dormitator maculatus showed a preference for them in the upper estuary. They may be taken as indicators of habitat disturbance due to shallow sedimentation.