Javidpour, Jamileh (2008) Ecological assessment of the ctenophore invader Mnemiopsis leidyi in the Western Baltic Sea. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 104 pp.

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Abstract

Species invasion is a conspicuous phenomenon in today’s human-dominated biosphere. With the changing configuration of marine ecosystems, the barriers limiting the range of species are changing, too. Studing species invasions allows scientists to observe and measure many ecological processes (such as spatial distribution, genetic changes) directly, which are difficult to study with long-established native species. Therefore the study of invasion ecology gained the name of “an experiment in nature” (Grinnel 1919 as referred in Sax et al. 2005). Because the frequency of gelatinous zooplankton increases globally, their future ecological role is a matter of concern for marine invasion ecologists. The Baltic Sea is a recipient of species from several different donor systems and referred to as ‘a sea of invaders’ by Leppaekoski et al. (2002). The recent invasion by the comb jelly Mnemiopsis leidyi became a topic of major concern after its appearance in the Baltic Sea because of the vast ecological and economic impacts it had in its previously invaded habitats such as the Black Sea. In the first chapter, we established a morphological key to distinguish Mnemiopsis leidyi from Bolinopsis infundibulum. Both species are very similar. This key enabled us to identify this species from time series data of Helgoland Road station where B. infundibulum naturally occurs. A permanent weekly sampling in the Western Baltic Sea provided the basic knowledge on M. leidyi seasonal dynamics and ability of being established. In chapter II we show the late summer outbreak in 2007 with a 10 fold increase in abundance in a short time that coincided with high reproduction activity. The drop of mesozooplankton prey in late spring was due to predatory control of fish larvae and no seasonal overlap between M. leidyi and fish eggs or larvae could be detected. We have also provided data on the main environmental conditions which might trigger the outbreaks of M. leidyi population in the Western Baltic Sea. In chapter III, we simulated the drift pattern of M. leidyi during its first year of observation in 2007 by using a hydrographical model. The model illustrated the possible advection route of M. leidyi through the Baltic Sea. It is hardly possible that M. leidyi has penetrated from Kategat Skagerak as a single source of spread. Instead ballast water release and the subsequent spread away from different recipient harbors might have led to the concentration of its population in the deep basin of North and Central Baltic Sea. In the last chapter we show the predatory impact of M. leidyi on mesozooplankton population of Western Baltic Sea was measured. During cold season this species showed a high preference for small sized and slow swimming prey. Copepods were preferred just for a short time in August. The most abundant prey in summer were planula larvae of the other gelatinous carnivore in the Baltic Sea, Aurelia aurita. However adults of M. leidyi got their major energy intake via cannibalism on their own larvae.

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