Lake Assemblages Research Articles

Macroinvertebrate assemblages of peatland lakes: Assessment of conservation value with respect to anthropogenic land-cover change

Small blanket bog lakes can contain many rare and threatened aquatic invertebrate species. Their conservation value, however, is threatened throughout Europe by peat extraction and particularly conifer afforestation, which can compromise the physico-chemical habitat quality of peatland lakes through excessive inputs of forestry-derived dissolved and particulate substances. To quantify the effect of conifer plantation forestry on the conservation value of these habitats, we compared the hydrochemistry and assemblages of aquatic Coleoptera, Heteroptera and Odonata of replicate lakes across three distinct catchment land uses: (i) unplanted blanket bog only present in the catchment, (ii) mature conifer plantation forests only present in the catchment and (iii) catchments containing mature conifer plantation forests with recently clearfelled areas. All three catchment land uses were replicated across regions of sedimentary and igneous geology. Lakes with afforested catchments, in both geologies, had elevated concentrations of plant nutrients, total dissolved organic carbon and heavy metals, the highest concentrations being recorded from the clearfell lakes. Coleoptera and Heteroptera assemblages responded strongly to forestry-mediated changes in water chemistry, whereas Odonata assemblages responded more to catchment geology – geology being confounded by altitudinal differences between lakes. The greatest species-quality scores (SQSs) and species richness were recorded from the clearfell lakes. Three of the four International Union for the Conservation of Nature (IUCN) nationally red-listed species recorded during this study were, however, absent from clearfell lakes. Our findings demonstrate that plantation forestry can have a profound impact on the aquatic macroinvertebrate assemblages and conservation value of small blanket bog lakes, primarily via eutrophication. Despite indices such as SQS scores and species richness appearing to reveal a beneficial response of blanket bog lake communities to habitat deterioration, they mask that certain ‘emblematic’ species are being severely negatively impacted by the disturbance caused by plantation forestry. Considering the need for fertiliser to produce economically viable plantation forest crops, coupled with the inefficiencies of peat soils in retaining applied nutrients, the degradation of peatland lakes is likely to become more prevalent as plantation forestry continues to expand worldwide.

Chironomidae (Diptera) in the Himalayan Lakes – A study of sub-fossil assemblages in the sediments of two high altitude lakes from Nepal

Chironomid head capsules were identified from sediment cores taken from Lake Gokyo (4750 m) and Lake Gosaikunda (4350 m) in the east-central Himalaya, to determine taxonomic composition of chironomid assemblages over time. The sedimentation rate of Lake Gosaikunda was estimated at 0.05 cm/yr and that of Gokyo was estimated at 0.07 cm/yr by 210Pb and 137Cs dating. Micropsectra sp. was dominant in the sediments of both lakes. Lake Gokyo sediments also contained Pseudodiamesa sp., Eukiefferiella/Tvetenia sp., Orthocladius/Cricotopus sp. and Rheocricotopus sp. The concentration of headcapsules was nearly an order of magnitude greater in the Lake Gosaikunda core, which contained mostly Micropsectra sp. and Pseudodiamesa sp. These taxa are typical of cold oligotrophic lakes. Differences in lake depth, dissolved minerals, plus epi- and hypolimnetic temperature and dissolved oxygen suggest that stratification and temperature-induced increases in primary production may affect chironomid assemblages in these pristine lakes. Palaeolimnological studies of Himalayan lakes should include replicate cores within lake, to increase headcapsule sample sizes given potentially high rates of sedimentation from glacial runoff. Key words: high altitude lakes, Himalaya, Chironomidae, palaeolimnology, Nepal

Use of lake morphometry models to reconstruct water level changes from diatom assemblages in closed-basin lakes of West Greenland

Use of lake morphometry models to reconstruct water level changes from diatom assemblages in closed-basin lakes of West Greenland

