Andmebaasi logo

Sirvi Autor "Ercoli, Fabio (juhendaja)" järgi

Nüüd näidatakse 1 - 2 2
  • Pisipilt
    Kirje
    Effects of temperature on marbled crayfish (Procambarus virginalis, Lyko 2017) invasion ecology
    (Eesti Maaülikool, 2021) Muuga, Johanna-Maria; Ercoli, Fabio (juhendaja); Teesalu, Paul (juhendaja)
    Biological invasions are crucial issues worldwide and marbled crayfish (Procambarus virginalis, Lyko 2017) is one of the examples of freshwater invaders spreading across Europe and beyond. Marbled crayfish has high growth rate and reproduces via parthenogenesis, making it unique among other decapod species. Even though it is a warm water species, they can resist colder temperatures and are highly adaptable. Furthermore, it is also a vector for Aphanomyces astaci, causing crayfish plague. Due to its high adaptability, fast growth and reproduction, since one individual is enough to start a new population, it is important to understand its invasion ecology in order to implement better management plan in the new invaded ecosystems. In this thesis the main goal was to assess whether the temperature is the main factor of marbled crayfish establishment and distribution in the artificially warm outflow channel of Balti Power Plant in Narva. We hypothesised to find temperature gradient along the channel which reflects marbled crayfish distribution and trophic niche. We analysed marbled crayfish and their potential food sources for stable carbon (13C) and nitrogen (15N) isotopes to assess its trophic niche. Temperature data did not show the gradient in the channel, however the channel was significantly warmer than Narva Reservoir. Stable isotope results showed change in marbled crayfish diets and trophic niche along the channel and between seasons, indicating a shift from enriched carbon to depleted carbon values from head to mouth of the channel and a shift from high to lower trophic level from spring and summer to autumn. Moreover, results showed diets being similar in head and middle of channel where crayfish mostly rely on macroinvertebrates and macrophytes, while in the mouth of the channel diet seems to shift more towards periphyton. Diet also changed from protein-rich in spring to vegetation-based diet in autumn. Based on the results, temperature had important role in the marbled crayfish establishment in the invaded channel, however the distribution of its population might have been affected by ecological aspects rather than temperature, like better food availability in the head of the channel.
  • Pisipilt
    Kirje
    The Role of trophic niche in eel head shape dimorphism
    (Eesti Maaülikool, 2019) Teesalu, Paul; Ercoli, Fabio (juhendaja); Silm, Maidu (juhendaja); Vesiviljelus
    The European eel is a critically endangered fish species with a complex life cycle. Many aspects of eel ecology are poorly investigated; therefore, it is crucial to have a thorough understanding of this fish species for better stock management practices and conservation actions. In this thesis we caught and measured the head width of eels from the Estonian lakes of Saadjärv and Võrtsjärv. We hypothesised that individuals with narrow heads would be primarily benthivorous, whereas broad-headed individuals were likely to be piscivorous. Lake ecosystems and the subsequent difference in food availability could play a role in the formation of either head morph. Thus, our second hypothesis is that Lake Saadjärv, with an average macroinvertebrate biomass of 2.5 g/m2 would have more broad-headed eels than Lake Võrtsjärv, which has a higher macroinvertebrate biomass of 6.6 g/m2 . We combined gut content analyses and stable isotopes of δ 15N and δ 13C to determine and compare trophic niches of eel populations. Gut content analyses results confirm that eels in Saadjärv are affected by head shape in their feeding habits, with narrow-headed eels consuming proportionally more macroinvertebrates and broad-headed eels consuming more fish. This was confirmed with stable isotope analyses- broad-headed eels were significantly more enriched in δ 15N and therefore had a higher trophic position than narrow-headed eels. In Lake Võrtsjärv nearly all eels (95%) displayed a narrow head shape, suggesting a diet based mainly on macroinvertebrates, particularly chironomids. In line with our expectations stable isotope analyses indicated that the eel population in Võrtsjärv rely mostly on Chironomus plumosus and marginally on other benthic macroinvertebrates. The occurance of broad-headed eels was indeed higher in Saadjärv (31%) than in Võrtsjärv (2.3%) indicating that food availability plays a crucial role in eel head morphology