Eulittoral macroinvertebrate communities of lowland lakes: discrimination among trophic states

1. Nutrient inputs from urban and agricultural land use often result in shifts in species composition of pelagic and profundal invertebrate communities. Here, we test if nutrient enrichment affects the composition of eulittoral macroinvertebrate communities, and, if so, if macroinvertebrate communities of five different habitat types reflect differences in trophic state. 2. Macroinvertebrate community composition of 36 lakes was significantly correlated with total phosphorus (TP) concentration, the proportion of coarse woody debris (CWD) and root habitats and the proportion of grassland. 3. However, macroinvertebrate communities of five major habitat types from eight lakes were more dissimilar among habitats than among trophic states. Community composition of reed and stone habitats was significantly correlated with wind exposure but not TP concentration, while macroinvertebrate composition of sand habitats was related to TP concentration and coarse sediments. In CWD and root habitats, both TP concentration and a predominance of invasive species covaried, which made it difficult to relate the observed compositional differences to either trophic state or to the effects of competition between native and invasive species. 4. Trophic state influenced the composition of eulittoral macroinvertebrate communities but to a lesser extent than has been previously reported for profundal habitats. Moreover, the effects of trophic state were nested within habitat type and were partially superseded by biotic interactions and small‐scaled habitat complexity. Although eulittoral macroinvertebrate communities were not strong indicators of the trophic state of lowland lakes, they may be used to assess other anthropogenic impacts on lakeshores.     

Resistance to ship-induced waves of benthic invertebrates in various littoral habitats

1. Ship‐induced waves disturb benthic invertebrate assemblages colonizing littoral zones of lakes and rivers. However, the impact of ship‐induced waves on invertebrates has rarely been quantified, and the influencing factors have not been addressed. 2. In an experimental wave tank, five benthic invertebrate species, Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeseli and Laccophilus hyalinus, were exposed to waves of increasing shear stress (0.43–2.19 N m^?2). Mean number of detached individuals was recorded for five littoral habitats [coarse woody debris (CWD), reeds, sand, stones and tree roots], representing different levels of structural complexity as quantified by their fractal dimensions (FD). 3. Results showed that detachment of invertebrates was significantly related to shear stress in all habitats except tree roots. Detachments averaged for the five species were significantly lower in habitats with a high degree of structural complexity, decreasing in the habitat sequence: sand, CWD, stones, reeds and tree roots. 4. Consistent with their different morphologies and methods of attachment to substrates, the five species displayed differences in their response to hydraulic stress that were dependent on habitat. 5. The increasing sheltering effect of structural habitat complexity was mirrored by increasing dissipation of the kinetic energy of waves; i.e. the FD of the habitat was positively correlated with shear stress reduction due to the flow resistance of the habitat. 6. Network habitats such as tree roots provided the best sheltering conditions against hydraulic disturbance, because they combined good refuge availability for all studied invertebrate species and maximal dissipation of kinetic wave energy. Consequently, persistent anthropogenic impacts, such as lakeshore modification or long‐term exposure to ship‐induced waves, which cause disappearance of complex littoral habitats such as tree roots or dense reed belts, will drastically increase the adverse effects of boating and ship traffic on littoral invertebrate assemblages.     

Ecological effects of increasing time since invasion by the exotic African olive (<Emphasis Type="Italic">Olea europaea</Emphasis> ssp<Emphasis Type="Italic">. cuspidata</Emphasis>) on leaf-litter invertebrate assemblages

Invasive African olive, Olea europaea ssp. cuspidata (Wall. ex G.Don) Cif., forms increasingly dense stands between initial and mature stages of invasion, leading to a progressive decline in native plant diversity. Here, we examined the response of leaf-litter invertebrates to increasing time since olive invasion. We compared invertebrate assemblages among early-stage olive (0–7 years since invasion, scattered olive shrubs and seedlings in native woodland), mature olive (>15 years, uniform olive stands dominated by multi-trunked trees) and uninvaded native grassy woodland habitats (both mature stands and edges) in a critically endangered ecological community of south-eastern Australia. Invertebrate species richness was significantly reduced in mature olive compared with early-stage olive and mature native woodland habitats. Species richness did not differ significantly between early-stage olive habitat and mature native woodland, demonstrating resistance in species richness to initial invasion. Invertebrate species composition of native woodlands differed significantly from both mature olive and early-stage olive habitats, demonstrating a lack of resistance in species composition to initial olive invasion. Compositional differences were principally driven by reduced abundances within Coleoptera, Hymenoptera and Polyxenida in mature olive habitat compared with mature native woodland. These changes were significantly correlated with an increase in bare ground, plant canopy cover and litter depth, and higher moisture and lower temperature within leaf litter, in mature olive habitat. Our findings show that negative ecological impacts of invasive African olive extend beyond plants to leaf-litter invertebrate assemblages and that significant impacts on invertebrate species assemblage composition occur early in the invasion process.     

