Fishless Alpine Lakes Research Articles

Disentangling effects of droughts and heatwaves on alpine periphyton communities: A mesocosm experiment

AbstractThe accelerating rate of global climate change at higher elevations and latitudes is increasing the potential for extreme climatic events. Here, a knowledge gap exists in how the order of exposure to, and duration of droughts and heatwaves affect their cumulative impact on aquatic communities. We tested experimentally for the legacy effects of simultaneous vs. sequential exposures to drought and heatwave on sediment‐dwelling algal communities (epipelon) from small fishless alpine lakes. In both simultaneous, and sequential exposure treatments involving drought followed by a heatwave, the negative effect of drought masked the effects of warming on chlorophyll‐inferred algal biomass and taxonomic composition. Reversal of order of exposure (i.e., heatwave followed by drought) lowered their cumulative effect on community structure. These findings highlight the potential for drought events to dominate over heatwaves in altering shallow littoral ecosystems at high elevations under a rapidly warming climate.

Contrasting resistance and resilience trajectories of zooplankton communities in restored fishless alpine lakes

AbstractCatastrophic state changes often occur in ecosystems as consequences of shifts in the dominant life forms, such as in the case of sportfish introduction into naturally fishless mountain lakes. While the pronounced ecological displacement of native communities by these novel predators (i.e., weak resistance) is well documented, few studies have also examined the dynamics of their recovery rates (i.e., “engineering resilience”) following stressor removal. We addressed this knowledge gap by quantifying the taxonomic and species trait‐based ordination trajectories of crustacean zooplankton communities in stocked alpine lakes, which differed in how they were restored to a natural fishless state over a period of six decades. Resilience and resistance trajectories differed in each lake as the ecological importance of trait‐based species recolonization potential (e.g., asexual vs. sexual reproduction) replaced that of tolerance of size‐selective predation by fish (e.g., body size, pigmentation, motility). As a result, re‐establishment of large‐bodied zooplankton following the elimination of fish restored annual secondary production. In contrast, a more gradual unidirectional ordination trajectory toward smaller zooplankton body size and a decline in total zooplankton biomass occurred in a nearby alpine lake containing a protected native bull trout population. Although recovery trajectories returned via routes that differed from those of earlier resistance trajectories (i.e., hysteresis), we discovered that full taxonomic and functional recovery was realized in all the restored fishless lakes within three decades, regardless of the approach used to achieve ecosystem restoration.

Consequences of Fish Introduction in Fishless Alpine Lakes: Preliminary Notes from a Sanitary Point of View

Consequences of Fish Introduction in Fishless Alpine Lakes: Preliminary Notes from a Sanitary Point of View

A Functional Approach to Zooplankton Communities in Mountain Lakes Stocked With Non‐Native Sportfish Under a Changing Climate

AbstractCumulative impacts of multiple stressors on freshwater biodiversity and ecosystem function likely increase with elevation, thereby possibly placing alpine communities at greatest risk. Here, consideration of species traits enables stressor effects on taxonomic composition to be translated into potential functional impacts. We analyzed data for 47 taxa across 137 mountain lakes and ponds spanning large latitudinal (491 km) and elevational (1,399 m) gradients in western Canada, to assess regional and local factors of the taxonomic composition and functional structure of zooplankton communities. Multivariate community analyses revealed that small body size, clonal reproduction via parthenogenesis, and lack of pigmentation were species traits associated with both introduced non‐native sportfish and also environmental conditions reflecting a warmer and drier climate—namely higher water temperatures, shallower water depths, and more chemically concentrated water. Thus, historical introductions of sportfish appear to have potentially induced greater tolerance in zooplankton communities of future climatic warming, especially in previously fishless alpine lakes. Although alpine lake communities occupied a relatively small functional space (i.e., low functional diversity), they were contained within the broader regional functional structure. Therefore, our findings point to the importance of dispersal by lower montane species to the future functional stability of alpine communities.

