Search

The ability of communities to withstand stress or maintain their species composition over extended periods of environmental changes is a matter of major concern. Here, we utilize a dataset where microcrustacean communities were related to water chemistry in 82 boreal‐alpine lakes over a 50‐yr time span (1968 and 2016), with the same person involved in sampling both times ensuring identical sites and sampling protocols. Over this time span, there has been a 1–2°C increase in mean annual temperatures and prolonged growing seasons. Also, the strong changes in SO4 deposition and acidification, peaking in the early 1980s, followed by a recovery period, have caused not only an increase in pH but also a pronounced browning (elevated DOC) and reduced levels of Ca over the past three decades. Despite this, the microcrustacean diversity and community composition have remained remarkably stable, and this holds both for the species‐rich larger, boreal sites and the species‐poor alpine sites. While likely there are interannual fluctuations in species abundance, and perhaps species may also be missing for certain periods, a combination of local refugia, resting egg seed‐banks and a regional recolonization that may occur at the meta‐population level, aims at maintaining a strong stability in community composition.

Covariation in species richness and community structure across taxonomical groups (cross‐taxon congruence) has practical consequences for the identification of biodiversity surrogates and proxies, as well as theoretical ramifications for understanding the mechanisms maintaining and sustaining biodiversity. We found there to exist a high cross‐taxon congruence between phytoplankton, zooplankton, and fish in 73 large Scandinavian lakes across a 750 km longitudinal transect. The fraction of the total diversity variation explained by local environment alone was small for all trophic levels while a substantial fraction could be explained by spatial gradient variables. Almost half of the explained variation could not be resolved between local and spatial factors, possibly due to confounding issues between longitude and landscape productivity. There is strong consensus that the longitudinal gradient found in the regional fish community results from postglacial dispersal limitations, while there is much less evidence for the species richness and community structure gradients at lower trophic levels being directly affected by dispersal limitation over the same time scale. We found strong support for bidirectional interactions between fish and zooplankton species richness, while corresponding interactions between phytoplankton and zooplankton richness were much weaker. Both the weakening of the linkage at lower trophic levels and the bidirectional nature of the interaction indicates that the underlying mechanism must be qualitatively different from a trophic cascade., Species richness is known to be affected by spatial dispersal, local environmental filtering, and biotic interactions. After adjusting for known dispersal gradients (longitude) and local filtering (total phosphorus (TP) and organic carbon (TOC)), we find positive, reciprocal interactions between species richness at three trophic levels (phytoplankton, zooplankton, and fish) across 73 lakes in Southern Norway and Sweden. While we found strong congruence across trophic levels in species richness and community structure, we did not find support for unidirectional top‐down or bottom‐up effects, as would have been expected from a trophic cascade.

This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the mean Millennial temperatures during the 11th, 13th, 15th and 20th centuries and 1–2 °C lower during the 12th, 14th, 17th–18th centuries. A persistent cold period, the Little Ice Age (LIA), occurred between 1550 and 1800 CE, was interrupted by a short warming at 1650 CE. The recognized regional climate fluctuations during the last Millennium affected the lake and its catchment, of which the strongest impact was caused by the LIA cooling. During the LIA the catchment vegetation was impacted by climate deterioration and the lake productivity reached its lowest level during the last Millennium. The current temperature reconstruction is in agreement with a previous continental scale temperature reconstruction for Europe. From obtained results it emerges that during the LIA the climate of western Scandinavia has been dictated by the atmospheric patterns originating from the North Atlantic. peerReviewed

We conducted a paleolimnological study to examine how changes in human activity interacted with climate to influence productivity and biodiversity over the past millennium in oligotrophic Lake Atnsjøen, SE Norway. The study included analyses of sediment geochemistry, subfossil diatoms and cladocerans, and macrofossils. Results were compared with the historical record of human activities in the catchment, pollen analysis and paleoclimate inferences from the lake. During the first 750 years of the record (1000–1750 CE), a time of relatively low human activity, lake productivity and biodiversity were strongly related to climate. During the Little Ice Age (1550–1800 CE), lake productivity and diatom diversity were constrained by cold climate. A century of climate warming (1780–1880 CE) initiated an increase in productivity. Accelerated human settlement after 1850 CE, however, had an even stronger impact on productivity, mediated by increased agriculture and/or forestry, which led to greater nutrient loading of the lake. Similarly, diatoms in the lake responded to the rise in temperature, but increasing human activity also had a moderate impact on the diatom community, which displayed weak signs of nutrient enrichment. From 1980 to 1990 CE onwards, lake productivity declined as a consequence of a recent decrease in human activity and changing land use. The human-induced increase in lake productivity starting ca. 1850 CE propagated through the food web and increased consumer productivity, as reflected by greater accumulation rates of cladocerans, trichopterans and turbellarians. The cladoceran community was likely under top-down control of fish, as indicated by changes in size structure and diversity. Our study showed that increasing human activity during the settlement period had a stronger impact on lake productivity than did climate. Furthermore, the slight human-mediated increase in nutrient loading had different impacts on productivity and biodiversity in the study lake. This study demonstrates that even relatively small changes in human activities in watersheds can have measurable impacts on nutrient-poor lakes.

