Hydromorphological restoration of running waters: effects on benthic invertebrate assemblages

1. River restoration has received considerable attention, with much recent focus on restoring river hydromorphology to improve impoverished aquatic communities. However, we still lack a clear understanding of the response of aquatic biota to river restoration. 2. We studied the effects of hydromorphological restoration on benthic invertebrate assemblages in 25 river sites in Germany using standardised methods. Restoration efforts were primarily aimed to restore habitat heterogeneity; correspondingly, habitat diversity increased at most sites. 3. Similarity of benthic invertebrate assemblages between restored and unrestored river sections was low (mean similarity was 0.32 for Jaccard and 0.46 for Sørensen). Community‐based metrics, such as the percentage of Ephemeroptera, Plecoptera and Trichoptera taxa, also differed between restored and unrestored sections. 4. Only three of the 25 restored sections were classified as having ‘good ecological quality’ class according to the European Water Framework Directive criteria; hence, poor water quality is probably one factor impeding recolonisation. 5. Our results show that isolated restoration measures do not necessarily result in positive effects on aquatic biota and that better understanding of the interconnectedness within a catchment is required before we can adequately predict biotic responses to structural river restoration.     

Taphonomy of Early Permian benthic assemblages (Carnic Alps, Austria): carbonate dissolution versus biogenic carbonate precipitation

During the Early Permian, in the area of the Carnic Alps, a quartz-gravelly beach fringed a mixed siliciclastic-carbonate lagoon with fleshy algal meadows and oncoids; seaward, an ooid shoal belt graded down dip to a low-energy carbonate inner shelf with phylloid algal meadows. In limestones, foraminiferal biomurae and bioclast preservation record tapholoss by rotting of non-calcified organisms (interpreted as fleshy algae) and by dissolution of aragonitic fossils. Carbonate loss by dissolution was counteracted and, locally, perhaps exceeded by carbonate precipitation of encrusting foraminifera and as oncoids. Sites of abrasion and carbonate dissolution (beach), sites with tapholoss by rotting and dissolution, but with microbialite/foraminiferal carbonate precipitation (lagoon, inner shelf), and sites only of carbonate precipitation (ooid shoals) co-existed on discrete shelf compartments. Compartmentalized, contemporaneous carbonate dissolution and precipitation, to total amounts yet difficult to quantify, impede straightforward estimates of ancient carbonate sediment budget.     

Absolute depths of Silurian benthic assemblages

A variety of evidence can be used to estimate the absolute depth of the well-established depth gradient of Silurian onshore-to-offshore benthic assemblages (BA 1–5); this evidence is reviewed herein. There is a fair degree of consistency between fossil benthic assemblages and the occurrence of certain primary sedimentary structures, particularly those involved in storm deposition. A second, probably stronger, line of evidence for absolute depth of Silurian benthic assemblages involves the distribution of fossils of light-sensitive organisms and of reefs. Among these, the most important are the calcified dasycladacean algae, to which the cyclocrinitids of the Middle Ordovician - Early Silurian may belong. The modem dasycladaceans have a narrowly restricted bathymetric range. Maximum depth for modern calcified dasycladaceans is about 90 m, but the vast majority occur at 30 m or less. Some Silurian occurrences of these algae are abundant, particularly in BA 3 and 4; rarely, small specimens of cyclocrinitids and receptaculitids are found in the lower, outer portions of BA 4 and even into 5. This evidence constrains much of the spectrum (BA 1–5) of Silurian fossil communities to a rather narrow depth range, within the photic zone. Based on taxonomic uniformitarianism, we would place the depth of Silurian BA 1 through 4 between 0 and about 40–60 m. The common coincidence of the lower end of storm wave base and the lower end of the photic zone near the BA 4–5 boundary also suggests that this position may represent water depths on the order of 50 m. Several other lines of evidence -including algal borings, widths of facies belts, separation of communities by basalt flows whose thicknesses are known - also support a relatively shallow depth range for BA 14. The absence of storm-disturbed beds over large parts of several major platforms below about the BA 3–4 boundary region suggests that major storms of the Silurian may have been far weaker than those of the present, possibly owing to a different climatic regime. □Absolute depth, Silurian, photic zone, calcareous algae, Benthic Assemblage, storms.     

