A biological trait approach to assess the functional composition of subtidal benthic communities in an estuarine ecosystem

Within transitional/estuarine environments ‘ecosystem functioning’ has been mostly investigated with “traditional” taxonomic analysis, based on the taxonomic composition of benthic invertebrate communities. However, ‘ecosystem functioning’ depends also greatly on the functional characteristics (biological traits) of organisms.It was a priori suggested that the biological traits of the subtidal benthic invertebrate communities within an estuarine environment would respond to the high variability of environmental pressures (natural and human induced) within this type of ecosystem.For this study, traditional taxonomic analysis (species richness, species density and Shannon–Wiener diversity) as well as biological trait analysis were used together for the first time to investigate the response of the subtidal benthic invertebrate communities to the environmental pressures within the Mondego estuary (Portugal).Biological trait analysis, in addition to traditional taxonomic analysis provided a more comprehensive understanding of the functioning within this type of ecosystem. Some of the most important outcomes are: (i) the trait “salinity preference” was the most important trait that distributed the species along the estuary, (ii) the central part of the estuary appeared to be under higher environmental stress levels than the other areas, as suggested by a dominance of some “opportunistic” traits (e.g. small short-lived species), (iii) the ratio between functional diversity (FD) and Shannon–Wiener diversity (H′) indicated lower functional redundancy at the upper reaches of the estuary. Our results, suggest that the ratio (FD/H′) might be a helpful tool to visualize this functional attribute and could potentially be applied to different communities from distinct environments. Using the traditional taxonomic analysis alone, this last functional aspect would not be detectable. Therefore, the inclusion of biological traits analysis is recommendable for estuarine ecological studies.     

Assessment of the subtidal macrobenthic community functioning of a temperate estuary following environmental restoration

Biological Traits Analysis (BTA) is a recently proposed method for addressing ecological functioning based on traits exhibited by members of biological assemblages. This multi-trait approach was applied to the soft-bottom subtidal macrobenthic communities of the Mondego estuary (Portugal), aiming to assess its functioning following a management measure implemented in this system. In particular, the response of benthic assemblages to restoration efforts was investigated over a 5-year period, testing for temporal differences before and after management, in order to assess the effectiveness of this recovery action.BTA revealed to be a useful approach providing valuable information on the functioning of the subtidal benthic communities. Overall, results suggested that there have been some changes in the ecosystem over the study period, although the success of the management measure at the benthic functional level revealed unclear. The climatic variability experienced in the estuary over the monitoring period seemed to have played a significant role in masking the potential effects of restoration. Furthermore, evidence suggested a possible persistence in the benthic functioning despite the occurrence of shifts in taxonomic composition, assured by the potential ability of different species with an alike set of traits to perform similar roles in the ecosystem.To best of our knowledge, this study constituted one of the first attempts to investigate the effects of a management measure in an estuary by means of Biological Traits Analysis. As such, it can thus be useful as a guideline for further management actions in the Mondego estuary extendable to other poikilohaline estuaries as well, and to provide insights on the BTA application to this type of ecosystems.     

Benthic invertebrate assemblage in Samborombón River (Argentina,S. America), a brackish plain river

The spatial and temporal differences in the structure and composition of benthic invertebrates were studied at three sites of the Samborombón River, which is an important tributary of the Río de la Plata Estuary (Argentina), having a low slope and brackish drainage. Biological samples were taken during each season. Physico-chemical variables were measured to determine their association in the benthic fauna distribution. Site 1, in the headstream, was characterized by freshwater Pampean organisms; site 2 showed the highest density, taxa diversity, and richness; brackish species, e.g., Laeonereis culveri, were found here. Site 3, close to the Samborombón Bay, was characterized by an unstable taxonomic composition that is strongly influenced by the estuary. The lowest density and taxonomic diversity of organisms were registered and distinguished by estuarine species. The multivariate method (redundancy analysis) showed the benthic groups having an important spatial variability, superimposed on the temporal variability, associated with the salinity gradient of the river.     

