Shallow Littoral Zone Research Articles

Area-use patterns and diel movements of white steenbras Lithognathus lithognathus in a temporarily open/closed South African estuary, inferred from acoustic telemetry and long-term seine-netting data

Acoustic telemetry and long-term seine-netting data were used to assess distribution, area use, home range dynamics and movement patterns of estuarine-dependent juvenile white steenbras Lithognathus lithognathus in the temporarily open/closed East Kleinemonde Estuary. Using 15 years of biannual seine-netting data, it was shown that white steenbras abundance was highest in the mouth region and decreased with distance from the mouth. Fifteen fish equipped with acoustic transmitters were monitored for eight months using an array of stationary acoustic receivers, while five of these fish were also manually tracked for two months. Results from both telemetry methods indicated that activity was greatest in the mouth region and lower reaches of the estuary. All individuals exhibited site fidelity and remained resident near their sites of capture. The mean length of estuary used by the 15 individuals was 1 888 m (SD 666). There was a distinct diel activity pattern, with certain individuals utilising deeper parts of the estuary during the day and shallow regions at night. The results indicate that the shallow littoral zone is a critical habitat for juvenile white steenbras.

Indigenous Unionid Clam Refugia from Zebra Mussels in Michigan Inland Lakes

Zebra mussel presence and lake water calcium concentrations were compared to determine if a calcium concentration threshold exists which might preclude colonization of zebra mussels in Michigan inland lakes. The shallow littoral zones of nine northern Michigan inland lakes with calcium concentrations near 28.3 mg/L and considered to have had potential zebra mussel introductions through recreational boating were studied. A survey of native unionids was carried out in the lakes for the purpose of establishing a species inventory list for each lake. Zebra mussel densities were determined for lakes where zebra mussels were detected. Water samples were collected and calcium concentrations determined for each study lake. In five softwater lakes (lakes with calcium concentrations <28.3 mg/L), zebra mussels were not found. Zebra mussels had colonized three of four lakes where calcium concentrations were >28.3 mg/L. Five unionid species were found in seven of the nine lakes surveyed. Unionids were present in four of five lakes where calcium concentrations <28.3 mg/L and where zebra mussels were not detected suggesting a possible unionid refuge from zebra mussel induced mortality and/or extirpation in softwater lakes.

Diel fish movements in the littoral zone of a temporarily closed South African estuary

The importance of shallow littoral habitat is a long standing paradigm of estuarine ecology, particularly in facilitating the nursery role they play for many fish. Diel cycles have been linked to the redistribution of fish between habitats and may also influence the movement of various sized fish within littoral zone of estuaries. Fine scale temporal (hourly) movements of four size classes of fish (< 100 mm, 100–300 mm, 301–500 mm and > 500 mm total length) onto a shallow (< 0.7 m) littoral zone within a South African estuary was examined using a duel frequency identification sonar (DIDSON) continuously over 24 h periods. Fish within the size classes of 100–300 mm and 301–500 mm were more abundant in the littoral zone during twilight and at night compared to day, whilst the largest size class (> 501 mm) showed no difference in abundance among these three diel periods. The strongest patterns were observed within the small fish (< 100 mm), which were abundant in the littoral zone during the day but never observed in this habitat after dark. Daily commuting onto and off the shallow littoral zone occurred within tight time periods (< 45 min), and were synchronous with sunrise and sunset respectively. It is hypothesized that these movements are linked to the presence/absence of zooplankton (feeding ecology) and predator avoidance. Large predatory fish up to 1010 mm were also observed on the littoral zone, and whilst rare, indicate very large fish will swim into shallow estuarine waters. Our results support the theory that littoral zone habitats harbour high abundances of small fish and may provide refuge from large piscivorous predators in deeper waters. However, observations of the diel movement behaviour of small fishes indicate that the use of littoral habitats is more complicated than often suggested.

