Carbon flows in the Westerschelde estuary (The Netherlands) evaluated by means of an ecosystem model (MOSES)

The autotrophic production and heterotrophic consumption of organic matter in the Westerschelde, a highly turbid and eutrophic estuary in the Southwest Netherlands is examined by means of a dynamic simulation model. The model describes the ecologically relevant processes in thirteen spatial compartments and adequately fits most observed data.Three autotrophic processes are included in the model. Net pelagic photosynthetic production is relatively low (average 41 gC m^–2 yr^–1) and three spatial compartments near the turbidity maximum zone are respiratory sinks of phytoplankton biomass. According to the model, net phytobenthic primary production is more important than pelagic primary production in the upstream half of the Westerschelde. On the scale of the entire estuary, benthic primary production amounts to about 60% of pelagic primary production. Water-column nitrification, which is very important in the nitrogen cycle, is most pronounced near the turbidity zone where it accounts for the major autotrophic fixation of carbon (up to 27 g C m^–2 yr^–1). Viewed on the scale of the total estuary, however, the process is not very important.Less than 20% of total organic carbon input to the estuary is primary produced, the remainder is imported from waste discharges and from the river.The degree of heterotrophy of the Westerschelde estuary proved to be one of the highest yet reported. On average 380 g carbon per square metre is net lost per year (range 200–1200 gC m^–2 yr^–1). The yearly community respiration (bacterial mineralization, respiration of higher trophic levels and sedimentation) is 4 to 35 times (estuarine mean of 6) higher than the net production. This degree of heterotrophy is highest near the turbidity maximum and generally decreases from the freshwater to the seaward boundary. About 75% of all carbon losses can be ascribed to pelagic heterotrophic processes; the sediment is only locally important.Mineralisation rates are highest in the turbidity region, but as only a fraction of total carbon resides here, less than 20% of all organic carbon is lost in this part of the estuary. This result is in contradiction with a previous budget of the estuary, based on data of the early seventies, where more than 80% of all carbon was estimated to be lost in the turbidity zone. Part of this discrepancy is probably caused by changes that have occurred in the estuary since that time.Due to the high heterotrophic activity, nearly all imported and in situ produced carbon is lost in the estuary itself and the Westerschelde is an insignificant source of organic matter to the coastal zone.The model estuary acts as a trap for reactive organic matter, both from the land, from the sea or in situ produced. Internal cycling, mainly in the water column, results in the removal of most of the carbon while the more refractory part is exported to the sea.     

Tidal dispersal of salt marsh insect larvae within the Westerschelde estuary

In the Westerschelde estuary, salt marshes are present as isolated patches fringing the estuary. In the present paper tidal transport of stem-boring larvae of Agapanthia villosoviridescens (Coleoptera) from salt marshes of the upper reaches of the Westerschelde estuary to marshes of the lower reaches is demonstrated. The evidence for the origin of the larvae is based on comparisons of growth and development characteristics of larvae found in flood debris belts and resident larval populations. These characteristics are different on the various salt marshes along the Westerschelde, probably as a result of estuarine gradients. Additional evidence for the larval origin comes from the plant composition of the flood debris. The occurrence of upward tidal transport is discussed. Considering the comparatively large area of salt marshes in the upper estuary, tidal dispersal of larvae probably will be dominated by transport in seaward direction. So far, very little is known on the role of tidal currents with regard to the exchange between salt marsh populations. The present results suggest that tidal transport may not only be important for dispersal of aquatic organisms in an estuary, but also for organisms inhabiting the semi-terrestrial estuarine salt marshes.     

Estimating estuarine residence times in the Westerschelde (The Netherlands) using a box model with fixed dispersion coefficients

The residence time of the water masses in the Westerschelde estuary was determined using a simple compartment-model that simulates the advective-diffusive transport of a conservative dissolved substance (chlorinity). The residence time of a water parcel in the upstream part of the estuary (i.e. the time needed for this water parcel to leave the estuary) varied from about 50 days in winter to about 70 days in summer. The most seaward compartment had residence times of about 10-15 days.Dispersive coefficients that are fixed in time were able to reproduce the observed salinity distributions very well in the Westerschelde. They were obtained by calibration on observed chlorinities. It is argued that the apparent relationship of dispersive coefficients with freshwater flow, which is observed in certain studies, could (partly) reflect the deviation from steady state conditions which are required assumptions to calculate these dispersive coefficients directly from salinity profiles.     

