Lakes In Denmark Research Articles

Landscape Democracy in a Globalizing World: The Case of Tange Lake

The main topic of the article is the question of landscape democracy in a world where local issues are seldom just local. This topic is treated both in general terms and in relation to one particular case: the artificial Tange Lake in Denmark. The first part narrates the story of Tange Lake. It identifies the most important international drivers that have influenced landscape development in the area directly or indirectly through the actions of a variety of local actors with conflicting conceptions of landscape quality. The variety of drivers, actors and conceptions present at Tange as well as in a great number of similar cases raises questions concerning levels and models of landscape democracy. This is the main theme of the second part. First, three basic democratic values are identified together with three orders or levels of impartiality. Second, the relation between levels of democratic decision-making is discussed with the principle of subsidiarity and the concentric circle theory as guiding lines. In the final section, these general considerations are discussed in relation to the Tange case.

Lake metabolism scales with lake morphometry and catchment conditions

We used a comparative data set for 25 lakes in Denmark sampled during summer to explore the influence of lake morphometry, catchment conditions, light availability and nutrient input on lake metabolism. We found that (1) gross primary production (GPP) and community respiration (R) decline with lake area, water depth and drainage ratio, and increase with algal biomass (Chl), dissolved organic carbon (DOC) and total phosphorus (TP); (2) all lakes, especially small with less incident light, and forest lakes with high DOC, have negative net ecosystem production (NEP < 0); (3) daily variability of GPP decreases with lake area and water depth as a consequence of lower input of nutrients and organic matter per unit water volume; (4) the influence of benthic processes on free water metabolic measures declines with increasing lake size; and (5) with increasing lake size, lake metabolism decreases significantly per unit water volume, while depth integrated areal rates remain more constant due to a combination of increased light and nutrient limitation. Overall, these meta-parameters have as many significant but usually weaker relationships to whole-lake and benthic metabolism as have TP, Chl and DOC that are directly linked to photosynthesis and respiration. Combining water depth and Chl to predict GPP, and water depth and DOC to predict R, lead to stronger multiple regression models accounting for 57–63% of the variability of metabolism among the 25 lakes. It is therefore important to consider differences in lake morphometry and catchment conditions when comparing metabolic responses of lakes to human impacts.

Modelling diffuse nitrogen loadings of ungauged and unmonitored lakes in Denmark: Application of an integrated modelling framework

According to the EU Water Framework Directive all freshwater bodies must obtain good ecological status by 2015. In Denmark this means that all lakes with a surface area above 5 ha (∼600 lakes) must be evaluated individually and mitigation measures must be enforced if the ecological status is below “good”. In consequence, the nutrient pressures from point and diffuse sources must be assessed based on a quantification of the nutrient loading of each lake. In this study we focus on the loading of nitrogen. Few of the 600 lakes are monitored for runoff and nitrogen loading. Therefore, a national 3D hydrological model covering all major parts of the country was used to estimate runoff from the lake catchments. The diffuse nitrogen input to each lake was simulated with an empirical nitrogen model. Where lakes are located upstream/downstream of each other, a calculation chain involving the nitrogen retention in lakes was created. A case study was selected using a large river basin including 23 lakes in Denmark. The cost‐effectiveness of reducing nitrogen loadings from different sub‐catchments in the case study river basin to the sea was calculated. The cost‐effectiveness associated with reducing the N‐loading from the most expensive sub‐catchment is shown to be 20 times more expensive than from the cheapest sub‐catchment.