Temporal patterns in macrograzer effects on epilithic algae and meiofauna: a comparative approach to test for single species and whole grazer community effects

Within the shallow littoral zones of lakes, periphyton is an essential component, representing an important source of primary production and a food resource for herbivores. Periphytic communities are abundantly inhabited by meiofaunal organisms, which are mostly dominated by nematodes. During the last 3 decades, consumer–resource interactions between herbivore consumers and periphytic components (mainly algae) have been intensively studied. Although whole grazer community and single species effects on periphyton are known from field and laboratory experiments, the importance of single, dominant grazer taxa in direct comparison to whole community impacts is unknown. To investigate the continuity of grazing effects of a single, dominant macrograzer (Theodoxus fluviatilis, Gastropoda, Prosobranchia) on epilithic meiofauna and algae with respect to the whole grazer community, a temporally structured field experiment was carried out in Lake Erken (Sweden). Grazer impacts on periphytic algae and meiofauna were tested by controlling macrograzer access to littoral periphyton communities for 8 weeks in an exclosure/enclosure experimental design. Overall, the results showed macrograzer presence to have temporally constant, strongly negative effects on algal biomass as well as meiofaunal abundance and community composition. Moreover, T. fluviatilis alone accounted for up to 80% of the grazing effects, indicative of their ability to regulate periphytic communities in lakes. The present study yields new insights into the effects of a single grazer species and stressed temporal patterns of consumer–resource interactions in freshwater lakes.

Variability of nutrient concentrations in sediments and wetland plants during the vegetation season under different sediment moisture conditions

Variability of nutrient concentrations in sediments and wetland plants during the vegetation season under different sediment moisture conditionsChanges of nutrient concentrations in sediments and plant biomass as well as above-ground biomass production of four emergent macrophytes during the vegetation season were studied. Particularly, variations over time in N:P and N:K ratios in sediments between sites with and without vegetation as well as seasonally flooded and permanently flooded sites were investigated. In plant covered sites, biomass production and nutrient concentrations in the four wetland plant species were measured monthly from March to September 2008. The study was conducted in the littoral zone of the polymictic Lake Niepruszewskie. The performed analyses of N, P and K concentrations in plants and sediments indicated that measurements of nutrients in plant biomass better reflected nutrient availability for plant growth than analyses of nutrient contents in sediments. The vegetation biomass and nutrient concentrations in plant biomass in the shallow littoral zone were more sensitive to changes of water depth in comparison with the permanently flooded part of the littoral zone. The present study showed that the N:P biomass ratio was a better indicator of moisture changes than the N:K ratio or individual nutrients. Preferences of the studied macrophytes for nutrient concentrations in sediments depended more on the N:P ratio in the sediment than N or P or K concentrations individually.Glyceria maximapreferred sites with high N and K concentrations (N:K=0.9) whileTypha angustifoliaoccurred in sites with the lowest nutrient concentrations among the studied species (N:P and N:K = 0.1).

Flood duration determines the reproduction success of fish in artificial oxbows in a floodplain of a potamal river

Janáč M, Ondračková M, Jurajda P, Valová Z, Reichard M. Flood duration determines the reproduction success of fish in artificial oxbows in a floodplain of a potamal river. Ecology of Freshwater Fish 2010: 19: 644–655. © 2010 John Wiley &amp; Sons A/S.Abstract – Fish reproduction was studied in six man‐made water bodies (borrow pits) adjacent to the channelised Dyje River (Danube basin) over five seasons. Terrestrial vegetation provided spawning and nursery habitats when inundated by raised water levels in the borrow pits (hereafter referred to as ‘floods’). The diversity of 0+ fish and the density of 0+ cyprinids (mainly Abramis bjoerkna, Scardinius erythrophthalmus and Rutilus rutilus) in June–October were positively correlated with flood duration in previous months. The density of 0+ Perca fluviatilis was independent of the flood duration. The density of spawners and predators did not influence the diversity of 0+ fish and the density of 0+ cyprinids. Receding flood and associated lack of shelters resulted in decreasing density of 0+ cyprinids, numbers sometimes decreasing to zero. Prolonged floods facilitated the survival of 0+ fish and resulted in high 1+ cyprinid density in the following season. Specific hydromorphological conditions (e.g., the presence of shallow littoral zone or flooded vegetation) are necessary to enable successful spawning and provide shelters for 0+ fish in artificial water bodies.

