Complex metacommunity structure for benthic invertebrates in a low‐diversity coastal system

The majority of studies in metacommunity ecology have focused on systems other than marine benthic ecosystems, thereby providing an impetus to broaden the focus of metacommunity research to comprise marine systems. These systems are more open than many other systems and may thus exhibit relatively less discrete patterns in community structure across space. Metacommunity structure of soft‐sediment benthic invertebrates was examined using a fine‐grained (285 sites) data set collected during one summer across a large spatial extent (1700 km²). We applied the elements of metacommunity structure (EMS) approach, allowing multiple hypothesis of variation in community structure to be tested. We demonstrated several patterns associated with environmental variation and associated processes that could simultaneously assemble species to occur at the sites. A quasi‐Clementsian pattern was observed frequently, suggesting interdependent ecological relationships among species or similar response to an underlying environmental gradient across sites. A quasi‐nested clumped species loss pattern was also observed, which suggests nested habitat specialization. Species richness declined with depth (from 0.5 to 44.8 m). We argue that sensitive species may survive in shallower water, which are more stable with regard to oxygen conditions and present greater habitat complexity, in contrast to deeper waters, which may experience periodic disturbance due to hypoxia. Future studies should better integrate disturbance in terms of temporal dynamics and dispersal rates in the EMS approach. We highlight that shallow water sites may act as sources of recruitment to deeper water sites that are relatively more prone to periodic disturbances due to hypoxia. However, these shallow sites are not currently monitored and should be better prioritized in future conservation strategies in marine systems.     

The relative contributions of refugium types to the persistence of benthic invertebrates in a seasonal snowmelt flood

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Sedimentation in McMurdo Sound, Antarctica: a disturbance mechanism for benthic invertebrates

A slumping event that occurred on permanent transect lines from 12- to 30- m depth located at Arrival Heights, McMurdo Sound, Antarctica in 1993, provided an opportunity to examine the effects of sediment-mediated disturbance on the benthic invertebrate fauna. The disturbance had a particularly significant impact on the soft coral Alcyonium paessleri, which resulted in 84% colony mortality downslope from the slump site compared to an average annual mortality rate of 14% on control transects. In contrast, anchor ice at the same site accounted for removal of 5% of the population in 1992. Laboratory experiments with A. paessleri colonies under conditions of periodic sediment resuspension indicate that the soft corals are susceptible to this form of disturbance. Our observations suggest they are capable of shedding fine silt in the laboratory, which might explain the presence of A. paessleri in soft-sediment sites around McMurdo Sound. However, scarring by larger gravel in laboratory assays was slow to heal and may account for much of the colony mortality we observed. Several invertebrate-barren rocky benthic regions in McMurdo Sound were suggestive of historical slumping events. Given the removal of the smaller grain size sediments from these areas – a typically slow process – it appears these communities are slow to recover. The long-term effects of sedimentation on the benthic communities are unknown, but the impact on A. paessleri, one of the most common and fastest growing species, suggests this disturbance mechanism could lead to significant restructuring of these communities. Received: 29 November 1996 / Accepted: 23 February 1997     

The distribution of juvenile benthic invertebrates in an arctic glacial fjord

The distribution of juvenile benthic invertebrates with respect to their abiotic environment was investigated at four locations along a gradient in Kongsfjorden (79°N, 12°E), Spitsbergen, in September 1997. Heavy discharge of inorganic sediments released by the three glaciers was expected to be one of the main structuring factors of benthic communities in the fjord. Juveniles of 76 species/families are identified. Total abundance increases with distance from the fjord head due to the dominance of opportunistic polychaetes, while diversity is highest close to the glacier. Juvenile polychaetes are the most abundant taxon over all stations (92%), followed by bivalves, crustaceans and others. Polychaetes also provide most species (55%) and are the dominant taxon at every station. Their abundance is highly correlated with total organic carbon, indicating that most of them are deposit feeders. Young crustaceans rapidly decrease towards the fjord mouth, probably due to stronger bottom currents. Even though young oligochaetes are exclusively found near the glacier, no species seem to be well adapted to the high sedimentation rate close to the glacier. Juvenile suspension-feeding bivalves seem to be less disturbed by glacial discharge but appear to be more vulnerable to currents on the more exposed sites. The importance of deposit feeders and carnivores increases towards the outer stations. Non-metric multidimensional scaling confirms the distinct gradient in community composition along the fjord. Coupling the biotic data to abiotic factors (depth, bottom-water salinity, bottom-water temperature, sediment grain size and sedimentation rate) using canonical correspondence analysis revealed that hydrographic factors are more responsible for the structuring of the benthic juvenile community at the shallow stations close to the glacier (except the station directly at the glacier). At the outer deeper stations, sediment grain size and related properties may play a more important role.     

