Estuarine Communities Research Articles

Fish community diversity analyses in the Yangtze River estuary, China

Estuarine systems are considered as a typical ecotone,and an estuarine fish community study is consid-ered to be a fundamental ecological research study.Four facets(number of species,Pielou evenness,taxonomic distinctness and average taxonomic distinctness) of community diversity characteristics structuring by species level,abundance,binary data and classification levels were analyzed within the Yangtze River estuary,China,which is divided into three zones(Zone 1,Zone 2,and Zone 3) along the estuarine gradient.Fish sampling was conducted using bottom trawling seasonally from 2010–2011.The results showed that all four diversity parameters did not differ significant among seasons.However,number of species and average taxonomic distinctness both differed significantly among the different zones.An increasing trend in mean numbers of species from Zone-1(3.49 species)–Zone-3(10.13 species) was related to the stronger marine influence on the latter zones.Lower val-ues of average taxonomic distinctness in Zone-1 suggested that more species were closely related in Zone-1 than in Zone-2 or Zone-3,for example,8,20,and 19 families were recorded in Zone-1,Zone-2,and Zone-3,respec-tively.Although spatial changes in taxonomic distinctness and evenness were not significant,inverse patterns of the two parameters occurred.Nevertheless,evenness peaked in Zone-1 whereas more individuals were closely related in Zone-1 than in Zone-2 or Zone-3.Moreover,spatial patterns in community diversity were stronger than seasonal variations.This may reflect that salinity plays the major role in driving the estuarine fish community.This work analyzed the four facets of diversity estimations of fish community within the Yangtze River estuary,and further demonstrated that different measured parameters may highlight different information regarding com-munity structure,and will be useful for assessing estuarine fish community diversity.

Seasonal variability in stable isotopes of estuarine consumers under different freshwater flow regimes

Freshwater inflow from riverine sources is essential for estuarine productivity. How- ever, human alterations to freshwater flow have resulted in modifications to the seasonal complex- ities of estuarine communities. To quantify changes in energy transfer at the trophic guild and consumer levels that result from anthropogenic-altered flow, we evaluated seasonal trends over a 1 yr period in stable isotopes of carbon (δ 13 C), nitrogen (δ 15 N) and sulfur (δ 34 S) in nekton species sampled from 2 subtropical tidal rivers, one that is relatively natural and one that experiences reg- ulated flow discharges that result in autumnal high-flow events. Primary and secondary con- sumers in the flow-altered estuary exhibited a significant depletion in 13 C and enrichment in 15 N (~2‰ in both isotopes respectively) with the onset of the wet season, while the stable isotope val- ues of high trophic level species (i.e. ≥ tertiary consumers) remained relatively consistent, trends were not apparent in the natural estuary. These isotopic trends were evident in both benthic and pelagic consumers, suggesting a food web-wide influence of altered flow on nutrient dynamics. Although the relative trophic structure, based on δ 15 N, was consistent across seasons and among estuaries, the δ 34 S values were less seasonally variable in the flow-altered estuary and were indicative of more terrestrial/freshwater-influenced values compared to the natural estuary, suggesting a lengthened influence of high flow. Although limited in temporal scope, our results indicate a noteworthy difference in seasonal isotope dynamics of lower trophic level consumers in a flow-altered estuarine food web. The importance of this effect on ecosystem function warrants further attention.

Evaluation of seasonal variability in the food-web properties of coastal lagoons subjected to contrasting salinity gradients using network analyses