Wave‐induced release of methane: Littoral zones as source of methane in lakes

This study investigates the role of surface waves and the associated disturbance of littoral sediments for the release and later distribution of dissolved methane in lakes. Surface wave field, wave‐induced currents, acoustic backscatter strength, and the concentration and distribution of dissolved methane were measured simultaneously in Lake Constance, Germany. The data indicate that surface waves enhance the release of dissolved methane in the shallow littoral zone via burst‐like releases of methane during the passage of wave groups. The amount of released methane depends on the surface wave field and the water temperature that controls the methane production in the sediments. The dissolved methane concentrations in the shallow littoral zone were always higher than concentrations in the deep water and open water, while methane concentrations in the epilimnion were typically higher than methane concentrations in the metalimnion and upper hypolimnion. The relatively high epilimnetic methane concentrations in the pelagial can be explained by lateral transport of methane from the littoral zone to the pelagic zone. Littoral zones can thus be an important source of methane in lakes. Methane released by surface waves from littoral sediments may cause elevated near‐surface methane concentrations in large areas that enhance the flux of methane at the air‐water interface and, thus, the overall methane emissions from lakes to the atmosphere.

Порівняння захисної реакції Rasbora paviei (Cyprinidae) із різних місцеперебувань

Experimental investigation of defensive behavior of Rasbora paviei Tirant, 1885 from riverine and limnetic habitats was carried out. Fish for the experiment were caught in the upper stream of Cai river and shallow littoral of Cam Lam reservoir of Khanh Hoa province of Central Vietnam. Billfish Lepisosteus sp. was used as a model predator for the experiment. Distinctions in defensive reaction of R. paviei from different ecological conditions were found. It was revealed that defensive behavior of fish from river’s upper stream was more effective than that of fish from the shallow littoral zone of the reservoir.

The Effects of Species Interaction and Pond Stocking Density on Tilapia Aquaculture:

This paper describes the effects of predatory catfishes Clarias gariepinus (Burchell) and Heterobranchus bidorsalis (Geoffrey Saint-Hilaire) and pond stocking density on the culture of tilapia species which display different parental care strategies. In the presence of catfishes, the maternal mouth-brooder O. niloticus (Linnaeus), and the bi-parental mouth-brooder S. galiliaeus (Steindachner) reproduced easily. However, the substrate-brooder T. guineensis (Bleeker) bred with difficulty as the persistent, aggressive, bottom feeding habit of the catfishes inhibited reproduction to some extent by destroying spawning nests and killing developing eggs, or by frightening the breeders to abandon ventilation and parental care of developing eggs inside the nests. Therefore the control of tilapia overpopulation with predatory catfishes to enhance tilapia growth is more likely to be successful in substrate-brooders than in mouth-brooders. T. guineensis was also more susceptible to direct catfish predation than either O. niloticus or S. galilaeus probably because of its more attractive body colouration. When the three tilapia species were reared together, T. guineensis built spawning nests almost exclusively in the shallow littoral zone, whereas O. niloticus and S. galilaeus concentrated their nests in the deeper part of the pond. Site-dependent segregation of the tilapia species at the time of breeding could be a strategy to avert inter-specific territorial competition. Offspring population of O. niloticus showed an inverse relationship with pond stocking density. As stocking density was increased, agonistic encounters between territorial males intensified and inhibited successful fertilization and recruitment. Growth rate of O. niloticus decreased with pond stocking density up to 3 fish/m2, but the differences were not significant. Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 12-19

The identification, characterization and conservation value of isoetid lakes in Ireland