A benthic perspective in assessing the ecological status of estuaries: The case of the Mondego estuary (Portugal)

In transitional waters the process of defining reference conditions (in the scope of the WFD) must account for the natural great variability of such environments. Therefore, stretches reflecting different physical–chemical and biological conditions throughout the system should be defined in order to correctly establish benthic specific reference conditions. Both salinity and sediment structure are major factors controlling physical–chemical conditions and therefore organisms’ distribution within an estuary. These environmental variables (salinity, sediment grain size composition and organic matter content) patterns were studied in the Mondego estuary and some clear gradients emerged. Also, ecological indices (AMBI, Margalef and Shannon-Wiener) were applied to subtidal benthic communities of the Mondego estuary and, generally, there was not only evidence of a decrease in diversity in the estuary from the downstream section towards its inner parts, but also differences were found between areas of distinct sediment composition. After comparing environmental patterns with biodiversity trends, the information was used to define homogeneous sectors along a temperate estuary in Portugal. In the Mondego estuary six zones, covering the main physical gradients affecting benthic communities, were defined: four in the northern arm and two in southern arm. Zones established will allow future determination of benthic reference conditions adjusted for each of the sectors, according to their characteristics, and consequently the conditions they provide for benthic assemblages settlement.     

Response of intertidal macrobenthic communities and primary producers to mitigation measures in a temperate estuary

The main goal of this study was to evaluate the response of intertidal macrobenthic communities associated with Zostera noltii meadows in a temperate estuary (Mondego, Portugal) to the application of mitigation measures aimed at decreasing eutrophication symptoms. In order to assess possible ecological improvements regarding the seagrass habitat and associated macrobenthic communities, data from four different periods, corresponding to the prevailing conditions of distinct systems, were considered. This study (1) gives concrete examples of pathways of benthic intertidal communities’ degradation and recovery; (2) it analyses a long-term dataset (covering almost 25 years) of intertidal communities from a southern European estuary; (3) it is focused on a worldwide problem, and so has potentially far-reaching interest; (4) it exemplifies some of what may be the consequences of the dialogue between science and managers; (5) it assesses the impact and effectiveness of a large-scale mitigation intervention paid for by public funding.The application of preliminary mitigation measures (in 1998) and the full re-establishment of the communication between the two estuarine subsystems (in 2006) allowed for an improvement in the macrobenthic condition and confirmed that hydrologic conditions in the estuary have been the major drivers of the changes observed over the last two decades. However, evaluating the efficiency of the large-scale intervention proved to be a complex task since different communities showed distinct pathways and momentums of recovery.The present study provided valuable insights concerning sustainable long-term management solutions regarding the Mondego Estuary. These particular insights could therefore be useful as a management action guideline applied to other estuarine ecosystems undergoing similar eutrophication problems.     

Spatial heterogeneity recognition in estuarine intertidal benthic macrofaunal communities: influence of sieve mesh-size and sampling depth

Estuarine intertidal soft-bottom macrobenthic infauna of the Tagus estuary was characterised using different mesh size sieves and sediment sampling depth. The study sampled 105 sites using a hand held 0.01 m² corer. The top layer (0–5 cm) was sieved through nested 1.0 and 0.5 mm meshes whereas the bottom layer (5–20 cm) was through a 1 mm mesh. The total survey took 26 taxa of more than 5800 individuals and a total wet weight biomass of over 650 g. The top layer, using both sieves, gathered 23 taxa (92% of the total), more than 5600 specimens (96%) but less than 8 g of biomass (1%) whereas the 1.0 mm sieve retained 21 taxa (91%), more than 1700 specimens (31%) and almost 7 g of biomass (1%). Abundance was dominated by small annelids, of which Streblospio shrubsolii was 68%, whereas biomass was dominated by molluscs, with the bivalve Scrobicularia plana representing 98%. Multivariate analyses showed an abundance pattern where the top layer data was very similar to that obtained with both layers. The bottom layer data were needed to accurately represent the total biomass pattern. The macrofaunal spatial pattern identified with the 0.5 mm sieve data differed from that identified by the 1.0 mm and was essential to discriminate a faunal assemblage located along the upper part of the shore. It was concluded that in order to characterize the macrofauna community structure, based on the presence/absence of taxa, the top layer and a 1.0 mm sieve would be sufficient. An abundance-based characterization requires the top layer and a 0.5 mm sieve whereas a biomass-based characterization requires data for both layers but it is sufficient to use the 1.0 mm sieve. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Is polychaete family-level sufficient to assess impact on tropical estuarine gradients?