Fish foraging effects on benthic assemblages along a warm-temperate stream: differences among drift feeders, benthic predators and grazers

In streams, physical and biotic conditions change from the headwaters to the mouth, shaping longitudinal patterns in community structure. We examined how fish foraging effects on periphyton and benthic invertebrates changed along a longitudinal gradient of a warm-temperate stream in southwestern Japan. We established three study sites according to changes in the composition of fish feeding guilds (upper site characterized by drifting-invertebrate feeders, Oncorhynchus masou ; middle site by benthic invertebrate feeders, Rhinogobius spp.; lower site by the presence of periphyton grazers, Sicyopterus japonicus ), and performed two manipulative experiments to examine effects of different fish assemblages on periphyton and benthic invertebrate abundances. Results of an exclosure experiment suggested that fishes had no effect on the benthic assemblages at the upper and middle sites whereas fishes reduced the abundances of both periphyton and invertebrates on stone surfaces at the lower site, where both benthic invertebrate feeders and grazers inhabited. A subsequent enclosure experiment showed that the reduction of invertebrate densities at the lower site was caused by the grazers rather than benthic invertebrate feeders. These experimental results suggested that effects of fishes on benthic assemblages are intensified downstream, owing to the occurrence of the grazing fish. Furthermore, observational data based on field sampling suggested that such grazing effects were reflected in longitudinal patterns in periphyton and invertebrate abundances. Overall results emphasize an important role of the grazing fish ( S. japonicus ) in shaping longitudinal patterns in benthic assemblage structure.     

Detecting the effects of physical disturbance on benthic assemblages in a subtropical estuary: A Beyond BACI approach

The effects of dredging on the benthic communities in the Noosa River, a subtropical estuary in SE Queensland, Australia, were examined using a ‘Beyond BACI’ experimental design. Changes in the numbers and types of animals and characteristics of the sediments in response to dredging in the coarse sandy sediments near the mouth of the estuary were compared with those occurring naturally in two control regions. Samples were collected twice before and twice after the dredging operations, at multiple spatial scales, ranging from metres to kilometres. Significant effects from the dredging were detected on the abundance of some polychaetes and bivalves and two measures of diversity (numbers of polychaete families and total taxonomic richness). In addition, the dredging caused a significant increase in the diversity of sediment particle sizes found in the dredged region compared with elsewhere. Community composition in the dredged region was more similar to that in the control regions after dredging than before. Changes in the characteristics of the sedimentary environment as a result of the dredging appeared to lead to the benthic communities of the dredged region becoming more similar to those elsewhere in the estuary, so dredging in this system may have led to the loss or reduction in area of a specific type of habitat in the estuary with implications for overall patterns of biodiversity and ecosystem function.     

Geometry of biodiversity patterning: assemblages of benthic macroinvertebrates at tributary confluences

We assessed whether tributaries in upland catchments (=watersheds) affected assemblages of benthic macroinvertebrates in mainstems, as has been reported in northern hemisphere systems. Eight confluences of small to medium streams (stream orders 1–4, 2.2–10.8 m wide) were studied in the Acheron River basin in Victoria, Australia. For each confluence, two transects were sampled at each of five zones relative to the confluence: two zones upstream in the mainstem, one zone upstream in the tributary, one zone at the confluence and one zone downstream in the mainstem. Surveys were conducted in both high-flow and low-flow conditions. In mainstems, there was no change in macroinvertebrate density, taxonomic richness or functional feeding group composition downstream relative to upstream of the confluences. While tributaries statistically had distinctive benthic macroinvertebrate assemblages compared to mainstems, these distinctions were small. In low flows, densities in tributaries were substantially lower than in mainstems, but densities during high flows were more similar (albeit only about one-third as high as in low flow) in tributaries and mainstems. An inverse pattern was evident for taxonomic richness, where richness in tributaries and mainstems was similar in low flows but was greater in mainstems than in tributaries in high flows. We found little evidence of tributary effects in macroinvertebrate assemblages in this basin, which is at odds with some previous results from other continents. To explain this divergence, we suggest a conceptual model outlining factors that control variation in effects of tributaries on assemblages of benthic macroinvertebrates in mainstems.     

