Rocco Tiberti

The use of invertebrates as indicators of environmental change in alpine rivers and lakes.

In alpine regions climatic change will alter the balance between water sources (rainfall, ice-melt, snowmelt, and groundwater) for aquatic systems, particularly modifying the relative contributions of meltwater, groundwater and rain to both rivers and lakes. While these changes are expected to have implications for alpine aquatic ecosystems, little is known about potential ecological tipping points and associated indicator taxa. We examined changes in biotic communities along a gradient of glacier influence for two study systems: (1) a stream network in the French Pyrénées; and (2) a network of lakes in the Italian Alps, with the aim of identifying potential indicator taxa (macroinvertebrates and zooplankton) of glacier retreat in these environments. To assess parallels in biotic responses across streams and lakes, both primary data and findings from other publications were synthesised. Using TITAN (Threshold Indicator Taxa ANalysis) changes in community composition of river taxa were identified at thresholds of <5.1% glacier cover and <66.6% meltwater contribution. Below these thresholds the loss of cold stenothermic benthic invertebrate taxa, Diamesa spp. and the Pyrenean endemic Rhyacophila angelieri was apparent. Some generalist taxa including Protonemura sp., Perla grandis, Baetis alpinus, Rhithrogena loyolaea and Microspectra sp. increased when glacier cover was <2.7% and <52% meltwater. Patterns were not as distinct for the alpine lakes, due to fewer sampling sites; however, Daphnia longispina grp. and the benthic invertebrate groups Plectopera and Planaria were identified as potential indicator taxa. While further work is required to assess potential indicator taxa for alpine lake systems, findings from alpine river systems were consistent between methods for assessing glacier influence (meltwater contribution/glacier cover). Hence, it is clear that TITAN could become a useful management tool, enabling: (i) the identification of taxa particularly sensitive to glacier retreat; and (ii) conservation efforts/resources to be better directed in alpine aquatic systems.

Ecological impact of introduced fish in high altitude lakes: a case of study from the European Alps

Fish introduction is a major threat to alpine lake biota leading to the loss of native species and to the degeneration of natural food-webs. This study provides an extensive investigation on the impact of the introduced fish Salvelinus fontinalis on the native communities of alpine lakes in the Gran Paradiso National Park. We compared the macroinvertebrate and zooplankton communities of six stocked and nine fishless lakes with a repeated sampling approach during the summers 2006–2009. The impact of fish presence on alpine lake fauna is often mediated by the strong seasonality governing these ecosystems, and it dramatically affects the faunal assemblage of littoral macroinvertebrates and the size, structure, and composition of the pelagic zooplankton community with a strong selective predation of the more visible taxa. Direct ecological impacts include a decrease or extinction of non-burrower macroinvertebrates and of large zooplankton species, while small zooplankton species and burrower macroinvertebrates were indirectly advantaged by fish presence. Due to the existence of a compensation between rotifers and crustaceans, fish presence does not affect total zooplankton biomass and diversity even if fish are a factor of ecological exclusion for large crustaceans. These compensatory mechanisms are a key process surrounding the impact of introduced fish in alpine lakes.

Impact of introduced fish on Common frog (Rana temporaria) close to its altitudinal limit in alpine lakes

Alien fish species have been introduced into naturally fishless mountain lakes worldwide, with negative consequences for native fauna. This study describes the impact of introduced Brook trout (Salvelinus fontinalis) on Common frog (Rana temporaria) in the Gran Paradiso National Park (Western Italian Alps). We conducted an extensive, six years long (2006-2011) monitoring campaign over 12 fishless and 8 stocked lakes, close to the new altitudinal limit of R. temporaria (2811 m a.s.l.). This new altitudinal limit is reported for the first time in this study. The presence of introduced fish was a factor of ecological exclusion, negatively affecting the presence of frogs and compromising the suitability of alpine lakes as breeding sites. These results are likely to depend on larval predation or to selective avoidance of stocked lakes by R. temporaria. Eradication of introduced fish is proposed as a conservation measure to recover amphibian populations in alpine lake ecosystems.

Does the fish presence influence the diurnal vertical distribution of zooplankton in high transparency lakes

The avoidance of visually feeding fish has long been considered as the primary driver of diel vertical migration of zooplankton. The diurnal vertical distribution of Cyclops gr. abyssorum, Arctodiaptomus alpinus, and Daphnia gr. longispina from 13 alpine lakes with fish (Salvelinus fontinalis) and without, was compared in order to understand whether fish in transparent lakes reduce the presence of large zooplankton from the irradiated zone. We used the light level at each sampling depth and the size of each specimen as proxies of predation risk, and we tested two predictions: (P1) the relative abundance of zooplankton in the well-lit surface waters vs. the darker waters will be greater in fishless lakes; (P2) the size of zooplankton in the well-lit surface waters vs. the deeper, darker waters will be greater in fishless lakes. We did not find any evidence of the validity of P1, but we confirmed P2 for Arctodiaptomus alpinus. These results support with new field data the Transparency Regulator Hypothesis, which argues that in transparent lakes, fish predation is less important for the vertical distribution of zooplankton than ultraviolet radiation, and further suggest that zooplankton size rather than vertical distribution may be more effective against visual predators in transparent lakes.