Regular, robust monitoring programs set up to assess the environmental conditions of aquatic systems often target different biological groups. And, of these, macroinvertebrate communities and particularly the class Polychaeta are frequently used. Identifying these organisms takes time, money and specialized expertise to ensure correct identification to the lowest possible taxonomic level. Identification errors can lead to an erroneous assessment. The concept of taxonomic sufficiency has been proposed both to minimize errors and to save time and money. This study tested the usefulness of this concept in tropical estuaries in northeast Brazil. We selected two transitional systems with different degrees of human impact due to different land uses and different conservation systems: the Mamanguape estuary, which is in an environmental conservation unit for sustainable use, and the highly impacted, urban Paraíba do Norte estuary. The results clearly showed that nutrient concentrations were markedly higher in the Paraíba do Norte estuary in the dry season and that the composition of the polychaete assemblages differed between the two estuaries as well as along the spatial gradient of each estuary. The use of either genus or family level led to equivalent representation in each system in terms of taxon richness and both the Margalef and Shannon-Wiener diversity indices. Both taxonomic levels described similar changes in the polychaete assemblage along the estuarine gradients. Based on our findings, the use of a coarser taxonomic level (i.e., family) is a good option when the aim is to implement a monitoring program in tropical estuaries with the polychaete assemblages as one of the target groups. This time-efficient taxonomic resolution can help improve sampling designs and allow long-term monitoring studies without losing much vital information.     

Analysis of the reproductive strategy of <Emphasis Type="Italic">Jenynsia multidentata</Emphasis> (Cyprinodontiformes,Anablepidae) with focus on sexual differences in growth,size, and abundance

The habitat heterogeneity generated and sustained by the connectivity of floodplain habitats, the seasonal flood pulse, and the variability of the physical structures typically found in floodplains of large rivers results in a variable space–time mosaic of water sources that results in a high biodiversity of the river-floodplain system. In order to assess the implications of natural connectivity and the heterogeneity on the patterns of macroinvertebrate assemblages at different spatial scales, monthly samplings in six different mesohabitats (lakes with different hydrological connection and secondary channels with permanently and intermittent flow) of the Paraná River floodplain were performed from April 2005 to March 2006. The mesohabitats had different granulometry and detritus composition of their bottom sediments. They also had different conductivity, transparency, and depth in relation to the different connectivity degrees. Mesohabitats differed in the abundance of macroinvertebrates of different taxonomic groups and diversity. The environmental variables were correlated to the patterns of macroinvertebrate abundance, with dominance of different species of annelids and mollusks at the patch, mesohabitats, and island scales. An alpha diversity gradient from the isolated lake (65 taxonomic units) to the secondary channels (25 taxonomic units) was obtained. The analyzed mesohabitats showed a high taxa turnover, with high values not only among the mesohabitats located in the different islands, but also among the mesohabitats in relation to different connectivity degrees. The mesohabitats showed negative co-occurrence of macroinvertebrate assemblages. The spatial heterogeneity, sustained by the connectivity degree, played a key role in structuring benthic assemblages at different scales, positively influencing the regional diversity.     

Estuarine colonization, population structure and nursery functioning for 0-group sea bass (Dicentrarchus labrax), flounder (Platichthys flesus) and sole (Solea solea) in a mesotidal temperate estuary

The function of the Mondego estuary as a fish nursery habitat was investigated from June 2003 to June 2004 by comparing the timing of estuarine colonization with juveniles of sea bass Dicentrarchus labrax, flounder Platichthys flesus, and sole Solea solea, while also analysing their population structure, growth and diet composition. Differences in the onset of estuarine colonization were observed, since sole juveniles were the first to enter the estuary (in January), followed by flounder in April and sea bass in June. The estuarine population of these species consisted of several age‐groups, although the majority of individuals belonged to age‐groups 0 and 1. The growth rates determined for 0‐group fish were within the range of those reported for other European estuarine systems. Some differences were also recognized regarding the timing of estuarine colonization and the length of the growing season. Diet of 0‐group sea bass consisted mainly of Crustacea, Polychaeta and Mollusca. Flounder juveniles fed chiefly on Amphipoda (especially Corophium spp.), with Polychaeta, Isopoda and Decapoda also being common prey. The diet of 0‐group sole was dominated by Polychaeta, with Amphipoda, Mollusca and Decapoda ranking highest, with other important benthic organisms also being present. Dietary overlap among these species was relatively low.     