Recent climate change has led to advanced spring phenology in many temperate regions. The phenological response to variation in the local environment, such as the habitat characteristics of the territories birds occupy, is less clear. The aim of this study is to understand how ecological conditions affect breeding time, and its consequences for reproduction, in a white-throated dipper Cinclus cinclus population in a river system in Norway during 34 years (1978–2011). Hatching date advanced almost nine days, indicating a response to higher temperatures and the advanced phenology in the area. Earlier breeding was found in warm springs and at lower altitudes. High population density facilitated earlier breeding close to the coast. Furthermore, when population density was low, breeding was early at territories that were rarely occupied, while in years with high density, breeding was early at territories that were frequently occupied. Also, when population density was low, earlier breeding occurred at territories that on average produced more offspring than other territories, while there was no difference in breeding time in high population years. Selection for early breeding was dependent on spring temperatures and high spring temperatures contributed to higher breeding success during the study period. We found that breeding phenology may have strong effects on fitness in the white-throated dipper, and thus that breeding time is an important ecological factor in a species that feeds mainly on aquatic rather than terrestrial prey.

Given the major ecological and evolutionary role of dispersal abilities for organisms, as well as the current interest in species' potential for further migration and colonization as a result of climatic changes or human-mediated invasions, our knowledge about dispersal abilities on spatial and temporal scales in many taxa is surprisingly limited. Zooplankton inhabit lakes and ponds that functionally are “aquatic islands” in the landscape, and both community composition and richness depend on their ability to disperse, and their post-dispersal colonization abilities. We here assess the diversity and dispersal of freshwater microcrustaceans based on three types of data; (1) > 2000 lakes on mainland Norway spanning a wide range in longitude, latitude and altitude, (2) a more limited number of ponds at Svalbard that are differently affected by migrating birds, and (3) immigration and colonization of recently constructed wetlands and man-made ponds. At all scales we discuss whether observed patterns in diversity can be explicitly linked to birds as vectors, or if confounding factors such as climate, productivity, age of locality—or other means of immigration, precludes conclusive evidence. The spatial patterns of zooplankton distribution strongly suggest that local sorting is a major determinant of richness and community composition. This sorting may not necessarily lead to similar community composition (the “quorum effect”) however. Despite the fact that rapid colonization occurs at local scales, and that birds undoubtedly can transmit animals or resting stages, their role in modulating community structure and richness is still an unsettled issue due to the many confounding parameters. The fact that birds often play a dual role in shaping diversity and community composition, first by direct dispersal, and secondly via affecting post-dispersal species sorting by changing water quality and productivity, is an important aspect of zoochory. Direct experimental evidence (colonization with and without bird exclusion), or genetic analysis of zooplankton species along migration routes, would however be the only ways to establish firm evidence for this case of zoochory.

1. The high Arctic, including the Svalbard archipelago in the North Atlantic, has been exposed to direct and indirect drivers of climatic change such as rising temperatures and associated changes in hydrology and nutrient fluxes. In addition, the number of migrating birds, particularly geese, increased remarkably in the Svalbard archipelago during the second half of the last century. The higher number of breeding birds potentially affects water quality and the biota in ponds and lakes. 2. We aimed to investigate the potential influence of increasing goose abundance on trophic state, taxon richness, and species composition of freshwater communities in the high Arctic. We hypothesised that higher goose abundance affects the trophic state of shallow lakes and ponds and their taxon richness and species composition. We conducted a survey of selected ponds at Svalbard along a goose abundance gradient. We used the number of area-specific goose droppings (range of 0–94 droppings m2) as a proxy of goose presence and measured proxies for productivity as well as taxon richness and composition of phytoplankton and invertebrate communities. 3. Presence and abundance of geese were associated with higher productivity of ponds. Invertebrate and phytoplankton taxon richness correlated (positively) with goose abundance. Both phytoplankton and invertebrate taxon richness increased with increasing nitrogen (N) concentrations. Goose abundance significantly affected phytoplankton species composition, while concentrations of total-N and total phosphorus (P) did not. Species composition of aquatic invertebrates was most strongly affected by goose abundance, but the effect of total-N concentration was also significant. 4. Increased goose abundance was associated with bird driven nutrient enrichment, increased phytoplankton and invertebrate taxon richness and changes of these biological communities. Thus, in addition to climate change, the higher abundances of large migratory water fowl in many polar areas may pose a major additional stress to arctic lakes and ponds. In fact, climate change and bird impact may interact, accelerating ongoing environmental change of arctic freshwater ecosystems. climate change, geese, invertebrates, phytoplankton, Svalbard