A Direct‐Gradient Multivariate Index of Biotic Condition

AbstractMultimetric indexes constructed by summing metric scores have been criticized despite many of their merits. A leading criticism is the potential for investigator bias involved in metric selection and scoring. Often there is a large number of competing metrics equally well correlated with environmental stressors, requiring a judgment call by the investigator to select the most suitable metrics to include in the index and how to score them. Data‐driven procedures for multimetric index formulation published during the last decade have reduced this limitation, yet apprehension remains. Multivariate approaches that select metrics with statistical algorithms may reduce the level of investigator bias and alleviate a weakness of multimetric indexes. We investigated the suitability of a direct‐gradient multivariate procedure to derive an index of biotic condition for fish assemblages in oxbow lakes in the Lower Mississippi Alluvial Valley. Although this multivariate procedure also requires that the investigator identify a set of suitable metrics potentially associated with a set of environmental stressors, it is different from multimetric procedures because it limits investigator judgment in selecting a subset of biotic metrics to include in the index and because it produces metric weights suitable for computation of index scores. The procedure, applied to a sample of 35 competing biotic metrics measured at 50 oxbow lakes distributed over a wide geographical region in the Lower Mississippi Alluvial Valley, selected 11 metrics that adequately indexed the biotic condition of five test lakes. Because the multivariate index includes only metrics that explain the maximum variability in the stressor variables rather than a balanced set of metrics chosen to reflect various fish assemblage attributes, it is fundamentally different from multimetric indexes of biotic integrity with advantages and disadvantages. As such, it provides an alternative to multimetric procedures.

Strong correspondence between gillnet catch per unit effort and hydroacoustically derived fish biomass in stratified lakes

Summary1. Sampling of lake fish assemblages is a challenging task in fish science, and the information obtained strongly depends on the choice of sampling gear. The use of more than one sampling technique is generally preferred in order to achieve a comprehensive view on fish assemblage structure. Therefore, the knowledge of whether catches between fishing gears are comparable is crucial.2. We compared catches in benthic multi‐mesh gillnets with fish biomass estimates obtained by vertical hydroacoustics in 18 European lakes strongly varying in morphometry and trophic status. Separate analyses were conducted for different depth strata and for several fish length thresholds to account for depth‐ and size‐selective gillnet catches.3. Gillnet catches and hydroacoustically obtained fish biomass estimates were significantly correlated. The strength of correlations was independent of the fish length thresholds applied, but varied across different depth strata of the lakes, with the strongest correlations occurring in the shallow strata.4. The results support the applicability of vertical hydroacoustics for the quantification of fish biomass in stratified lakes. Survey designs combining hydroacoustics with limited gillnetting at sampling dates shortly one after the other, the latter for the purpose of inventory sampling only, are a cost‐effective strategy for sampling fish assemblages in lakes. However, gillnet sampling does not provide reliable fish density estimates in very deep lakes with separate, pelagic‐dwelling fish assemblages.

Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

Summary1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data.2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake).3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake.4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity.5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.

Palaeogeographic, palaeoclimatic, palaeohydrological and chemical/biochemical controls on accumulation of late Eocene coastal lacustrine–palustrine limestones, Southern England

The shallow-lacustrine to palustrine Hatherwood Limestone Member of the late Eocene Headon Hill Formation, Southern England, is in a succession of fluvio-estuarine and laguno-lacustrine siliciclastic sediments. It is up to 8.0m thick and is subdivided by metric-scale palaeotopographic erosion surfaces, one of which underlies lenticular humic siliciclastic mudstones. The limestone lithologies are (1) biocalcilutites/biocalcisiltites, (2) biocalcarenites, (3) calcirudites, and (4) laterally-discontinuous laminar and fenestral crusts. Lithology (1) accumulated in a low-energy shallow-lacustrine depositional environment, indicated by the predominance of pulmonate pond-snails in the mollusc assemblage. In contrast, lithologies (2) and (3) are the coarse-grained fills of shallow palaeotopographic lows, and also form basal lags and palaeokarst-fills. Lithology (3) comprises remnant autochthonous lags that resulted from selective erosion during lacustrine transgressions. Brecciation and proto-intraclast to nodular differentiation in lithology (2) suggests derivation of the intraclasts from subaerially- and pedogenically-modified shallow-lacustrine muds. Laminar crusts (4), 0.5–6.0cm in thickness, display irregularly undulose and anastamosing laminations 150–400μm thick, that display differential staining by iron oxide. The abundance of rootlet traces and calcitised parenchymatic root tissues in the fenestral crusts suggests a palustrine depositional environment for these lithologies. The siliciclastic mudstone lithologies are (1) black humic muds and (2) blue-green silty muds and marls. The high C/N molar ratio of the black muds suggests derivation of the humic content mainly from vascular plants in local wetlands. The mollusc assemblage of the blue-green siliciclastic muds resembles floodplain lake assemblages from the regional Palaeogene succession. Mean stable isotopic values for limestone samples, of −4.75±1.53 for δ13C and −2.77±1.47 for δ18O, indicate a relatively heavy tendency within published spectra for Tertiary lacustrine carbonates. The δ18O isotope results agree with published subtropical surface-water palaeotemperatures for this succession. The total characteristics of the Member therefore suggest a shallow-lacustrine to palustrine depositional environment. Pedogenic overprinting and mechanical reworking displayed by the limestones are attributable to seasonal fluctuations of water level during lake highstands, but in this marine-influenced setting, major long-term lake lowstands, resulting in deep erosion and palaeokarsting of the limestones, may be attributable to falls in relative sea-level. The biocalcilutites and humic muds accumulated during the ensuing lake transgressions.

