Aquatic Macrofauna Research Articles

Oyster reefs as habitat for aquatic macrofauna in a Gulf of Mexico estuary: biotic complexity at spatial, ecological, and demographic scales

Oysters are important marine foundation species across the world, particularly in estuaries of the Gulf of Mexico. One important function of oysters in estuaries is the provision of 3-dimensional habitat that is used by a wide range of species. In this study, the biotic diversity of mid-bay intertidal oyster reefs found in a Gulf of Mexico estuary was examined at nested ecological and demographic scales. Fishery-independent data collections made in East Matagorda Bay, Texas, USA, were used to compare community structure and diversity at mid-bay reefs to undifferentiated shoreline habitats. Despite similar diversity metrics, there were differences in community structure that were driven by differences in spatial habitat use by several common species. Below the community scale, demographic differences in spotted seatrout Cynoscion nebulosus habitat use were observed, with smaller and younger individuals found along reefs, and larger and older individuals found along shorelines. This finding was more pronounced for male spotted seatrout in the spring. The observed spatial habitat use patterns at nested ecological scales (community, inter-species, intra-species) highlight the importance of oyster reefs for maintaining diversity in Gulf of Mexico estuaries, and more broadly support the notion that heterogeneity in localized habitats drives biotic diversity at the estuary scale. Conservation of oyster reefs as critical habitat should be considered along with conservation of oysters themselves when balancing the ecological value of oysters against the commercial value of oyster fisheries.

Nuanced impacts of the invasive aquatic plant Crassula helmsii on Northwest European freshwater macroinvertebrate assemblages

Invasive alien species are considered one of the greatest threats to global biodiversity, and are particularly problematic in aquatic systems. Given the foundational role of macrophytes in most freshwaters, alien aquatic plant invasions may drive strong bottom-up impacts on recipient biota. Crassula helmsii (New Zealand pygmyweed) is an Australasian macrophyte, now widespread in northwest Europe. Crassula helmsii rapidly invades small lentic waterbodies, where it is generally considered a serious threat to native biodiversity. The precise ecological impacts of this invasion remain poorly understood, however, particularly with respect to macroinvertebrates, which comprise the bulk of freshwater faunal biodiversity. We conducted a field study of ponds, ditches and small lakes across the core of C. helmsii's invasive range (United Kingdom, Belgium and the Netherlands), finding that invaded sites had higher macroinvertebrate taxon richness than uninvaded sites, and that many infrequent and rare macroinvertebrates co-occurred with C. helmsii. Alien macroinvertebrates were more abundant in C. helmsii sites, however, particularly the North American amphipod Crangonyx pseudogracilis. At the order level, water beetle (Coleoptera) richness and abundance were higher in C. helmsii sites, whereas true fly (Diptera) abundance was higher in uninvaded sites. Taxonomic and functional assemblage composition were both impacted by invasion, largely in relation to taxa and traits associated with detritivory, suggesting that the impacts of C. helmsii on macroinvertebrates are partly mediated by the availability and palatability of its detritus. The nuanced effects of C. helmsii on macroinvertebrates found here should encourage further quantitative research on the impacts of this invasive plant, and perhaps prompt a more balanced re-evaluation of its effects on native aquatic macrofauna.

Aquatic worms: relevant model organisms to investigate pollution of microplastics throughout the freshwater-marine continuum.

Plastic pollution has become a global and emergency concern. Degradation processes of plastic macrowaste, either at the millimetre- and micrometre-size scales (microplastics, MP) or a nanometre one (nanoplastic, NP), is now well documented in all environmental compartments. It is hence necessary to study the environmental dynamic of MNP (micro(nano)plastic) on aquatic macrofauna considering their dispersion in different compartments. In this context, worms, having a large habitat in natural environments (soil, sediment, water) represent a relevant model organism for MNP investigations. In aquatic systems, worms could be used to compare MNP contamination between freshwater and seawater. The aim of this review was to discuss the relevance of using worms as model species for investigating MNP pollution in freshwater, estuarine, and marine systems. In this context, studies conducted in the field and in laboratory, using diverse classes of aquatic worms (polychaete and clitellate, i.e. oligochaete and hirudinea) to assess plastic contamination, were analysed. In addition, the reliability between laboratory exposure conditions and the investigation in the field was discussed. Finally, in a context of plastic use regulation, based on the literature, some recommendations about model species, environmental relevance, and experimental needs related to MNP are given for future studies.