The high Arctic is in a rapid transition due to climate change, and both direct effects due to warming and an extended growing season, as well as an indirect effect caused by increased bird activity and density (notably geese), strongly affect ponds and lakes. Our study presents the hitherto most comprehensive data on invertebrate freshwater diversity at Svalbard and had three main purposes: to provide a current “baseline” of community composition, to compare current species distribution and occurrence with older data to identify changes that have already occurred, and finally to identify how diversity and community composition are related to the age of localities. To address these aims, we conducted a survey of freshwater invertebrates in 75 ponds and lakes at Svalbard in August 2014 and 2015. We provide a full report of the species’ inventory data for zooplankton, benthos, and meiofauna. We also provide data for species that have likely colonized the sites over the previous decades. Finally, our study also clearly demonstrates a diversity gradient related to ecosystem age and/or parameters confounded with age (e.g., productivity), which may hint at the rate of colonization over the time span from the oldest to the youngest localities.

Arctic landscapes are characterised by an immense number of fresh and brackish water habitats – lakes, ponds and puddles. Due to a rather harsh environment, there is a limited number of species inhabiting these ecosystems. Present biological communities are impacted and changed by recent climate-driven regime shifts. New species may appear, and existing communities may become supressed or even disappear depending on how their ecological needs interact with ongoing changes. This study provides data on presently existing and probably recently arriving fresh and brackish water microcrustacean species in Norwegian High Arctic - Svalbard archipelago. The study focused on two taxa groups, Cladocera and Copepoda and altogether we found seven taxa new for Svalbard: Alona werestschagini, Polyphemus pediculus, Diaptomus sp., Diacyclops abyssicola, Nitokra spinipes, Epactophanes richardi and Geeopsis incisipes. Compared with an existing overview for the area, our study increased the number of species by more than 20 %, and some of the new species have never been found that far north. Finally, we present a complete and critically updated revised species list of fresh and brackish water cladocerans and copepods for Svalbard.

We investigated the relative importance of flood defenses and other environmental variables for the cladoceran and copepod communities in floodplain water bodies in Southeastern Norway. The water bodies covered gradients of size, distance to the river and water chemistry, and half of them were located behind flood defenses. The effects of environmental variables on the communities were analyzed using redundancy analysis. The set of environmental variables accounted for more of the explained variation in the cladoceran community than in the copepod community. Water quality was much more important than flooding-related variables for both communities. Although cladoceran species richness was slightly higher in water bodies outside flood defenses, total nitrogen, total organic carbon (TOC), and water body area were the most important factors for the cladocerans. Macrophyte coverage was the most important variable for both species richness and community structure of copepods. Although our results show that water quality and spatial/structural variables are more important than flood defenses in structuring the communities, the effect of TOC on the cladoceran community could likely be mediated through effects of flood defense on TOC. Prospects for a continued anthropogenic pressure on river floodplains raise concern for the future of these unique ecosystems.

Summary A dataset of 1735 Norwegian lakes, spanning a wide range of geographical, physical, chemical and biological properties, was analysed to assess the role of the top invertebrate predator, Bythotrephes longimanus, on the crustacean species richness and community structure. Bythotrephes was associated with a 25.5% increase in mean richness of other zooplankton species, and this effect could not be related to confounding factors. Based on presence–absence data, community composition did not differ significantly between lakes with and without this top predator. Neither fish predation nor lake area, altitude, and geographical or physicochemical parameters offer any obvious impact on the observed diversity patterns. We suggest that Bythotrephes facilitates species richness by reducing the abundance of species controlling subdominant species. This pattern of increased diversity offers an interesting contrast to North American lakes recently invaded by Bythotrephes, where species richness typically has decreased, suggesting different short-term and long-term effects of predatory invaders.

