Stoll, Stefan
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Cross-realm assessment of climate change impacts on species' abundance trends
Climate change, land-use change, pollution and exploitation are among the main drivers of species' population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species' population trends to species- and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species' abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.
Three different patterns of how low-intensity waves can affect the energy budget of littoral fish : a mesocosm study
In a mesocosm study, somatic and otolith growth of six types of juvenile cyprinids differing in body size and body shape were studied in a low-intensity wave treatment and a no-wave control. Depending on fish type, somatic growth was either reduced by up to 60% or increased by up to 50% following exposure to the wave treatment. Somatic growth and otolith daily increment width (ODIW), the latter being used as a proxy for the fish energy turnover, were compared to reveal the effects of waves on the energy budget of the fish. Three different reaction types to waves, which correlated to the body morphology of the six fish groups, could be distinguished. Small and fusiform fish benefitted from low-intensity waves and showed higher somatic growth rates and greater ODIW in the wave treatment. In small, deep-bodied fish, growth and ODIW were reduced by waves. Finally, in larger fish with either a fusiform or deep-bodied shape, ODIW was decoupled from somatic growth, with larger ODIW in waves, but reduced somatic growth. These results show that low-intensity hydrodynamic stress is a much more important and complex habitat factor than previously assumed. It is concluded that hydrodynamic stress by waves should be accounted for in bioenergetic models and studies on habitat choice in littoral fish species.
Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakes
Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes.
Spawning site selection by Eurasian perch (Perca fluviatilis L.) in relation to temperature and wave exposure
The selection of spawning depth by Eurasian perch Perca fluviatilis was investigated in an experiment using artificial substrata in Lake Constance during the spawning season of 2007. The experiment compared spawning behaviour at substrata between 0.5 and 15 m depth at two sites exposed to different regimes of ship-generated wave action. The total abundance of egg ribbons did not differ significantly between the two sites, but the preferred spawning depth was deeper at the wave exposed site (5 m) compared to the sheltered site (2 m). While water temperatures could not account for the observations, differences in wave exposure may explain the different spawning depth preferences. At both sites, large egg ribbons were generally found in deeper water, and large egg ribbons occurred more frequently at the sheltered site. Because the egg ribbons of perch are likely to have a size-dependent susceptibility to hydrodynamic stress, large females may be expected to select deeper spawning locations where the effects of surface waves are considerably attenuated.
Complex interactions between pre-spawning water level increase, trophic state and spawning stock biomass determine year-class strength in a shallow-water-spawning fish
Pre spawning water level increase (PWLI) is a recently discovered parameter of water level dynamics affecting juvenile year class strength (YCS) in shallow water spawning fish. By analysing a time series of commercial common bream (Abramis brama) yields in Lake Constance from 1950 through 2007, this study showed that the differences in juvenile YCS are conserved until the adult life stage. Adult YCS was best explained by complex interactions of PWLI with both stock intrinsic and extrinsic environmental variables. The correlation between PWLI and YCS of adult bream became more pronounced as the trophic state of the lake increased. It is argued that this mediator effect of the trophic state results from increased growth of the algal biofilms during high trophic state periods. These biofilms are known to impair safe attachment of the eggs to the substratum and affect mortality rates of the eggs. Furthermore, reproductive stock size exhibited a positive effect on the resulting YCS. However, a marginally significant interaction between reproductive stock size and PWLI indicates that the two positive effects of PWLI and reproductive stock size on YCS were not fully additive, probably because the very large year classes resulting from the combined positive effects suffered from strong intra specific competition. This study demonstrates that anthropogenic water level regulation, e.g. for flood protection or for the generation of hydroelectric power, and climate change altering PWLI have the potential to affect YCS throughout the whole life cycle of bream, particularly in eutrophic water bodies. Similar effects of PWLI are anticipated in other shallow water spawning species.
Post-release stranding rates of stocked allis shad (Alosa alosa) larvae exposed to surface wave action
The objectives of the present study were to test the effects of sudden wave action caused by ships on newly released larval shad thriving along shallow river beaches because heavy shipping traffic has developed in many shad river systems. Experiments were conducted in a wave tank simulating a crosssection of the river shore. Up to 17% of the one week old allis shad stranded within the first 7 h after their release, but with increasing age of the released larvae, stranding rates decreased. Stranding rates were always highest directly after the release of fish and decreased throughout the experimental period of 7 h. The stranding rates were further influenced by weather, with higher stranding rates when it was sunny and when water temperatures were low. These results can be used to improve release strategies and stocking procedures of shad larvae and may probably be applied to other larval fish species as well.