Colonization of Artificial Substrates by Invertebrate Macrofauna in a River Ecosystem-Implications for Forensic Entomology.

Forensic entomology includes the analysis of organisms colonizing various parts of the body in order to determine the circumstances of an incident, mainly the time, place, and cause of death. The presence of insects and other arthropods on carcasses can be a source of knowledge for the judicial system. However, this type of research (on submerged bodies) is less published. The aim of our study was to analyse the qualitative and quantitative structure of macroinvertebrates colonizing potential evidence in an upland river. The experimental research involved an eight-week exposure to articles of clothing made of different materials: natural materials (bottom sediments with plants from a river), synthetic (socks), and cotton (t-shirts). Control samples of water after 2, 4, 6, and 8 weeks were taken from experiment locations in the River Bystrzyca with a tube apparatus and hand net. The results indicated that the abundance of organisms on a given substrate depended on the period of development of invertebrate macrofauna and the time of exposure of the substrates. The abundance of aquatic macrofauna on the exposed items increased in direct proportion to the duration of the experiment, which may indicate the adaptability of these organisms to new habitat conditions. Among the taxonomic groups used in forensic entomology, Diptera, Coleoptera, and Odonata were the most abundant. The remaining taxa (including Heteroptera), though not widely used in judicial proceedings, can also provide valuable information about the circumstances of an incident.

Warming and top predator loss drive direct and indirect effects on multiple trophic groups within and across ecosystems.

The interspecific interactions within and between adjacent ecosystems strongly depend on the changes in their abiotic and biotic components. However, little is known about how climate change and biodiversity loss in a specific ecosystem can impact the multiple trophic interactions of different biological groups within and across ecosystems. We used natural microecosystems (tank-bromeliads) as a model system to investigate the main and interactive effects of aquatic warming and aquatic top predator loss (i.e. trophic downgrading) on trophic relationships in three integrated food web compartments: (a) aquatic micro-organisms, (b) aquatic macro-organisms and (c) terrestrial predators (i.e. via cross-ecosystem effects). The aquatic top predator loss substantially impacted the three food web compartments. In the aquatic macrofauna compartment, trophic downgrading increased the filter feeder richness and abundance directly and indirectly via an increase in detritivore richness, likely through a facilitative interaction. For the microbiota compartment, aquatic top predator loss had a negative effect on algae richness, probably via decreasing the input of nutrients from predator biological activities. Furthermore, the more active terrestrial predators responded more to aquatic top predator loss, via an increase in some components of aquatic macrofauna, than more stationary terrestrial predators. The aquatic trophic downgrading indirectly altered the richness and abundance of cursorial terrestrial predators, but these effects had different direction according to the aquatic functional group, filter feeder or other detritivores. The web-building predators were indirectly affected by aquatic trophic downgrading due to increased filter feeder richness. Aquatic warming did not affect the aquatic micro- or macro-organisms but did positively affect the abundance of web-building terrestrial predators. These results allow us to raise a predictive framework of how different anthropogenic changes predicted for the next decades, such as aquatic warming and top predator loss, could differentially affect multiple biological groups through interactions within and across ecosystems.