Influence of pollution on the harpacticoid copepods of two North Sea estuaries

Seasonal monitoring of the meiobenthos in the Dutch estuaries revealed an anomaly in density and diversity of harpacticoid copepods in the Westerschelde.Another Dutch estuary, the Eems Dollard, has comparable hydrodynamical, physical and sedimentological, characteristics and a similar fauna, but even in the severely organically polluted oligohaline mudflats of this estuary, annual average density and diversity of endo-epibenthic harpacticoid communities are higher than at similar less enriched meso- to polyhaline biotopes of the Westerschelde.Besides the concentrations of inorganic pollutants, such as phosphates and nitrates, the concentrations of pesticides, cyanide, detergents, phenoles, oils, polychlorobenzenes, polycyclic aromatic hydrocarbons and heavy metals were compared in both estuaries and compared to suggested permissive levels when available. From this it appears that these pollutants are present in the Westerschelde either in too low concentrations to be considered dangerous or at concentrations comparable to those occurring in the Eems Dollard, except for heavy metals.The load of a.o. Zn, Cu and Pb is distinctly and persistently higher in sediments and suspensions of the Westerschelde than in the Eems Dollard and copper is continuously present in a concentration at which, according to bioassays, egg production and larval development of planktonic copepods are severely affected. The remarkable scarcity of harpacticoid life on nutrient rich mudflats of the Westerschelde is thus probably due to heavy metal pollution.Since no other hardbodied meio- and macrobenthic taxa nor the plankton of this estuary show such a marked impoverishment, benthic harpacticoids prove to be suitable as indicators for the first stages of ecosystem-breakdown in estuarine and coastal zones polluted by trace-metals.     

Meiobenthic distribution and nematode community structure in five European estuaries

Meiofauna from the intertidal zone of five European estuaries (Ems, Westerschelde, Somme, Gironde, Tagus) was investigated. Samples represented a cross section of various benthic habitats from near-freshwater to marine, from pure silts to fine-sandy bottoms. The meiobenthic community comprised everywhere a fauna strongly dominated by nematodes, with meiobenthic density increasing with increasing salinity. The Ems differed from the other estuaries due to the presence of a well developed community of Copepods, Gastrotrichs, large Ciliates and/or soft-shelled Foraminiferans in some sites. The Westerschelde stood out due to the near-absence of harpacticoid copepods and, as in the Tagus, the lower meiobenthic densities in the marine part of the estuary. For nematode community analysis, we also included data from the Tamar which were obtained from the literature (Warwick &; Gee, 1984). This resulted in the enumeration of 220 species, belonging to 102 genera, each with a characteristic distribution along the salinity, sedimentary and latitudinal gradients. Using the multivariate technique CANOCO, a zonation along these different physicochemical determinants was observed as well although salinity and sediment characteristic (scale of hundreds of meters to kilometers) proved to be more important in explaining community structure than latitudinal differences (scale of hundreds of kilometers). Nematode diversity was nearly entirely determined on the genus level and was positively related to salinity. Deviations from this general trend in the Gironde and the Tamar were attributed to sedimentary characteristics or to low macrobenthic predation. The presence of a typical opportunistic colonizing nematode species Pareurodiplogaster pararmatus in the low-salinity region of the Gironde could indicate (organic?) pollution or disturbance of the intertidal mud-flats.     

Distribution et écologie des associations d’ostracodes récents de l’estuaire de Tahadart (Maroc Nord-Occidental)

Forty-five ostracod species were identified for the first time in the Tahadart estuary (NW Morocco). They can be grouped into five different ecological assemblages, which characterise four estuarine ecozones. A first ecozone occurs in temporary waters located between the tidal channels of the inner estuary and it is characterised by ostracod species typical of fresh to brackish waters. In the main estuary area, the ostracod fauna is dominated by clearly euryhaline species that account for nearly 70% of the entire fauna. The relative abundance of the different assemblages allows us to subdivide the estuarine environment along a longitudinal profile into mouth, outer and inner estuary. The estuary's mouth displays the highest values of marine euhaline, phytal and periphytal as well as ubiquitous species and the lowest values of very euryhaline species; the latter are the only species present in the inner estuary. The outer estuary exhibits intermediate percentages of the different ecological assemblages. This distribution, characterized by the absence of limnic species, points to the influence of marine waters in an open estuary with a low fresh water input. In the estuary's mouth, as well as in the outer estuary, where the slikke and schorre are well developed, the distance to the emersion line is underlined by the lower occurrence of marine and ubiquitous species and the higher occurrence of the very euryhaline ones. The Tahadart estuary displays a moderate to high ostracod diversity with distinct differences among the ecological zones. The stress of this environment is highlighted by the low diversity characteristics of extreme environments, alike in the inner estuary and in some areas located far from the emersion level. The relative position with respect to the emersion line, as well as the presence of gross detritic sediments and vegetation, appear to be of importance for the good development of the ostracods.     