Long-term oxygen conditions assessed using chironomid assemblages in brook trout lakes from Nova Scotia, Canada

We examined the larval remains of chironomids in 12 stocked brook trout lakes from Nova Scotia using 2 paleolimnological approaches (i.e., top–bottom approach and stratigraphic analyses). Limited monitoring data have indicated that almost all of the survey lakes contained poor coldwater-fish habitat; therefore, concerns have been raised that oxygen conditions have deteriorated and suitable habitat for brook trout may have declined. Our goal was to evaluate shifts in water quality, with a focus on understanding trends in hypolimnetic oxygen concentrations. No strong directional changes in the relative abundances of chironomids were recognized using top–bottom (12 lakes) and downcore stratigraphic (4 lakes) analyses. Chironomid assemblage compositions have not differed significantly between modern and preindustrial time periods (ANOSIM: R = −0.06, P = 0.94). Changes (if any) in oxygen conditions over the last ∼2 centuries likely were subtle and not of sufficient duration and (or) magnitude to strongly influence chironomid assemblage compositions through time. Detrended correspondence analysis of downcore assemblages indicated that taxa turnover was minimal (≤1 SD) at 3 of 4 lakes. We conclude that oxygen conditions (which our proxy data indicate were likely naturally low) have not deteriorated significantly since preindustrial times, and no overall directional trends are yet obvious in the paleolimnological record. Combining the often complimentary information gained from paleolimnological, monitoring, and modeling analyses, as we do here, can aid in the management of aquatic ecosystems and highlight the relative importance of regional trends in water quality and its influence on aquatic organisms such as recreationally significant salmonids.

Temporal variations in epilithic nematode assemblages in lakes of different productivities

Temporal variations in epilithic nematode assemblages in lakes of different productivities

Regulatory factors in crustacean zooplankton assemblages in mountain lakes of northern Chilean Patagonia (38 41°S): a comparison with Bulgarian counterparts (42°N)

Chilean Patagonia has protected mountainous areas with evergreen native forests; in which the lakes and rivers, of volcanic or glacial origin, are oligotrophic. In Bulgaria, there are mountainous zones with native forests and associated lakes of volcanic origin. The aim of the present study is to carry out a preliminary comparison of zooplanktonic crustaceans in lake ecosystems associated with native forests of Chilean Patagonia and of Bulgarian mountains. The study revealed that the lakes studied in Chilean Patagonia are associated mainly with Nothofagus forests; they are oligotrophic, with a low number of zooplanktonic crustacean species. Similar results were observed for Bulgarian mountain lakes associated with Fagus forests. A null model analysis of species co-occurrence was applied to the two groups of lakes, and the result revealed the absence of regulatory factors in species associations. These studies agree with similar descriptions of lakes in Andean Patagonia and New Zealand. They highlight the important role of native Nothofagus forests in Argentina and Chile, and of Fagus forests with associated soil properties in Bulgaria, in the oligotrophy of the lakes studied.