Aquatic suspended particulate matter as source of eDNA for fish metabarcoding

The use of environmental DNA (eDNA) for monitoring aquatic macrofauna allows the non-invasive species determination and measurement of their DNA abundance and typically involves the analysis of eDNA captured from water samples. In this proof-of-concept study, we focused on the novel use of eDNA extracted from archived suspended particulate matter (SPM) for identifying fish species using metabarcoding, which benefits from the prospect of retrospective monitoring and also analysis of fish communities through time. We used archived SPM samples of the German Environmental Specimen Bank (ESB), which were collected using sedimentation traps from different riverine points in Germany. Environmental DNA was extracted from nine SPM samples differing in location, organic content, and porosity (among other factors) using four different methods for the isolation of high-quality DNA. Application of the PowerSoil DNA Isolation Kit with an overnight incubation in lysis buffer, resulted in DNA extraction with the highest purity and eDNA metabarcoding of these eDNA fragments was used to detect a total of 29 fish taxa among the analyzed samples. Here we demonstrated for the first time that SPM is a promising source of eDNA for metabarcoding analysis, which could provide valuable retrospective information (when using archived SPM) for fish monitoring, complementing the currently used approaches.

Does Size Matter? An Experimental Evaluation of the Relative Abundance and Decay Rates of Aquatic Environmental DNA

Environmental DNA (eDNA) is increasingly used to monitor aquatic macrofauna. Typically, short mitochondrial DNA fragments are targeted because these should be relatively more abundant in the environment as longer fragments will break into smaller fragments over time. However, longer fragments may permit more flexible primer design and increase taxonomic resolution for eDNA metabarcoding analyses, and recent studies have shown that long mitochondrial eDNA fragments can be extracted from environmental water samples. Nuclear eDNA fragments have also been proposed as targets, but little is known about their persistence in the aquatic environment. Here we measure the abundance of mitochondrial eDNA fragments of different lengths and of short nuclear eDNA fragments, originating from captive fish in experimental tanks, and we test whether longer mitochondrial and short nuclear fragments decay faster than short mitochondrial fragments following fish removal. We show that when fish are present, shorter mitochondrial fragments are more abundant in water samples than both longer mitochondrial fragments and short nuclear eDNA fragments. However, the rate of decay following fish removal was similar for all fragment types, suggesting that the differences in abundance resulted from differences in the rates at which different fragment types were produced rather than differences in their decay rates.

Trait modality distribution of aquatic macrofauna communities as explained by pesticides and water chemistry.

Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.Electronic supplementary materialThe online version of this article (doi:10.1007/s10646-016-1671-5) contains supplementary material, which is available to authorized users.

The effect of pesticides on the composition of aquatic macrofauna communities in field ditches

Ditches surrounding agricultural fields in the Netherlands are predominantly used for flood control, and they accommodate aquatic plant and animal species. Studies addressing the effects of pesticides in combination with abiotic and biotic factors on aquatic biota in ditches are scarce. The current study aimed to investigate the effects of pesticides along with environmental factors, presence of other biota and time on the community composition of aquatic macrofauna in ditches next to flower bulb fields and pastures. Macrofauna samples and environmental data were collected during two consecutive years. Ponds in a sandy dune area of a nature reserve next to the polders were sampled as control sites. Data was analyzed with the variance partitioning procedure based on the redundancy analysis (RDA). The total variance in macrofauna community composition was divided into the variance explained by pesticides, environmental factors (water chemistry parameters and macrophyte coverage), time (study year and the number of the month), shared variance, and unexplained variance. The total explained variance in macrofauna community reached 22.6%. The largest proportion of explained variance was attributed to environmental factors (10.1%) followed by pesticides (5.4%) and time (4.8%). When each macrofauna group was analyzed separately, presence of other biota and environmental factors explained the largest proportion of variance in most of the macrofauna groups. Results of the study indicate that environmental factors, biotic interactions and temporal variation influence freshwater macrofauna considerably along with pesticides. We suggest that environmental managers should consider the multiple stressor contexts of aquatic ecosystems.