Fish assemblages associated with urban structures and natural reefs in Sydney,Australia

Abstract Fish ecology in urban estuaries is poorly understood. As coastal landscapes are transformed, recognizing the impact that urban structures, such as marinas, seawalls and wharfs, have on local fish populations is becoming increasingly important. The extent to which fish are able to maintain natural ecological assemblages can be measured, to a certain extent, by how closely they mimic natural habitats. In Sydney Harbour, assemblages of fish associated with artificial structures were compared with those associated with natural rocky reefs. Sampling was carried out in five locations, each with a marina, swimming enclosure and natural reef. In each location, different habitats supported different assemblages, but differences between habitats were not consistent among locations. Subsequent sampling compared artificial and natural sites in three different areas in each of three different estuaries. Results indicated that differences in fish assemblages between artificial and natural sites were greater than differences between sites within each habitat, but there were no patterns among different positions in an estuary or from estuary to estuary. This study provides initial evidence that, although artificial habitats generally support the same species as found on natural reefs, assemblages usually differed between natural and artificial habitats. In addition, without knowing if these habitats do, in fact, sustain viable populations of fish, it would be premature to label artificial structures as effective habitat for fish.     

Evolutionary refugia and ecological refuges: key concepts for conserving Australian arid zone freshwater biodiversity under climate change

Refugia have been suggested as priority sites for conservation under climate change because of their ability to facilitate survival of biota under adverse conditions. Here, we review the likely role of refugial habitats in conserving freshwater biota in arid Australian aquatic systems where the major long‐term climatic influence has been aridification. We introduce a conceptual model that characterizes evolutionary refugia and ecological refuges based on our review of the attributes of aquatic habitats and freshwater taxa (fishes and aquatic invertebrates) in arid Australia. We also identify methods of recognizing likely future refugia and approaches to assessing the vulnerability of arid‐adapted freshwater biota to a warming and drying climate. Evolutionary refugia in arid areas are characterized as permanent, groundwater‐dependent habitats (subterranean aquifers and springs) supporting vicariant relicts and short‐range endemics. Ecological refuges can vary across space and time, depending on the dispersal abilities of aquatic taxa and the geographical proximity and hydrological connectivity of aquatic habitats. The most important are the perennial waterbodies (both groundwater and surface water fed) that support obligate aquatic organisms. These species will persist where suitable habitats are available and dispersal pathways are maintained. For very mobile species (invertebrates with an aerial dispersal phase) evolutionary refugia may also act as ecological refuges. Evolutionary refugia are likely future refugia because their water source (groundwater) is decoupled from local precipitation. However, their biota is extremely vulnerable to changes in local conditions because population extinction risks cannot be abated by the dispersal of individuals from other sites. Conservation planning must incorporate a high level of protection for aquifers that support refugial sites. Ecological refuges are vulnerable to changes in regional climate because they have little thermal or hydrological buffering. Accordingly, conservation planning must focus on maintaining meta‐population processes, especially through dynamic connectivity between aquatic habitats at a landscape scale.     

Copepod biomass in an estuarine and a stagnant brackish environment of the S. W. Netherlands

In the mesohaline zone of the Westerschelde estuaryEurytemora affinis is the dominant copepod, demonstrating large biomass values nearly throughout the year. In the meso-polyhaline Lake VeereAcartia tonsa is abundant, mainly during summer. In spring a small population ofEurytemora americana is found. The tidal estuary harboured far denser copepod populations throughout the year than the stagnant brackish lake water. The average yearly copepodid+adult biomass in the Westerschelde estuary was approx. 850 mg/m³ (wet weight), in Lake Veere approx. 130 mg/m³. Temporarily low oxygen values did not influence negatively the copepod populations in the Westerschelde estuary. The seasonal distribution of the dominant copepods in both areas is explained in the light of recent litterature data. PerennialEurytemora affinis abundance in the Westerschelde estuary must be mainly caused by large concentrations of nannodetritus particles, bacteria included, throughout the year.Acartia tonsa in Lake Veere has to thrive mainly on nannophytoplankton. Communication no. 141 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherland.     

