Telmatogeton japonicus - Marine splash midge
SCIENTIFIC NAME
Telmatogeton japonicus Tokunaga, 1933T. japonicus is native to Japan and Hawaii. Other parts of the Pacific Ocean – such as Australia – may also belong to its natural range [2-4].
First observation in Belgium
In Belgium, the presence of T. japonicus was reported for the first time in 2004. At the time, this non-native species was already very common on buoys off our coast [5].
Spreading in Belgium
The Marine splash midge is present in high densities on buoys, both near the coast and at sea [5]. Shortly after the building of wind turbines in the Belgian part of the North Sea, these constructions were colonized by T. japonicus [6]. Nowadays, this species is abundant in the splash zone around wind turbines [7]. Furthermore, the Marine splash midge can be found on ship hulls. Exceptionally, it occurs on hard substrates in Belgian harbours (e.g. Port of Antwerp) and on beach groynes or dikes [8].
Spreading in neighbouring countries
In 1963, the Marine splash midge was observed for the first time in Europe, near Kiel in northern Germany. The specimen was considered a new species to science and given the name T. remanei [9]. The same mistake occurred in 1977 in Gdańsk Bay (Poland). This time the species was named T. gedanensis [10].
In 1999, traces of the Marine splash midge (mainly pupae moults, but also adult remains) were retrieved from the water along the rocky west coast of Ireland [11]. Later, in 2003, the species was observed at the Danish offshore wind farm ‘Horns Rev’, where it has been prominently present since 2004. At some locations, more than 4,000 individuals can be observed per m² [12]. The populations of this species are following the advance of the European wind farms. As a result, the species was found in 2018 along the British, Irish, Belgian, Dutch, German, Polish, Swedish, Finnish, Norwegian and Icelandic coasts [4, 12, 13].
Given the location of the first observation in Europe (Kiel Canal), the suspicion arose that shipping must be responsible for the introduction of the Marine splash midge to Europe. Because the larvae can attach themselves to ship hulls with their tubes, they can spread easily. On a more local scale (secondary dispersal), the mobility of adult individuals and the sea currents (transport of eggs) play an important role
When new artificial habitats – such as wind turbines or buoys – are placed at sea, indigenous species are not necessarily present to efficiently colonize these new substrates. In these habitats, it is more likely that an invasive species will turn out to be more competitive than the native species [15].
In their new habitat, the larvae of the Marine splash midge dominate the upper part of the intertidal area and the supralittoral (splash) zone [4, 15]. In Belgian waters, green algae grow in these zones [15], which appear to be a good food source for these larvae [16, 17]. Since the number of artificial habitats in the future will most likely increase, these can serve as ‘stepping stones’ for T. japonicus. These ‘stepping stones’ make it easier for non-native animals, including the Marine splash midge, to expand their habitat [7].
Additionally, T. japonicus is well-adapted to widely varying conditions and intense eutrophication (an excess of nutrients in the seawater). This latter trait would have facilitated the colonization of the eutrophic Baltic Sea [4]
The Marine splash midge requires a hard substrate in the supralittoral zone to attach its eggs. These include ship hulls, buoys, pylons of offshore platforms and wind farms, rocky coasts and dikes [2, 18]. Therefore, artificial constructions contribute significantly to the spreading of this species [2, 4]. In the Netherlands, the construction of beach groynes promotes the spreading of the Marine splash midge [18].
The species is mainly found in the marine environment, although it also occurs in the brackish water environment of the Gulf of Finland with salinity below 4 PSU [13]. For comparison: the seawater of the North Sea has a salinity of approximately 35 PSU. It seems unlikely that the species will also colonize freshwater habitats [19]
In the Netherlands, this non-indigenous midge is an important food source for sandpipers and turnstones [18]. Especially during the winter, when other food is scarce, the contribution of this non-native species to their diet is important. Migratory birds have also been observed foraging for the Marine splash midge [4].
Although T. japonicus occurs in large numbers in its specific habitat (vertical walls in the supralittoral zone), the species poses little danger to other indigenous species, since they do not inhabit this type of habitat. As a result, the Marine splash midge will not compete with indigenous species and, hence, not outcompete them [20].
Along with many other attaching organisms, the Marine splash midge is part of the so-called biofouling community [6]. Fouling can affect various substrates and even cause economic damage. The prevention of fouling on ship hulls by treatment with antifouling paints is very expensive [21]. In addition, many of these paints damage the ecosystem long after their use has been stopped. An example is tributyltin (TBT), which is banned since 2003 [22].
The Marine splash midge belongs to the marine chironomids (nonbiting midges). The larvae (Figure 1) live in tubes attached to solid substrates in the upper intertidal and supralittoral zone. They feed on, among other things, green and blue algae (cyanobacteria) [4, 17]. The larvae grow to 10 mm in size. Later, a pupa of max. 6.5 mm is formed. After 2-3 days, the adult midge emerges [10, 17] and lives for only four days [13].
Adults can fly, but like other related chironomids, it is better adapted to walking. This species folds its wings towards each other at rest, allowing the legs to move freely [23]. Adults mainly occur on hard substrates along the supralittoral zone, where the waves’ splashing water does not seem to harm them, not even during mating [14]. The species does not bite – unlike mosquitoes (Culicidae) – since it does not require blood to be able to reproduce.
The pupal exuviae (moults) of the Marine splash midge – left behind after the adults emerge from their pupae – can be distinguished from other species by being translucent and having only eight (instead of nine) posterior segments [13].
Figure 1: (Left) Tubes with larvae of Telmatogeton japonicus in the splash zone on a buoy off the Belgian coast (© Bob Rumes); (Middle) T. japonicus larva (© Francis Kerckhof); (Right) Characteristic larval mouthparts (mentum and mandibles) of T. japonicus (© Bob Rumes).
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VLIZ Alien Species Consortium (2020). Telmatogeton japonicus – Marine splash midge. Non-indigenous species in the Belgian part of the North Sea and adjacent estuaries anno 2020. Flanders Marine Institute (VLIZ). 6 pp.