Live bait capture and crayfish trapping as potential vectors for freshwater invasive fauna

Fishing activities strongly contribute to biological invasions in freshwaters. The purpose of this study was to investigate the potential risks of live bait capture using dip nets and of crayfish trapping as vectors for invasive freshwater macrofauna dispersal. In the Tagus river basin (Portugal), where both activities are common, we evaluated the probability of capture and the electivity of the local aquatic macrofauna according to the method used. During the compulsory removal of the invasive species captured we also quantified fish desiccation survival capacities. We found, for both vectors, that the species exhibiting the highest probability of capture and the highest electivity were invasive, respectively, Gambusia holbrooki and Crangonyx pseudogracilis with the dip net, Procambarus clarkii and several invasive species with special relevance for Ameiurus melas with the crayfish trapping. Moreover, the desiccation survival capacities, of all invasive fishes analyzed, are compatible with long distance dispersal out of water, with special relevance to G. holbrooki . This study demonstrates that fishing activities contribute to long-distance dispersal of invasive fauna. Therefore, according to our findings, it is important to update the fishing regulation and simultaneously to raise fishermen awareness of this problem.

Fish environmental DNA is more concentrated in aquatic sediments than surface water

Genetic identification of aqueous environmental DNA (eDNA) provides site occupancy inferences for rare aquatic macrofauna that are often easier to obtain than direct observations of organisms. This relative ease makes eDNA sampling a valuable tool for conservation biology. Research on the origin, state, transport, and fate of eDNA shed by aquatic macrofauna is needed to describe the spatiotemporal context for eDNA-based occupancy inferences and to guide eDNA sampling design. We tested the hypothesis that eDNA is more concentrated in surficial sediments than in surface water by measuring the concentration of aqueous and sedimentary eDNA from an invasive fish, bigheaded Asian carp (Hypophthalmichthys spp.), in experimental ponds and natural rivers. We modified a simple, low-cost DNA extraction method to yield inhibitor-free eDNA from both sediment and water samples. Carp eDNA was 8–1800 times more concentrated per gram of sediment than per milliliter of water and was detected in sediments up to 132days after carp removal – five times longer than any previous reports of macrobial eDNA persistence in water. These results may be explained by particle settling and/or retarded degradation of sediment-adsorbed DNA molecules. Compared to aqueous eDNA, sedimentary eDNA could provide a more abundant and longer-lasting source of genetic material for inferring current-or-past site occupancy by aquatic macrofauna, particularly benthic species. However, resuspension and transport of sedimentary eDNA could complicate the spatiotemporal inferences from surface water sampling, which is currently the predominant eDNA-based approach. We discuss these implications in the context of conservation-oriented monitoring in aquatic ecosystems.

Improved methods for capture, extraction, and quantitative assay of environmental DNA from Asian bigheaded carp (Hypophthalmichthys spp.).

Indirect, non-invasive detection of rare aquatic macrofauna using aqueous environmental DNA (eDNA) is a relatively new approach to population and biodiversity monitoring. As such, the sensitivity of monitoring results to different methods of eDNA capture, extraction, and detection is being investigated in many ecosystems and species. One of the first and largest conservation programs with eDNA-based monitoring as a central instrument focuses on Asian bigheaded carp (Hypophthalmichthys spp.), an invasive fish spreading toward the Laurentian Great Lakes. However, the standard eDNA methods of this program have not advanced since their development in 2010. We developed new, quantitative, and more cost-effective methods and tested them against the standard protocols. In laboratory testing, our new quantitative PCR (qPCR) assay for bigheaded carp eDNA was one to two orders of magnitude more sensitive than the existing endpoint PCR assays. When applied to eDNA samples from an experimental pond containing bigheaded carp, the qPCR assay produced a detection probability of 94.8% compared to 4.2% for the endpoint PCR assays. Also, the eDNA capture and extraction method we adapted from aquatic microbiology yielded five times more bigheaded carp eDNA from the experimental pond than the standard method, at a per sample cost over forty times lower. Our new, more sensitive assay provides a quantitative tool for eDNA-based monitoring of bigheaded carp, and the higher-yielding eDNA capture and extraction method we describe can be used for eDNA-based monitoring of any aquatic species.