Salinity is a major factor influencing the abundance and composition of species and the overall organization of natural communities but its relevance in the maintenance of important functional processes such as energy flows, trophic structure, resilience and stability is lesser known. Estuarine communities from coastal lagoons in the Ebro Delta (Tancada, Encanyissada and Clot; Catalonia, NW Mediterranean) are subjected to anthropic variability in their salinity regime and offer a suitable setting for investigating differences in ecosystem functioning. To this aim, we conducted seasonal sampling of estuarine communities (from phytoplankton to birds) and we describe the structural and functional changes in carbon flows and trophic relationships using ecological network analysis (ENA). Results showed that summer biomass of Ruppia cirrhosa (annual species) in the two higher salinity lagoons is sufficient to sustain fish and invertebrate communities, whereas in winter they become plant-limited and enhanced detrital consumption is necessary for balancing the trophic models. In contrast, consumers in the low salinity lagoon dominated by Potamogeton pectinatus (pseudo-annual species) were not limited by plant abundance and seasonal differences in NPP:biomass ratios, total system troughoutput (TST), and ascendancy were the lowest, suggesting more stable functioning. The biomass of phytoplankton was low compared to that of benthic macrophytes, but accounted for similar rates of primary production (from 0.21 to 0.54gCm−2d−1 and from 0.01 to 1.96gCm−2d−1, respectively) and contributions to the TST (from 7.2 to 33.9% and from 0.6 to 39.3%, respectively). Therefore, seasonal variability in ecosystem fluxes was both controlled by the influence of salinity on plant species and by fluctuations in the abundance of phytoplankton. The combined effect of nutrients and salinity was found to have a strong influence on the ratio between pathways originated from phytoplankton and from benthic producers (R=0.99, p< 0.05). Overall, our results suggest that plant persistence could help to stabilize ecosystem functioning by providing a permanent source of food and habitat to consumers, and by removing some nutrients from the water column.

Effects of Shoreline Development on Composition and Physical Structure of Plants in a South Carolina High Marsh

Increased freshwater and nutrient runoff associated with coastal development is implicated in dramatically altering estuarine communities along eastern US shorelines. We examined effects of three categories of shoreline development on high-marsh environments within Murrells Inlet, South Carolina, USA by measuring sediment nutrients, porewater salinity, plant species diversity, and above- and belowground plant biomass. Effects on new plant growth also were examined in plot clearing and transplantation experiments. Greater nutrient availability in sediments along developed shorelines was reflected in greater aboveground biomass and nitrogen storage in Juncus roemerianus plant tissue. Plant species composition was not significantly different among levels of shoreline development. Zinc concentrations were greater in sediments from developed shorelines and may represent an easily measured indicator of shoreline development. Recently accelerating shoreline development in the southeastern USA may alter plant production, nitrogen storage, and sediment metal content in salt marshes.

Weak and Habitat-Dependent Effects of Nutrient Pollution on Macrofaunal Communities of Southeast Australian Estuaries

Among the impacts of coastal settlements to estuaries, nutrient pollution is often singled out as a leading cause of modification to the ecological communities of soft sediments. Through sampling of 48 sites, distributed among 16 estuaries of New South Wales, Australia, we tested the hypotheses that (1) anthropogenic nutrient loads would be a better predictor of macrofaunal communities than estuarine geomorphology or local sediment characteristics; and (2) local environmental context, as determined largely by sediment characteristics, would modify the relationship between nutrient loading and community composition. Contrary to the hypothesis, multivariate multiple regression analyses revealed that sediment grain size was the best predictor of macrofaunal assemblage composition. When samples were stratified according to median grain size, relationships between faunal communities and nitrogen loading and latitude emerged, but only among estuaries with sandier sediments. In these estuaries, capitellid and nereid polychaetes and chironomid larvae were the taxa that showed the strongest correlations with nutrient loading. Overall, this study failed to provide evidence of a differential relationship between diffuse nutrient enrichment and benthic macrofauna across a gradient of 7° of latitude and 4°C temperature. Nevertheless, as human population growth continues to place increasing pressure on southeast Australian estuaries, manipulative field studies examining when and where nutrient loading will lead to significant changes in estuarine community structure are needed.