AbstractSoft‐water, oligotrophic isoetid lakes are vulnerable to eutrophication, acidification and alkalinization. As a result of these pressures a large proportion have undergone substantial deterioration in several European countries. The understanding of these systems has been limited by either a lack of lakes close to natural conditions or through receiving less focus in broader scale macrophyte surveys. This has resulted in a dearth of information on specific lake types in their natural condition. Sixty‐eight soft‐water lakes in Ireland were studied in order to achieve a better understanding of the biological and environmental conditions defining such lakes.Eight groups of lakes were identified using cluster analysis and indicator species analysis. Three groups were representative of isoetid‐rich lakes displaying a high frequency of occurrence ofIsoetes lacustris,Lobelia dortmannaorEriocaulon aquaticumtogether with the almost ubiquitousLittorella uniflora. Canonical variates analysis indicated that alkalinity, total phosphorus (TP), catchment area, altitude, moors and heathlands, mean transect depth, colour and lake area were significant variables discriminating among the eight groups. Soft‐water lakes with high amounts of isoetids tended to be less exposed, have broad shallow littoral zones with a high transparency and be situated in smaller catchments. Total phosphorus and alkalinity were typically low, although one group of isoetid‐rich lakes had higher mean TP and alkalinity values. This group may contain lakes under threat from nutrient enrichment and alkalinization and also lakes that have higher TP and alkalinity naturally.Lakes with a prevalence of isoetids supported a greater diversity of macrophytes and chironomids indicating that such lakes may represent suitable conservation targets as they act as surrogates for soft‐water lakes of high biodiversity. Other factors favouring a focus on isoetids in conservation strategies are their importance as a functional component in soft‐water lakes and their sensitivity to lake and catchment environmental change.Copyright © 2008 John Wiley &amp; Sons, Ltd.

Do aquatic macrophytes co-occur randomly? An analysis of null models in a tropical floodplain

One of the main issues in community ecology is the detection of structure and the identification of its related causes. In this study, co-occurrence null models were used to identify possible spatio-temporal patterns in the assemblage of aquatic macrophytes in the Upper Paraná River floodplain. The samples were obtained through the Long Term Ecological Research (LTER) Program at two different grains: (1) a coarser spatial grain in January and August 2001 (entire floodplain lagoons); (2) and a finer spatial grain in November 2006 (1 m(2) quadrats). The study was conducted in 36 lagoons, both connected and disconnected to the main river channel, located in the sub-basins of the Baía, Ivinheima and Paraná rivers. Two null models of species co-occurrence, the C-Score and Checkerboard indices, were used to test the null hypothesis of random structure of the aquatic macrophyte assemblages. The null models showed that the aquatic macrophyte assemblages were spatially structured in the distinct spatial grains. However, despite this general pattern, macrophyte assemblages are organized differently depending on the degree of connectivity, seasonal period and, at a finer grain, depth. Species co-occurrences were random in the disconnected lagoons during flood periods, in deep zones of the lagoons of the Baía River and in the shallow littoral zone in the lagoons of the Paraná River. Analysis of the patterns of co-occurrence indicated that competition and/or habitat preferences are probably important influences on the nonrandom structure of assemblages. However, we suppose that at least three important factors (disturbances by water level fluctuation, dispersion and facilitation) counteract potential effects of competition in specific situations, leading macrophyte assemblages to assume random structure.

Complex spatial and temporal patterns of littoral benthic communities interacting with water level fluctuations and wind exposure in the littoral zone of a large lake

The spatial and temporal organisation of benthic invertebrate communities was studied in a large oligotrophic lake in central Europe. Three shallow littoral sites at 0.4 m depth were sampled monthly from May 2002 to April 2003. On a spatial scale, the benthic community composition at all sites and in all samplings significantly differed in both abundance and biomass. On a temporal scale, the benthic communities at all sites gradually changed each month; monthly samples always significantly differed, but samples from consecutive months were more similar to each other than to samples of non-consecutive months. The observed variability within benthic communities corresponded with changes in the abiotic parameters water level and wind exposure, but was best explained by short- and long-term fluctuations in the water level. Effects of wind exposure were most pronounced in the winter months, when high wind events most often occurred. However, wind effects were masked by stronger effects, such as water-level fluctuation within the shallow littoral zone, or diminished by parameters with opposite effects, e.g. slope vs. exposure. Wind-induced shear stress in the upper eulittoral zone directly influenced the abundance and biomass of the benthic community to a lesser extent. We conclude, however, that this stress alters habitats constantly (e.g. substrate composition, periphyton growth, resuspension vs. sedimentation) and is therefore the driving force for the reported permanent site differences. Furthermore, benthic communities were well adapted to frequent minor changes and also to regular major changes of their habitat, as bare substrates were rapidly recolonised within a month.