Genetic diversity of planktonic eukaryotes in high mountain lakes (Central Pyrenees, Spain)

The genetic diversity of planktonic eukaryotic microorganisms (size range 3-40 µm) inhabiting 11 alpine lakes of the Central Pyrenees (Spain) was analysed by cloning and sequencing of the 18S rRNA gene. The selected lakes covered a wide range of environmental conditions representative of the regional landscape heterogeneity. Overall, we obtained 953 sequences (averaged length 750 bp) that were grouped in 343 representative OTUs (98% identity). The genetic richness was high, and the 18S rRNA gene sequences spread within nine high-rank taxonomic groups and grouped in 26 eukaryal classes. Most of the sequences affiliated with Stramenopiles (> 55% of total sequences, mostly Chrysophyceae), Cryptophyta and Alveolata (15% each). Three groups had relative abundance < 5%, i.e. Opisthokonta (mostly Fungi), Viridiplantae (mostly Chlorophyceae) and Rhizaria (cercomonads). Finally, minor groups were related to Katablepharidophyta, Euglenozoa and Telonemida. The lakes showed a different community structure being pH, and phosphorous and Chl a concentrations the main environmental drivers. The novelty level was high, and a quarter of the retrieved OTUs were notably divergent (< 97% identity) from any previously known sequence, mainly for Rhizaria and Opisthokonta. More than 50% of the sequences affiliated with clusters exclusively formed by uncultured protists. Cryptophyta and Viridiplantae showed the largest number of sequences closely related to cultured counterparts. This work is the first description of the genetic diversity of eukaryotic assemblages in ultraoligotrophic high mountain lakes, and the study unveils alpine environments as an important reservoir of microbial eukaryotic biodiversity.

Seasonal examination of phytoplankton abundance and assemblages in Myall Lake and Bombah Broadwater, New South Wales, Australia

The Myall Lakes are a series of interconnected, shallow and poorly flushed coastal lakes located within the Myall Lakes National Park in NSW, Australia. The following field study aims to uncover patterns in temporal variability in water quality and phytoplankton abundance, diversity and assemblage structure, in the upper and lower water bodies of the Myall Lakes system. The result showed that the two lakes differ greatly in their catchment to lake area ratios, freshwater inputs, degree of saline intrusion, light attenuation and submerged macrophyte biomass. The broadwater, which receives large inputs of freshwater from the catchment, and is influenced by saline inputs from the Port Stephen’s estuary, exhibited highly variable water quality and dissolved nutrient concentrations, and phytoplankton assemblages with much temporal variation in taxa present, biovolume, cell size and abundance, and taxonomic diversity. In contrast, the upper lake, Myall Lake, shows much greater stability in water chemistry and nutrient availability; the phytoplankton community is diverse, with relatively low and constant biovolume, and is dominated year-round by small-celled cyanobacteria. Differences in phytoplankton between the two lakes were greatest during the autumn and winter, and least during the summer, when the phytoplankton assemblages in both lakes were dominated by similar cyanophyte taxa.

Regionally nested patterns of fish assemblages in floodplain lakes of the Magdalena river (Colombia).

We investigated if fish assemblages in neotropical floodplain lakes (cienagas) exhibit nestedness, and thus offer support to the managers of natural resources of the area for their decision making. The location was floodplain lakes of the middle section of the Magdalena river, Colombia. We applied the nested subset analysis for the series of 30 cienagas (27 connected to the main river and three isolated). All fish were identified taxonomically in the field and the matrix for presence–absence in all the lakes was used for the study of the pattern of nestedness. The most diverse order was Characiformes (20 species), followed by Siluriformes (19 species). Characidae and Loricaridae were the richest families. The species found in all the lakes studied were migratory species (17), and sedentary species (33). Two species (Caquetaia kraussii and Cyphocharax magdalenae) were widespread across the cienagas archipelago (100% of incidence). Nestedness analysis showed that the distribution of species over the spatial gradient studied (840 km) is significantly nested. The cienagas deemed the most hospitable were Simiti, El Llanito, and Canaletal. Roughly, 13 out of the 50 species caught show markedly idiosyncratic distributions. The resulting dataset showed a strong pattern of nestedness in the distribution of Magdalenese fishes, and differed significantly from random species assemblages. Out of all the measurements taken in the cienagas, only the size (area) and local richness are significantly related to the range of order of nested subset patterns (r=–0.59 and –0.90, respectively, at p < 0.01). Differential species extinction is suggested as the cause of a nested species assemblage, when the reorganized matrix of species occurring in habitat islands is correlated with the island area. Our results are consistent with this hypothesis.