Interactions between birds and fish are often overlooked in aquatic ecosystems. We studied the influence of Atlantic salmon and brown trout on the breeding population size and reproductive output of the white‐throated dipper in a Norwegian river. Acidic precipitation led to the extinction of salmon, but salmon recolonized after liming was initiated in 1991. We compared the dipper population size and reproductive output before (1978–1992) and after (1993–2014) salmon recolonization. Despite a rapid and substantial increase in juvenile salmon, the breeding dipper population size and reproductive output were not influenced by juvenile salmon, trout, or total salmonid density. This might be due to different feeding strategies in salmonids and dippers, where salmonids are mainly feeding on drift, while the dipper is a benthic feeder. The correlation between the size of the dipper population upstream and downstream of a salmonid migratory barrier was similar before and after recolonization, indicating that the downstream territories were not less attractive after the recolonization of salmon. Upstream dipper breeding success rates declined before the recolonization event and increased after, indicating improved water quality due to liming, and increasing invertebrate prey abundances and biodiversity. Surprisingly, upstream the migratory barrier, juvenile trout had a weak positive effect on the dipper population size, indicating that dippers may prey upon small trout. It is possible that wider downstream reaches might have higher abundances of alternative food, rending juvenile trout unimportant as prey. Abiotic factors such as winter temperatures and acidic precipitation with subsequent liming, potentially mediated by prey abundance, seem to play the most important role in the life history of the dipper.

Interactions between birds and fish are often overlooked in aquatic ecosystems. We studied the influence of Atlantic salmon and brown trout on the breeding population size and reproductive output of the white-throated dipper in a Norwegian river. Acidic precipitation led to the extinction of salmon, but salmon recolonized after liming was initiated in 1991. We compared the dipper population size and reproductive output before (1978–1992) and after (1993–2014) salmon recolonization. Despite a rapid and substantial increase in juvenile salmon, the breeding dipper population size and reproductive output were not influenced by juvenile salmon, trout, or total salmonid density. This might be due to different feeding strategies in salmonids and dippers, where salmonids are mainly feeding on drift, while the dipper is a benthic feeder. The correlation between the size of the dipper population upstream and downstream of a salmonid migratory barrier was similar before and after recolonization, indicating that the downstream territories were not less attractive after the recolonization of salmon. Upstream dipper breeding success rates declined before the recolonization event and increased after, indicating improved water quality due to liming, and increasing invertebrate prey abundances and biodiversity. Surprisingly, upstream the migratory barrier, juvenile trout had a weak positive effect on the dipper population size, indicating that dippers may prey upon small trout. It is possible that wider downstream reaches might have higher abundances of alternative food, rending juvenile trout unimportant as prey. Abiotic factors such as winter temperatures and acidic precipitation with subsequent liming, potentially mediated by preyabundance, seem to play the most important role in the life history of the dipper. birds, breeding, predators, river, salmonids

Warmer winters alter the dynamics of a local bird population and reduce immigration rate due to density-dependent feedback., Climate change will affect the population dynamics of many species, yet the consequences for the long-term persistence of populations are poorly understood. A major reason for this is that density-dependent feedback effects caused by fluctuations in population size are considered independent of stochastic variation in the environment. We show that an interplay between winter temperature and population density can influence the persistence of a small passerine population under global warming. Although warmer winters favor an increased mean population size, density-dependent feedback can cause the local population to be less buffered against occasional poor environmental conditions (cold winters). This shows that it is essential to go beyond the population size and explore climate effects on the full dynamics to elaborate targeted management actions.

PurposeThe purpose of this paper is to identify the importance of floodplains in preserving biodiversity, and call attention to alternative ways of managing floodplains in relation to probable scenarios of climate change.Design/methodology/approachIn total, 20 water bodies on the floodplain at Flisa along the River Glomma (Hedmark County, Eastern Norway) were investigated with regards to crustacean zooplankton and water beetle species richness.FindingsBoth on a national and regional scale, the species diversity in the investigated water bodies was high. A total of 57 crustacean plankton and 77 water beetle species were recorded. Of these, ten and eight were new records of zooplankton and water beetle species in Hedmark County, respectively. Seven recorded water beetle species were specified in the 2010 Norwegian Red List of Species. Further, the localities on the Flisa floodplain are relatively unique with regard to the composition of species compared to other investigated localities in Hedmark County.Social implicationsFloodplains are intensively used and are considered as among the most threatened ecosystems in the world. More frequent and less predictable floods can be expected in the future due to climate change's influence. In some settings more frequent larger floods may work to re‐establish the connectivity, but larger floods might also result in demand for construction of more extensive flood mitigation measures.Originality/valueThe results from this case study underpin the high biodiversity of floodplains, an ecosystem infrequently examined in Norway. The results of this study are of importance regarding management and maintenance of ecosystem services (e.g. biodiversity and water retention) from floodplains.