Spatial variation of grazer effects on epilithic meiofauna and algae

Periphyton is a key component of shallow littoral zones of lakes and streams because it is an important source of primary production and a food resource for herbivores. Meiofauna are abundant in periphyton, but macroinvertebrate grazer (macrograzers) effects on periphytic meiofauna have not been studied so far. We used a spatially structured field experiment (hierarchical nested design consisting of 3 subsites at each of 3 sites) in Lake Erken (Sweden) to investigate the effect of macrograzers on epilithic meiofauna and algae in periphyton by controlling macrograzer access to littoral periphyton communities. Overall, we found a strong negative effect of macrograzer presence on algal biomass and some evidence for negative macrograzer effects on meiofaunal abundance and community composition. The impact of macrograzers on both algae and meiofauna were highly variable between sites and subsites. The largest spatial differences were for macrograzer effects on meiofaunal abundance and composition. We also investigated the ability of macrograzers to reduce spatial heterogeneity of periphyton biomass, but the presence of macrograzers did not alter the variation in algal biomass and associated meiofauna among replicates. We conclude that strong local variability in algal biomass and meiofauna abundance exists between neighboring sites even in the presence of strong overall macrograzer effects. This local variability could be based on factors known to cause spatial heterogeneity, such as hydrodynamics, nutrients, substrate characteristics (size, texture, exposure), or biotic interactions.

Are there hot spots for Elliptio complanata in the shallow littoral zone of a large Canadian Shield lake?

The variability in habitat conditions in large lake basins may provide areas favourable for unionid recruitment and growth. Here we test whether the distribution, body size, and growth rate of Elliptio complanata differ between upwind and downwind sites in a 5.8 km long lake basin. We measured density and morphological characteristics of E. complanata at nine upwind and nine downwind sites. We also measured growth rates and stable isotope (δ13C, δ15N) signatures at three upwind and three downwind sites. We found no difference in density or body size of E. complanata between upwind and downwind sites, despite clear differences in water temperature and food availability. Contrary to our expectations, the growth rate of E. complanata was higher (by 62%) at upwind sites. The reason for this difference is uncertain, but higher shell erosion and a negative relationship between δ13C and C/N ratio suggest that E. complanata may be more stressed at downwind sites. The δ15N of E. complanata did not differ systematically between upwind and downwind sites, but increased with increasing body size. It would therefore be prudent to standardize the size of E. complanata used to measure the baseline of lake food webs.

Vertical, lateral and longitudinal movement of zooplankton in a large river

Summary1. The spatial distribution and movement patterns of zooplankton in large rivers are little known compared with those in lake environments. We conducted a series of studies in the Ohio River (U.S.A.) during the low flow period to assess diel vertical (DVM), longitudinal and lateral movement of crustacean zooplankton.2. The dominant large zooplankter, the copepod Eurytemora affinis, showed a consistent vertical migration pattern of daytime ascent and night‐time descent during all sampling periods – the reverse of the most common migratory pattern of zooplankton in lakes. The cladoceran Bosmina migrated in a similar way in two of the three sampling periods. Surveys taken longitudinally in the river showed similar trends for both taxa.3. During the lateral surveys, E. affinis was significantly more abundant in the shallow littoral zone during the night than in the daytime. The combination of vertical and lateral movement patterns along with the diel distribution of zooplanktivorous fish suggest that these movements are a predator‐avoidance mechanism.4. Sampling programmes in large rivers should consider that larger zooplankton such as E. affinis may not be randomly distributed in the river channel and behaviours such as diel vertical migration may be just as evident in river habitats as in lakes.