Evidences of zooplankton vertical migration in stocked and never-stocked alpine lakes in Gran Paradiso National Park (Italy)

Zooplankton vertical migration was described in four high altitude lakes in Gran Paradiso National Park (Northern Italy) during 2008 summertime. The authors succeeded in describing the vertical distribution of 6 species: diel vertical migrations were observed in the case of adult crustacean species (Cyclops gr. abyssorum, Arctodiaptomus alpinus and Daphnia gr. longispina), whereas the remaining rotifer species (Keratella quadrata, Polyarthra gr. dolichoptera and Synchaeta gr. stylata-pectinata) and naupliar stages of copepods did not undergo migrations. Migratory behavior of Daphnia gr. longispina and Cyclops gr. abyssorum was influenced by the size of individuals, especially larger individuals use to migrate deeper during the day compared to the smaller conspecific. This study provides new evidences of zooplankton vertical migration in never-stocked lakes and highlights the need to consider the zooplankton migration as result of multiple causal factors.

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

Abstract 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.

Why Should We Preserve Fishless High Mountain Lakes

High mountain lakes are originally fishless, although many have had introductions of non-native fish species, predominantly trout, and recently also minnows introduced by fishermen that use them as live bait. The extent of these introductions is general and substantial often involving many lakes over mountain ranges. Predation on native fauna by introduced fish involves profound ecological changes since fish occupy a higher trophic level that was previously inexistent. Fish predation produces a drastic reduction or elimination of autochthonous animal groups, such as amphibians and large macroinvertebrates in the littoral, and crustaceans in the plankton. These strong effects raise concerns for the conservation of high mountain lakes. In terms of individual species, those adapted to live in larger lakes have suffered a higher decrease in the size of their metapopulation. This ecological problem is discussed from a European perspective providing examples from two study areas: the Pyrenees and the Western Italian Alps. Species-specific studies are urgently needed to evaluate the conservation status of the more impacted species, together with conservation measures at continental and regional scales, through regulation, and at local scale, through restoration actions, aimed to stop further invasive species expansions and to restore the present situation. At different high mountain areas of the world, there have been restoration projects aiming to return lakes to their native fish-free status. In these areas autochthonous species that disappeared with the introduction of fish are progressively recovering their initial distribution when nearby fish-free lakes and ponds are available.

Changes in the insect emergence at the water–air interface in response to fish density manipulation in high altitude lakes

Emerging insects are important nutrient vectors for lake-to-land linkages, but they are affected by fish predation. We manipulated the fish density in four high altitude lakes in connection with a brook trout eradication project. We used a paired benthic and surface funnel trap design to test whether fish density affects abundance, size, and proportion of aquatic insects reaching the surface in the pelagic zone. The study was complemented with benthic macroinvertebrates and fish diet data. Due to sample size, we focused on midge pupae, which rely on water surface tension (water–air interface) to emerge. Conspicuous insects emerging along the shoreline (water–land interface) were rarely collected in the traps, even if they rapidly recovered through the eradication. There was a positive relationship between fish density and midge abundance, and negative relationship for size and proportion reaching the surface. The increase in the emergence of midges in the presence of fish supports several other studies, but we have provided evidence that this pattern exists in conjunction with a size reduction even when fish consume a substantial amount of midges. The inclusion of small Diptera emergence at the water–air interface is a likely keystone in understanding fish impact on insect subsidy.

Widespread bacterial infection affecting Rana temporaria tadpoles in mountain areas

Periodic mass die-offs of Rana temporaria tadpole populations have occurred in the ponds of prealpine mountain areas of Brescia (northern Italy) since the early 2000s. The author reports some observational data and analytical results from three sites: tadpoles from mortality events had erythema, especially on the legs, suggestive of septicemia. Bacterial culture of these tadpoles revealed Aeromonas hydrophila and Aeromonas sobria , two organisms often associated with Red leg disease. Egg mass counts from 29 pastureland ponds did not revealed breeding activity declines over five years in the Monte Guglielmo area. Aeromonas hydrophila and Aeromonas sobria usually behave as opportunistic bacteria that can become pathogenic after suppression of the immune system by endogenous or exogenous stressors. Thus, a plurality of environmental factors may contribute to mortality events; some of them are discussed, including loss of high altitude breeding ponds resulting in overcrowding and poor water quality in remaining ponds and the presence of other pathogens.