松嫩平原不同生境芦苇种群分株的生物量分配与生长分析

在松嫩平原8月中旬,4个旱地生境芦苇种群分株的生长和生产力以季节性临时积水的低洼地为最高,以碱斑地为最低,两个生境之间分株高度相差2.8倍,分株生物量相差4.4倍,其它2个生境沙地和草甸混生 少也达到了显著或极显著水平,不同生境芦苇种群分株生物量分配的差异,蕴涵着重要的生长调节和物质分配策略。在分株株较小而又有充分生长空间的沙地生境和三斑生境,以及具有种间竞争的草句生境,分株将50％以上的物质分配给叶的建造上,以保证充分的物质生产;在环境条件相对较好的低洼地生境,分株将近40％的物质分配给茎的伸长生长,以提高个体对空间和光资源的竞争力。4个生境芦苇种群在分株增高与增重,以及茎、叶与分株的相对增重均具有相同的幂函数异速生长规律。     

Top-down and bottom-up impacts of juvenile fish in a littoral reed stand

1. Research has often focused on pelagic food chains and processes of lakes; less is known about the contribution of benthic energy flows to whole‐lake ecosystem energetics. This stems from the fact that the shoreline and littoral habitats, which provide a key linkage between sediment and water column, have only recently become a significant focus for study. 2. This study aimed to quantify the feeding and phosphorus allocation of a juvenile fish community in a littoral zone of a shallow lake in response to the biomass succession of the invertebrate prey community. Habitats comprising reed and adjacent open water were sampled over two consecutive years during day and night. 3. Although there were substantial year‐to‐year differences in the biomass of invertebrates, the fish community composition, diet consumption rates and phosphorus allocations were very similar in both study years. Biomasses and predation impacts by juvenile fish on prey groups were substantially higher within the reeds than in the adjacent open water habitat. This may be explained by the refuge‐seeking behaviour of the fish. 4. In general, invertebrates were negligibly influenced by fish feeding, with the exception for a strong top‐down control of large cladocerans. In response to the resulting low Daphnia biomass, fish were forced to switch to a higher degree of benthivory. Consequently, juvenile fish in littoral reed stands may shift benthic‐derived energy and phosphorus via the excretion of soluble reactive phosphorus into the open water.     

Determinants of the distribution of juvenile fish in the littoral area of a shallow lake

1. Research has often focused on the pelagic areas of lakes; the littoral zone has received less attention. The few studies concerning fish distribution in littoral habitats have concentrated on stands of submersed macrophytes, whereas other littoral habitat types have seldom been investigated. 2. This study aimed to predict the occurrence of juvenile fish in several littoral habitats of a shallow lake as a function of food availability, complexity of habitat structure, water depth and substrate. Habitats comprising reed, woody structures, and two open water areas differing in depth were sampled for fish and invertebrate biomasses on two shores, over 6 months and during both daylight and at night. 3. The juvenile fish community consisted almost exclusively of 0+ and 1+ roach and perch. There was a strong diel component in habitat use, with a predominant occurrence of fish in complex habitats (mainly woody structures) during the day, and a partial migration towards the open habitats at night, more strongly expressed in roach than in perch. 4. The diet of all fish groups was relatively constant over the seasonal cycle, and was independent of habitat. There was a higher degree of planktivory in roach than in perch, but both species fed on benthic macroinvertebrates to a substantial extent. 5. According to a logistic regression model, the biomass of potential food organisms in the different habitats had little predictive effect on the spatial distribution of the fish, whereas the structural complexity of the habitats combined with the diel cycle explained about 28% of the occurrence patterns in 0+ and 1+ perch and 1+ roach.     