Priming the productivity pump: flood pulse driven trends in suspended algal biomass distribution across a restored floodplain

Summary1. Chlorophyll a (Chl a) distribution across a 0.36 km2 restored floodplain (Cosumnes River, California) was analysed throughout the winter and spring flood season from January to June 2005. In addition, high temporal‐resolution Chl a measurements were made in situ with field fluorometers in the floodplain and adjacent channel.2. The primary objectives were to characterise suspended algal biomass distribution across the floodplain at various degrees of connection with the channel and to correlate Chl a concentration and distribution with physical and chemical gradients across the floodplain.3. Our analysis indicates that periodic connection and disconnection of the floodplain with the channel is vital to the functioning of the floodplain as a source of concentrated suspended algal biomass for downstream aquatic ecosystems.4. Peak Chl a levels on the floodplain occurred during disconnection, reaching levels as high as 25 μg L−1. Chl a distribution across the floodplain was controlled by residence time and local physical/biological conditions, the latter of which were primarily a function of water depth.5. During connection, the primary pond on the floodplain exhibited low Chl a (mean = 3.4 μg L−1) and the shallow littoral zones had elevated concentrations (mean = 4.6 μg L−1); during disconnection, shallow zone Chl a increased (mean = 12.4 μg L−1), but the pond experienced the greatest algal growth (mean = 14.7 μg L−1).6. Storm‐induced floodwaters entering the floodplain not only displaced antecedent floodplain waters, but also redistributed floodplain resources, creating complex mixing dynamics between parcels of water with distinct chemistries. Incomplete replacement of antecedent floodplain waters led to localised hypoxia in non‐flushed areas.7. The degree of complexity revealed in this analysis makes clear the need for high‐resolution spatial and temporal studies such as this to begin to understand the functioning of dynamic and heterogeneous floodplain ecosystems.

Habitat affinity, the seasonal flood pulse, and community assembly in the littoral zone of a Neotropical floodplain river

The annual flood pulse in tropical lowland rivers creates a continually moving land–water margin that forces aquatic organisms of the littoral zone to relocate to new habitats at intervals ranging from days to weeks. Thus, species assemblages in patchy littoral-zone habitats have large potential to be influenced by stochastic colonization dynamics, whereby organisms may exhibit weak selection for mesohabitat features and arrive on a patch in no particular sequence. We examined species assemblages of fishes and macroinvertebrates occupying habitats of varying structural complexity through an annual flood cycle of the Cinaruco River, a species-rich floodplain river in the southern llanos of Venezuela. We collected 268 standardized samples that contained 54,596 individual fishes representing 156 species (23 families) and 6973 macroinvertebrates representing 8 families. Analysis of species-specific patterns of habitat occupancy based on a randomization procedure indicated greater species selectivity during low water (92% of taxa) relative to rising- and falling-water periods (60% and 63% of taxa, respectively). Community-wide correspondence analysis (CA) revealed similar patterns. Assemblages from similar habitat types clustered together in the CA ordination, and these nonrandom patterns were most apparent during low water. Results from partial canonical correspondence analysis revealed that assemblage structure was strongly influenced by habitat type (patches of different composition located within the shallow littoral zone of either the river main channel or lagoons), which accounted for 56% of the total explainable variation in the species × sample matrix. Mesohabitat parameters (e.g., water velocity, depth), sampling period (month), and location on the landscape explained 30%, 23%, and 17% of variation, respectively. As water level changes and the aquatic–terrestrial interface moves across the landscape, species assemblages in patchy littoral habitats, while highly variable, reconstitute with significant determinism. At the same time, a large proportion of unexplained variation in assemblage structure probably is associated with unmeasured components of landscape variation as well as a stochastic element in colonization dynamics.

Flow variability in dryland rivers: boom, bust and the bits in between

AbstractAustralian dryland rivers are acknowledged as being among the most variable and unpredictable in the world in terms of their flow regimes. Although renowned for their spectacular floods over vast and complex floodplains, rivers exist for much of the time as discrete waterholes, which are important refugia for aquatic biota. Recent work has shown that waterholes are filled by surface flows and there is little evidence of groundwater contributions. The permanence of these refugia is largely determined by waterhole morphology and evaporative loss, and some waterholes can clearly persist for 2 years or more without surface flow connection. As a consequence, the spatial distribution of refugia for aquatic biota is determined not only by the physical template but also by the duration of dry spells and the timing of flow events. Flow variability also has a major influence on aquatic production in these systems and ultimately influences food availability for fish and other consumers. During dry spells, aquatic food webs in waterholes are largely supported by algal production in the shallow littoral zone. At the other extreme, during floods, the boom of aquatic production on floodplains provides an immense food resource. However, there are many occasions when in‐channel flows (flow pulses) result in periods where neither of these sources of production is likely to be available. Although such flow pulses are essential for the physical persistence and connectivity of waterholes, we propose that they may lead to food limitation and stress for populations of fish and other consumers. Water resource development in dryland rivers often leads to an increase in the frequency and duration of flow pulses, due to reduced floods and elevated base flows. This increase in the ‘bits in between’ natural boom or bust conditions may help to explain the observed decline in ecosystem health in dryland river systems with significant water resource development. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Designing Wetlands for Amphibians: The Importance of Predatory Fish and Shallow Littoral Zones in Structuring of Amphibian Communities

