Invasive Neogobius Melanostomus Research Articles

Invasive Neogobius melanostomus in the Lithuanian Baltic Sea coast: Trophic role and impact on the diet of piscivorous fish

The partitioning of trophic niches is central for understanding the ecosystem processes associated with biological invasions. The recent successful establishment of Neogobius melanostomus in the Baltic Sea posed questions whether this invader found its own trophic niche, to what extent it competes with native benthivores, and if commercially important fish could be affected. In this study conducted along the Lithuanian Baltic coast, we used the stable isotope approach to identify potential trophic competitors of N. melanostomus. We also employed gut content analysis to quantify the incorporation of N. melanostomus into the diet of native piscivores. Furthermore, pre-invasion gut content data enabled us to check if there were any changes in the piscivorous fish diet after the invasion. We found N. melanostomus to be a subdominant benthivorous fish during the warm season of 2012–2013. It occupied a higher trophic position in spring (3.9) than in autumn (2.9), but spring specimens were also larger. The invader exploited a narrow (standard ellipse area 0.3–0.5‰2) and distinct core isotopic niche, but total niche area overlaps indicated potential trophic competition with Pleuronectes platessa, Platichthys flesus, Pomatoschistus minutus and Gasterosteus aculeatus in spring, and with P. minutus in autumn. The invader dominated the warm season (spring–autumn) diet of piscivorous fish (Gadus morhua, Myoxocephalus scorpius, Perca fluviatilis, Scophthalmus maximus) and its invasion was generally associated with decreased crustacean and increased fish-prey content. Therefore, it is plausible that N. melanostomus has created novel trophic links within the food web.

Activity and competitive behaviour of invasive Neogobius melanostomus and Ponticola kessleri (Gobiidae) from the River Rhine, Germany

Behavioural experiments were conducted to gather information on how competitive behaviour between the invasive gobies Ponticola kessleri and Neogobius melanostomus may affect the development of populations in the River Rhine. Short-term experiments that were designed to measure activity could not discern any consistencies, neither between species nor based on gender. Although both species needed time to adapt to laboratory shelters, N. melanostomus hid conspicuously more often than P. kessleri. Few directly competitive interactions between species were observed. However, when such interactions were observed, N. melanostomus was stronger and won most inter-specific conflicts, even when it was the smaller opponent. It was also revealed in long-term feeding experiments that N. melanostomus preferred gammarids over fish during direct competition, while the opposite was true for P. kessleri. Behavioural results of the present study show these two species to exhibit different strategies, giving some evidence that P. kessleri and N. melanostomus may occupy different niches that enable them to coexist in the River Rhine.

Host‐specificity of the endangered thick‐shelled river mussel (Unio crassus, Philipsson 1788) and implications for conservation

ABSTRACT The complex life cycle of the endangered thick‐shelled river mussel (Unio crassus, Philipsson 1788) includes an obligatory parasitic phase on a host fish. Consequently, knowledge of the interaction of U. crassus with its host species is crucial for the development of effective conservation strategies. The objective of this study was to assess systematically the host suitability of eight different fish species, including six native species which naturally co‐occur with U. crassus, as well as two non‐native species. All tested fish species were successfully infected with glochidia of U. crassus, which were present on their gills 2 days after exposure. Phoxinus phoxinus and Squalius cephalus were the most suitable hosts as indicated by both the highest total glochidial load and the highest fish‐weight‐normalized glochidial load after 16 days and 48 days. Salmo trutta, Alburnoides bipunctatus and Cottus gobio were less suitable, losing ~90% of glochidia within 16 days. Alburnus alburnus, invasive Neogobius melanostomus and introduced Oncorhynchus mykiss lost more than 98% of glochidia within 16 days, indicating they are unsuitable hosts. U. crassus larvae did not grow significantly (<15%) during their metamorphosis on suitable hosts, suggesting that the most obvious advantage of the host‐dependent phase in the U. crassus life cycle is the dispersal by fish vectors. The observed differences in the developmental speed and the timing of excystment on different suitable host species are likely to increase the chances of successful dispersal and survival in adverse environmental conditions. The sustainable conservation management of U. crassus populations is closely linked to the effective management of their host fish populations. In particular, the currently underestimated ecological functions of low‐valued fish species such as S. cephalus and P. phoxinus clearly deserve better consideration in the conservation management of U. crassus habitats and stream ecosystems. Copyright © 2011 John Wiley & Sons, Ltd.