Fine-scale parallel patterns in diversity of small benthic Arctic charr (Salvelinus alpinus) in relation to the ecology of lava/groundwater habitats

It is critical to study factors that are important for origin and maintenance of biological diversity. A comparative approach involving a large number of populations is particularly useful. We use this approach to study the relationship between ecological factors and phenotypic diversity in Icelandic Arctic charr (Salvelinus alpinus). Numerous populations of small benthic charr have evolved in lava springs in Iceland. These charr appear morphologically similar, but differ in important morphological features related to feeding. We found a clear relationship between diversity in morphology, diet, and ecological factors among populations. In particular, there were clear differences in morphology and diet between fish coming from habitats where the lava spring flowed on as a stream compared to habitats where the lava spring flowed into a pond. Our study shows that ecological factors are important for the origin and maintenance of biological diversity. The relationship between phenotype and ecological factors are observed on a fine scale, when comparing numerous populations that are phenotypically similar. This strongly suggests that for understanding, managing, and conserving biological diversity important ecological variables have to be taken into the account.     

Comparative spring distribution of zooplankton in three macrotidal European estuaries

The zooplankton of three european estuaries (Ems, Gironde and Westerschelde) was investigated during spring 1992 by means of samples taken along the salinity gradient. The three estuaries are comparable in terms of total area, flushing time and salinity gradient but differ by their level of eutrophication (highest in the Westerschelde), suspended matter concentration (highest in the Gironde) and potential phytoplankton production (highest in the Ems). Copepods and meroplankton dominated the zooplankton in the three estuaries. The dominant copepod species were Eurytemora affinis and Acartia bifilosa. The distribution of E. affinis along the salinity gradient differed between the estuaries. Peaks of abundance were observed at 0 PSU in the Gironde, 6 PSU in the Ems and 9 PSU in the Westerschelde. The downstream shift of the population in the Westerschelde was likely due to anoxic conditions occurring in the oligohaline zone. In the Gironde the downstream distribution of E. affinis was limited by the very high suspended matter concentration found in the maximum turbidity zone. Whatever the estuary, the parameters of the population of E. affinis and maximum abundance values were similar. However, the influence of the better quality of the available food was suggested in the Ems where individual dry weights and egg production were higher than in the two other estuaries. The influence of a good quality of food in the Ems was confirmed by the development of a large population of Acartia bifilosa (as abundant as E. affinis) and highest values of adult individual weights.The meroplankton (essentially Polychaete and cirripede larvae) was much more developed in the Ems than in the Westerschelde and Gironde. This was likely due to the large extent of mudflats and hard substrates in the Ems favouring adult settlement and hence the number of larvae locally produced.     

Functional landscapes in cities: a systems approach

Human enterprise and endeavour increasingly influence global processes of change, from the planetary scale down to the very local. Cities are hubs of human activity, and as the places where the majority of the world’s population live we must, when looking into an uncertain future, consider how we think about urban design. Cities are densely inhabited, lived-in landscapes where human presence and perceptions are deeply enmeshed with biophysical and built infrastructures. As such, they present complex mosaics of different habitats and competing uses, ever changing in response to human and physical drivers. If designed properly, green infrastructure can contribute many important functions to a city. Efforts to strategically make use of green infrastructure can benefit considerably from a systems perspective where linkages and cross-boundary dynamics are at the very least as important as individual components. Design, planning and governance of requirements for green infrastructure also extend far beyond biophysical elements and components. Recognition of interconnections between individual green spaces, green infrastructure and the built environment, the physical environment and diverse actors, and formal and informal governance arrangements—as outlined in the four design principles in this article—is a first important step towards a more comprehensive and inclusive approach, not least to green infrastructure planning and design.     