Freshwater scarcity effects on the aquatic macrofauna of a European Mediterranean-climate estuary

In the Mediterranean-climate zone, recurrent drought events and increasing water demand generally lead to a decrease in freshwater input to estuaries. This water scarcity may alter the proper function of estuaries as nursery areas for marine species and as permanent habitat for estuarine species. A 12-year data set of the aquatic macrofauna (fish, decapod and mysid crustaceans) in a Mediterranean estuary (Guadalquivir estuary, South Spain) was analysed to test if water scarcity favours the nursery function of regional estuaries to the detriment of permanent estuarine inhabitants. Target species typically displayed a salinity-related distribution and estuarine salinisation in dry years resulted in a general upstream community displacement. However, annual densities of marine species were neither consistently higher in dry years nor estuarine species during wet years. Exceptions included the estuarine mysid Neomysis integer and the marine shrimp Crangon crangon, which were more abundant in wet and dry years, respectively. High and persistent turbidity, a collateral effect of water scarcity, altered both the structural (salinity-related pattern) and functional (key prey species and predator density) community characteristics, chiefly after the second drought period of the analysis. The observed high inter-year environmental variability, as well as species-specific effects of water scarcity, suggests that exhaustive and long-term sampling programmes will be required for rigorously monitoring the estuarine communities of the Mediterranean-climate region.

Response to Casey et al.'s sensitivity of detecting environmental DNA comment

Casey et al. correctly identified a need for clarification regarding the detection limits we reported for two PCR assays (Jerde et al. 2011). Serial dilutions of purified PCR amplicon DNA (not total genomic DNA) were used to evaluate sensitivity. One microliter of purified amplicon DNA from each assay was added to 25 μL reactions and the lowest detectable concentrations were approximately 207 copies/μL of DNA (3.30 × 10−8 ng/μL) for bighead carp, and 7 copies/μL of DNA (7.25 × 10−10 ng/μL) for silver carp. We determined the maximum sensitivity of our assays under ideal laboratory detection conditions because the detection limits of any PCR assay for bulk environmental samples is contingent on the complexity of the assayed DNA solution and water quality characteristics (Thompson et al. 2006). This clarification about the type of DNA used in the assay, that is amplicon DNA rather than total genomic DNA to determine maximum sensitivity, eliminates the concern of Casey et al. regarding credibility of our eDNA assays. No conclusions or observations reported by Jerde et al. (2011) are affected by the concerns raised by Casey et al. including: the sensitivity of eDNA surveillance exceeding that of traditional monitoring tools (Figure 3; Jerde et al. 2011); the presence of Asian carp above the electric barrier where eDNA first detected them (Figure S1; Jerde et al. 2011); and the eDNA approach, which has been applied by the U.S. Army Corps of Engineers using the protocols and procedures from our study resulting in similar detection patterns (http://www.lrc.usace.army.mil/AsianCarp/eDNA.htm). Finally, a number of recent studies demonstrate that eDNA is a reliable index of the occurrence and abundance of rare aquatic macrofauna (Dejean et al. 2011; Goldberg et al. 2011; Minamoto et al. 2011; Thomsen et al. 2012).

World Wide Food Webs: Power to Feed Ecologists

World Wide Food Webs: Power to Feed Ecologists

Nitrous oxide emission by aquatic macrofauna

A large variety of aquatic animals was found to emit the potent greenhouse gas nitrous oxide when nitrate was present in the environment. The emission was ascribed to denitrification by ingested bacteria in the anoxic animal gut, and the exceptionally high N(2)O-to-N(2) production ratio suggested delayed induction of the last step of denitrification. Filter- and deposit-feeding animal species showed the highest rates of nitrous oxide emission and predators the lowest, probably reflecting the different amounts of denitrifying bacteria in the diet. We estimate that nitrous oxide emission by aquatic animals is quantitatively important in nitrate-rich aquatic environments like freshwater, coastal marine, and deep-sea ecosystems. The contribution of this source to overall nitrous oxide emission from aquatic environments might further increase because of the projected increase of nitrate availability in tropical regions and the numeric dominance of filter- and deposit-feeders in eutrophic ecosystems.