Increased microbial activity in a warmer and wetter climate enhances the risk of coastal hypoxia

The coastal zone is the most productive area of the marine environment and the area that is most exposed to environmental drivers associated with human pressures in a watershed. In dark bottle incubation experiments, we investigated the short-term interactive effects of changes in salinity, temperature and riverine dissolved organic matter (rDOM) on microbial respiration, growth and abundance in an estuarine community. An interaction effect was found for bacterial growth, where the assimilation of rDOM increased at higher salinities. A 3 °C rise in the temperature had a positive effect on microbial respiration. A higher concentration of DOM consistently enhanced respiration and bacterial abundance, while an increase in temperature reduced bacterial abundance. The latter result was most likely caused by a positive interaction effect of temperature, salinity and rDOM on the abundance of bacterivorous flagellates. Elevated temperature and precipitation, causing increased discharges of rDOM and an associated lowered salinity, will therefore primarily promote bacterial respiration, growth and bacterivore abundance. Our results suggest a positive net outcome for microbial activity under the projected climate change, driven by different, partially interacting environmental factors. Thus, hypoxia in coastal zones may increase due to enhanced respiration caused by higher temperatures and rDOM discharge acting synergistically.

The effects of artificial sandbar breaching on the macrophyte communities of an intermittently open estuary

Artificial sandbar opening of intermittently open estuaries is a practice utilised worldwide to improve water quality, fishing, and recreational amenities and to prevent the flooding of adjacent properties. Breaching causes the water level to drop drastically, exposing plants to two water level extremes. With some exceptions, estuarine communities are adversely affected by this practice. Although breaching can happen naturally, artificial breaching is on the rise, and the impact of manipulating water levels on estuarine communities needs to be investigated. In this work, we described the breaching cycles of the Massaguaçu River Estuary and proposed flooding scenarios for the estuary's macrophyte banks based on our data. We calculated the relationship between plant distribution and flooding conditions and used our calculations to predict the estuary community's composition depending on the water level at breaching time. We discovered a strong relationship between plant distribution and flooding conditions, and we predicted that the estuarine community would be markedly different between flooding scenarios. Low frequency flooding scenarios would be related to submerged macrophytes and, as the flooding frequency increases, macrophytes would be replaced by amphibious plants, and eventually by the arboreal stratus. Therefore, we concluded that an increase in artificial breaching cycles would have a detrimental impact on the estuary community.

Impacts of plant invasions can be reversed through restoration: a regional meta-analysis of faunal communities

We quantified the effects of invasive Phragmites australis on estuarine faunal communities using meta-analysis to compare invaded to uninvaded marshes and then evaluated whether ecological restoration could reverse those effects. Relative to uninvaded marshes, the quantity and condition of fauna in invaded marshes was significantly poorer. We detected negative impacts to fauna residing in the mid-Atlantic but not in New England and to fauna utilizing the marsh surface but not to those inhabiting tidal creeks. By taxonomic group, we found that the invasion negatively affected nekton but not invertebrates. Both adult and sub-adult nekton were adversely affected, although the magnitude of the effect on the sub-adults was four times greater than that for adults. Our results indicate that negative effects on fauna within the mid-Atlantic region largely drove the overall results. When restored marshes were compared to uninvaded marshes there were no significant differences across all metrics assessed, suggesting that the negative impacts of the invasion were reversed. A separate qualitative review of trophic data indicated that benthic microalgae and dominant vascular plants are important primary producers at the base of the food web in uninvaded, invaded, and restored salt marshes but the overall quantity and importance of microalgae to diet decreased in highly invaded systems due to decreased light, potentially reducing energy availability. Our analyses revealed that while estuarine communities are adversely affected by P. australis, impacts vary by region, habitat, taxonomic group, and life history stage and that restoration can reverse long-term effects over relatively short time scales.

Detecting benthic community responses to pollution in estuaries: A field mesocosm approach

Biological stress responses in individuals are used as indicators of pollution in aquatic ecosystems, but detecting ecologically relevant responses in whole communities remains a challenge. We developed an experimental approach to detect the effects of pollution on estuarine communities using field-based mesocosms. Mesocosms containing defaunated sediments from four estuaries in southeastern Australia that varied in sediment contamination were transplanted and buried in sediments of the same four estuaries for six weeks. Mesocosm sediment properties and metal concentrations remained representative of their source locations. In each estuary, fauna communities associated with sediments derived from the site with the highest metal concentrations were significantly different from other communities. This pattern was evident for some of the individual taxa, in particular the polychaete Capitella sp. Consistent responses across estuaries suggest numbers of individuals, and especially Capitella sp., could be used to identify contaminated sediments in estuaries with similar fauna and site characteristics.

Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe

Baccharis halimifolia L. (Asteraceae) is a shrub native to North America which is invading estuarine communities in Europe. We report the invasion history and the distribution limits of B. halimifolia in Europe, with particular emphasis on the frequency of its presence in estuarine communities in Spain. B. halimifolia has been cultivated in Europe since the 17th century to present. It was first recorded as naturalized in the Bay of Biscay in 1906, where it forms currently stable and locally abundant populations in almost all the estuaries of Northern Spain and Western France. The ongoing invasion to the west could reach well conserved estuarine communities in Galicia (Spain). B. halimifolia also forms scattered populations in Northern and Southern France, Belgium, Netherlands, United Kingdom and Italy. In these countries it has experienced a rapid expansion during the last years. In Northern Spain, subhalophilous communities dominated by rush (Juncus maritimus) and/or sea couch (Elytrigia atherica), common reed stands (Phragmitesaustralis) and ungrazed wet meadows are the most vulnerable to invasion. The subhalophilous communities are part of natural habitats of community interest according to the habitats directive 92/43/EEC. In some areas of Northern Spain these communities have been totally replaced by monospecific stands of B. halimifolia. In contrast, halophilous communities of the low marsh are resistant to invasion, suggesting that the survival of B. halimifolia may be limited by threshold values of salinity and waterlogging. With this study we want to raise awareness about the risk of replacement of estuarine subhalophilous communities by the ongoing invasion of B. halimifolia in Europe.

Validation of growth zone deposition rate in otoliths and scales of flathead mullet Mugil cephalus and freshwater mullet Myxus capensis from fish of known age

Flathead mullet Mugil cephalus and freshwater mullet Myxus capensis are important components in South African estuarine fish communities and fisheries, but there is little information on their age and growth or age validation. This study validated the periodicity of growth zone formation in sectioned sagittal otoliths and scales of fish of known age that had been at liberty for 10 years. For both M. cephalus and M. capensis, the number of growth zones counted on otolith sections did not differ significantly from the known age of the fish. There were significantly fewer growth zones on scales than the known age of both M. cephalus and M. capensis. Growth zone deposition rate could therefore be validated as annual for otoliths but not for scales of the two species. It is recommended that future ageing studies focus on otoliths rather than scales.

Taxon-specific C/N relative use efficiency for amino acids in an estuarine community

Microbial activity plays a critical role in determining the nutrient status of an ecosystem (i.e. N or C limitation). While the balance of C/N assimilation has been measured at the whole community scale, quantitative detection of N and C assimilation from a single substrate at the scale of individual taxa has not been carried out. We recently developed Chip-SIP, a microarray and NanoSIMS-based method for linking microbial phylogeny and function that allows simultaneous measurement of (15)N and (13)C incorporation. Here, we measured the relative incorporation of C and N from dual-labeled substrates by individual microbial taxa in bottle incubations of samples collected from an estuary. Incubation times < 24 h were sufficient to successfully detect active microbes incorporating (15)N ammonium. In subsequent experiments, we used the incorporation of labeled amino acids (AAs) as a proxy for heterotrophic activity and showed different levels of incorporation among different taxonomic groups. Taxon-specific differences in the net incorporation of AA-derived C and N indicate that the C/N relative use efficiency ranged from 0.8 to 1.4, where 1 reflects stoichiometric incorporation of C and N. Our results revealed that microbial organic matter processing is affected by taxon-specific physiological diversity, both in terms of general activity levels and in the ratio of assimilated C/N.