Spatial distribution of introduced brook trout Salvelinus fontinalis (Salmonidae) within alpine lakes: evidences from a fish eradication campaign

Brook trout Salvelinus fontinalis have been used worldwide to stock fishless alpine lakes, negatively affecting native biota. Understanding its spatial ecology in invaded ecosystems can provide information to interpret and contrast its ecological impact. We opportunistically used capture points of brook trout gillnetted during an eradication campaign to assess the distribution patterns of four unexploited populations inhabiting high-altitude lakes. The main eradication method implies the use of many gillnets with several mesh sizes, which are selective for different fish sizes. For each lake we drew six capture maps associated with as many different mesh sizes, and we tested whether the distance from the coastline (which in alpine lakes is a reliable proxy of the most important spatial gradients, e.g. depth, temperature, prey availability, lighting conditions) influences the proportion of captured fish belonging to different size classes and the number of fish captured by the nets with different mesh sizes. To interpret the results, we also provide a cartographic description of the lakes’ bathymetry and littoral microhabitats. We found (1) a negative relationship between brook trout distribution and the distance from the coastline in all of the size classes, lakes and mesh sizes; (2) that large brook trout can thrive in the lakes’ center, while small ones are limited to the littoral areas; and (3) that the distance from the coastline alone cannot explain all the differences in the catch densities in different parts of the lakes. As in their native range, introduced brook trout populations also have littoral habits. Microhabitats, prey availability and distance from the spawning ground are other likely factors determining the distribution patterns of brook trout populations introduced in alpine lakes. The obtained results also provide useful information on how to plan new eradication campaigns.

Cloud cover does not clearly affect the diurnal vertical distribution of crustacean zooplankton in naturally fishless alpine lakes

The diurnal vertical distribution of zooplankton have been compared on a sunny and on a cloudy day in two shallow, oligotrophic and fishless alpine lakes, exploring the role of cloud cover in shaping zooplankton movements. UV ray avoidance is considered the ultimate reason for zooplankton vertical migration in the lakes, which are naturally devoid of zooplanktivorous fish. Thus, as a thick cloud cover reduces the visible and UV radiation, a shallower diurnal distribution was expected on cloudy days, since migrant zooplankton should balance the amplitude of migration with the light intensity. However, we found very little field evidence that zooplankton change their vertical distribution according to daytime light conditions.

Mitochondrial sequences do not support the independent taxonomic position of the extinct Alpine newt subspecies Mesotriton alpestris lacusnigri

Abstract Mesotriton alpestris lacusnigri is regarded as being an extinct subspecies of the Alpine newt endemic to a small fishless alpine lake called Črno jezero (Black Lake) in the Julian Alps in Slovenia. To re-assess its taxonomic position we sequenced fragments of two mitochondrial genes (309 bp of cytochrome b and 315 bp of 16S rRNA) of two museum specimens collected in 1953. Specimens of the ssp. lacusnigri yielded two new haplotypes which formed a monophyletic group within a cluster of other Slovenian and central European haplotypes of ssp. alpestis. The name lacusnigri is therefore merely a junior synonym of the nominotypical subspecies and should be removed from red data listing. Our study highlights the outstanding value of natural history collections as baselines for contemporary biodiversity assessments.

Bacterial grazing by mixotrophic flagellates and Daphnia longispina: a comparison in a fishless alpine lake