Recovery of benthic macroinvertebrate and adult dragonfly assemblages in response to large scale removal of riparian invasive alien trees

Invasive alien organisms can impact adversely on indigenous biodiversity, while riparian invasive alien trees (IATs), through shading of the habitat, can be a key threat to stream invertebrates. We ask here whether stream fauna can recover when the key threat of riparian IATs is removed. Specifically, we address whether IAT invasion, and subsequent IAT removal, changes benthic macroinvertebrate and adult dragonfly assemblages, for the worse or for the better respectively. Natural riparian zones were controls. There were statistically significant differences between stream reaches with natural, IAT-infested and IAT-cleared riparian vegetation types, based on several metrics: immature macroinvertebrate taxon richness, average score per macroinvertebrate taxon (ASPT), a macroinvertebrate subset (Ephemeroptera, Plecoptera, Trichoptera and Odonata larvae; EPTO), and adult dragonfly species richness. Reaches with natural vegetation, or cleared of IATs, supported greater relative diversity of macroinvertebrates than reaches shaded by dense IATs. Greatest macroinvertebrate ASPT and EPTO were in reaches bordered by natural vegetation and those bordered by vegetation cleared of IATs, and the lowest where the riparian corridor was IATs. Highest number of adult dragonflies species was along streams cleared of dense IATs. Overall, results showed that removal of a highly invasive, dense canopy of alien trees enables recovery of aquatic biodiversity. As benthic macroinvertebrate scores and adult dragonfly species richness are correlated and additive, their combined use is recommended for river condition assessments.     

Pliocene benthic foraminifera from the Blake Plateau: Faunal assemblages and paleocirculation

Relative abundance of benthic foraminifera have been analyzed from core V26-145 from the Blake Plateau. The investigated sequence represents the time interval between 1.8 and 4.6 Ma. In order to determine how different sieve sizes influence the relative abundance patterns, three sediment size fractions were studied separately. It becomes difficult to maintain consistent taxonomic concepts in the fraction 63–125 μm, partly because this fraction contains high abundances of juvenile forms. However, the 63–125 μm fraction holds high abundances of the important small speciesEpistominella exigua. Due to these reasons only the two larger fractions (125–250 μm and >250 μm) were considered meaningful to analyze for relative abundance patterns. An analysis of the two larger fractions (>125 μm; >250 μm) shows no consistency in relative abundance patterns.The relative abundance patterns for the 34 most common species in the size fraction >125 μm were analyzed by means of correspondence analysis. Three benthic foraminiferal assemblages (I, II, and III) were recognized and these can be associated with water masses. Assemblage I is associated with the Florida Current and consists of shallow water species (Amphistegina gibbosa, Compressigerina sp. A,Discorbinella biconcavus, Islandiella teretis, Reussella atlantica, andSiphonina pulchra). Assemblage II contains key species for North Atlantic Deep Water (NADW) (Cibicidoides kullenbergi, Epistominella exigua, Globocassidulina subglobosa, Lenticulina peregrina, Oridorsalis umbonatus, andPlanulina wuellerstorfi). The third assemblage (III) contains species associated with the Antilles Current (Bolivina rhomboidalis, Cassidulina obtusa, Cassidulina vortex, andNuttallides umbonifera). The correspondence analysis reveals an alternation in dominance between Assemblage I and Assemblage II prior to 3.3 Ma, suggesting lateral oscillations between the Florida Current and NADW. At about 3.3 Ma Assemblage I disappears and Assemblage III increases in importance, suggesting an increasing influence of the Antilles Current in the upper part of the record.     

Landscape‐scale effects of fire on bird assemblages: does pyrodiversity beget biodiversity?

Aim A common strategy for conserving biodiversity in fire‐prone environments is to maintain a diversity of post‐fire age classes at the landscape scale, under the assumption that ‘pyrodiversity begets biodiversity’. Another strategy is to maintain extensive areas of a particular seral state regarded as vital for the persistence of threatened species, under the assumption that this will also cater for the habitat needs of other species. We investigated the likely effects of these strategies on bird assemblages in tree mallee vegetation, characterized by multi‐stemmed Eucalyptus species, where both strategies are currently employed. Location The semi‐arid Murray Mallee region of south‐eastern Australia. Methods We systematically surveyed birds in 26 landscapes (each 4‐km diameter), selected to represent gradients in the diversity of fire age classes and the proportion of older vegetation (> 35 years since fire). Additional variables were measured to represent underlying vegetation‐ or fire‐mediated properties of the landscape, as well as its biogeographic context. We used an information‐theoretic approach to investigate the relationships between these predictor variables and the species richness of birds (total species, threatened species and rare species). Results Species richness of birds was not strongly associated with fire‐mediated heterogeneity. Species richness was associated with increasing amounts of older vegetation in landscapes, but not with the proportion of recently burned vegetation in landscapes. Main conclusions The preference of many mallee birds for older vegetation highlights the risk of a blanket application of the ‘pyrodiversity begets biodiversity’ paradigm. If application of this paradigm involved converting large areas from long unburned to recently burned vegetation to increase fire‐mediated heterogeneity in tree mallee landscapes, our findings suggest that this could threaten birds. This research highlights the value of adopting a landscape‐scale perspective when evaluating the utility of fire‐management strategies intended to benefit biodiversity.     