Taxon-specific C:N relative use efficiency for amino acids in an estuarine community

Taxon-specific C:N relative use efficiency for amino acids in an estuarine community

How selection structures species abundance distributions

How do species divide resources to produce the characteristic species abundance distributions seen in nature? One way to resolve this problem is to examine how the biomass (or capacity) of the spatial guilds that combine to produce an abundance distribution is allocated among species. Here we argue that selection on body size varies across guilds occupying spatially distinct habitats. Using an exceptionally well-characterized estuarine fish community, we show that biomass is concentrated in large bodied species in guilds where habitat structure provides protection from predators, but not in those guilds associated with open habitats and where safety in numbers is a mechanism for reducing predation risk. We further demonstrate that while there is temporal turnover in the abundances and identities of species that comprise these guilds, guild rank order is conserved across our 30-year time series. These results demonstrate that ecological communities are not randomly assembled but can be decomposed into guilds where capacity is predictably allocated among species.

Effect of Cyclone Aila on estuarine fish assemblages in the Matla River of the Indian Sundarbans

Abstract:The present study examined the effect of a catastrophic cyclone (Aila) on ichthyofaunal assemblages in a tidal river of the Sundarban Delta. Sampling in six stations with a gill-net of 20-m length and 1-cm mesh size resulted in the collection of 63 species in a pre-Aila survey. Among them, 16 species were not available in the year after the cyclone. However, 12 new species were added to the assemblages in the post-Aila year during which 59 species were recorded. Analysis of Similarity (ANOSIM) confirmed significant changes in fish assemblages after the cyclone with a corresponding reduction of the species diversity and variation in the seasonal pattern of abundance. Hydrological parameters also differed with a significant surge in nutrient concentrations. Tolerance to low dissolved oxygen seemed to be a determinant factor as evident from the higher abundance of certain fishes viz. Harpadon nehereus, Liza parsia, Pampus argentius, Tenualosa ilisha and Toxotes chatareus during post-Aila year. Despite the recovery of the ichthyofaunal assemblages at the later stage of the study, a strong seasonal variation was persistent. The study therefore suggests that environmental variation in terms of increasing temperature and salinity elicit greater response in an estuarine community than temporary natural disturbances even as severe as cyclones.

Partitioning the effects of environmental and spatial heterogeneity on distribution of plant diversity in the Yellow River Estuary

For successful conservation and restoration of biodiversity, it is important to understand how diversity is regulated. In the ecological research community, a current topic of interest is how much of the variation in plant species richness and composition is explained by environmental variation (niche-based model), relative to spatial processes (neutral theory). The Yellow River Estuary (YRE) is a newly formed and fragile wetland ecosystem influenced by both the Yellow River and Bohai Bay. Here, we applied variance partitioning techniques to assess the relative effects of spatial and environmental variables on species richness and composition in the YRE. We also conducted a species indicator analysis to identify characteristic species for three subestuaries within the YRE. Partial redundancy analysis showed that the variations in species richness and composition were explained by both environmental and spatial factors. The majority of explained variation in species richness and composition was attributable to local environmental factors. Among the environmental variables, soil salinity made the greatest contribution to species abundance and composition. Soil salinity was the most important factor in the Diaokou subestuary, while soil moisture was the most important factor influencing species richness in the Qingshui and Chahe subestuaries. The combined effects of soil salinity and moisture determined species richness and composition in the wetlands. These results increase our understanding of the organization and assembly of estuarine plant communities.

Community structure changes of macrobenthos in the South Yellow Sea

The ecological environment in the Yellow Sea has changed greatly from the 1950s to 1990s and this has had significant impact on marine organisms. In this study, data on soft-sediment macrobenthos occurring in depths from 25 m to 81 m in the South Yellow Sea were used to compare changes in community structure. The agglomerative classification (CLUSTER) and multidimensional scaling (MDS) methods were applied. Five communities were recognized by cluster analysis: 1. The Yellow Sea Cold Water Mass community dominated by cold water species, which changed slightly in species composition since the 1950s; 2. The mixed community with the coexistence of cold water species and warm water species, as had been reported previously; 3. The polychaete-dominated eurythermal community in which the composition changed considerably as some dominant species disappeared or decreased; 4. The Changjiang (Yangtze) River Estuarine community, with some typical estuarine species; 5. The community affected by the Yellow Sea Warm Current. The greatest change occurred in the coastal area, which indicated that the change may be caused by human activities. Macrobenthos in the central region remained almost unchanged, particularly the cold water species shielded by the Yellow Sea Cold Water Mass. The depth, temperature and median grain size of sediments were important factors affecting the distributions of macrobenthos in the South Yellow Sea.