We compared the bacterivory of mixotrophic flagellates (MxFl) and of Daphnia longispina in a fishless high altitude lake with a simple food web. During the ice-free period of Lago Paione Superiore (LPS, Italian Central Alps) we measured species-specific direct uptake of fluores- cently labelled bacteria (FLB) by MxFl and D. longispina. Bacterial production of DNA and protein and dissolved organic carbon (DOC) were also measured. Between ice melt and September, the most common groups of MxFl in the lake were Gymnodinium spp., Dinobryon sertularia, Chromulina spp. and Ochromonas sp. On average they ingested 2.9, 3.7, 9.3 and 14.6 bacterial cells ind. -1 h -1 , respec- tively, whereas D. longispina ingested 1.9 × 10 6 bacterial cells ind. -1 h -1 . The MxFl community inges- tion rate was always higher than the rate of D. longispina, except in mid August when the D. longispina population ingested 2.4 times more bacteria than MxFl. Rates of MxFl and D. longispina grazing did not show any significant correlation with bacterial abundance and biomass (ρ Spearman, p > 0.05), but a significant correlation was found between MxFl grazing and thymidine uptake at 9 m (ρ Spearman = 0.821, p < 0.014, xy pairs = 7). It appears that D. longispina actively feeds on bacteria when it first appears in the lake, but that overall the D. longispina population had a lesser impact on bacteria than did MxFl.

Shallow males, deep females: sex‐biased differences in habitat distribution of the freshwater calanoid copepod Arctodiaptomus alpinus

In a small, circular high‐altitude karst lake situated in the northeastern calcareous Alps of Austria the copepod Arctodiaptomus alpinus (Imhof) develops each spring from resting eggs after the lake basin fills in early spring. After mid‐summer, late developmental stages and adults concentrate in a thin layer near the sediment throughout the lake basin. During daytime an average 86% and 71% of female and male copepods respectively resided near the bottom. Males exhibited stronger diel vertical migrations than females and part of the population concentrated in near‐surface water at night, but the majority of copepods remained at the sediment during darkness. Macro‐photographs and core samples revealed that the proportion of epibenthic male A. alpinus decreased constantly from &gt;70% in 3 m depth to &lt;20% below the 8‐m isobath. The proportion of ovigerous females increased with depth, whereas non‐ovigerous females were comparatively more abundant in shallow water. Concurrently the highest frequencies of copulating copepods were detected in areas of high male density. Above the 3‐m isobath male A. alpinus formed dense swarms in scattered patches of the macrophyte Ranunculus eradicatus (&gt;93% males; maximum abundance: 362 600 individuals m−2). Adults and larvae of the alpine newt Triturus alpestris are the top predators in this fishless alpine lake, and A. alpinus constitutes a major component of their diet. However, predator densities and different predation rates on male and female copepods were not sufficient to explain the observed horizontal distribution of A. alpinus. We argue that the optimization of successful sexual encounters in copepods is the ultimate driving force behind this segregation of both sexes of A. alpinus (‘mate encounter hypothesis’).

Biological Pollutants: Alien Fishes in Mountain Lakes

Many lakes in the national parks of the Canadian Rockies were stocked with alien fish species in the early to mid 20th century. Changes to Parks Canada's mandate require the original communities of these lakes to be restored. We document the changes to invertebrate communities caused by the stocking of alien fishes into three fishless alpine lakes, and describe the results of two restoration experiments, one the reintroduction of Hesperodiaptomus arcticus, a planktonic predator that had been eliminated from Snowflake Lake by stocked fish, and the other the removal of brook trout (Salvelinus fontinalis) from Bighorn Lake. In both cases, there were great changes to the zooplankton communities, which required several years to complete, probably because of the cold water and unproductive nature of the lakes. Many of the invertebrate species extirpated by stocked alien fishes co-exist with native fish species in nearby lakes. Possible reasons are discussed.

Resistance and Resilience

ECOLOGY The “resistance” of an ecosystem to a perturbation, such as the introduction of an alien species, is a measure of how much the system changes. Its “resilience” is the extent to which it can recover after the source of change is removed. Knapp et al. have studied the effects of fish introductions and removals on the biota of hundreds of naturally fishless alpine lakes in western North America. The resistance of the lake faunal assemblages to trout stocking was low; the abundance of amphibians and larger invertebrates decreased dramatically, whereas the abundance of smaller planktonic invertebrates often increased. More surprisingly, the resilience of the lakes turned out to be high. In lakes where trout stocking ceased and where there was no suitable trout spawning habitat, the animal assemblages recovered to compositions characteristic of undisturbed lakes, depending on the length of fish occupancy. Thus, further fish removals may be required to protect the fauna of alpine lakes in U.S. national parks and forest wilderness areas, most of which still contain trout. — AMS Ecol. Monogr. 71 , 401 (2001).