The Water Framework Directive: Setting the phosphorus loading target for a deep lake in Denmark using the 1D lake ecosystem model DYRESM–CAEDYM

We used the one-dimensional DYRESM–CAEDYM model to elucidate and quantify the influence of the external phosphorus loading on ecosystem dynamics in moderately deep Lake Ravn, which is situated in an agricultural landscape in Denmark. Model simulations were used to quantify the extent to which the external phosphorus loading must be reduced to meet upcoming lake ecological quality requirements according to the European Union Water Framework Directive (WFD). The model generally showed good agreement with observed data for temperature and oxygen from the epilimnion and hypolimnion during the calibration period (7 years) as well as the validation period (5 years); although peaks of oxygen concentrations in epilimnion during late spring often were underestimated. Phosphate and total phosphorus (TP) concentrations were generally well reproduced in both the epilimnion and hypolimnion, though hypolimnetic phosphorus was occasionally underestimated in late summer. There was also good agreement between monitored data and modelled biomass of diatoms and dinoflagellates as well as the zooplankton biomass of cladocerans and calanoid copepods, although the timing of biomass peaks occasionally deviated from observations. Root-mean-square-errors (RMSE), used to quantify the model error, were overall similar for the calibration and the validation period. Simulations of scenarios with a reduced external TP loading suggest that a substantial reduction (40–50%) of the TP loading is required if phytoplankton biomass is to drop to a level sufficiently low to meet the proposed WFD requirements (summer average <6.5 μg chlorophyll a l −1). The predicted outcomes of considerable loading reductions should, however, be treated with some caution, as the conceptual model in this study could not fully account for the changes in trophic structure occurring at radically reduced TP loading. This particularly applies to changes in the fish stock, which may have extensive cascading effects via increased zooplankton grazing on the phytoplankton when external TP loading is reduced. This would most likely lead to higher transparency than that predicted by the model. To further improve the reliability of the predicted outcomes of various model scenarios, future work should include a series of test simulations also including fish predation. Today, fish predation is available in the DYRESM–CAEDYM model as well as other dynamic lake models; however, only sparse data is available on fish stock dynamics in Lake Ravn (as for most other lakes). An applicable test of the fish algorithms in today’s dynamic models will require reliable estimates of fish stock biomass in the study lakes during both the model calibration and validation period.

Lake restoration: successes, failures and long‐term effects

1. Eutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20–30 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. 2. In this study we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. 3. In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating an increased retention or loss by denitrification. The strongest effects seemed to be obtained 4–6 years after the start of fish removal. 4. The long-term effect of restoration initiatives can only be described for a few lakes, but data from biomanipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. 5. Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects ( > 8–10 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditions Eutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20-30 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. In this study we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating an increased retention or loss by denitrification. The strongest effects seemed to be obtained 4-6 years after the start of fish removal. The long-term effect of restoration initiatives can only be described for a few lakes, but data from biomanipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects (> 8-10 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditions.

Diapause of Cyclops vicinus (Uljanin) in Lake Søbygård: Indication of a Risk-spreading Strategy

Cyclops vicinus is reported to enter summer diapause triggered by day length in order to survive food scarcity and fish predation. Development ceases and the fourth or fifth copepodid stages persist in the sediment for several weeks. In Lake Sobygard, however, a small eutrophic lake in Denmark, C. vicinus is found in the sediment as well as in the open water throughout the year. We performed laboratory experiments to elucidate the life cycle strategy of this population. In order to find the factors that induce diapause we tested the influence of food composition and light regime on the proportion of copepods entering diapause. Further we examined the diapause pattern of the offspring from diapausing and non-diapausing parents to see whether the co-occurrence of diapausing and non-diapausing copepods results from genetic differentiation within the population. In all experiments some of the copepods developed directly into adults, while others remained at the fourth or fifth copepodid stage and displayed diapause features. The proportion of copepods that developed directly into adults was influenced by food supply. Fewer individuals entered diapause when they received a mixed diet of algae and ciliates or algae, ciliates and seston compared with a pure algal diet. The response to light was different than described in literature: about 30% of the copepods entered diapause under dark conditions, and the diapause frequency was not higher when copepods had been exposed to continuous light. The offspring from diapausing parents showed no higher tendency to enter diapause than the offspring of non-diapausing parents, indicating no genetic differentiation. We conclude that diapause in C. vicinus represents a risk-spreading strategy, modified by food. The simultaneous production of diapausing and non-diapausing offspring ensures survival under harsh conditions; the influence of the food supply on the proportion of individuals entering diapause may adjust the population to the actual environmental condition. This flexible life cycle strategy might contribute to the exclusive dominance of C. vicinus in Lake Sobygard.