The effects of aperiodic desiccation on the diversity of benthic desmid assemblages in a lowland peat bog

The lowland minerotrophic “Swamp” peat bog, located in the Czech Republic, is one of the most important European sites of desmidiacean diversity. The hydrological regime of the bog is driven by the water level of a nearby ancient manmade pond. Therefore, the bog experiences severe aperiodic drying events related to the pond draining. In this study, we investigated the drought-related response of the benthic desmid assemblages of the bog. The samples were taken bimonthly from 12th May 2008 to 19th May 2010, including the 8-month drying out period between October 2008 and June 2009. In addition to the species frequency data, morphometric methods were used to analyse the disparity, morphological turnover and surface-to-volume (S:V) ratios of Desmidiales. The drying event influenced the species composition, biovolume and S:V ratio data of the more species-rich pool, but its influence was less conspicuous in the species-poor acidic site. Accordingly, the species-rich site had generally higher species or morphological turnover between successive samples. The indicators based on the morphometric data were generally more sensitive than the species data. Therefore, we propose that the biovolume, S:V ratios or disparity measures of desmidiacean assemblages might be of benefit for future studies of peat bog microphytobenthos. Desmid assemblages at both sites recovered rapidly following the re-wetting of the bog, and they attained the pre-disturbance diversity, species composition and disparity values. We conclude that the drying event of the bog did not irreversibly influence its valuable desmid assemblages.     

Evolutionary significance of the microbial assemblages of large benthic Foraminifera

Large benthic Foraminifera (LBF) are major carbonate producers on coral reefs, and are hosts to a diverse symbiotic microbial community. During warm episodes in the geological past, these reef‐building organisms expanded their geographical ranges as subtropical and tropical belts moved into higher latitudes. During these range‐expansion periods, LBF were the most prolific carbonate producers on reefs, dominating shallow carbonate platforms over reef‐building corals. Even though the fossil and modern distributions of groups of species that harbour different types of symbionts are known, the nature, mechanisms, and factors that influence their occurrence remain elusive. Furthermore, the presence of a diverse and persistent bacterial community has only recently gained attention. We examined recent advances in molecular identification of prokaryotic (i.e. bacteria) and eukaryotic (i.e. microalgae) associates, and palaeoecology, and place the partnership with bacteria and algae in the context of climate change. In critically reviewing the available fossil and modern data on symbiosis, we reveal a crucial role of microalgae in the response of LBF to ocean warming, and their capacity to colonise a variety of habitats, across both latitudes and broad depth ranges. Symbiont identity is a key factor enabling LBF to expand their geographic ranges when the sea‐surface temperature increases. Our analyses showed that over the past 66 million years (My), diatom‐bearing species were dominant in reef environments. The modern record shows that these species display a stable, persistent eukaryotic assemblage across their geographic distribution range, and are less dependent on symbiotic photosynthesis for survival. By contrast, dinoflagellate and chlorophytic species, which show a provincial distribution, tend to have a more flexible eukaryotic community throughout their range. This group is more dependent on their symbionts, and flexibility in their symbiosis is likely to be the driving force behind their evolutionary history, as they form a monophyletic group originating from a rhodophyte‐bearing ancestor. The study of bacterial assemblages, while still in its infancy, is a promising field of study. Bacterial communities are likely to be shaped by the local environment, although a core bacterial microbiome is found in species with global distributions. Cryptic speciation is also an important factor that must be taken into consideration. As global warming intensifies, genetic divergence in hosts in addition to the range of flexibility/specificity within host–symbiont associations will be important elements in the continued evolutionary success of LBF species in a wide range of environments. Based on fossil and modern data, we conclude that the microbiome, which includes both algal and bacterial partners, is a key factor influencing the evolution of LBF. As a result, the microbiome assists LBF in colonising a wide range of habitats, and allowed them to become the most important calcifiers on shallow platforms worldwide during periods of ocean warming in the geologic past. Since LBF are crucial ecosystem engineers and prolific carbonate producers, the microbiome is a critical component that will play a central role in the responses of LBF to a changing ocean, and ultimately in shaping the future of coral reefs.     

