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Ichthyofauna structure of the Save River within the riprap zone as a specific habitat type, with emphasis on the presence of the round goby Neogobius melanostomus (Pallas, 1814)

Over the past decade, the spread of invasive species has become a global issue concerning the protection of native and threatened fish species. Invasive species degrade ecosystem balance, occupying habitats not otherwise inhabited by native species. Riprap is a specific manmade habitat type, installed to prevent river bank erosion. Cracks and interstitial space within the riprap are inhabited by numerous invasive species, including gobies from the genus Neogobius.Many studies have stressed that riprap is a suitable habitat for such species, enabling their longitudinal migration. In 2015, field studies were conducted on the ichthyofauna of the Sava River to collect quantitative data on the composition and abundance of fish species present. The collected data were used to examine the potential of riprap as habitat for invasive species settlement. The research area was divided into three zones based on the presence of rock: riprap 100%, riprap 50% and riprap 0%. To analyse the structure of the fish communities in these habitats, univariate and multivariate statistical methods were applied using the program PERMANOVA + for PRIMER, while graphic analysis was performed using multidimensional scaling (MDS) based on the Bray-Curtis similarity matrix. Statistical analysis showed that all three zones had a similar structure in terms of the number of species present (p=0.094). A similar pattern was found in the grouping of zones in the MDS analysis. Considering community structure, invasive species did not dominate in the composition or in abundance. In the findings, gobies were separated based on habitat type, and it was found that the round goby (Neogobius melanostomus) was more abundant in riprap habitats, while the monkey goby (N. fluviatilis) preferred silty substrates without riprap, with earthen river banks. It was also found that an increased abundance of round goby was associated with the abundance of other species, for which it likely serves as a food sources, particularly the burbot (Lota lota). Future surveys of the riprap zones are necessary to obtain a more complete overview of the manner of spread of invasive species and to prevent their detrimental impacts.

Neogobius melanostomus, Sava River, Riprap, invasive species

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