CONTROLS OF ALGAL ABUNDANCE AND COMMUNITY COMPOSITION DURING ECOSYSTEM STATE CHANGE

Shallow lake ecosystems can shift between clear-water, macrophyte-rich conditions and turbid states with abundant phytoplankton. However, little is known about the controls of algal community composition and primary production before, during, and after ecosystem state change, because long time series that monitor biological change through the transition are scarce. Using proxy data sets derived from sediment cores from two shallow hypertrophic lakes in Denmark, variance-partitioning analysis (VPA) was used to determine the relative importance of changes in total phosphorus (diatom inferred), planktivorous fish density (zooplankton inferred), and submerged macrophyte communities (as macrofossil abundance) as determinants of algal abundance and community composition (as sedimentary pigments) over ecosystem state transitions since 1750 (CE) for Lake Lading and 1900 for Lake Søbygaard. Past variation in densities of planktivorous fish explained 12.3% and 18.2% of historical algal community change in lakes Lading and Søbygaard, respectively, while a further 22.3% and 6% of algal variability was explained by variation in macrophyte abundance. Total phosphorus (TP) alone explained nonsignificant amounts of variance (1.5%, 3.6%) but had a significant effect in combination with macrophytes and fish (27%, 13.4%). State transitions occurred ca. 1940 but were preceded by increases in benthic diatoms and macrophytes, suggesting that transitions were gradual rather than instantaneous. In contrast, green, colonial blue-green, and cryptophyte algae were abundant only during turbid states after ca. 1960 and were correlated to changes in planktivorous fish or fish–TP interactions. Contrary to expectations, the shift from predominantly benthic to pelagic algal production represented only a change in habitat and did not result in an increase in total abundance of primary producers.

Reconstructing land cover from pollen assemblages from small lakes in Denmark

A calibration data set of AD 1800 pollen assemblages and land cover from 30 lake sites (3.5–33 ha) in Denmark is analysed. Canonical ordination (RDA) shows that the distance-weighted land cover of woodland, heathland and open field explain the highest proportion of the variation in the pollen data. Four different distance-weighting functions, 1, 1/ d, 1/ d 2 and an approximation of the Sugita model of pollen dispersal, are applied to the land-cover data, and the 1/ d function results in the strongest correlation between distance-weighted land cover and pollen proportions. Partial least squares (PLS) calibration is applied, and land cover around nine test sites (not included in the calibration data set) is reconstructed from pollen assemblages. The Extended R-value (ERV) model is applied to the pollen proportions and distance-weighted plant abundance inferred from the maps. Pollen productivity and background components are estimated from the calibration data set and used to reconstruct plant abundance around the test sites. The reconstructed land cover and plant abundance are compared with historical maps, and the performance of the two models is compared. Root-mean-squared errors for the two models are within the same ranges but tend to be slightly lower for the ERV model. Division of the data set into two regional subsets does not improve the reconstructions.

Activity and food choice of piscivorous perch (Perca fluviatilis) in a eutrophic shallow lake: a radio‐telemetry study

SUMMARY 1. Radio transmitters were implanted in large perch (27–37 cm) in a shallow lake in Denmark. Between 6 and 13 perch were tracked every 3 h for 24‐h periods twice (summer) or once a month (winter) from August 1997 to July 1998. Activity levels were recorded as minimum distance moved per hour.2. No significant differences in activity levels of individual fish were observed.3. Highest activities were observed at daytime with peaks at dawn and dusk or midday. This diel pattern was most pronounced from October to April, whereas diel variations were less in the summer months, with no peaks occurring in midsummer. The general lack of activity at night supports the idea that perch is a visually oriented forager.4. There was no significant relationship between daytime activity during the year and temperature or day length, but nighttime activity was correlated with temperature. In contrast with previous findings, activity levels varied little seasonally, except for high activity levels that occurred concomitantly with high temperatures in August. Instead, we found a significant relationship between the total distances moved per day and temperature, indicating that perch moved at the same average speed in the wintertime, but did so for shorter periods than in summer because of shorter day lengths.5. Diet of the tagged perch shifted from fish dominance between August and January to invertebrates from February to June. There was no correlation between the diet shift and activity levels, indicating that feeding on invertebrate requires similar activity levels as predation on fish.6. The results of this telemetry study throughout a year suggest that perch are more active during the winter than previously inferred from gill‐net catches. This observation underscores the importance of perch as a predator of 0+ planktivorous fish in lakes and has potential implications for pelagic food web structure and lake management by biomanipulation.

