2011-03, Stoll, Stefan, Fischer, Philipp

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.

2010, Stoll, Stefan, Probst, Wolfgang Nikolaus, Eckmann, Reiner, Fischer, Philipp

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

2011-01, Gabel, Friederike, Stoll, Stefan, Pusch, Martin T., Fischer, Philipp, Garcia, Xavier-Francois

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.

2010-05, Stoll, Stefan, Hofmann, Hilmar, Fischer, Philipp

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.