Multiscale landscape genomic models to detect signatures of selection in the alpine plant Biscutella laevigata

Plant species are known to adapt locally to their environment, particularly in mountainous areas where conditions can vary drastically over short distances. The climate of such landscapes being largely influenced by topography, using fine‐scale models to evaluate environmental heterogeneity may help detecting adaptation to micro‐habitats. Here, we applied a multiscale landscape genomic approach to detect evidence of local adaptation in the alpine plant Biscutella laevigata. The two gene pools identified, experiencing limited gene flow along a 1‐km ridge, were different in regard to several habitat features derived from a very high resolution (VHR) digital elevation model (DEM). A correlative approach detected signatures of selection along environmental gradients such as altitude, wind exposure, and solar radiation, indicating adaptive pressures likely driven by fine‐scale topography. Using a large panel of DEM‐derived variables as ecologically relevant proxies, our results highlighted the critical role of spatial resolution. These high‐resolution multiscale variables indeed indicate that the robustness of associations between genetic loci and environmental features depends on spatial parameters that are poorly documented. We argue that the scale issue is critical in landscape genomics and that multiscale ecological variables are key to improve our understanding of local adaptation in highly heterogeneous landscapes.     

Dispersal Potential is Affected by Growth-Hormone Transgenesis in Coho Salmon (Oncorhynchus kisutch)

Potential ecological consequences on the natural environment of fast‐growing transgenic fish with elevated intrinsic growth rates is an important question should such fish be allowed in commercial production systems. One trait that will strongly affect the spatial extent of consequences is the propensity of transgenic fish to disperse. We addressed this question in three experiments using different measures of spatial dispersal where we compared very young genotypically wild coho salmon with transgenic conspecifics in terms of: (i) group cohesion, (ii) exploratory behavior, and (iii) up‐ and downstream movements. Transgenic fish were more loosely aggregated, more likely to explore, and less likely to swim upstream, but equally likely to disperse downstream compared with genetically wild fish. These results show that dispersal behavior has been affected by transgenesis and that transgenic fish therefore may venture into habitats previously not used by wild fish. Given the importance of dispersal in ecological risk‐assessment of transgenic fish, continued work within this area is warranted and experimental habitats should mimic the potential receiving natural habitats to which transgenic fish are likely to escape or be released to.     

长江口潮沟大型底栖动物群落的初步研究

通过对长江口崇明东滩潮沟系统与大型底栖无脊椎动物进行取样调查 ,研究了潮沟不同生境的底栖动物群落及其多样性 ,分析了潮沟生境异质性与底栖动物群落的关系。研究发现 :①潮沟剖面中出现明显的动物群落分带现象 ,从潮沟底、潮沟边滩到草滩 ,底栖动物种类、生活型组成和生活类群比例反映了河口潮滩潮沟底栖动物生态系列 ;②密度和生物量的分布皆为潮沟边滩 >草滩 >潮沟底 ,但密度与生物量的面上群 /面下群值格局却有不同 ,说明了密度和生物量的优势生活型和生活类群随潮沟生境的差异而变化 ;③潮沟系统 3种生境的多样性指数D ,H′和J值均为草滩 >潮沟边滩 >潮沟底 ,是潮沟系统生境结构分化的结果。潮沟底和潮沟边滩等特殊生境的存在 ,提高了淤泥质河口潮滩的生境异质性 ,说明了潮沟系统在维持河口生态系统底栖动物物种多样性中的重要作用。     

Changes in phytoplankton biomass and primary production between 1991 and 2001 in the Westerschelde estuary (Belgium/The Netherlands)

The Westerschelde estuary is a very polluted and turbid estuary, but the last decade the waterquality improved. Dredging activity also increased in 1997 to allow bigger ships to enter the port of Antwerpen. This could potentially decrease the light conditions for the phytoplankton. Because of all these recent changes in the estuary we studied primary productivity in 2001 and compared it to values in 1991. The results show that due to a decrease in discharge in particulate and dissolved organic carbon the oxygen concentrations in general have increased in the upstream region, although in spring and summer low oxygen concentrations (10–30% saturation) can still be found. Phosphate and ammonia concentrations have decreased and the zone of nitrification which was very large in 1991 has become very small and is now located in the uppermost upstream region of the estuary. Si-concentrations have remained the same. All nutrient concentrations are still high enough not to limit phytoplankton growth. Turbidity remained unaltered as a result of the dredging works, and as a result phytoplankton biomass in most of the estuary did not show a decrease, although there were signs that in the upstream region phytoplankton biomass decreased, possible caused by increased grazing pressure. The relationship between phytoplankton biomass and primary productivity did not change, and from the data it can be concluded that the dredging activity will not influence the gross and net primary productivity of the phytoplankton.     