Applicability of ecological evaluation tools in estuarine ecosystems: the case of the lower Mondego estuary (Portugal)

In accordance with the Water Framework Directive guidelines (WFD, 2000, European Communities Official Journal L327 2000/60/EC), classification schemes and ecological evaluation tools (based on benthic invertebrate fauna data sets from 1990 to 2002) were applied in the lower Mondego estuary. Two distinct scenarios could be tested due to the implementation of mitigation practices in 1999, following a long eutrophication process, which started by the early 1980s. Some discrepancies in the results were found by the application of the different indices. The AMBI index (accounting for taxonomic composition) and the ABC method (accounting for abundance and biomass k-dominance patterns) classifications often disagreed with those based on species diversity (Margalef and Shannon-Wiener). The ambiguous results made the classification a complex task to achieve, contrary to the Directive’s objective of maintaining it simple and clear. Our results suggest the necessity of adjusting some of the indices and their ranges to estuarine characteristics, namely to account the typical dominance and abundance of some particular species. These aspects are not taken into consideration by some of the indices proposed, which are more adapted to typical marine conditions. Based on our results, these widely applied indices might still improve their efficiency in estuarine systems allowing their use in the resembling types already established within the new Directive agenda.     

Correlation of the distribution ofMesopodopsis slabberi (Crustacae,Mysidacea) with physico-chemical gradients in a partially-mixed estuary (Tamar,England)

The physical and chemical processes operating in the River Tamar Estuary (south-west England) have been comprehensively described and reported in the literature. There are well-established gradients of salinity, suspended sediment and oxygen which vary both on short-term (tidal) and long-term (seasonal) cycles. Freshwater runoff, the main factor determining salinity distribution, is also the cause of the high variability in suspended sediment concentrations. The biological processes are less well studied and information on the link between the benthic and pelagic systems is particularly lacking. Mysids, through their role as detritivores and as a major component in the diet of some fish, provide this link. Of the four species of mysid distributed longitudinally in the Tamar Estuary, the most abundant isMesopodopsis slabberi which occurs between 5 and 25 km from the estuary head. Observations over an annual cycle have shown marked seasonal changes in both abundance and distribution in the estuary. During winter and spring, densities remained generally low (<50 m⁻³) but, as water temperatures increased, the density increased and reachedca 1200 individuals m⁻³ in July. There was a shift in the longitudinal distribution ofM. slabberi in response to changes in the position of the salinity gradient. Adults comprised the majority of the population in salinities less than 10‰ whereas juveniles and immature animals were distributed over a wider area than the adults and occurred in water of higher salinity than the main adult distribution.M. slabberi appears to utilise the two-layered estuarine circulation to maintain its position in the estuary.     

Trends in water quality and subtidal benthic communities in a temperate estuary: Is the response to restoration efforts hidden by climate variability and the Estuarine Quality Paradox?

The analysis of temporal patterns in water quality and benthic assemblages in estuaries constitutes an important methodological issue for discriminating the effects of natural and anthropogenic pressures. Temporal trends in water quality and in the subtidal benthic community over a 5-year interval in the Mondego estuary (Portugal) were investigated with the aim of assessing changes in environmental quality as a response to restoration efforts and climate variability. Particularly, we addressed the following questions: (a) Would trends in water quality and benthos behave consistently over the whole study period for the different zones of the monitoring network and indicate improvement or degradation in ecological condition? (b) Could we distinguish the effects of climate variability and restoration efforts in water quality and benthos from trend analysis results? (c) Could the response of the benthic communities and water quality be useful to guide the planning of future management actions in this system?Clear cause–effect relationships regarding the ecological response to restoration efforts and climate variability were indeed challenging to identify and interpret. In fact, the response of water quality and benthic communities to restoration efforts seemed to have been masked by the effects of climatic variability. Furthermore, the present study illustrated clearly the high environmental variability inherent to estuarine systems and the difficulty of clearly distinguishing natural from anthropogenic stressors, in agreement with the “Estuarine Quality Paradox”. Implications for ecological quality assessment and management of the Mondego estuary and other poikilohaline systems are discussed, namely with regard to the “one-out, all-out” principle required by the European Water Framework Directive (WFD).     