We here exploit two large datasets on zooplankton in Norwegian lakes, spanning a wide range of geographical, physical, chemical and biological properties, to assess the ecological niches and habitats of Bythotrephes longimanus and Leptodora kindtii. The species overlapped geographically, yet co-occurred only in a limited number of lakes. Bythotrephes inhabited virtually all types of lakes, except alpine localities and productive lakes dominated by cyprinid communities where the hyaline Leptodora was most abundant. The zooplankton communities also differed in Bythotrephes and Leptodora lakes, probably both reflecting different predatory regimes, but also water quality and other lake-specific properties. We found no evidence for species being excluded by the presence of Bythotrephes, rather the diversity in general was higher in lakes with these predators present compared with those without. We found, however, a very close association between Bythotrephes and Daphnia galeata and to some extent also between Bythotrephes and D. longispina, suggesting that these species also may benefit from Bythotrephes invasion. Both Bythotrephes and Leptodora species occur naturally in this region, and knowledge about the ecological preferences and the zooplankton community composition in Bythotrephes—and Leptodora lakes will provide valuable information about the long-term effects of Bythotrephes invasion and potential interaction with of Leptodora as top invertebrate predator.

To study the ecological and evolutionary effects of climate change on timing of annual events, scientists need access to data that have been collected over long time periods. High-quality long-term phenology data are rare and costly to obtain and there is therefore a need to extract this information from other available data sets. Many long-term studies on breeding birds include detailed information on individually marked parents and offspring, but do not include information on timing of breeding. Here, we demonstrate how a study of repeated standard measurements of white-throated dipper Cinclus cinclus nestlings in our study system in southernmost Norway can be used for modeling nestling growth, and how this statistical model can be used to estimate timing of breeding for birds with sparser data. We also evaluate how the accuracies of nestling growth models based on different morphological traits (mass and feather length) differ depending on the nestling age, present user guidelines and demonstrate how they can be applied to an independent data set. In conclusion, the approach presented is likely to be useful for a wide variety of species, even if the preferred measurement may differ between species.

Summary 1. Climate change may have profound consequences for many organisms. We have studied fluctuations in a population of the white-throated dipper Cinclus cinclus during 31 years (1978–2008) in a river system in southern Norway in relation to both large-scale and local weather conditions occurring during the non-breeding season. 2. Multiple regression and partial least squares regression were used to model the growth rate of the population, accounting for population size in the previous year. 3. Population growth was influenced by North Atlantic Oscillation (NAO), mean winter temperature, precipitation and timing of ice formation on the main lake in the river system in autumn. These variables explained 84% of the variation in population growth over the 31 -year study period. 4. Local winter conditions played a prominent role in explaining the population fluctuations, which is plausible because the dipper depends on open water for foraging. In the study area, winters can be harsh and rivers and lakes may freeze and severely affect the subsequent population size of the dipper in spring. 5. The breeding population of the dipper does not seem yet to have reached a level where all possible territories in the area have been occupied, even after mild winters, and the estimated carrying capacity is also decidedly lower (66 breeding pairs) than the number of available territories. If the trend of milder winters continues, the population might increase in the future. However, strong climate variation is expected to continue in the future, and hence periods of rapid growth of the dipper population will probably be followed by severe declines.

Summary 1. Regional distribution, frequency of occurrence and relative abundance were scored in 2467 Norwegian lakes for all the recorded 130 species of crustacean zooplankton. The majority of species were rare in the sense that 65% of species were recorded in fewer than 10% of localities. Only six species were recorded in more than 50% of localities, and the median number of species in a given locality was 14 (i.e. 10% of the total species pool). 2. Abundances of all species were scored according to the fraction of lakes in which they were recorded, their geographical range of distribution, and their numerical abundance. Typically the most rare species were rare by all three criteria, and vice versa for the common species, pointing to rarity as an inherent property of some species. For some species this rarity reflects being on the edge of their distributional range, while for others rarity seems to be a consequence of their life cycle strategies. 3. Some of the truly rare species have high dispersal rates and high colonization abilities, but are rapidly replaced by other species. Others are confined to specific habitats, often highly eutrophic, pointing to highly specialized niche adaptations. 4. A major cause for the few truly common species seems to be the limited number of species that are able to coexist within a given locality, reflecting ‘the ghost of competition past’ and predation pressure. 5. While species composition and species richness may reflect colonization abilities and stochastic events, the presence or absence of species is not only a random lottery but also a consequence of species-specific attributes.