Changes in the fish community and water quality during seven years of stocking piscivorous fish in a shallow lake

SUMMARY 1. Piscivores (annual stocking of 1000 individuals ha−1 of 0+ pike and a single stocking of 30 kg ha−1 of large 20–30 cm perch) were stocked in seven consecutive years in a shallow eutrophic lake in Denmark. The stocking programme aimed at changing food‐web structure by reducing zooplanktivorous and benthivorous fish, with resultant effects on lower trophic levels and ultimately water quality.2. The fish community and water quality parameters (Secchi depth, concentrations of total phosphorus, chlorophyll a and suspended solids) were monitored between 1996 and 2000 and relationships were evaluated between predatory fish and potential prey and between zooplanktivorous or benthivorous fish and water quality parameters. In addition, potential consumption of piscivorous fishes was calculated.3. The density of fish feeding on larger zooplankton or benthos (roach &gt;15 cm, crucian carp &gt;15 cm) declined distinctly during the study period. This effect was attributed to predation by large (&gt;50 cm) pike. Based on scale readings, we cautiously suggest that the stocking of 0+ pike boosted the adult pike population to produce an unexpected impact in later years. Conversely, no direct impact of stocked 0+ pike was detected on 0+ roach.4. A major decline in the recruitment strength of 0+ roach was observed in 2000. A combination of (i) the indirect effect of large pike preying on adult roach, with negative effect on roach reproduction and (ii) the direct predation effect of 0+ pike and/or 1+ and 2+ perch recruited in the lake, provides the most likely explanation of this phenomenon.5. A marked increase in Secchi depth in 2000 and declining trends in suspended solids, chlorophyll‐a and total phosphorus concentrations were observed. These changes may also be attributable to changes in the fish community, although the relationships were not straightforward.6. This 7‐year study indicates that piscivorous fish may be a significant structuring force in shallow eutrophic lakes, suggesting that stocking piscivores can increase predation pressure on cyprinids. However, the general lack of impact of 0+ pike points to the need of refining current stocking practices in several countries across Europe.

Reconstructing the historical changes in Daphnia mean size and planktivorous fish abundance in lakes from the size of Daphnia ephippia in the sediment

The zooplankton community structure in lakes is highly influenced by size-selective predation by fish, with small zooplankton species dominating at high predation pressure. Remains of cladocerans are preserved in the sediment and may be used to trace historical changes in fish predation. We determined how contemporary data on planktivorous fish were related to the size of Daphnia ephippia (dorsal length) in the surface sediment (0-1 cm) of 52 mainly shallow lakes with contrasting densities of fish and nutrients (TP: 0.002-0.60 mg P l-1). Density of fish expressed as catch per unit effort, in terms of numbers in multiple mesh-sized gill nets (CPUEn), decreased significantly with increasing mean size of ephippia. The relationship was improved by adding TP as an independent variable, now explaining 90% of the variation in CPUEn on the full data set covering lakes in Denmark, Greenland and New Zealand, and 78% if only data on Danish lakes were used. CPUE by weight of planktivorous fish and mean weight of Daphnia in the pelagial during summer were also related to ephippial size. By including contemporary data on established relationships between the sizes of egg-bearing female Daphnia and ephippia, we inferred changes in the CPUEn, mean size of ephippia-bearing Daphnia and summer mean body weight of Daphnia from ephippial size in four lakes during the past 1-2 centuries. In a hypertrophic lake subject to periodic fish kills, Daphnia mean body weight was high and CPUEn was low compared with those in two eutrophic lakes, while CPUEn was low and Daphnia body weight was high in the least eutrophic, clearwater lake. Estimated CPUEn and Daphnia mean weight in the surface sediment of these four lakes corresponded well with contemporary data. Only small changes in ephippial size with time were observed in the clearwater lake and in one of the lakes that had suffered early eutrophication, while major changes occurred in the two other lakes that had been subjected to a major increase in nutrient input or fish kills. We conclude that Daphnia ephippia preserved in the surface sediments of lakes may be a useful and efficient method to quantify the present-day abundance of planktivorous fish and Daphnia mean size. The method is particularly valid in surveys aimed to give a general picture of the fish stock and the ecological state in a set of lakes in a region rather than a precise estimate for a single lake. Though some evidence is provided, more work is needed to evaluate whether the equations are valid for hind-casting in down-core palaeoecological studies.