Biological availability and humic properties of dissolved organic carbon in Lake Balaton (Hungary)

The nursery role of the Mondego estuary for marine fish species was studied between June 2003 and May 2004. The spatial and temporal distribution and abundance patterns of 0-group Dicentrarchus labrax (Linnaeus, 1758), Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758) were analyzed based on monthly sampling surveys in five stations along the estuarine gradient. Fishing took place during the night at low water of spring tides, using a 2 m beam trawl. The spatial patterns of estuarine colonization were different according to species. D. labrax showed a wider distribution, but the main nursery ground was the same as for S. solea. Highest densities of S. solea juveniles were found in oligohaline areas, with muddy bottoms and high benthic invertebrates availability, while P. flesus occurred mainly in the sandy uppermost areas. D. labrax was found in both these areas. Fish abundance in the estuary mainly reflected seasonal changes.     

Taxonomic level, trophic biology and the regulation of local abundance

• 1 Taxocenes — monophyletic ecological assemblages — are a key focus of macroecology. Abundance (individuals per area) is a basic property of taxocenes but has received less attention than diversity, although the two are probably related. Abundance reflects a taxocene’s ability to harvest and sequester available energy and divide it among individuals. This paper explores how two properties of all taxocenes — trophic makeup and taxonomic level (e.g. genus, tribe, subfamily, family … ) — may contribute to patterns of local abundance at geographical scales.
• 2 Forty‐nine ground ant taxocenes, in habitats ranging from New World deserts to rain forests, were surveyed along a three‐orders of magnitude productivity gradient using transects of 30 1‐m² quadrats at each site. Abundance — the number of nests per transect — varied over two orders of magnitude.
• 3 Over 80% of the genera collected were omnivores. However, herbivore, omnivore, and predator taxa were added to ant taxocenes in roughly 1 order of magnitude steps up the productivity gradient. Specialist detritivores were added last.
• 4 Net primary productivity and mean monthly temperature both consistently entered regression models predicting abundance. However, while productivity was the dominant predictor of abundance for higher taxa (families, subfamilies), temperature was the dominant predictor of abundance for lower taxa (tribes, genera). The answer to the question ‘What regulates the abundance of a taxocene?’ is thus sensitive to the taxonomic level of analysis.
• 5 These data support the following scenario. Lower taxa are abiotic specialists given the insufficient number of genomes and generations required for the exploration of the entire abiotic envelope. Higher taxa, in contrast, consist of suites of abiotic specialists arrayed along the entire productivity gradient, with access to productivity everywhere the taxon occurs. If this scenario is true, individual species may respond to global changes in temperature; the higher taxa they belong to may most respond to global changes in productivity.

     

Dynamic changes in seagrass assemblages under eutrophication and implications for recovery

Over the last 20 years, loss of seagrass beds, often related with increased eutrophication, became a common problem worldwide. In the Mondego estuary (Portugal), eutrophication has triggered serious biological changes, which led to an overall increase in primary production and to a progressive replacement of seagrass Zostera noltii beds by coarser sediments and opportunistic macroalgae.The effects of this eutrophication on benthic assemblages were studied along a spatial gradient in the Mondego estuary from 1993 to 1995. Over these short temporal and small spatial scales, distinct changes in the structure of the macrobenthic communities were observed. One of the main structural modifications was the decrease in species diversity along the eutrophication gradient and over time, with a marked impoverishment of the most disturbed inner area. Other changes included an increase in detritivores and a decline in herbivores together with a significant increase in small deposit-feeding polychaetes.In the long term, sustained eutrophication of this estuary is expected to lead to complete replacement of seagrass habitat by unvegetated coarser sediments, occasionally covered by green macroalgal blooms and dominated by opportunistic invertebrate taxa. Recovery from this situation may not only require reduction in nutrient loadings to the estuary, but also active seagrass restoration programmes to reverse the positive feedback processes thought to be presently taking place.     