What are the relative contribution of temperature and solar irradiance as types of energy deliveries for species richness at the ecosystem level? In order to reveal this question in lake ecosystems, we assessed zooplankton species richness in 1891 Norwegian lakes covering a wide range in latitude, altitude, and lake area. Geographical variables could largely be replaced by temperature-related variables, e.g. annual monthly maximum temperature or growth season. Multivariate analysis (PCA) revealed that not only maximum monthly temperature, but also energy input in terms of solar radiation were closely associated with species richness. This was confirmed by stepwise, linear regression analysis in which lake area was also found to be significant. We tested the predictive power of the ‘‘metabolic scaling laws’’ for species richness by regressing Ln of species richness over the inverse of the air temperature (in Kelvin), corrected for the activation energy (eV) as predicted by the Boltzmann constant. A significant, negative slope of 0.78 for ln richness over temperature, given as 1/kT, was found, thus slightly higher than the range of slopes predicted from the scaling law (0.60� 0.70). Temperature basically constrained the upper bound of species number, but it was only a modest predictor of actual richness. Both PCA-analysis and linear regression models left a large unexplained variance probably due to lake-specific properties such as catchment influence, lake productivity, food-web structure, immigration constraints or more stochastic effects.

We studied the effects of liming on fish and crustaceans in a watershed which is in a region known to have one of the highest diversity of aquatic biota in Norway. This watershed, Enningdal, is shared between Norway (1/3) and Sweden (2/3) and includes 61 lakes > 1.0 ha in Norway. Liming started on a large scale in the 1980s. Currently, a total of 26 of lakes (43%) are limed, covering 93% of the total lake area. The mean value ± S.D. of pH and the concentration of inorganic labile Al in these lakes is 6.62 ± 0.35 and 3 ± 4 μg l−1, respectively. Historical data of fish communities have been obtained from surveys, while test-fishing and sampling of crustaceans were conducted in 24 lakes in recent years (2002–2004). The present study shows that crustaceans to a greater extent than fish has responded to improved water quality after more than 20 years of liming. Of a total of 120 fish populations, 42 (35%) have gone extinct. Only five of the lost fish populations (12%) have been re-established, all due to human re-introductions. Physical barriers are considered to be the main factor preventing fish from invading limed lakes. In contrast, crustaceans have been re-established in most limed lakes. This may be mainly due to their good spreading capacity. However, they might also have survived in refuges within the watershed, or as resting-eggs in the sediment.

A study of pelagic and littoral species richness among microcrustaceans in 2,466 Norwegian lakes recorded 120 crustacean species: 77 cladocerans, 31 cyclopoids, and 12 calanoids, respectively. Very few species were strictly pelagic, and the pelagic crustacean zooplankton species were by far outnumbered by their littoral counterparts. More than two-thirds of the total crustacean species numbers in lakes were accounted for by species with a littoral preference. A considerable number of species occurred with low frequency, and the median total number of crustacean species in the lakes was only 14. A majority of littoral species also occurred commonly in pelagic samples, and vice versa. Some species are truly both littoral and pelagic, and nearly all species occurring in pelagic samples were also common in littoral samples. A high proportion of the common littoral species was only recorded occasionally in pelagic samples, and should thus be considered strictly littoral. There was no significant correlation between lake area and species richness for pelagic or littoral species. Our findings demonstrate the importance of including littoral species when assessing microcrustacean diversity in lakes, and we question the practice of considering species as either pelagic or littoral, because a majority of the recorded species was common in both habitats. It calls for a further discussion of the term "planktonic", since most of the species are at least partly "semiplanktonic."

A 7 year study (1992–1998) of littoral microcrustaceans (Cladocera and Copepoda) in the watercourse of the River Rore, South Norway, illustrates that qualitative data on cladocerans and copepods are well suited to indicate the recovery of lakes following liming. Eight limed, two acid and two circum neutral reference lakes, were sampled twice a year (June/July and September/October). In the limed lakes, species associated with neutral lakes have become more common, whereas apparently acid-tolerant species have become rarer. In Lake Rore and Lake Syndle, the two largest limed lakes which exhibited a gradual increase in pH, the changes in species composition indicated that these lakes were about to recover. Species composition in Lake Roynelandsvatn, which has reacidified after liming, first reflected improved water quality, then reverted to dominance by acid-tolerant species. In the remaining lakes, the species composition reflects a fauna which has recovered compared with the preliming situation. There is strong evidence, however, that temporary fluctuations in pH have a negative influence on the speed of recovery, confirming the importance of keeping pH stable.