Predominance ofFlavobacterium,Pseudomonas, andPolaromonaswithin the prokaryotic community of freshwater shallow lakes in the northern Victoria Land, East Antarctica

A polyphasic approach that included PCR-dependent and PCR-independent molecular techniques was applied to analyze the prokaryotic community in surface waters of shallow Antarctic lakes. The in situ abundance of different bacterial groups was determined by the fluorescence in situ hybridization, whereas bacterial diversity was investigated by 16S rRNA gene sequencing of bacterial clones and isolates. The different approaches allowed the identification of the significant microbial components of the lake bacterioplanktonic communities, indicating a predominance of Flavobacterium, Pseudomonas, and Polaromonas (up to about 56% of total sequences). These genera also appear to be important in freshwater systems elsewhere in the world. Interestingly, closest blast matches to our sequences were predominantly from polar lakes and ponds, in addition to streams and glaciers, suggesting a bipolar distribution of freshwater lake bacterioplankton. Bacteria that are more traditionally associated with the marine environment were also detected, thus indicating an external input by atmospheric deposition and/or seabird excreta. Finally, a slightly different microbial community occurred in the lake at Inexpressible Island that was characterized by low N : P ratio and very high conductivity value, reinforcing the idea that physicochemical and trophic status may affect the structure and composition of the bacterioplankton assemblages in Antarctic lakes.

Climate-mediated changes in small lakes inferred from midge assemblages: the influence of thermal regime and lake depth

Subfossil midge (Chironomidae and Chaoboridae) assemblages were examined in the surficial sediments (0–1 cm) from small inland lakes in the Experimental Lakes Area (ELA) of northwestern Ontario, Canada. In these boreal lakes, maximum depth (Zmax), alkalinity, Secchi depth and chlorophyll-a concentrations explained significant amounts of variation in the subfossil assemblages. Constrained ordinations (redundancy analysis) indicated that the relationship between Zmax (as sqrt Zmax) and assemblage composition was strong enough to develop a paleolimnological inference model. Model statistics suggested that a robust model was generated (r 2 = 0.78, RMSEP = 0.533, max bias = 0.674); however, when the model was applied to a subfossil stratigraphy from an ELA lake sediment core, results suggested that the inference model had produced an unrealistically shallow Zmax inference. Further analyses indicated that thermal regime had a strong influence on assemblage composition; when the influence of thermal regime was partialled out, there was a much weaker relationship between Zmax and assemblage composition, particularly for stratified lakes. A thermal regime inference model was subsequently developed, which, when applied to the lake sediment core stratigraphy, indicated that the shallow Zmax inference may have been the result of a period of increased mixing or polymixis in this stratified lake. Water column mixing may increase due to hypolimnetic warming and increased water clarity resulting from declines in dissolved organic carbon. In a training set where there are strong correlations between lake depth and assemblage composition, this relationship is not necessarily a strict function of lake depth, but of some other highly correlated variable, likely thermal conditions.

Fish assemblages in floodplain lakes in a Neotropical river during the wet season (Magdalena River, Colombia)

Abstract:A number of studies have pointed out that abiotic factors and recolonization dynamics appear to be more important than biotic interactions in structuring river–fish assemblages. In this paper, we studied the fish assemblages in 27 floodplain lakes, with perennial connection to the river, in the middle section of the Magdalena River (Colombia), to examine spatial pattern in freshwater fish diversity in relation to some environmental parameters. Our objective was to examine relationships between floodplain-lake fish communities and environmental variables associated with lake morphology, water chemistry and river–floodplain connectivity in a large river–floodplain ecosystem. During the study, a total of 18 237 fish were caught from 50 species (regional richness; 17 were migrants and 33 residents). In the present study, the most diverse order was Characiformes with 20 species, followed by Siluriformes, with 19 species. Characidae and Loricaridae were the richest families. The range of species richness (local richness) varied between five and 39 species. Similarity of local assemblages (using the presence–absence data) depends on the distance between lakes. A positive relationship was observed between the Ln of the total abundance of each species and the number of lakes where they were found. Out of all the environmental parameters taken in the lakes, only the size (Log Area) and relative perimeter length are significantly related to local assemblage species richness. It has not been possible to demonstrate that the connectivity (distance) from lakes to the main river can be considered a predictor of the local richness.