Ecological status assessment of European lakes: a comparison of metrics for phytoplankton, macrophytes, benthic invertebrates and fish

Data on phytoplankton, macrophytes, benthic invertebrates and fish from more than 2000 lakes in 22 European countries were used to develop and test metrics for assessing the ecological status of European lakes as required by the Water Framework Directive. The strongest and most sensitive of the 11 metrics responding to eutrophication pressure were phytoplankton chlorophyll a, a taxonomic composition trophic index and a functional traits index, the macrophyte intercalibration taxonomic composition metric and a Nordic lake fish index. Intermediate response was found for a cyanobacterial bloom intensity index (Cyano), the Ellenberg macrophyte index and a multimetric index for benthic invertebrates. The latter also responded to hydromorphological pressure. The metrics provide information on primary and secondary impacts of eutrophication in the pelagic and the littoral zone of lakes. Several of these metrics were used as common metrics in the intercalibration of national assessment systems or have been incorporated directly into the national systems. New biological metrics have been developed to assess hydromorphological pressures, based on aquatic macrophyte responses to water level fluctuations, and on macroinvertebrate responses to morphological modifications of lake shorelines. These metrics thus enable the quantification of biological impacts of hydromorphological pressures in lakes.     

Responses of benthic invertebrates in an experimental channel to artificial flushes

A large experimental channel was used to examine the responses of benthic invertebrate communities to artificial flushes. Two artificial flushes were done at a 20-day interval with a 2-fold difference in peak discharge and duration between them. The effects of the flushes on macroinvertebrates were monitored by comparing the abundance of individual taxa, taxon richness, diversity measures, and similarity indices. Taxon richness and abundances of invertebrates were drastically reduced by every flush. However, the diversity of invertebrates was not significantly reduced by the flushes, and the composition was similar before and after each flush. The fast recruitment of some taxa, having short life cycles, reduced the diversity of invertebrates in the interval between the two flushes. The flushes caused significant reductions in the abundance of epiphytes and fauna living in the streambed. The fauna more resistant to flushes were invertebrates that fasten their cases or retreats by silk threads to substrata. Taxa living in sediment under stones and having a sucking apparatus were also resistant to flushes. Handling editor: R. Bailey     

Drifting algal mats as an alternative habitat for benthic invertebrates: Species specific responses to a transient resource

Patchy occurrences of benthic drift algae (i.e. loose lying macroalgal mats) may increase habitat complexity on normally bare soft bottoms, but at the same time, extensive amounts of drifting algal mats are known to stress the benthic fauna. This paper presents results of the first detailed study of the fauna associated with drift algal mats in the northern Baltic Sea. In order to assess the importance of drifting algae as an alternative habitat for benthic fauna, benthic drift algal mats were sampled on shallow (2-9 m) sandy soft bottoms in the outer archipelago of the ?land Islands (Finland). Species composition, abundance and biomass of the macrofauna associated with algal mats were recorded. The results show that drifting algae at times can harbour very high abundances of invertebrates (up to 1116 individuals/g algal dryweight), surpassing invertebrate densities recorded in seagrass communities. The algal fauna varied between sites and over time, and factors such as ambient benthic fauna, exposure to wind-wave disturbance, depth, and algal coverage and condition influenced the invertebrate community composition of the algal mats. Abundance increased while individual biomass of the animals decreased over time (summer season; July-October). A series of laboratory experiments were conducted in order to test the ability of a few important benthic species to move up into, and survive in a drifting algal mat. Macoma balthica, Hydrobia spp., Nereis diversicolor and Bathyporeia pilosa were used in the experiments, and significant differences in their survival and mobility within drifting algae were recorded. This study shows that benthic species differ significantly in their ability to utilise the algal mats, with mainly opportunistic and mobile taxa such as Hydrobia spp., Chironomidae and Ostracoda benefiting from the algae, whereas infaunal species such as M. balthica and B. pilosa are negatively affected. The occurrence of eutrophication induced drifting macroalgal mats has increased significantly during the last decade in the northern Baltic Sea. Hence, the importance of drifting algae as a stress factor and as an alternative habitat for benthic fauna increases.     