Increased pH in acid lakes changes the crustacean fauna from communities dominated by acid-tolerant species to communities dominated by more acid-sensitive species. Studies from Canada (Killarney) and southeastern Norway (Ostfold county) have demonstrated that planktonic and littoral crustaceans can be used as indicators of such recoveries. In both places the cladocerans Alona rustica and Acantholeberis curvirostris were found in acidic lakes, whereas Alona costata and the copepod Eucyclops macrurus were found in near neutral lakes. The calanoids Diaptomus minutus in North America and Eudiaptomus gracilis in Europe, both dominate in acidic water, and may ecologically be equivalent species. Sometimes the same species occur at different pH in the two continents. Bosmina longirostris and Alonella excisa may serve as examples, but a pertinent question is whether or not they are really the same species.

(1998). Occurrence of Eucyclops species in acid and limed waters. SIL Proceedings, 1922-2010: Vol. 26, No. 4, pp. 2007-2012.

(1997). History of acidification and restoration of the fauna in Lake Nordre Boksjo. SIL Proceedings, 1922-2010: Vol. 26, No. 2, pp. 760-764.

Numerous boreal lakes across the Northern Hemisphere recovering from acidification are experiencing a simultaneous increase in chloride (Cl) concentrations from road salting. Increasing Cl may have profound effects on the lake ecosystem. We examine if an increase in Cl from road salting has modified the recovery of the microcrustacean community in an acidified boreal lake undergoing chemical recovery (study lake). Results from the study lake were compared with an acidified “reference lake”. The community changed during the study period in the study lake mainly driven by the reduction in acidification pressure. Despite the community changes and an increase in species richness, the absence of several acid sensitive species, previously occurring in the lake, indicates a delayed biological recovery relative to the chemical recovery. Moreover, changes in occurrence of acid sensitive and acid tolerant species indicated that the biological recovery was slower in the study lake compared to the “reference”. Although recurrent episodes of high aluminum and low pH and decreasing Ca are likely important factors for the delay, these do not explain, for instance, the shift from Cyclops scutifer to Bosmina longispina in the study lake. Although the contribution of Cl was not significant, the correlation between Cl and the variation in microcrustacean community was twice as high in the study lake compared to the “reference”. We argue that small, sheltered forest lakes may be especially sensitive to increased Cl levels, through changes in pattern of stratification, thus providing a mechanism for the shift from C. scutifer to B. longispina. The reduction of the acidification pressure seems to override the Cl effects on microcrustaceans at low Cl levels in salt-affected lakes recovering from acidification. However, prognoses for growing traffic and increasing road salting raise concern for many recovering lakes located in proximity to roads and urbanized areas.

[In 1992 Acanthodiaptomus tibetanus was found in material from northern Norway sampled in 1979, 1992, and 1993, and in 1992 also in Sor-Trondelag, Central Norway. This species has previously been recorded from only a few other localities, and has a very sparse and scattered distribution. In this paper, we discuss the distribution of this rare species and the reasons for its puzzling distribution pattern., In 1992 Acanthodiaptomus tibetanus was found in material from northern Norway sampled in 1979, 1992, and 1993, and in 1992 also in Sor-Trondelag, Central Norway. This species has previously been recorded from only a few other localities, and has a very sparse and scattered distribution. In this paper, we discuss the distribution of this rare species and the reasons for its puzzling distribution pattern.]

1. Climate change may have profound consequences for many organisms. We have studied fluctuations in a population of the white-throated dipper Cinclus cinclus during 31 years (1978-2008) in a river system in southern Norway in relation to both large-scale and local weather conditions occurring during the non-breeding season. 2. Multiple regression and partial least squares regression were used to model the growth rate of the population, accounting for population size in the previous year. 3. Population growth was influenced by North Atlantic Oscillation (NAO), mean winter temperature, precipitation and timing of ice formation on the main lake in the river system in autumn. These variables explained 84% of the variation in population growth over the 31-year study period. 4. Local winter conditions played a prominent role in explaining the population fluctuations, which is plausible because the dipper depends on open water for foraging. In the study area, winters can be harsh and rivers and lakes may freeze and severely affect the subsequent population size of the dipper in spring. 5. The breeding population of the dipper does not seem yet to have reached a level where all possible territories in the area have been occupied, even after mild winters, and the estimated carrying capacity is also decidedly lower (66 breeding pairs) than the number of available territories. If the trend of milder winters continues, the population might increase in the future. However, strong climate variation is expected to continue in the future, and hence periods of rapid growth of the dipper population will probably be followed by severe declines.