A mesocosm experiment investigating the effects of substratum quality and wave exposure on the survival of fish eggs
In a mesocosm experiment, the attachment of bream (Abramis brama) eggs to spawning substrata with and without periphytic biofilm coverage and their subsequent survival with and without low-intensity wave exposure were investigated. Egg attachment was reduced by 73% on spawning substrata with a natural periphytic biofilm, compared to clean substrata. Overall, this initial difference in egg numbers persisted until hatching. The difference in egg numbers was even increased in the wave treatment, while it was reduced in the no-wave control treatment. Exposure to a low-intensity wave regime affected egg development between the two biofilm treatments differently. Waves enhanced egg survival on substrata without a biofilm but reduced the survival of eggs on substrata with biofilm coverage. In the treatment combining biofilm-covered substrata and waves, no attached eggs survived until hatching. In all treatments, more than 75% of the eggs became detached from the spawning substrata during the egg incubation period, and
Larval fish in troubled waters - is the behavioural response of larval fish to hydrodynamic impacts active or passive?
In a mesocosm experiment, we tested whether larval fish show an active behavioural response to hydrodynamic impacts. Exposing 1- to 3-week-old allis shad (Alosa alosa) larvae to a pulsed wave regime, we found that already 1-weekold larvae immediately adapt their microhabitat use and activity patterns at the onset of the wave pulses. The fish larvae instantaneously increased their activity level and moved downwards, concentrating in the calmer lower third of the water column. Within 4 min after the end of the wave pulse, the fish returned to their former distribution. Two- and 3-week-old fish larvae foraged close to the bottom substratum during calm periods but avoided this zone during the wave pulses. Thus, larval fish show an active response to hydrodynamic impacts. With the ability to adjust microhabitat use and activity level, already fish larvae are able to trade costs and benefits associated with spatio-temporal hydrodynamic heterogeneity. In particular, fish larvae should be able to minimize some of the harmful effects of navigation-induced waves where calmer evasion habitats are available.
Waves affect predator–prey interactions between fish and benthic invertebrates
Little is known about the effects of waves on predator–prey interactions in the littoral zones of freshwaters. We conducted a set of mesocosm experiments to study the differential effects of ship- and wind-induced waves on the foraging success of littoral fish on benthic invertebrates. Experiments were conducted in a wave tank with amphipods (Gammarus roeseli) as prey, and age-0 bream (Abramis brama, B0), age-0 and age-1 dace (Leuciscus leuciscus, D0 and D1) as predators. The number of gammarids suspended in the water column was higher in the wave treatments compared to a no-wave control treatment, especially during pulse waves mimicking ship-induced waves in comparison to continuous waves mimicking windinduced waves. The resulting higher prey accessibility in the water column was differently exploited by the three types of predatory fish. D0 and D1 showed significantly higher foraging success in the pulse wave treatment than in the continuous and control treatments. The foraging success of D0 appears to be achieved more easily, since significantly higher swimming activity and more foraging attempts were recorded only for D1 under the wave treatments. In contrast, B0 consumed significantly fewer gammarids in both wave treatments than in the control. Hence, waves influenced predator–prey interactions differently depending on wave type and fish type. It is expected that regular exposure to ship-induced waves can alter littoral invertebrate and fish assemblages by increasing the predation risk for benthic invertebrates that are suspended in the water column, and by shifting fish community compositions towards species that benefit from waves.
Lake water level increase during spring affects the breeding success of bream Abramis brama (L.)
In Lake Constance, Eurasian bream Abramis brama (L.) spawn in very shallow littoral areas by the beginning of May. They attach their adhesive eggs to pebble and cobble substratum at 40 cm depth. Increasing water levels before spawning inundate bare substratum to which bream eggs may attach better than to deeper substratum covered by epilithon. Consequently, the water level increase prior to spawning should determine the amount of pristine spawning substratum available to bream and thus influence their breeding success. In order to test this hypothesis, the influence of hydrology and climate on the abundance of age-0 bream was combined with the results from field investigations on the egg survival and abundance of age-0 bream. A strong positive correlation between the mean water level increase during the spawning season of bream (April May) and the abundance of juvenile bream was found. In contrast, the absolute water level during spawning and during the nursery stage in summer, the cumulative temperature during the egg, larval and juvenile stages and two North Atlantic Oscillation (NAO) indices did not affect the abundance of juvenile bream. The field investigations confirmed that bream eggs attach better to and have higher survival rates on bare substratum than on substratum with epilithon cover. Accordingly, eggs within a spawning habitat of bream were most abundant between 10 and 20 cm depth, where the epilithon cover was lower than at depths exceeding 30 cm. The results of this study confirm an adverse influence of epilithon cover on the attachment and subsequent survival of bream eggs and emphasize the importance of spring inundations for the successful breeding of the bream.