A comparison of bacteria and benthic invertebrates as indicators of ecological health in streams

1. We set out to evaluate the reliability of bacterial communities as an indicator of freshwater ecological health.
2. Samples of epilithic biofilm were taken over a 1-year period from four streams, each impacted by varying degrees of human modification. The bacteria within each sample were characterised using a whole community DNA fingerprinting technique (automated ribosomal intergenic spacer analysis). Spatial and temporal differences in community structure between samples were visualised using multi-dimensional scaling and quantified using permutational multivariate anova . Macrobenthic invertebrates, which are commonly used as indicators of stream ecological health, were also sampled for comparison.
3. Multivariate analysis revealed a clear gradient in macroinvertebrate community structure between sites exposed to increased human impact. Bacterial communities, however, could only distinguish the most impacted site from the remainder.
4. Additional research is required to increase the sensitivity of bacterial community analyses before endorsing their use as an indicator of freshwater ecological health.     

Feeding by benthic invertebrates: Classification and terminology for paleoecological analysis

A trophic terminology is proposed, based on the feeding function of benthic invertebrates. This function has four aspects; (I) food resources can bc characterized on the basis of composition, condition, size, and dispersion; (2) the location of benthic food resources is not random, but most are concentrated at the sediment-water interface with a decreasing amount above and below; (3) an organism accomplishes food resource selection on the basis of particle size, specific gravity relationships, and nutrient capacity; finally (4) organisms have developed food acquisition mechanisms which arc adaptations for dealing with small particles, large particles and masses, or fluids. The classification, comprising nine main groups of animals, makes clear the distinction between site-of-life and location of food acquistion. It accounts logically for the four aspects of feeding, and yet has the advantage of simplicity.     

Functional roles of an engineer species for coastal benthic invertebrates and demersal fish

Through their tissues or activities, engineer species create, modify, or maintain habitats and alter the distribution and abundance of many plants and animals. This study investigates key ecological functions performed by an engineer species that colonizes coastal ecosystems. The gregarious tubiculous amphipod Haploops nirae is used as a biological model. According to previous studies, the habitat engineered by H. nirae (i.e., Haploops habitat) could provide food and natural shelter for several benthic species such as benthic diatoms belonging to the gender Navicula, the micrograzer Geitodoris planata, or the bivalve Polititapes virgineus. Using data from scientific surveys conducted in two bays, this study explored whether (1) the Haploops sandy‐mud community modifies invertebrate and ichthyologic community structure (diversity and biomass); (2) H. nirae creates a preferential feeding ground; and (3) this habitat serves as a refuge for juvenile fish. Available Benthic Energy Coefficients, coupled with more traditional diversity indices, indicated higher energy available in Haploops habitat than in two nearby habitats (i.e., Sternaspis scutata and Amphiura filiformis/Owenia fusiformis habitats). The use of isotopic functional indices (IFIs) indicated (1) a higher functional richness in the Haploops habitat, related to greater diversity in food sources and longer food chains; and (2) a higher functional divergence, associated with greater consumption of a secondary food source. At the invertebrate‐prey level, IFIs indicated little specialization and little trophic redundancy in the engineered habitat, as expected for homogenous habitats. Our results partly support empirical knowledge about engineered versus nonengineered habitats and also add new perspectives on habitat use by fish and invertebrate species. Our analyses validated the refuge‐area hypothesis for a few fish species. Although unique benthic prey assemblages are associated with Haploops habitat, the hypothesis that it is a preferential feeding area was not verified. However, specialist feeding behavior was observed for predators, which calls for further investigation.     

Functional diversity and species turnover of benthic invertebrates along a local environmental gradient induced by an aquaculture unit: the contribution of species dispersal ability and rarity

The relation of macrobenthic species turnover (beta diversity) and species plylogenetic variation with functional diversity patterns, across an environmental gradient induced by an aquaculture unit, in a coastal area of the island of Lesvos (NE Aegean) has been investigated in this study. The contribution of rare species response and species dispersal ability in the variation of functional diversity patterns along the environmental gradient, on a spatio-temporal scale, has been also examined. Our results revealed that benthic functional diversity was decreasing monotonically with increasing species turnover rate and hence with increasing spatial variability along the environmental gradient. Increased environmental stress which was detected in the immediate vicinity of the fish cages resulted to low species functional redundancy, since different species didn’t perform the same functional role at the most disturbed part of the established gradient. Functional diversity patterns were found to be correlated with species population size, whereas a strong linear relationship was also detected with phylogenetic diversity patterns, thus supporting the claim that wider local taxonomic trees can support a wider range of species functions even in small spatial scales. Rare species loss seemed to be one of the dominant factors ruling functional diversity variation. Species with the minimum possible dispersal ability, which were mostly rare, tend to diminish both in species number and population size faster than species with wider dispersal ability towards the most disturbed areas. The aforementioned results indicate that rare species variation and endemic species loss are critical factors in determining functional diversity loss across a human-induced environmental gradient in soft bottom benthic communities.     