Island benthic assemblages: With examples from the Late Ordovician of Eastern Australia

The Benthic Assemblage (B.A.) concept, developed by A.J. Boucot two decades ago principally for continental marine margins, is extended to offshore island settings. Characteristics of modern island biotas, including ecological displacement, and the effects of r and K selection, can be identified in Late Ordovician volcanic islands of central New South Wales. Two variants of B.A.1 are represented, a quiet‐water lingulide biofacies, and a rough‐water rhynchonellide biofacies. The quiet‐water Eodinobolus biofacies occupied a B.A.1–2 position, onshore of and sheltered by a Tetradium wave‐baffle (B.A.2). The offshore shelfal high diversity strophomenide biofacies is equivalent to B.A.3. Remnants of periplatformal B.A.4–5 communities are recognised in allochthonous limestone breccias which were displaced downslope into graptolitic B.A.6 sediments. Steeper offshore gradients, typical of islands, laterally compress the B.A. profiles, and also contribute to downslope slumping. Ecological displacement in island environments results in extension of the habitat range of species into adjacent B.A.s. Reefs complicate the usual B.A. profile by introducing distinct sheltered and turbulent water environments. These characteristics may have applicability in interpretation of islands throughout the Palaeozoic record.     

Interactive effects of porewater nutrient enrichment, bioturbation and sediment characteristics on benthic assemblages in sandy sediments

Effective management of eutrophic ecosystems requires an understanding of how nutrient input affects the structure and function of benthic communities. The effects of nutrients in soft sediment habitats can be influenced by a variety of factors including sediment characteristics, hydrodynamic exposure, and the presence of bioturbating macroinvertebrates. We used a large scale exclusion experiment (400 m² areas, n = 6) to test if bioturbating lugworms, Arenicola marina mediate the effects of nutrient enrichment. We incorporated small plots (30 × 30 cm) dosed with household garden fertilizer within the lugworm exclusion and corresponding control areas and predicted that the effects of nutrient enrichment would be greater in the absence of lugworms. We found that the increases in nutrient concentrations were higher in the absence of lugworms, but only in the less permeable sediment in the low intertidal zone compared to the more permeable sediment in the high intertidal. Contrary to expectations, the accumulation of nutrients in the plots did not affect the organic matter and chlorophyll levels in the sediment. Interestingly, there were overall negative effects of nutrient additions on some of the most abundant molluscs, Hydrobia ulvae, Retusa obtusa and juvenile Cerastoderma edule. Possible explanations for these adverse effects such as the changes in the sediment chemistry or the physical presence of the fertilizer in the sediment caused by the nutrient additions are discussed. We conclude that the effects of nutrient enrichment in soft sediment habitats on benthic assemblages are determined by the interplay between the presence of bioturbating macroinvertebrates, tidal height and sediment characteristics.     

Origin of jurassic ammonite concretions assemblages at Alfeld,Germany: a biogenic alternative

The ecology of macrofossils in ammonite-rich concretions and in coeval host sediments from Lower Bajocian mudstones in N.W. Germany indicates a predominantly epifaunal suspensionfeeding community living at maximally 50–90 m on a firm mud bottom during a hiatus or reduced sedimentation. Concretions are lined below with shell debris and contain numerous dimorphicStephanoceras [Ammonitina]. The dimorphs, however, are not a corresponding pair, showing instead extreme and uniquely inverse dimorphic ratios. Distribution of fossils and other debris within the concretions and the host sediments suggests the ammonite shells were swept by currents into subcircular depressions, lined with shell debris. We propose a biogenic alternative to the current/wave scour hypothesis for the origin of the depressions, which are essential to the accumulation of concretion assemblages: the pits were produced by rays feeding on the benthic fauna. Extant rays (Elasmobranchia) excavate such subcircular pits by jetting water through the gills (or mouth) for winnowing of the fauna from the sediment. The ammonite shells were transported post-mortem into the pits by moderate bottom currents. Rapid burial occurred by either a mudflow or renewal of strong sedimentation. Concretion growth was initiated by decomposition of organic matter within the mud.     

