Browsing by Subject "Palaemon elegans"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Candolin, Ulrika; Bertell, Elina; Kallio, Jarkko (2018)
    1. Alien species are altering ecosystems around the globe. To predict and manage their impacts, the underlying mechanisms need to be understood. This is challenging in ecosystems undergoing multiple disturbances as unexpected interactions can alter the impact of individual disturbances. Such interactions are likely to be common in disturbed ecosystems, but have so far received little attention. 2. We investigated whether interactions between an invading shrimp Palaemon elegans and another human-induced disturbance, the population growth of a native mesopredator, the threespine stickleback, influences a third human-induced disturbance, the increase in biomass of filamentous algae. Increases in both the native mesopredator population and algal biomass have been promoted by eutrophication and a trophic cascade triggered by declining predatory fish stocks. 3. We used mesocosm and field enclosure experiments, combined with analyses of long-term trends in the abundance of the invader and the native mesopredator, to dissect the influence of the two species on algal biomass when alone and when co-occurring. 4. The impact of the invader on algal biomass depended on the native mesopredator; shrimp on their own had no effect on algal growth, but mitigated algae accumulation when competing with the stickleback for resources. Competition caused the shrimp to shift its diet from grazers to algae, and its habitat choice from open to vegetated habitats. The native mesopredator, in contrast, increased algal biomass irrespective of the presence of the invader, by preying on grazers and inducing a trophic cascade. 5. Our results show that the presence of a native mesopredator causes an invader to alter its behaviour and thereby its ecological impact. This demonstrates that interactions between invaders and other anthropogenic disturbances can alter the ecological impact of invaders, and, notably, that the impact of invaders can be positive and stabilize disturbed ecosystems. These results stress the importance of considering interactions among disturbances when investigating the ecological impact of alien species.
  • Kangas, Anna (Helsingin yliopisto, 2022)
    Aims and methods: Global plastic production is increasing annually and microplastics (MPs, particles of <5 mm in size) have been reported in the environment worldwide. In aquatic systems plastic pollution is present especially in coastal habitats, and MPs can concentrate within littoral zone vegetation. Numerous marine animals are known to be able to ingest MPs, and plastics can also have adverse effects on the health and behaviour of the exposed animals. This Master’s thesis examined trophic transfer of MPs in a Baltic Sea littoral food chain. Laboratory experiments with 10 µm fluorescence microspheres were conducted to study trophic transfer between food chains of different lengths. The longest food chain had three trophic levels: zooplankton, chameleon shrimp (Praunus flexuosus) and rockpool prawn (Palaemon elegans). Also, the gut passage time of rockpool prawn was experimentally studied. The digestive tracts of the studied animals were analysed for MPs under an epifluorescence microscope. Results: The results show that trophic transfer may be an important pathway of microplastic exposure for animals at higher trophic levels. The number of ingested microspheres in both chameleon shrimp and rockpool prawn was higher when the animals were exposed through pre-exposed prey in comparison to direct exposure from the water. In addition, the prawns ingested more MPs in the experiment with three trophic levels than in the two-level experiment. The results support earlier findings, that the feeding mode affects the microplastic exposure of animals. There were no clear results from the gut passage time experiment.