The gut microenvironment of sediment-dwelling Chironomus plumosus larvae as characterised with O2, pH, and redox microsensors

We devised a set-up in which microsensors can be used for characterising the gut microenvironment of aquatic macrofauna. In a small flow cell, we measured microscale gradients through dissected guts (O(2), pH, redox potential [E ( h )]), in the haemolymph (O(2)), and towards the body surface (O(2)) of Chironomus plumosus larvae. The gut microenvironment was compared with the chemical conditions in the lake sediment in which the animals reside and feed. When the dissected guts were incubated at the same nominal O(2) concentration as in haemolymph, the gut content was completely anoxic and had pH and E ( h ) values slightly lower than in the ambient sediment. When the dissected guts were artificially oxygenated, the volumetric O(2)-consumption rates of the gut content were at least 10x higher than in the sediment. Using these potential O(2)-consumption rates in a cylindrical diffusion-reaction model, it was predicted that diffusion of O(2) from the haemolymph to the gut could not oxygenate the gut content under in vivo conditions. Additionally, the potential O(2)-consumption rates were so high that the intake of dissolved O(2) along with feeding could be ruled out to oxygenate the gut content. We conclude that microorganisms present in the gut of C. plumosus cannot exhibit an aerobic metabolism. The presented microsensor technique and the data analysis are applicable to guts of other macrofauna species with cutaneous respiration.

Effect of the regulation of freshwater inflow on the physical-chemical characteristics of water and on the aquatic macrofauna in the Guadalquivir estuary

From June 1998 to May 1999, the water temperature, salinity and turbidity, together with the macrofaunal (nekton and hyperbenthos) abundance, biomass and number of species, were estimated in the Guadalquivir estauary at five sampling stations (8, 20, 30, 40 and 50 km from the river mouth). Samples were taken from an anchored boat by using nets with a 1-mm mesh. There was a horizontal salinity gradient along the estuary: monthly mean salinities ranged from 17 to 27 at the outermost sampling station, whilst salinity was rarely higher than 4 in the inner estuary. Water temperature was homogenous throughout the estuary, with maximum values in summer (28ºC) and minimum values in winter (10ºC). Turbidity was also relatively homogenous throughout the estuary, with a maximum in winter (362 NTU) and a minimum in summer (10 NTU). Maximum turbidity occurred in the zone where seawater and freshwater merge. Results of stepwise multiple regression analysis indicated that both the distance to the river mouth and the freshwater input (in the previous month) from the Alcalá del Río dam (110 km from the river mouth) explained 70% of the variance in salinity, but that the freshwater input only explained 17% of the variance respecin water temperature and turbidity. Salinity explained 50% of the variance in the number of species, whereas salinity and temperature were the environmental variables that controlled the macrofaunal abundance and biomass. Salinity and temperature together explained 75% and 71% of the variance for nekton abundance and biomass, respectively, and 54% and 48% of the variance for the abundance and biomass of hyperbenthos, respectively. Salinity was, in all cases, the individual variable that explained the highest portion of variance.

Spatial and temporal variation of the nekton and hyperbenthos from a temperate European estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.

Shrimp—a dynamic model of heavy‐metal uptake in aquatic macrofauna

AbstractA dynamic model for prediction of bioaccumulation in aquatic macrofauna is described. The model, entitled SHRIMP (Simulation of Heavy‐metal Rate of Intake for Macrofaunal sPecies), consists of five coupled submodels, which simulate individual growth, population dynamics, metal transport in the abiotic part of the system, metal bioaccumulation at the organism level, and upscaling of individual contamination to the population scale. The sublethal effects of metal toxicity on individual and population levels are shown to act through the reduction of individual growth rates. The model was tested for cadmium and mercury using epibenthic crustacea from an estuarine system. Individual and population patterns of bioaccumulation were analyzed by comparing the simulated results of five different scenarios of dissolved metal concentrations. Model results suggest that the subtle effect of growth reduction due to metal toxicity is sufficient to cause a decrease on population numbers simply by affecting the growth of the mature females and males.