Patterns of benthic invertebrate assemblages in rivers of northwestern North America

SUMMARY. 1. Biogeographical and on-site. hydrological variables were evaluated to determine spatial distribution of benthic invertebrate assemblages at 100 river sites in northwestern North America.
2. Results of cluster analysis suggested that the river sites comprised sixgroups (A-F), each supporting a characteristic invertebrate assemblage.Distinct groups were best represented by abundant Tricorythidae (C), Amphipoda (F), Rhyacophilidae and Systellognatha (E), and Elmidae and Hydroptilidae (A). Brachycentridae (B) and Oligochaeta (D) were widespread throughout the study area.
2. Both biogeographical and hydrological features contributed to the correct classification of site groupings characterized by distinctive fauna. However, biogeographical features were more useful than variables measured at the river site in discriminating among the site groupings.Groups C and F were most prevalent within the Hudson Bay drainage.Groups A, C and F were typically located within plains; group E sites were in mountainous regions.
4. The hydrological variables most useful in delineating site groupings were mean current velocity and mean depth. Slow, deep waters characterized amphipod sites; shallow, fast flowing waters occurred at Rhyacophilidae Sysellognatha sites.
5. Results substantiate previous views of a strong association between benthic invertebrates in small rivers and the terrestrial biome through which the river flows.     

贻贝养殖海域表底层的鱼类组成比较

为了解贻贝养殖生境表底层水体的鱼类组成差异,利用2013年11月和2014年2月在枸杞岛贻贝养殖海域采集的鱼类数据,采用多样性和相对渔获率指标结合聚类和排序方法,对表底层的鱼类组成、多样性、密度以及群落格局差异进行了分析。结果表明:鲻(Mugil cephalus)和斑鰶(Konosirus punctatus)为秋冬季贻贝养殖区表层水体的优势鱼类,而褐菖鲉(Sebastiscus marmoratus)和小黄鱼(Larimichthys polyactis)、龙头鱼(Harpadon nehereus)和皮氏叫姑鱼(Johnius belangerii)分别为底层水体秋季和冬季的优势种;其中小黄鱼在养殖区的表底层皆有较大数量的分布;渔获率上,两季皆呈现表层高于底层的特征,除冬季的丰度渔获率外,其余皆有显著差异;鱼类在养殖区表层水体的平均丰度和生物量皆高于底层;多元分析显示,无论秋冬,表底层的鱼类群落格局皆有显著差异。可见,贻贝养殖设施相当于规模庞大的浮鱼礁系统,在泥质海域建设海洋牧场时,可结合类似浮体结构以增加海域立体养护能力;另一方面,可在养殖区底部增设人工鱼礁,以进一步发挥其海洋牧场效应。     

Effects of habitat complexity on benthic assemblages in a variable environment

1. Habitat complexity is thought to exert a significant influence on ecological communities, but its operation under variable natural conditions is not well understood, particularly in freshwater. To elucidate the role of habitat complexity, in particular the fractal structure of surface irregularity, in a stream system, field colonisation experiments were conducted at three times of year (summer, winter and spring) using natural substrates with different levels of fractal dimension in a small coastal mountain stream of southern Japan. 2. In the winter experiment, comparison was also made between the standard (control) treatment and the resource‐preconditioning treatment whereby experimental plates were conditioned in the natural stream environment to allow the accumulation of potential food resources (algae and detritus) for 1 month prior to the experiment. 3. Species abundance patterns observed at different times of year showed little systematic variation with levels of habitat complexity but largely followed the patterns expected from, or lying in between, the Random Assortment model and the random fraction model. 4. Taxon richness and density increased with habitat complexity in all seasons except for density in spring. Different taxa showed different patterns of change with habitat complexity, which also varied with seasons. Biomass of invertebrates showed no systematic trend with an increase in habitat complexity. 5. Chlorophyll‐a concentrations tended to be lower in more complex habitats, particularly in summer. In contrast, fine particulate organic matter (FPOM) tended to increase with habitat complexity. However, the relationship between these potential food resources and invertebrate assemblages remain unclear. 6. While there were no significant differences in taxon richness and biomass of invertebrates between the resource‐preconditioning and the control treatment, density was higher in the former than in the latter. The abundance of relatively large, surface‐dwelling animals showed more marked temporal variation over the entire period of colonisation in the resource‐preconditioning treatment than in the control treatment. 7. Body size of invertebrates tended to decline with fractal complexity, indicating that crevice sizes could affect habitat use by benthic animals of different sizes. In addition, body size was larger in the resource‐preconditioning treatment than in the control treatment, suggesting that body size in invertebrate assemblages was controlled by a mixture of factors. Thus, the present study demonstrates that habitat structure affects benthic invertebrate assemblages in a complex manner.