Pelagic crustacean zooplankton were collected from 336 Norwegian lakes covering a wide range of latitude, altitude, lake area, mean depth, production (as chlorophyll a), and fish community structure. Mean zooplankton species richness during the ice-free season was generally low at high latitudes and altitudes. Further, lower species richness was recorded in western lakes, possibly reflecting constraints on migration and dispersal. However, despite obvious spatial limitations, geographic boundaries were only weak predictors of mean zooplankton richness. Similarly, lake surface area did not contribute positively to mean richness such as seen in other ecosystem surveys. Rather, intrinsic factors such as primary production and fish community (planktivore) structure were identified by regression analysis as the major predictors of zooplankton diversity, while a positive correlation was observed between species richness and total zooplankton biomass. However, in spite of a large number of variables included in this study, the predictive power of multiple regression models was modest (

On a large scale, the acidified River Bjerkreim, southwestern Norway, has been treated with lime since the autumn 1996. During the Atlantic salmon (Salmon salar) smolting period pH has been above 6.2 and LAI concentrations below 10 μg L-l. Before 1996, only the western part of the watercourse harboured acid-sensitive species, such as the Atlantic salmon, snails, mayflies, daphnids and Gammarus lacustris. Prior to liming in 1996, Atlantic salmon fry (0+) and parr (≥1+)were found in 4 of 20 sampling sites, contrary to 17 (fry) and 12 (parr) in 1999. Atlantic salmon catches have increased from about 0.8 tons in 1994 to about 10 tons in 1998 and 1999. Acid-sensitive invertebrates have invaded the limed parts of the river.

Multivariate methods were used to relate microcrustacean (pelagic and littoral) richness and composition (presence/absence) to water quality and other environmental variables. All acidification variables (pH, aluminium, ANC) snowed significant correlation with both species richness and composition. The variation in microcrustacean richness was best explained by the combination of dissolved organic carbon (DOC), fish species richness and lake area. Of 16 variables tested, pH showed strongest correlation with the main gradient in the crustacean composition explaining between 13 and 16% of the variance in the species data (CCA). pH, elevation, lake area, average depth, DOC., conductivity and fish species richness explained 30–54% of the total variance. Stronger correlation was obtained between species composition and environmental data in analyses which included the between-year differences than analyses based on the cumulative species records. Analyses based on the pelagic species exclusively gave similarly stronger correlation than analyses based on all crustacean species. Small changes in the species composition during the three years of study may be an indication of recovery of microcrustaceans in Killarney lakes.

Summary 1. Emergence traps were set overnight on the sediment surface to sample the littoral microcrustaceans of 22 Canadian Shield lakes that ranged in pH from 4.56 to 6.92. Traps were randomly allocated in quintuplicate in both wave-washed sandy habitats where pipewort (Eriocaulon septangulare) was the dominant macrophyte (termed pipewort habitats), and more protected habitats dominated by floating-leaved macrophytes (termed floating-leaved habitats). 2. In total, 50 cladoceran and 22 copepod species were found, with 16–45 species in each lake. Lakes that had never acidified exhibited a more diverse fauna than lakes that had acidified. 3. There were only minor differences between the numbers of species found in floating-leaved versus pipewort habitats except for one lake. Non-chydorid cladoceran, chydorids and copepods constituted 45%, 26% and 29% of the total number of individuals, respectively. 4. Based on presence/absence, dominance scores and frequency of occurrences of species, the microcrustacean faunal composition was similar in the two habitats. A detrended correspondence analysis confirmed that there was no separation between the two main types of habitat, and that pH was the parameter most strongly correlated with the dominant microcrustacean compositional gradient among lakes.

The WHAM-FTOX model quantifies the combined toxic effects of protons and metal cations towards aquatic organisms through the toxicity function (FTOX), a linear combination of the products of organism-bound cation and a toxic potency coefficient for each cation. We describe the application of the model to predict an observable ecological field variable, species richness of pelagic lake crustacean zooplankton, studied with respect to either acidification or the impacts of metals from smelters. The fitted results give toxic potencies increasing in the order H+

We identify littoral microcrustacean indicators of acidification in 2 surveys of Canadian Shield lakes conducted 10 years apart. We found a total of 90 cladoceran and copepod species with richness increasing severalfold from acidic to nonacidic lakes. The fauna of the nonacidic lakes differed between the surveys. The 1987 survey employed activity traps, and caught more littoral taxa than the more recent, net-haul-based survey. Similar faunas were identified in the acidified lakes in both surveys, and several good indicator species were identified. For example, Acanthocycops vernalis was restricted to lakes with pH6. Sinobosmina sp. was very common but only in lakes with pH4.8. Tropocyclops extensus, Mesocyclops edax, and Sida crystallina were commonly found but only at pH5, and Chydorus faviformis only at pH5.9. These indicators showed promise in gauging the early stages of recovery from acidification in 3 lakes that were included in both surveys.