Development of vegetation and environmental conditions in an oligotrophic Danish lake over 40 years

1. Oligotrophic ‘Lobelia‐lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years.2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today.3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species.4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long‐term changes in nutrient concentration have been difficult to detect.

Confirmation of anatoxin-a(s), in the cyanobacterium Anabaena lemmermannii, as the cause of bird kills in Danish Lakes

Cyanobacterial blooms were implicated in bird kills at lakes in Denmark in July 1993 and June–July 1994. These blooms were dominated by Anabaena lemmermannii and were shown to contain a neurotoxin with anticholinesterase activity. In this study, the toxin was isolated by mouse lethality guided column chromatographies from the field sample collected at Lake Knud sø in 1993. Various spectroscopic data indicated that the toxin was anatoxin-a(s), an irreversible anticholinesterase, first reported in Anabaena flos-aquae. Chemical detection of the same toxin in cultured A. lemmermannii also confirmed this species as the cause of the deaths of the wild birds.

Seasonal distribution and timing of migration of Cormorants Phalacrocorax carbo sinensis breeding in Denmark

The recent expansion of the Cormorant Phalacrocorax carbo population in Europe has led to management conflict throughout Europe, increasing the relevance of describing the migration pattern of each country's breeding population. We use 2279 recoveries and 16 769 resightings of 4735 colour-ringed individuals to describe dispersal and timing of movements of Danish Cormorants. Most Cormorants dispersed from the colonies to coastal areas and freshwater lakes in Denmark, Sweden and northern Germany in July. Southward movements took place throughout July to December. Major departure from the post-breeding areas occurred from August to mid-October, with many birds staging at Dutch and Alpine lakes between September and October, and with arrival in the Mediterranean mainly from October to November. Spring migration was fast, occurring from mid-February to March. First-year birds migrated south faster and reached the wintering areas sooner than adults, but left these later and moved north more slowly than adults. Wintering occurred from Portugal in the west to Greece in the east, and from Denmark in the north to North Africa in the south. The majority of Cormorants spent the winter in Mediterranean France, Italy, Yugoslavia, Albania, Algeria and in particular in Tunisia. Adult males stayed closer to the breeding areas in winter than females, and adults tended to winter further north than first-year birds. Sex differences in body size and advantages of arriving early at the breeding sites may explain why males wintered further north than females.

Parasites in European eelAnguilla Anguilla(L.) from Danish Freshwater, Brackishand Marine Localities

Abstract The parasite fauna of 370 specimens of European eel, Anguilla anguilla(L.), (35–55 cm long) caught in three lakes in Denmark, three brackish localities and in the western Kattegat, was examined. A total of 46 species of parasites were found, the highest number (27) was found in a lake, and the lowest (10) in the western Kattegat. Myxidium giardi and Myxobolus sp. were found at all seven localities. Pseudodactylogyrus anguillae, Diplostomum sp. metacercariae, Bothriocephalus clauiceps, Proteocephalus macrocephalus, Raphidascaris acus, Anguillicola crassus and Ergasilus gibbus were found in both freshwater and brackish localities. Podocotyle atomon, Deropristis inflate, Hemiurus communis, Brachyphallus crenatus, Derogenes varicus, Lecithaster gibbosus, Lecithochinum rufotnride and Cryptocotyle lingua metacercariae occurred in brackish or marine localities. Gyrodactylus spp., tetraphyllidean larvae and Hysterothylacium aduncum occurred in brackish localities. The freshwater dracunculoid nematodes Ph...