Using macroinvertebrate species assemblages to identify river channel habitat units: an application of the functional habitats concept to a large,unpolluted Italian river (River Ticino,northern Italy)

The functional habitat concept was applied to a large Italian river for the first time. The characteristically wide range of hydraulic conditions present in this river (compared to previously-studied small, lowland, English rivers) were expected to be of central importance to biota and, therefore, to habitat definition. TWINSPAN analysis of the invertebrate assemblages sampled in the Ticino river identified five distinct habitats: two habitats in lotic areas (run-riffle and macrophytes in current), two along the river margins (with and without macrophytes) and one in backwater areas. These correspond to five of the functional habitats identified in U.K. lowland rivers. Each of these five functional habitats could be defined either in terms of hydraulics, substratum and/or presence/absence of macrophytes. Representative taxa are presented for each habitat and community structure discussed. Macrophyte and run-riffle habitats supported the most heterogeneous and abundant benthic fauna. No match was found between replicates grouped by invertebrate assemblage (the five functional habitats identified by TWINSPAN) and the grouping of the same replicates by PCA, carried out on the physical data matrix. While obvious velocity differences were found between the functional habitats, of particular note was the fact that the Froude number did not show any clear association with habitat type. In the future, improved river management will follow improved understanding of river habitats.     

Factors influencing the appearance of spider (Araneae) and beetle (Coleoptera) assemblages in nests of great reed warbler Acrocephalus arundinaceus

The appearance of spider (Araneae) and beetle (Coleoptera) assemblages found in nests of great reed warbler Acrocephalus arundinaceus was studied, firstly to investigate breeding success and the amount of precipitation as potential factors which might affect the abundance and species richness of both groups. In addition, we compared the diversity of spider and beetle assemblages between nests found in different reed habitats, and considered the position of nests (above water or dry ground). In this study we selected five different randomly chosen reed habitats: two mining ponds, two small canals and one large canal. Great Reed Warbler nests were collected either shortly after fledging, or after the clutch had failed. Altogether, 12 species of spider and 19 species of beetle were collected. In both groups there was no significant difference in abundance between successful, lost and cuckoo-parasitized nests; however, there was a significant difference in species richness between the three nest categories in spider assemblages, which was not the case in beetle assemblages. The amount of precipitation did not affect beetle or spider abundance; only the species richness of spiders showed significant growth. Furthermore, we found no significant relationship between vegetation cover and the species richness and abundance of spiders and beetles. The diversity of both groups differed significantly according to reed habitat: beetle assemblages were most diverse by the large canal and spiders at the mining ponds.     

Effects of ship‐induced waves on littoral benthic invertebrates

1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m^?2 was found for a structurally complex reed habitat, compared to 0.37 N m^?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h^?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance.     

Influences of aquatic macrophytes on invertebrate community structure,guild structure,and microdistribution in streams

The aquatic macrophytes Ranunculus aquatilis and Rorippa nasturtium-aquaticum were transplanted into substrate trays and placed in a stream alongside unvegetated substrate. Macrophytes were observed to have significant effects on 1) invertebrate community structure, 2) guild structure, and 3) microdistribution. 1) Significantly higher taxa richness and community abundances were associated with macrophytes. 2) Significantly higher abundances of shredder, scraper, and predator guilds were associated with macrophytes in fall, and all guilds had higher abundances in macrophytes in spring. However, guild frequency distributions did not differ among habitats except in spring. 3) Enallagma, Gammarus, Gyraulus, Physa, and Pisidium exhibited a strong association with macrophytes, while Hydropsyche, Simulium, Baetis tricaudatus, Glossosoma velona, and Helicopsyche borealis appeared to avoid them. A strong correlation appeared to exist between current velocity preferences of these taxa and their selection or avoidance of vegetated habitat. Thus, the effect of macrophytes in reducing current velocities appeared to be the most important influence on invertebrate microdistribution. However, macrophytes also increase physical heterogeneity and their large surface areas benefit invertebrate community abundances by creating additional living spaces in the water column where none exist above unvegetated substrate.     