Alpha and beta components of diversity of freshwater nematodes at different spatial scales in subtropical coastal lakes

Small organisms usually occur in large numbers and are easily dispersed by passive means. Accord- ingly, one could expect these assemblages to exhibit low spatial structure, at least at small (m) and intermediate (1-100 km) scales. We assessed the community structure of freshwater nematodes (0.063 - 0.5 mm) associated with five spatial scales (ranging from 10 cm to 10 - 35 km) in three coastal lakes in southern Brazil. We assessed whether dissimilarities among assemblages are structured according to spatial scales, using an NMDS ordination. We also tested the hypothesis that most of the total diversity is associated with the intermediate (2 - 2.5 km) spatial scale that reflected distinct habitats (lakeshores), using additive partitioning of total species richness and two null models. We obtained 13,358 individuals and 59 morphospecies of nematodes. The NMDS ordination indicated that the nema- tode assemblages were mostly structured according to the spatial hierarchical sampling design. Lakes harbored dis- tinct nematode assemblages, and within-lake ordination indicated that the type of lakeshore (protected or exposed) and areas within lakeshores were important. The mean number of morphospecies recorded for the core sampling units (α1) was 12.26 -16.90, and represented 30 - 33 % of the total species richness found in the three lakes. Accord- ingly, beta diversity accounted for most of the total diversity. The partitioning for individual-based randomization over all lakes revealed that the observed local richness (14.19 species) was significantly lower than expected. The magnitude of the observed beta diversities in relation to the expectation for the lowest scales depended on the null model used. The observed beta diversity at high spatial scales, reflecting distinct lakes and habitat types, tended to be larger than the expected. The nematode assemblages showed intraspecific aggregation and low beta diversity at fine spatial scales, but high beta diversity at coarse spatial scales. We conclude that despite their microscopic size, the spatial distribution of nematode assemblages in lakes is mostly similar to the general pattern observed for macroscopic organisms.

Reply to Discussion: a critique of Possible waterways between the Marmara Sea and the Black Sea in the late Quaternary: evidence from ostracod and foraminifer assemblages in lakes İznik and Sapanca, Turkey, Geo-Marine Letters, 2011

In their discussion of our 2011 paper dealing with possible waterways between the Marmara Sea and the Black Sea in the “late” Quaternary, based on data from ostracod and foraminifer assemblages in lakes Iznik and Sapanca, Turkey, Yaltirak et al. (Geo-Mar Lett 32:267–274, 2012) essentially reject the idea of any links whatsoever, be they between the Marmara Sea and the lakes Iznik and Sapanca, or further to the Black Sea via the valley of the Sakarya River. The evidence they provide in support of their view, however, is essentially circumstantial, in part conjectural, and also inconclusive considering the findings in favour of linkage between the Marmara Sea and the lakes at the very least, while the proposed connection with the Sakarya River valley remains speculative because of the lack of unambiguous data. On the other hand, Yaltirak et al. (Geo-Mar Lett 32:267–274, 2012) do raise valid points of concern which deserve careful future investigation, the most important being the possibility of sample contamination from dumped marine sediment used for construction purposes along some parts of the shore of Lake Iznik. We agree that a concerted multidisciplinary effort is required to address the many unresolved issues in connection with the potential waterways proposed by us and others before us.

A Landscape‐Based Classification of Fish Assemblages in Sampled and Unsampled Lakes

AbstractWe related fish species patterns and landscape‐scale environmental data from 216 Michigan lakes to identify repeatable types of fish assemblages, identify environmental factors related to assemblage types, and classify fish assemblages in unsampled lakes. Multivariate regression tree modeling of fish species abundances identified six assemblage types that were explained by degree‐days during the ice‐free period, lake surface area, and mean lake surface temperature. Warmwater species dominated southern lakes, while coolwater and coldwater species had higher abundances in northern lakes. Coolwater species were present in large southern lakes, whereas warmwater species were excluded from northern lakes that had low mean surface temperatures or low degree‐days. These results suggest that patterns of lake fish assemblages are shaped by differences in climate as well as lake‐specific differences in surface temperature regimes and in vertical availability of coldwater and coolwater habitats. Because we related fish patterns to readily available landscape‐level data, our approach can be used to characterize fish assemblages in all lakes across broad geographic extents.

Use of the flooded forest by fish assemblages in lakes of the National Park of Anavilhanas (Amazonas, Brazil)

We evaluated diversity and distribution of fish species in two habitats: flooded forest and open water of lakes of Rio Negro. Each of four lakes within the Anavilhanas Archipelago was sampled three times from 2009-2010. Species diversity generally was higher in flooded forests and at night, according to correspondence analysis. Predators were most active at night, but showed no preference between the flooded forest and open water habitats. Omnivores, filter feeders, and detritivores were most active during the day.