[ SPECIES ] Uninvited guests: Invasion of the gobies
Small invaders conquer our waters Almost half a dozen goby species originating from brackish water areas of the Black, Azov and Caspian Seas are spreading almost explosively in Central and Eastern Europe. The round goby (Neogobius melanostomus) has been particularly successful, even making it to North America’s Great Lakes. Such neozoa, which are difficult to contain, are a risk to regional ecosystems.
However, no one can say with absolute certainty why PontoCaspian gobies in particular, which barely grow larger than 20 centimetres, have managed to penetrate numerous water systems in Central Europe from their natural ranges in just three decades. In addition to the bighead goby (Neogobius kessleri) and tubenose goby (Proterorhinus marmoratus), monkey goby (Neogobius fluviatilis) and
Peter van der Sluijs 2013 (Wikimedia commons)
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he spread and settlement of a new fish species can occur naturally, but today it is often supported and accelerated by human activities. Fish eggs and larvae travel around the world in the ballast water of ships, the construction of canals connects once isolated bodies of water and opens up new migration routes, aquarists and anglers sometimes release foreign species into native waters. An example of this is the spread of lionfish (Pterois spp.) in the Caribbean, where they were presumably released by aquarists out of a misguided love for animals and now threaten the biodiversity of the reefs. Economic motives also often play an important role in the introduction of new fish. Rainbow trout, originally at home in North Pacific coastal waters, are now farmed in more than 100 countries worldwide. In some places, escapes from trout farms have led to independent, self-sustaining fish populations, which then often endanger the native wildlife.
Round goby caught in the Netherlands. Characteristic features of this fish species are the pelvic fins, which have grown together to form a suction disc, and the distinctive black spot at the back of the first dorsal fin.
the racer goby (Neogobius gymnotrachelus), is the round goby (Neogobius melanostomus), which is considered particularly invasive. Colloquially, these five goby species are sometimes grouped together as “Black Sea gobies”, but this only describes one of the areas of origin. This quintet is complemented by the Chinese sleeper (Perccottus glenii) from Asia, another species that is already included in the first Union list of EU Regulation No. 1143/2014 on invasive alien species. Once established, goby populations often proliferate and can even become the numerically dominant fish species in the newly “conquered” waters. Thus, it is hardly surprising that in many places they are perceived as a nuisance and a serious risk to ecosystems because they threaten invertebrates, amphibians, and fish.
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Frugal, undemanding and environmentally tolerant If one looks for reasons for the gobies success in spreading, one will first encounter the enormous species richness of this family (Gobiidae), which comprises at least 1,100 species. Most of them live in the salt water of the oceans, but plenty are also found in brackish and fresh water. What all goby species have in common is their frugality and adaptability, their ecological plasticity, so to speak. These characteristics are also shared by the round goby, which seems to be even better at conquering new habitats than its relatives and has therefore become the most common goby neozoan in Central European waters. Round gobies are relatively tolerant of oxygen deficiency. This
warmth-loving species feels most comfortable at temperatures around 26°C (which suggests that its spread is favoured by climate change), but also tolerates cold periods in winter. In addition, this goby has a pronounced salt tolerance and copes well in both fresh and salt water, as its spread in the brackish water of the Baltic Sea proves. In the saltier North Sea, however, its occurrence is limited to the sweeter estuaries. The spawning season extends from April to September, so that the animals can reproduce about four to six times a year. With an average of 200 to 1,000 eggs, the fertility per spawning cycle is relatively low, but because the male lures several females one after the other into his breeding cave to spawn with them and selflessly protects and cares for the batches of eggs, the reproductive success is nevertheless