The Effects of Stocking and Removal of a Nonnative Salmonid on the Plankton of an Alpine Lake

Bighorn Lake, a fishless alpine lake, was stocked with nonnative brook trout, Salvelinus fontinalis, in 1965 and 1966. The newly introduced trout rapidly eliminated the large crustaceans Hesperodiaptomus arcticus and Daphnia middendorffiana from the plankton. In July 1997, we began to remove the fish using gill nets. The population comprised 261 fish that averaged 214 g in wet weight and 273 mm in fork length. Thereafter, zooplankton abundance increased within weeks. Early increases were caused by the maturation of Diacyclops bicuspidatus, few of which reached copepodid stages before the removal of the fish because of fish predation. Daphnia middendorffiana, absent when fish were present, reappeared in 1998. Hesperodiaptomus arcticus, which had been eliminated by the stocked fish, did not return. The proportion of large zooplankton increased after fish removal, but their overall biomass did not change. Algal biomass was low and variable throughout the 1990s and correlated with water temperature but not with nutrient concentrations or grazer densities. Diatoms were the most abundant algal taxon in the lake, followed by Dinophyceae. Chrysophyceans and cryptophyceans were eliminated after the fish were removed. Chlorophyll a concentrations were unaffected. Gill netting is a viable fish eradication technique for smaller (less than 10 ha), shallow (less than 10 m deep) lakes that lack habitable inflows and outflows or other sensitive species. Further work is required to define appropriate removal methods for larger lakes and watersheds.

Contribution of Gammarus lacustris to phosphorus recycling in a fishless alpine lake

We estimated the net P transport by Gammarus lacustris from the benthic to pelagic regions of a fishless alpine lake and compared it with P regeneration by the entire plankton community. Gammarus lacustris released between 5.2 and 18.1 ng P·L-1·h-1 (adults only and adults plus immatures, respectively) in the pelagic region during nighttime vertical migration. Additional P released into and removed from the water column due to predation on zooplankton was estimated at 1.87 and 2.3 ng P·L-1·h-1, respectively. The net daily regeneration of 52.2-181.4 ng P·L-1·day-1 by the G. lacustris population represented 9.5-32.9% of the total P regenerated by the planktonic community. The majority of the P released by G. lacustris represents "new" P to the pelagic zone because it originated in sediments. We conclude that G. lacustris can represent an important link in benthic-pelagic coupling in oligotrophic mountain lakes.

Effects ofGammarus lacustris(Crustacea: Amphipoda) on plankton community structure in an alpine lake

The amphipod Gammarus lacustris is generally considered as a herbivore or a detritivorous scavenger, but we and others have observed it preying on pelagic zooplankton in fishless alpine lakes of the Canadian Rockies. We tested the hypothesis that G. lacustris predation alters the plankton community structure of alpine lakes by manipulating G. lacustris density in large (2800 L) in situ enclosure experiments. Compared with control enclosures (no Gammarus), Daphnia middendorffiana abundance was reduced 49, 85, and 100% in the low, medium, and high (40, 200, and 400 individuals·m-2) Gammarus density enclosures, respectively. Hesperodiaptomus arcticus density was not significantly related to G. lacustris density. Comparison of mesocosm results with lake data showed that G. lacustris predation on D. middendorffiana in the lake was lower, possibly because a pelagic deepwater refugium allows Daphnia to escape predation. The results show that G. lacustris predation can affect the plankton community structure in small fishless alpine lakes.