Ground spider assemblages as indicators for habitat structure in inland sand ecosystems

Open inland sand ecosystems harbour a specialised flora and fauna and are among the most endangered habitats in Central Europe. Land-use changes and lack of habitat dynamics are acknowledged as significant drivers for habitat loss and degradation. It is imperative for nature conservation to obtain criteria such as community structure and biodiversity of model groups to assess the conservation value of threatened habitats. By investigating the correlation between ground spider assemblages and habitat structure, the study aimed to find out the indicator potential of spiders in order to promote conservation objectives and management strategies for open inland sand ecosystems. Non-metric multidimensional scaling revealed four habitat groups with distinct spider assemblages that clearly reflected the whole variety of habitat structure types within the study area. Species distribution was constrained by biotic and abiotic gradients while the ecological traits of spiders differed significantly among the groups. Generalised linear models showed that abundances of particular species were significantly correlated with environmental factors and habitat structure, making them thus suitable as focal species to assess natural habitat modifications as well as success of management efforts. Based on these findings, we derived major aims for successful habitat management of inland sand ecosystems taking into account also the needs of arthropod conservation. Management should include both small and large reserves when aiming for higher levels of disturbance, and sand dynamics to prevent increasing scrub encroachment and to create a larger number of early succession stages.     

Contemporary Parallel Diversification,Antipredator Adaptations and Phenotypic Integration in an Aquatic Isopod

It is increasingly being recognized that predation can be a strong diversifying agent promoting ecological divergence. Adaptations against different predatory regimes can emerge over short periods of time and include many different traits. We studied antipredator adaptations in two ecotypes of an isopod (Asellus aquaticus) that have, diverged in parallel in two Swedish lakes over the last two decades. We quantified differences in escape speed, morphology and behavior for isopods from different ecotypes present in these lakes. Isopods from the source habitat (reed) coexist with mainly invertebrate predators. They are more stream-profiled and have higher escape speeds than isopods in the newly colonized stonewort habitat, which has higher density of fish predators. Stonewort isopods also show more cautious behaviors and had higher levels of phenotypic integration between coloration and morphological traits than the reed isopods. Colonization of a novel habitat with a different predation regime has thus strengthened the correlations between pigmentation and morphology and weakened escape performance. The strong signature of parallelism for these phenotypic traits indicates that divergence is likely to be adaptive and is likely to have been driven by differences in predatory regimes. Furthermore, our results indicate that physical performance, behavior and morphology can change rapidly and in concert as new habitats are colonized.     

Seedling growth variation in response to sand burial in four <Emphasis Type="Italic">Artemisia</Emphasis> species from different habitats in the semi-arid dune field

We compared seedling growth of four Artemisia species dominated at different habitats to determine whether interspecific seedling growth variation of a same genus in tolerance to burial can be used to explain plant distribution in the sand dune field. Interdune lowland species, Artemisia gmelinii, stabilized dune species, A. frigida, semi-stabilized dune species, A. halodendron, and active dune species, A. wudanica were selected. Seedlings grown for 3 weeks were treated at five burial depths for three burial times in pot experiments. Species from the habitats with little burial had smaller survival rate, dry weight and stem elongation speed than those from the habitats with intensive burial when buried. Furthermore, when buried, the former tended to adjust biomass allocation between shoot and root and produce adventitious buds, while the latter tended to maintain a constant root:shoot ratio and produce adventitious roots. We conclude that (1) seedlings of species with a long evolutionary history of exposure to sand burial (from the active sand dune), show quicker stem growth when buried than do seedlings of species from the habitats with little or no sand burial; (2) seedlings of species which do not change root:shoot ratio might be more tolerant of sand burial than those do; (3) seedlings of species from the habitats with intensive sand burial is prone to produce adventitious roots and seedlings of species from the habitats with little or no sand burial tend to produce adventitious buds when buried.     