Seasonal composition and spatial distribution of hyperbenthic communities along estuarine gradients in the Westerschelde

The hyperbenthic fauna of the Westerschelde estuary was sampled in spring, summer and winter of 1990 at 14 stations along the salinity gradient. Mysids dominated the hyperbenthos in each season. Other important species, either permanently (e.g. amphipods and isopods) or temporarily (e.g. fish larvae and decapod larvae) hyperbenthic, belong to a variety of faunistic groups. Spatial structure was stable through time: the estuary could be divided in the same geographically defined zones in each season. Each zone had a characteristic fauna. Gradients in salinity, dissolved oxygen and turbidity correlated strongly with the observed variation in community structure. The spatial patterns dominated over the temporal patterns, especially in the brackish part of the estuary. In the marine part, seasonal differences in the communities were more pronounced due to the occurrence of a series of temporary hyperbenthic species in spring and summer. In each season, the upstream (brackish) communities were characterized by few species occurring in very high numbers, whereas the downstream (marine) communities were composed of many species but at lower densities.     

Evidence for spatial limitation of the bluestripe snapper Lutjanus kasmira in French Polynesia from parasite and otolith shape analysis

The study focused on small‐scale location and movement patterns of the bluestripe snapper Lutjanus kasmira on the north coast of Moorea (Society Archipelago, French Polynesia, south‐central Pacific). Juveniles of this species occur in the estuary, and adults occur widely in the lagoon, the outer slope and in the intermediate channel, where fish aggregate in large schools during daytime. While fish were all sampled within a few hundred metres, they exhibited significantly different parasite fauna and otolith shapes according to their locality: estuary, lagoon, channel and outer slope. While juveniles did not exhibit any parasites in the estuary parasitological and otolith‐shape data suggest that adults rarely move between their three adjoining habitats, and more interestingly that large aggregations in the channel are formed predominantly by resident individuals with limited local movement, including at night. Besides giving some information on the host biology, such findings may have application in local fisheries management.     

Unravelling the life-history patterns and habitat preferences of the Japanese eel (Anguilla japonica) in the Pearl River,China

Eels have fascinated biologists for centuries due to their amazing long-distance migrations between freshwater habitats and very distant ocean spawning areas. The migratory life histories of the Japanese eel, Anguilla japonica, in the waters of south China are not very clear despite its ecological importance, and the need for fishery regulation and management. In this study, strontium (Sr) and calcium (Ca) microchemical profiles of the otoliths of silver eels were measured by X-ray electron probe microanalysis based on data collected from different habitats (including freshwater and brackish habitats), in the large subtropical Pearl River. The corresponding habitat preference characteristics were further analysed using redundancy analysis (RDA). A total of 195 Japanese eels were collected over 6 years. The collected individuals ranged from 180 to 771 mm in total length and from 8 to 612 g in body weight. Two-dimensional pictures of the Sr:Ca concentrations in otoliths revealed that the A. japonica in the Pearl River are almost entirely river eels, spending the majority of their lives in fresh water without exposure to salt water, while the catadromous migration time has delayed about 1 month in the Pearl River estuary in the past 20 years. RDA analysis further indicated that juveniles and adults preferred water with high salinity and high tide levels. Youth preferred habitats with high river fractals. Our findings contribute to a growing body of evidence showing that the eels are extremely scarce currently and conservation measures against them are imminent, including the protection of brackish and freshwater areas where they live in south China.     

河口盐沼植物对大型底栖动物群落的影响

通过对长江口崇明东滩盐沼海三棱燕草带大型底栖无脊椎动物进行取样调查,研究了不同盐沼底栖动物群落结构及其多样性特征,分析了盐沼植物群落特征与底栖动物群落的关系。研究发现。（1）沿着河口盐沼海拔梯度,从低位盐沼到高位盐沼,底栖动物群落结构及多样性具有明显的梯度变化;（2）盐沼植被与底栖动物群落有密切的关系,尤其是植株高度,地下部分生物量与底栖动物密度,Shannon-Weiner多样性指数,物种丰度的相关性最显著。（3）盐沼植被影响底栖动物群落,是由于植物的地下部分和地下部分结构导致盐沼生境结构复杂,增加了沉积物表层环境的结构异质性,使生境多样化,给底栖动物提供大量生活空间,（4）不同盐沼带海三陵蔗草群落的差异,提供了盐沼表层地貌的变化,这种变化及植物结构的复杂化,在这一些动物提供拓殖地的同时,也为底栖动物躲避捕食者提供了避护所;（5）盐沼植被可以改变口潮滩生境中的沉积环境,并通过消浪、缓流及调节有机质的输入动态和沉积作用而影响底栖动物群落的组成和结构。