Food Resource Partitioning between Two Invasive Gobiid Species (Pisces, Gobiidae) in the Littoral Zone of the River Danube, Hungary

Abstract

At present, the invasive round and bighead gobies are the most abundant benthic fish species in the near shore zone of the Middle Danube. We compared their diet seasonally in natural and artificial habitats and contrasted it with the food supply. The composition of the macroinvertebrate community was determined mainly by seasonal changes, whereas habitat type had smaller effect. Round gobies followed these changes flexibly. They consumed mainly chironomids in the spring, whilst amphipods and molluscs in the summer and autumn. Bighead gobies relied on amphipods in each season and in both habitats, and consumed fish, too, including round goby (intraguild predation). Diet overlap was determined by the morphological differences of the species allowing a varying degree of differentiation according to the seasonally changing food supply. IntroductionOne of the most spectacular changes in the fauna of Central and Eastern European large river systems in the last decades has been the ongoing spread and proliferation of PontoCaspian fauna elements, primarily macroinvertebrates (crustaceans, molluscs) and gobiid fishes (BIJ DE VAATE et al., 2002;COPP et al., 2005). These aquatic invaders have been reported to cause serious changes in the structure and functioning of their newly invaded habitat including the displacement of their native counterparts or the reconstruction of the food web (RICCIARDI, 2001;MINCHIN et al., 2002;VAN RIEL et al., 2006). Round goby (Apollonia melanostoma (PALLAS, 1814), formerly Neogobius melanostomus) for example, the most successful invasive goby species caused substantial changes in the composition and abundance of benthic macroinvertebrates (BARTON et al., 2005), declines of native fish species (FRENCH and JUDE, 2001;CORKUM et al., 2004) and increased energy transfer to predators in the well studied Laurentian Great Lakes. Gobiid fishes * Corresponding author 610 P. BORZA et al.

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

“…when available (Table III). The seasonal changes found in the diet of round goby from the Slovak stretch of the Danube followed a similar scenario as those in round goby from Hungary (Borza et al, 2009). In spring, fishes consumed mainly the same food items, i.e.…”

“…Similarly, bighead goby exploit the genus of amphipods with the largest body size (Dikerogammarus sp.) almost everywhere in their invaded area (Table II; Borza et al, 2009). Round goby is not reported to be piscivorous in its native range (Pinchuk et al, 2003), nevertheless remnants of fish were found in stomachs of a relatively high number of individuals from the invasive Slovak population (Table II).…”

“…in Slovakia and Dikerogammarus sp. in Hungary, which were followed by molluscs in Hungary (Borza et al, 2009), and by Dikerogammarus sp. in Slovakia (Table III).…”

“…Dikerogammarus sp. was a predominant prey in each season but fishes were also important in spring (on the gravel-sand beach habitats; Borza et al, 2009).…”

“…Bighead goby and round goby are now very abundant, which implies that they could play an important role in foodweb interactions in the River Danube. A few studies devoted to diet of invasive populations of bighead goby and/or round goby have brought some basic information on the species diet composition (Simonović et al, 2001;Adámek et al, 2007;Copp et al, 2008;Polačik, 2009), some of them being more comprehensive, analysing seasonal and habitat variation (Borza et al, 2009). However, none of these papers provide a complex insight into the diet niche of these successful invaders.…”