The impact of hydromorphological restoration on river ecological status: a comparison of fish, benthic invertebrates, and macrophytes

The European Water Framework Directive (WFD) has led to an increase in hydromorphological restoration attempts in European rivers, but data on the ecological responses of rivers to these restoration attempts are scarce. We investigated the effects of 24 hydromorphological river restoration projects in Germany. We compared hydromorphological parameters and biological diversity of macroinvertebrates, fish, and macrophytes in restored reaches to nearby unrestored sections. We applied, for the first time, the WFD to assess the results of these restoration projects. While hydromorphology changed significantly in the restored sections, differences between restored and unrestored sections in terms of biological parameters were lower. Positive restoration effects were observed for fish (11 of 24 cases) only. Based on the synthesis of results from the different organism groups, only one of the 24 restored sections reached a “good” Ecological Quality Class as demanded by the WFD. Our results indicate that stressors other than hydromorphological degradation still affect the biota in restored sections. We emphasize the need for advanced restoration strategies based on catchment analyses considering water pollution, source populations, and dispersal capacities of sensitive species, and recommend the inclusion of additional parameters, including societal and stakeholder perspectives, in assessing the initial success of restoration projects.     

Centrifugal flotation as an aid to separating invertebrates from detritus in benthic samples

Efficiency of hand sorting versus centrifugally floating benthic samples of high detritus composition was compared. Centrifugal flotation removed a large proportion (up to 90%) of the detritus, significantly increased recovery of several taxa (e.g. copepods, mites and chironomids), and decreased overall sorting time. Centrifugal flotation was effective for both live and preserved samples and was 3 to 10 times more efficient than hand sorting.     

Size matters: extraordinary rodent abundance on an Australian tropical flood plain

Abstract: Published estimates of the total biomass of natural populations of mammalian herbivores generally have ignored small‐bodied taxa (especially, rodents). Including such taxa may dramatically change our understanding of total biomass and energy flow in such systems. Dusky rats (Rattus colletti) are small (up to 210 g) native Australian mammals, and our 5‐year mark‐recapture study on a tropical flood plain (Adelaide River, Northern Territory) revealed that rat biomass can reach extraordinary levels (up to 4.7 t km^?2). Because their small body size results in high mass‐specific metabolic rates, a given biomass of rodents has a several‐fold higher total energy requirement than the same mass of large‐bodied herbivores. Accordingly, during some years dusky rat biomass can be double that estimated for large herbivores on the world's most productive savannas in eastern and southern Africa. The huge rodent biomass strongly suggests that the Adelaide River flood plain must be an incredibly productive habitat. Considering the immense biological importance of these productive ecosystems, flood plain conservation must be placed high on the priority list of habitats that require immediate protection.     

Small-sized invertebrates in a gravel stream: community structure and variability of benthic rotifers

1. The Rotifera assemblage inhabiting the streambed surface and the hyporheic zone of a gravel stream was investigated between October 1991 and October 1992. Forty-two species of Monogononta and 27 of Bdelloidea were identified. Within these two classes, dominant species differed between the surface and the hyporheic zone. At the streambed surface, the abundance of monogonont rotifers showed a seasonal pattern with significantly higher densities in pools, whereas bdelloids showed no clear temporal trend and did not differ significantly among sites. In the hyporheic zone, the depth distribution differed among the two rotifer groups, bdelloids occurred in highest densities between 0 and 30 cm sediment depth, while monogononts were most abundant at greater depths.
2. Species composition differed greatly between successive sampling dates (min. 5 to max. 26 days) at both the streambed surface and the hyporheos. At the streambed surface and in the shallow hyporheos a significantly higher percentage of species was replaced in riffles than in pools.
3. Few measured hydrophysical variables were associated with the Rotifera assemblage structure. At the streambed surface, species richness was negatively correlated with water temperature and substratum heterogeneity, and Monogononta rotifer densities declined with water depth and substratum roughness.
4. Permutation tests carried out on temporal serial correlations showed that, at riffle sites at the streambed surface, bdelloid rotifer densities, rotifer species richness and diversity did not differ significantly from a temporal, near-random pattern. The hyporheic rotifer assemblage followed similar near-random patterns.     