Restoration of the food web of an alpine lake following fish stocking

Trout stocking in the mid‐1960s eliminated the calanoid copepod Hesperodiaptomus arcticus and other large‐bodied crustaceans such as Gammarus lacustris, Daphnia middendorffiana, and Daphnia pulex from many alpine lakes in the Rocky Mountain Parks of Canada. H. arcticus frequently dominates the plankton communities of fishless lakes, preying on rotifers and nauplius larvae. Following the extirpation of H. arcticus, rotifers and small‐bodied cyclopoid copepods dominate the zooplankton assemblages of alpine lakes.We studied the zooplankton community of Snowflake Lake, Banff National Park, from 1966 to 1995. H. arcticus was eliminated following stocking of the lake with trout in the 1960s. It failed to become reestablished after the disappearance of the fish population in the mid‐1980s. Several species of rotifers and small‐bodied crustaceans, species originally rare or absent from the plankton, became abundant following fish stocking and remained so after the fish population declined.In 1992, we reintroduced H. arcticus to Snowflake Lake. The H. arcticus population grew exponentially for 4 yr, but had not reached stable densities typical of unmanipulated alpine lakes by 1995. By 1994, however, even the small population of Hesperodiaptomus was beginning to suppress populations of rotifers, copepod nauplii, and large diatoms. Because H. arcticus is omnivorous, a simple model of cascading trophic interactions did not predict the outcome of trophic manipulations in this alpine lake.

Direct and indirect effects of predation by a calanoid copepod (subgenus: Hesperodiaptomus) and of nytrients in a fishless alpine lake

The calanoid copepod Diaptomus (subgenus: Hesperodiaptomus) arcticus is a keystone predator in fishless alpine lakes of the Canadian Rockies. We quantified the effects of predation by D. arcticus on other copepods, rotifers, and algae in large mesocosm experiments (2250 L) using two levels of predator (present and absent) and two levels of nutrient addition (ambient and 4×). Standing stocks of algal taxa were assessed by high performance liquid chromatography of phytoplankton pigments. Diaptomus arcticus suppressed the biomass of rotifers and cyclopoid nauplii at both nutrient levels. The indirect effect of D. arcticus on algal biomass was minimal under ambient nutrient conditions, possibly owing to high rates of nutrient recycling by grazers. Biomass of algae, cyclopoid nauplii, and rotifers responded positively to nutrient additions. Nutrient addition increased algal standing crop 2- to 4-fold and changed dominance from diatoms and chrysophytes to blue-green algae. Diaptomus arcticus accelerated these changes, possibly by eliminating grazing by rotifers. These results suggest that in the absence of increased nutrients D. arcticus directly limits the biomass of herbivorous zooplankton but the indirect effect on phytoplankton is minimal.

Fossil Pigment Records of Phytoplankton in Trout-stocked Alpine Lakes

Paleolimnology, bioenergetics modelling, and mesocosm experiments were used to quantify changes in phytoplankton following introduction of trout into fishless alpine lakes in the Canadian Rocky Mountains. During the 1960s, Snowflake and Pipit lakes were stocked with brook (Salvelinus fontinalis), cutthroat (Oncorhynchus clarkii) and rainbow trout (O. mykiss) either singly or in combination. Stocked trout eliminated large invertebrates (Daphnia spp., Hesperodiaptomus arcticus, Gamrnarus lacustris), but the fish died within 15 yr. High performance liquid chromatographic analysis of carotenoids and chlorophylls in sediments inferred that algal abundance increased 4- to 10-fold shortly after fish stocking. In contrast, phytoplankton composition and biomass were constant in nearby, unstocked Harrison Lake, as inferred from fossils. Pigment analysis of mesocosms showed that phytoplankton were sensitive to moderate fertilization: 11 μg P∙L−1resulted in four- to six-fold increases in algal biomass. Bioenergetics modelling was used to estimate phosphorus (P) excretion from trout. The flux of excreted P was highly correlated (r2 = 0.76, p &lt; 0.0001, N = 12) to changes in algal biomass, as estimated from fossil pheophytin b. Consequently, we infer that nutrient recycling by stocked trout was one of several mechanisms that contributed to increased algal biomass.