A simulation model for phytoplankton growth and nutrient cycling in eutrophic, shallow lakes

A simulation model has been developed for phytoplankton growth and phosphorus and nitrogen cycling in eutrophic, shallow lakes. The model describes a seasonal cycle in a lake which, on a 1-year time scale, is assumed to be in equilibrium with respect to the inputs of nutrients, and forecasts made using the model of the effects of altered inputs predict new future equilibria. The model is rather simple and oriented towards practical applications. It is intended to describe average conditions only and the time scale resolution is of the order of several days. The model has been used to simulate 12 different lakes in Denmark, some of which have been described by two or more boxes. Most parameter values in the model were common to all simulations, while a few key parameters were allowed to vary somewhat from lake to lake. These parameters, however, could generally be chosen within quite a narrow range and if deviations from this range were necessary a qualitative explanation could usually be given. For lakes with short hydraulic retention times the simulations generally gave reasonably good results, and forecasts made with the model were in qualitative agreement with “educated guesses”. The paper describes the concepts and the structure of the model. Further, parameter values and selected numerical results, such as annual primary production, are listed for all simulations performed. Finally, a few examples are discussed in more detail.

WORLDWIDE DISTRIBUTION AND ECOLOGY OF EURYCERCUS AND SAYCIA (CLADOCERA)1

The two species of Eurycercus are largely allopatric in the Northern Hemisphere, glacialis tending to be peripheral in distribution in the far north, occurring only as far south as 51‐52° N in the outer Aleutians, Labrador, and the northern Kuriles. There are vigorous disjunct populations of unknown history in oligotrophic heath and dune localities in Denmark and the Netherlands. The center of distribution is Greenland–Iceland. Eurycercus lamellatus is widely distributed over much of continental North America south to Mexico City and over much of Eurasia south to Algeria and southern Tibet. It also is known from farther north than glacialis. It is the only species occupying the large mountain masses of the Northern Hemisphere, where glacialis might be expected to occur. The center of distribution seems to be western Europe. Co‐occurrence of the two species in the same water bodies is known only for a few scattered lakes in Denmark, northern Sweden, Iceland, and Alaska.Eurycercus lamellatus also occurs as disjunct populations in Argentina and South Africa, but not at comparable latitudes in Australia and New Zealand. Here, Saycia cooki occurs, which might be considered an ecological equivalent of E. lamellatus except that it is confined to temporary water bodies.The finding of three males of Saycia from Australia—the first males ever recorded— stimulated a detailed study of the morphology of the species and a comparison with Eurycercus. Retention of the two genera in separate subfamilies seems justified. The male of Saycia is unique among chydorid Cladocera in having a plumose sexual seta on the antennule and in having the postabdominal claw spatulate at the tip. The sperm ducts open near the tip of the postabdomen, rather than at the base as in Eurycercus, the latter condition being unique among the chydorids.Saycia from New Zealand differs from the population in Australia chiefly in having more preanal teeth on the postabdomen and in being higher and having a shorter posterior margin relative to length of the animal. All these characters change with size. These regressions are presented and their significance discussed. The New Zealand population has been designated a new geographic subspecies, pending the eventual recovery of males.The number of postabdominal teeth in E. lamellatus increases with increasing size, making it likely that the species described as E. polyodontus merely represents individuals from the upper end of this regression. The number of teeth in E. glacialis is smaller than in lamellatus and does not increase with size of animal. The variability of tooth number within each species is so great that the number 100 proposed in the past cannot be used to separate the two species with any reliability. Similarly, the subspecies of Saycia from New Zealand has a larger tooth number, which shows a marked increase with size of animal, than that from Australia.