Mercury in benthic invertebrates of the Elbe estuary

Hg concentrations in benthic invertebrates of the Elbe estuary were analyzed by atomic absorption spectrophotometry and instrumental neutron activation analysis. In general Hg levels in organisms decreased from the limnic region to the marine environment. Highest Hg levels were found inAsellus aquaticus andRadix balthica taken from the Elbe upstream of Hamburg (0.35 and 0.34 ppm wet weight). The concentrations in gammarid species decreased from 0.20 ppm (limnic region) to 0.02–0.05 ppm (brackish and marine environment). Hg levels in organisms from the brackish region proved to be 0.08–0.16 ppm(Littorina littorea), 0.04–0.09(Crangon crangon) 0.05–0.10(Corophium volutator) and 0.04–0.08 ppm (wet weight)(Nereis diversicolor). Some factors which may influence the heavy metal concentrations in aquatic organisms are discussed, such as: food chain, weight of organisms, and elimination via moulting products in the case of crustaceans.     

Biodiversity of benthic invertebrates and organic matter processing in shallow marine sediments: an experimental study

The main objective of this study was to measure the impact of benthic invertebrate diversity on processes occurring at the water-sediment interface. We analyzed the effects of interactions between three shallow water species (Cerastoderma edule, Corophium volutator, and Nereis diversicolor). The impacts of different species richness treatments were measured on sediment reworking, bacterial characteristics, and biogeochemical processes (bromide fluxes, O₂ uptake, nutrient fluxes, and porewater chemistry) in sediment cores. The results showed that the three species exhibited different bioturbation activities in the experimental system: C. edule acted as a biodiffusor, mixing particles in the top 2 cm of the sediments; C. volutator produced and irrigated U-shaped tubes in the top 2 cm of the sediments; and N. diversicolor produced and irrigated burrow galleries in the whole sediment cores. C. edule had minor effects on biogeochemical processes, whereas the other species, through their irrigation of the burrows, increased the solute exchange between the water column and the sediment two-fold. These impacts on sediment structure and solute transport increased the O₂ consumption and the release of nutrients from sediments. As N. diversicolor burrowed deeper in the sediment than C. volutator, it irrigated a greater volume of sediments, with great impact on the sediment cores.Most treatments with a mixture of species indicated that observed values were often lower than predicted values from the addition of the individual effects of each species, demonstrating a negative interaction among species. This type of negative interaction measured between species on ecosystem processes certainly resulted from an overlap of bioturbation activities among the three species which lived and foraged in the same habitat (water-sediment interface). All treatments with N. diversicolor (in isolation and in mixture) produced similar effect on sediment reworking, water fluxes, nutrient releases, porewater chemistry, and bacterial characteristics. Whichever species associated with N. diversicolor, the bioturbation activities of the worm hid the effect of the other species. The results suggest that, in the presence of several species that use and modify the same sediment space, impact of invertebrates on ecosystem processes was essentially due to the most efficient bioturbator of the community (N. diversicolor). In consequence, the functional traits (mode of bioturbation, depth of burrowing, feeding behaviour) of an individual species in a community could be more important than species richness for some ecosystem processes.     

Patterns and processes in abundance-body size relationships for marine benthic invertebrates

1. The nature of abundance-body size relationships in animal communities, and especially the drivers behind the observed patterns, have been a focus of persistent debate in animal ecology. In a recent review, Allen et al. (2006) categorized five mechanistic explanations behind the commonly observed polymodality in these relationships: energetic constraints; phylogenetic constraints; biogeographical determinants; habitat structure; and community interactions. Progress in understanding of these patterns and the processes underlying them have been hindered by the use of a range of methods that differ in their validity and robustness. 2. Here, we used data on invertebrate body sizes from a variety of sandy beaches in the UK to test the hypothesis that these communities display modality in their abundance-body size relationships. We quantified modality in the relationships using kernel density estimation and smoothed bootstrap resampling and then evaluated the competing explanations for this modality based on the patterns identified in conjunction with measurements of the physical beach environment. 3. We found bimodal distributions in the body size spectrum for benthic invertebrates at nine of 16 sites. There was a consistent trough in the spectrum at around 0·5-1 mm diameter, which reflected the traditional split between meiofauna and macrofauna. Beaches with finer particle sizes and more heterogeneous macrofauna hosted communities with more than two modes. 4. Our results suggest that modality in sandy beach benthic communities is unlikely to be explained by any single hypothesis. There will be an interplay between physical and biological factors, with different explanations accounting for modality at different scales.