Portal de Periódicos da CAPES

The Caucasian dwarf goby, a new alien Gobiidae spreading at the Lower Rhine, Germany

2021; Wiley; Volume: 37; Issue: 3 Linguagem: Inglês

10.1111/jai.14196

1439-0426

Jost Borcherding, Dominik Aschemeier, Jacqueline Bruhy, Lisa Heermann, Lindner Jan, Sophia Lara Schröder, Katalin Wagner, S. Staas,

Ichthyology and Marine Biology

Monitoring the fish community in September 2019 of the floodplain waters near Bislich at the Lower Rhine, an unknown, small Gobiid species was firstly caught that differed considerably from all other known alien Gobiids in our region. Based on morphological descriptions and keys provided by Kottelat and Freyhof (2007), it was most probable that the new species belonged to the genus Knipowitschia. This refers especially to morphological structures at the head (e.g. oculoscapular canals) as well as the scaling (e.g. on the caudal penduncle). Because the species is also spreading massively in the Rhine delta in the Netherlands (Stichting RAVON, 2020), colleagues from the Netherlands and Belgium initiated a first genetic survey proving that the species belongs to the Knipowitschia caucasica-complex (Jelger Herder, RAVON, pers. comm., a paper on this topic is in preparation). We therefore decided to name the species as Knipowitschia cf. caucasica (Figure 1, for a detailed morphological description refer to Kottelat & Freyhof, 2007). Relevant literature on the distribution of Knipowitschia species in Europe (e.g. Didenko et al., 2020; Halasi-Kovacs et al., 2011) offered the next closest distribution areas in the middle section of the Danube River Basin. This distribution with an extremely high distance between the southeastern distribution limit in the Danube basin and the northwestern areas of the Lower Rhine is quite similar to what is known from Neogobius fluviatilis (Roche et al., 2013) and clearly differs from more continuous distributions as described for Neogobius melanostomus and Ponticola kessleri (Adrian-Kalchhauser et al., 2016; Borcherding et al., 2011). With the first catch of the Caucasian dwarf goby at the Lower Rhine, we now want to describe the distribution in this area, to add first data on the population structure and feeding in the new habitat, and to draw the attention to this new member of the fish community in western European countries. The Rhine and its backwaters near the field station of the University of Cologne (Rhine km 842) are sampled on a very regular basis. At least once a year in autumn, beach seining has been performed since 2009 at groin fields close to the station (Borcherding et al., 2013). Therefore, a beach seine (10 × 1.5 m) with a very small mesh size (<1 mm) was hand-dragged against the current yielding approximately 100 m2. Additionally, as part of an EU project to renature a side channel in Bislich-Vahnum (SCBV, Rhine km 823–826, LIFE08 NAT/D/000007) electro fishing was performed there in August/September 2018 and 2019 based on Point Abundance Sampling (PAS; Copp & Garner, 1995) as well as stretch fishing (Borcherding et al., 2011). In September 2020, the SCBV fish fauna was also sampled by beach seining as described above (Figure 2). In all years, all fishes caught were identified to species level. Total length (TL) was measured to the nearest 1 mm. All gobies were collected and anaesthetized and either preserved in 96% ethanol (individuals 50 mm TL). For gobies, we performed stomach analyses in the lab as described by Borcherding et al. (2013). Calculations of the diet overlap between the Caucasian dwarf goby and the monkey goby of similar size classes were conducted as described in detail by Borcherding et al. (2019; values >0.6 are assumed to reveal significant diet overlap, Wallace, 1981). By comparing fishing effort in 2018 and 2019 at the SCBV, we can state that the Caucasian dwarf goby firstly appeared here in 2019. In total, seven individuals were caught (size range 21–28 mm TL) that made up less than 0.5% of the total catch in 2019. At the same time this species was also found in the Flürener Altrhein, a connected floodplain area about 1 km upstream (A. Scharbert, pers. comm.). In the catch of the regular fishing in autumn 2019 at the banks of the River Rhine (19 km downstream of the SCBV), the Caucasian dwarf goby was absent. In 2020, however, we found with a similar effort as in 2019 (5 beach seinings) two individuals of 25 and 28 mm TL. Despite intensive fishing effort at floodplain areas and the main stream of the Lower Rhine in 2019 and 2020 by several other institutions, to the best of our knowledge, the dwarf goby was not found elsewhere in Germany (Figure 2). Concentrating on the 6 samples from beach seining in September 2020 at the SCBV (mean density: 55 ± 23 fish per 100 m2), the total catch (n = 338) consisted mainly of K. caucasica (31.7%), N. fluviatilis (26.6%), Rutilus rutilus (15.7%), Rhodeus amarus (7.1%) and Perca fluviatilis (5.3%). All other species occurred in frequencies 40%, Borcherding et al., 2013), which is also true for bighead goby at the SCBV that also preyed predominantly on fish (Figure 4), including the Caucasian dwarf goby. The occurrence of bighead goby in the side channel was surprising as this species regularly prefers the rip rap structures on the banks of the main stream (Borcherding et al., 2013). In contrast and in correlation to fishing results of former years (2011, 2018, 2019), we expected monkey goby in the side channel as a dominant species due to the habitat characteristics found there. Further, we also expected some competitive interactions on food resources of monkey goby and the Caucasian dwarf goby. The calculated diet overlap between all individuals of the Caucasian dwarf goby and small individuals of the monkey goby (<37 mm TL) was significant (0.74). Thus, these fish competed for the same food resources, which consisted mainly of zooplankton and small Chironomid larvae (Figure 4, cf. also Didenko et al., 2020). Though there is a bulk of literature on where the Caucasian dwarf goby was found so far in Europe (for a comprehensive summary cf. Didenko et al., 2020), information on population dynamics, feeding and competition, predatory-prey interaction and dispersal abilities are rare (except Didenko et al., 2020). Thus, our future studies will concentrate on such analyses in order to fill the gap of knowledge for this alien species far outside its native range. It also has to be studied on which way the Caucasian dwarf goby reached the Lower Rhine and the delta area in the Netherlands, where the species is actually spreading massively (Stichting RAVON, 2020). As already described for the monkey goby (Roche et al., 2013), the findings for the Caucasian dwarf goby show a somewhat strange continental distribution, with dwarf goby occurring only at the Lower and the Delta Rhine and the catches upstream far away in the middle reaches of the Danubian watershed, respectively. To our opinion transport by ships, either by ballast water or by eggs attached to the hull of ships seems not very likely, as the distance between the actual areas of occurrence are too far away from each other. Fortunately, for studying these questions new genetic methods are now available that may help to focus on such topics, despite a lot of exciting questions about the ecology and reproduction strategy of this annual species. We thank Andreas Scharbert (Rheinischer Fischereiverband) for sharing actual fishing data at the Rhine in NRW with respect to K.c. and N.f., and information by Jürgen Geist (TU München) and Alex Cerwenka (Zoologische Staatssammlung München) on distribution of Gobiids in the German Danube catchment. Our thanks are also due to Jelger Herder (Stichting RAVON) who provided us first information on the spreading of the species in the Dutch Rhine delta as well as first results on genetics, and two anonymous reviewers for their comments on an earlier version of the manuscript. The authors declare no conflict of interest. In case of publication all data will be available via Dryad.