Feeding and niche differentiation in three invasive gobies in the Lower Rhine, Germany

Abstract

a b s t r a c tSince 2006, three invasive Gobiids from the Ponto-Caspian area established in the River Rhine and their abundances nowadays regularly exceed 80% of the fish community. Between 2009 and 2011, densities of gobies in the Rhine increased while their condition decreased, assuming that the populations are approaching or even reached the capacity of the ecosystem. Consequently, we hypothesized a high level of competition on food resources within this group of invasive gobies that all exhibit the same sedentary life style, which might strengthen the differentiation of the ecological niche on a spatial and temporal axis. Invasive gobies were caught with electro fishing and beach seining in different types of habitats over a period of two years in the Lower Rhine, analyzing the food of more than 1500 gobies of the three species Neogobius fluviatilis (NF), Neogobius melanostomus (NM) and Ponticola kessleri (PK). All species showed an opportunistic feeding strategy. In NF and PK, a clear shift in preferred food resources was observed between individuals smaller and larger 50 mm that occurred in parallel with a habitat shift from sandy areas to riprap structures in PK, but not in NF that were only found on gravel and sand. In contrast, there were no distinct changes in food and habitat preference in NM. Small NM were found from spring to autumn on the sandy nearshore areas where they competed on food resources with juvenile PK in spring, and with NF in late summer, respectively. Abundance of juvenile NF and NM increased during the night in sandy nearshore areas in October. This behavior is assumed as predator avoidance against large piscivorous NF as well as native pikeperch, because active feeding occurred mainly during the day. The results on the three invasive Gobiids in the Lower Rhine give important hints how fine-tuned spatial and temporal characteristics in intra-and inter-specific competition shape the ecological niche of these invaders in their new environment.

A review of Gobiid expansion along the Danube-Rhine corridor – geopolitical change as a driver for invasion

“…In the same publications, successful upstream migration (including over two weirs) was also noted between 2008 and 2011 along the River Morava, a non-navigable tributary of the Danube, helped in part by the availability of rip-rap bank stabilisation along the river's channelised banks. Downstream drift and plentiful rip-rap habitat have no doubt also played a major role in the relatively rapid spread of goby species along the Rhine (see also Borcherding et al, 2013). In addition, upstream movement (e.g.…”

“…In monkey goby, a preference for shallow, sandy/muddy habitats Miller, 2003;Borcherding et al, 2013) and backwaters (Haertl et al, 2012) may explain this, i.e. not only will they be less competitive in those ecological niches preferred by round, bighead and tubenose gobies, it is also less likely that they will be detected during surveys based along main rivers or channelised habitats.…”

“…It is possible, though not proven, that monkey gobies were transported there via transport of wet sand/gravel in open Remorker barges, while further downstream migration may have been aided by presence of preferred habitat, e.g. mudflats and sandbanks, in the Rhine delta system and downstream drift of juveniles (Borcherding et al, 2013).…”

Do invasive bighead gobyNeogobius kessleriand round gobyN. melanostomus(Teleostei, Gobiidae) compete for food?

“…Nevertheless, recently, two comprehensive studies on the diet of invasive gobies have been published. The first is from the Lower Rhine (Borcherding et al, 2013), and the second from the Upper Danube (Brandner et al, 2013). Thus, to complement the picture, a detailed taxonomic analysis of the diet spectrum of bighead goby and round goby from the Middle Danube, including seasonal changes in its composition, was undertaken in this study.…”

Diet of a Cryptic but Widespread Invader, the Oriental Weatherfish (Misgurnus anguillicaudatus) in Idaho, USA

“…Currently, the invaded range of the oriental weatherfish includes disparate locations around the globe, and the species may adapt its diet to locally available food sources, a strategy employed by other invasive fishes (Harms and Turingan 2012, Kornis et al 2012, Borcherding et al 2013). Consequently, determina tion of diet is necessary to elucidate the ecological role-and the potential threats to native fishes-that the oriental weatherfish holds within each of its invaded regions.…”