Under section 401 and section 404 of the Clean Water Act, permission to degrade existing natural wetlands in the USA may be conditional on restoring or creating ‘replacement’ wetlands. Success of wetland mitigation efforts in adequately replacing lost wildlife habitats depends on our good understanding of key ecological attributes that affect the structure of wetland faunal communities. We examined the effects of the presence of predatory fish, shallow vegetated littoral zone, emergent vegetation cover, wetland age and size on amphibian diversity in 42 replacement wetlands located in the Ohio’s North Central Tillplain ecoregion. We recorded 13 species of pond-breeding amphibians, and the average local species richness (α-richness) was 4.2 ± 1.7 species per site (range 1–7). There is strong evidence for the positive association between amphibian species richness and presence of a shallow littoral zone, and the negative association with presence of predatory fish. There was no evidence for the association between species richness and age, size, amount of forest cover within 200 m, nor the amount of emergent vegetation cover at the study sites. It is estimated that local species richness in wetlands with shallows was 1.76 species higher on average than in wetlands without shallows (95% CI from 0.75 to 2.76). The presence of predatory fish was associated with an average reduction in species richness by an estimated 1.21 species (95% CI from 0.29 to 2.11). Replacement wetlands were placed in areas with little or no existing forest cover, and amphibian species associated with forested wetlands were either rare (eastern newt, spotted salamander) or not present at all (marbled salamander, wood frog). In addition, we surveyed all replacement wetlands constructed under section 401 in Ohio since 1990, and found that predatory fish were present in 52.4% of the sites and that shallows were absent from 42.7% of the sites. Our results indicate that current wetland replacement practices could have a negative effect on the amphibian diversity within our region.

Heterotrophic dinitrogen fixation (acetylene reduction) in phosphate-fertilised Microcoleus chthonoplastes microbial mat from the hypersaline inland lake ?la Salada de Chiprana? (NE Spain)

Microcoleus chthonoplastes dominated microbial mats are conspicuous along the shallow littoral zone in Lake Chiprana, a hypersaline lake located in the Ebro river basin in north-eastern Spain. Pigment data show that these mats included diatom species and anoxygenic phototrophs, Chloroflexus-type bacteria and purple bacteria. In situ, these mats showed low rates of dinitrogen fixation (acetylene reduction). Acetylene reduction was stimulated about 30-fold in excised mats after moderate phosphate fertilisation during 2 weeks incubation in a mesocosm. Pigment analyses showed that this treatment had little impact on the phototrophic community structure, except that it induced a decrease of Chloroflexus-type bacteria. The use of metabolic inhibitors indicated that methanogenic archaea and aerobic heterotrophic bacteria were the major dinitrogen fixers in this system. This is in agreement with the fact that the mat-building cyanobacterium M. chthonoplastes lacks the dinitrogenase reductase nifH gene and with the fact that acetylene reduction rates were strongly stimulated by additions of H2/CO2, methanol, fructose and sucrose, but not by lactate, acetate, formate and glucose. No significant differences where found for acetylene reduction rates when comparing light and dark incubations of these microbial mats. However, acetylene reduction rates were enhanced in the light when the near infrared (NIR) light was filtered out, which arrested anoxygenic photosynthesis. We suggest, therefore, that the chemoheterotrophic dinitrogen fixing bacteria were in competition with anoxygenic phototrophic bacteria for organic substrates, while the latter did not contribute to dinitrogen fixation in the mat.