莱州湾小清河口近岸海域底栖生境健康评价

于2019年7月、8月和9月对莱州湾小清河口近岸海域的大型底栖动物进行调查，对该海域大型底栖动物群落的种类组成和群落结构等进行研究，利用丰度/生物量比较曲线法、AMBI指数法和M-AMBI指数法对研究海域大型底栖动物群落健康和底栖生境健康状况进行评价。研究结果表明，2019年7月、8月和9月共采集到大型底栖动物64种，其中多毛类24种，甲壳类19种，软体动物17种，其他类群4种。该海域的优势种为光滑河蓝蛤（Potamocorbula laevis）、彩虹明樱蛤（Moerella iridescens）、半褶织纹螺（Nassarius semiplicatus）、四角蛤蜊（Mactra veneriformis），寡鳃齿吻沙蚕（Nephthys oligobranchia）、中蚓虫（Mediomastus californiensis）、东方长眼虾（Ogyrides orientalis）、尖齿拳蟹（Philyra acutidens）和短角双眼钩虾（Ampelisca brevicornis），其中彩虹明樱蛤和寡鳃齿吻沙蚕在三次调查中均为优势物种，优势度明显。群落结构聚类分析和多维尺度分析表明，7月研究海域的大型底栖动物群落以10%的相似性可以分为3组，8月以18%相似性可以分为4组，9月以19%的相似性可以分为3组，三次调查的群落结构相似度均较低。丰度/生物量比较曲线法研究结果显示，底栖动物群落生物量优势显著，群落处于未干扰状态。AMBI指数及M-AMBI指数分析结果表明，莱州湾小清河口近岸海域底栖生境处于未干扰或者轻度干扰的状态，健康状况处于高等或者优良的状态。     

Estuarine intertidal meiofauna and nematode communities as indicator of ecosystem's recovery following mitigation measures

The Mondego estuary (Portugal) has been under environmental pressure since the early 1990s due to different anthropogenic stresses. The system has been studied following benthic communities’ features from an impacted situation until the recovery phase, focusing mostly on macrobenthos. Following the application of mitigation measures in the estuary, this study is focused on the variability of the intertidal meiobenthic and nematode communities in a system that has recovered after different anthropogenic stresses. While at the spatial level (among areas along the eutrophication gradient) no significant differences were observed regarding the structure and function of the nematode communities, at the seasonal level some differences stood out. These results broadly suggest that the system has recovered from the early situations of pressures being, to the best of our knowledge, the first attempt to investigate the variability of intertidal meiobenthic and nematode communities in the scope of a system's recovery along an estuarine gradient of eutrophication. Even if performed in a short timeline, this study provides a good baseline analysis of conditions, being important for future comparisons.     

环境污染对小清河口大型底栖动物多样性的影响

利用2008年7月小清河口和黄河口各8个站位的底栖动物调查资料,运用多种多样性指数对两河口底栖动物群落多样性特征进行了比较,并运用Spearman相关分析分析了14个环境因素和底栖动物群落多样性特征的相关关系。结果显示,小清河口共有大型底栖动物4门6纲17目35科37属38种,平均分类差异指数为85.7,分类差异变异指数为585.6,黄河口共有大型底栖动物6门9纲24目42科45属48种,平均分类差异指数为89.3,分类差异变异指数为435.8。小清河口的多样性指数(H’)仅约为黄河口的1/3。Spearman相关分析表明,H’与铵盐、硝酸盐、铜和汞含量呈负相关性,说明底栖动物群落多样性随着富营养化程度的提高而相应降低,营养物质氮的大量输入和重金属的污染对小清河口大型底栖动物群落产生了一定负面影响。ABC曲线法分析显示,小清河口底栖动物的丰度优势度曲线与生物量优势度曲线相交,表明小清河口底栖动物群落处于中度干扰状态;BOPA指数显示,小清河口8个站位中有4个站位受到不同程度的环境污染,生活污水和工业废水的排放可能对小清河口底栖动物生态特征带来巨大影响,加强工业和生活污水排放管理,强化清洁生产,加强工业污染源的治理力度,对恢复小清河流域水质、改善生态环境具有重要意义。