Representation of aquatic invertebrate communities in subfossil death assemblages sampled along a salinity gradient of western Uganda crater lakes

We analysed subfossil death assemblages of aquatic invertebrate communities in a salinity series of 35 western Uganda maar-crater lakes to evaluate their potential as biological indicators of past habitat conditions in paleo-environmental research. The study region encompasses the climatological and hydrological gradient between the dry floor and moist shoulders of the Edward-George branch of the East African Rift Valley, and includes mesotrophic to hyper-eutrophic, and shallow unstratified to deep meromictic lakes with a surface-water salinity range between 101 and 135 400 μS/cm. Focusing on non-chironomid aquatic invertebrates with good fossil preservation, we found that fossil larval remains of the Dipteran families Culicidae, Ephydridae, and Stratiomyidae are good indicators of saline environments. Our data further suggest that the abundances of Bryozoan statoblasts and Chaoboridae are indicative of, respectively, the fraction of the littoral zone covered by aquatic macrophytes and of lake trophic state, but a lake reference data set more specifically designed to cover variation in these environmental factors will be needed to determine the strength of these relationships. In these small, simple lake basins, recent death assemblages recovered from a single mid-lake surface-sediment sample provides a more complete inventory of local aquatic invertebrate communities and the distribution of species among lakes than exploratory live sampling of those taxa in a selection of littoral, benthic and pelagic habitats.     

Distributional ecology and behaviour of the early life stages of the box-jellyfish Chironex fleckeri

Laboratory observations on reared life stages of Chironex fleckeri (Cubozoa: Chirodropidae) have been combined with field sampling and observations to outline the life cycle of the species and the spatial and temporal distribution of populations in Queensland, Australia. A seasonal alternation of polypoid and medusoid generations from winter to summer respectively is accompanied by a shift in preferred habitat from tidal estuaries to the open eulittoral zone. The system appears to be constrained by predictable fluctuations in the suitability of the alternate habitats to their resident generations. Observations on behaviour, feeding, physiological tolerances, and sexual and asexual reproduction provide insights into the adaptiveness of this pattern.     

Viruses in subarctic lakes and their impact on benthic and pelagic bacteria

Virus–bacterium interactions were investigated in the pelagic and benthic habitats in a set of lakes along an altitudinal gradient in the subarctic northern Sweden. Viral and bacterial abundances showed a significant variation between the lakes, with the highest benthic microbial abundances recorded in a high-altitude lake [993 m above sea level (a.s.l.)], whereas the highest pelagic microbial abundances were found in a low-altitude lake (270 m a.s.l.). In the pelagic habitat, there was also a distinct difference in microbial abundances between the summer–autumn and the winter sampling occasion. A positive relationship was noted between viruses and bacteria in both the pelagic and the benthic habitats. Visibly virus-infected bacterial cells were uncommon in the pelagic habitat and undetectable in the benthos. Both lytic and lysogenic pelagic viral production rates were undetectable or low; thus, a possible explanation for the relative high viral abundances found in the water column could be an allochthonous input of viruses or release of sediment-derived viruses. Overall, our results provide novel information about the relevance of viruses in the subarctic region and indicate that viruses play only a minor role in the nutrient and carbon cycling in the microbial communities of subarctic lakes.     

不同生境对金马河温江段河岸带草本群落物种多样性和构件生物量的影响

采用典型样地法,以金马河流域温江段河岸带草本植物为研究对象,经实地踏查,根据采沙运沙干扰程度及样地具体使用情况,将样地划分为河滩地（未受采沙行为干扰,但后期受人类其他活动影响较大）、砾石地（采沙后经河水水位变化形成）、芦苇地［经运沙的车辆碾压形成,后长满芦苇(Phragmites australis)］、斑茅地［采沙后不再受水位影响的高地部分,后长满斑茅(Saccharum arundinaceum)］、沙坑（采沙后直接形成）5个生境类型,以探究不同生境对河岸带草本植物物种多样性和构件生物量的影响。结果表明：（1）在5个生境类型样地中共记录草本植物113种,隶属32科80属,其中沙坑生境草本植物物种数最多,共计59种,隶属21科46属,物种丰富度高,菊科(Compositae)、禾本科(Gramineae)植物在各样地中均较多。（2）斑茅地、芦苇地物种多样性指数较小,优势度指数较大,均匀度指数较小,群落物种分布极不均匀,集中度与均匀度较差,群落存在极大的不稳定性。（3）河滩地植物构件生物总量最少,斑茅地最多且根、茎干重与其他生境存在显著差异。（4）与其它生境类型相比,沙坑物种多样性丰富,分布均匀,构件生物量较多,其环境有利于河岸带植物生长。     