Composition of humic acid-degrading estuarine and marine bacterial communities

We examined the bacterial decomposition of humic acids (HA) in two flow-through culture experiments, one inoculated by marine and one by estuarine bacterial communities. In both experiments, the cultures were fed with HA media of salinities of 28 and 14, close to their ambient and a distinctly different, foreign salinity. HA were decomposed to >60% of the initial concentration within 70days, and the foreign salinity yielded the highest decomposition. A detrended correspondence analysis of denaturing gradient gel electrophoresis (DGGE) banding patterns showed that during incubation, the bacterial community composition underwent distinct changes. A phylogenetic analysis of DGGE bands excised and bacteria isolated at the end on HA as the sole carbon source showed that Alphaproteobacteria and Gammaproteobacteria largely dominated the communities in the marine flow-through cultures, whereas Gammaproteobacteria, Actinobacteria and Alphaproteobacteria dominated the estuarine communities. Eleven of 13 isolates obtained from both experiments were able to grow on HA as the sole carbon source, seven on phenol and three, affiliated to the Roseobacter clade, on various aromatic acids. The bacteria retrieved from the flow-through cultures were closely (96-99%) affiliated to organisms capable of degrading humic matter, aromatic and aliphatic compounds and also to other bacteria reported previously from the Wadden Sea and Weser estuary.

Spionidae (Annelida) from shallow waters around the British Islands: an identification guide for the NMBAQC Scheme with an overview of spionid morphology and biology

This is the third guide in a series aimed to help in the identification of northern European samples through the NationalMarine Biological Analytical Quality Control (NMBAQC) Scheme. A review is presented of general morphology andbiology of one of the most common groups in marine and estuarine communities worldwide, spionid polychaetes(Annelida: Spionidae). An identification key to 20 genera and a list of 80 species likely to occur in waters around Britainand Ireland are provided based on the taxonomic literature, collection records and the author’s examination of various collections. The names are updated but some records need verification.

Seasonal and Ontogenetic Variation in the Diet and Daily Ration of Estuarine Red Drum as Derived from Field‐Based Estimates of Gastric Evacuation and Consumption

AbstractThe application of ecosystem‐based approaches in fisheries management has been limited by a lack of empirical data for quantifying the ecological interactions among many common and valuable fishery species. The red drum Sciaenops ocellatus, a large, carnivorous member of estuarine communities, is experiencing population recovery throughout its range in the U.S. South Atlantic and Gulf of Mexico. Using a field‐based approach, we determined seasonal and ontogenetic variation in the contribution of valuable fishery resource species to red drum diets, estimated red drum daily ration, and quantified per capita and population‐level predation by juvenile and subadult red drum in a North Carolina estuarine system. Despite seasonal, interannual, and ontogenetic variation in diet composition, red drum fed mainly on macrocrustaceans and juvenile fishes, including several economically important resource species (e.g., blue crab Callinectes sapidus, penaeid shrimp, and Atlantic menhaden Brevoortia tyrannus). Both juvenile and subadult red drum demonstrated strong diel feeding patterns, with peak feeding occurring during the hours just after dark. Gastric evacuation rates during periods of declining gut fullness were estimated on seven sampling dates and produced mean daily ration estimates between 1.2% and 3.4% of predator mass depending on age‐group. Combining field‐observed red drum growth rates with published laboratory estimates of gross growth efficiency suggested that our estimates of daily ration were likely biased low. During the seasonal period of rapid growth, the aggregate consumption of blue crabs, penaeid shrimp, and Atlantic menhaden by juvenile and subadult red drum in North Carolina waters was estimated at 3.4 × 106 to 5.1 × 106 kg/year.Received October 12, 2011; accepted May 24, 2012