Distinctive invertebrate assemblages in rockface seepages enhance lotic biodiversity in northern New Zealand

We measured water quality, recorded physical habitat characteristics and collected aquatic invertebrates from 17 rockface seeps, five springs and five streams in a geologically diverse region of New Zealand's North Island to investigate factors influencing invertebrate distribution and community composition within and among these habitats. A total of 147 aquatic invertebrate taxa was found; 84 taxa occurred in seepage samples and 53% of these were found only in those habitats, including several new species. Where paired stream-seepage comparisons could be made, seeps contributed on average 35% of new species to the total species pool. The invertebrate faunas of all habitats were dominated taxonomically by Trichoptera and Diptera, but seepages were relatively depauperate in Ephemeroptera and richer in Coleoptera taxa compared to streams and springs. Seepage faunas were dominated numerically by Mollusca, and had lower percent abundance of aquatic insects (23% overall) compared to springs (77%) and streams (93%). Seepages underlain by different geologies generally had distinct water quality signatures, with seeps draining greywacke, sandstone and volcanic rocks grouping close to their receiving streams in a Principal Component Analysis. Seepage invertebrate community composition reflected underlying geology and associated differences in water chemistry, as well as seepage size and cover by moss. Incorporation of seepage habitats into conservation planning and aquatic ecosystem protection, and maintenance of their function and connectivity with lotic and groundwater ecosystems are important considerations for freshwater biodiversity management. Maintenance of riparian plant cover over seepages should help sustain supplies of organic matter, moss cover and shade, providing habitat complexity and low water temperatures.     

Colonisation of Introduced Timber by Algae and Invertebrates, and its Potential Role in Aquatic Ecosystem Restoration

As part of a habitat restoration experiment wood substrates (red gum) were introduced to two lowland streams of SE Australia in which habitat has been severely degraded by deposition of sand eroded from higher in the catchment. We monitored net primary production (NPP) and community respiration (CR), nutrient concentrations and the succession of algae and invertebrates (abundance and species richness), sampling at 2, 4, 8, 12, 16 and 20 weeks. Colonisation by algae was rapid, and there were distinct changes in the assemblages over the first 4 weeks. Thereafter, changes were much less marked. There were also differences in nutrient concentrations and some measures of algal abundance between the two creeks. As with the algae, invertebrates colonised these substrates extremely rapidly, peaking in abundance and richness in week 8. Invertebrate abundances closely tracked changes in the abundance of algae. By the end of the study both algal and invertebrate communities were in apparent decline, with sharp decreases in invertebrate and algal abundance and invertebrate species richness. Rates of GPP also declined toward the end of the experiment, and this coincided with the detachment of large mats of filamentous algae and the recession of flows over the summer months. However, in both streams the added timber quickly created habitat with high levels of primary production in an otherwise strongly heterotrophic stream system. These hotspots of autotrophic production were quickly colonised by high numbers of macroinvertebrates indicating timber addition may provide an effective means of augmenting habitat for algae and invertebrates in sanded streams.     

Invertebrate assemblages in relation to habitat types on a floating mat in Mizorogaike Pond, Kyoto, Japan

Abiotic environmental variables and invertebrate assemblages were compared among four habitat types (bare hollow, sphagnum-rich hollow, pool, and mat edge) on a floating mat in Mizorogaike Pond, Kyoto. We found differences in abiotic environments between two hollows and two inundated habitats (pool and mat edge); pH was significantly lower in hollow habitats than in inundated habitats, and water depths were significantly shallower in sphagnum-rich hollows than in inundated sites. The composition of invertebrate assemblages in the hollow was distinct from that in the inundated habitats. The abundances of some dominant invertebrate taxa or functional feeding groups on the floating mat differed between the hollows and inundated habitats, and were correlated with water temperature, pH and depth. These results indicate that habitat heterogeneity created by the coexistence of hollows and inundated habitats contributes to species diversity on the floating mat in Mizorogaike Pond. A comparison of the pH values in different wetlands revealed that both bog- and fen-specific components coexist within this system. In order to adequately manage and conserve peatland ecosystems, it is necessary to consider the importance and vulnerability of both hollows and inundated habitats in peatlands.