Invasion
Invasion Description
1st record: Southsea, Portsea Island/England/Solent (1971, Farnham 1980)
Geographic Extent
Orkney Islands/Scotland/North Sea (2019, Want et al. 2023, 59 N); Morvern/Scotland/Loch na Droma Buidhe (2007, Moore and Harries 2009, most northern UK location); Strangeford Lough, Northern Ireland (1995, Boaden 1995; Strong and Dring 2011); Isle of Cumbrae, Ayrshire/Scotland/Firth of Clyde (2005, Harries et al. 2007, attached plants, 55.758599N, 4.898848W); Wigtownshire/Scotland/Loch Ryan (2004, Harries et al. 2007, attached plants, 54.966416N, 5.018046W); Ardrossen/Scotland/Firth of Clyde (2006, Ashton et al. 2006); Whiting Bay, Isle of Arran/Scotland/Firth of Clyde (2005, Harries et al. 2007, attached plants, 55.487731N, 5.094222W); Campbeltown Loch, Kintyre, Argyll/Scotland/Firth of Clyde (2005, Harries et al. 2007, attached plants, 55.417797N 5.550281W);Southsea, Portsea Island/Solent (1971, Farnham 1980); Southsea, Gosport Marinna/England/English Channel (2004, Arenas et al. 2006); Bembridge, Isle of Wight/England/Bembridge Lagoons, English Channel (1973, Farnham 1980); Brighton/England/English Channel (2004, Arenas et al. 2006); Eastbourne/England/English Channel (1980, Farnham 1980); Cherbourg/France/English channel (1984, Belsher and Pommelec 1988); Saint Vaaste-la Houge (Normandy)/France/English Channel (1977, Gruet 1977, cited by Farnham 1980); Boulogne (Normandy)/France/English Channel (1977, Farnham 1980); Le Havre/France/English Channel (2012, Verlaque and Breton 2019); Zeebrugge/Belgium/Sluice Dock, North Sea (1999, Kerckhof et al. 2007); Texel/Netherlands/Wadden Sea (1980, Farnham 1980; Critchley 1983; Gittenberger et al. 2010); Netherlands/Lake Grevelingen and Eastern Scheldt (1980, Critchley et al. 1987, by 1984, most of the available hard substrate was colonized); Isle of Sylt/Germany/Denmark/Wadden Sea (Buschbaum et al. 2012); Limfjord (1984, dominant by 1997, Staehr et al. 2000; Thomsen et al. 2006; Jensen et al. 2023);
Vectors
| Level | Vector |
|---|---|
| Probable | Oyster Accidental |
Regional Impacts
| Ecological Impact | Competition | |
| Sargassum muticum has been reported to displace native algae in the Limfjord, Denmark, (Stæhr et al. 2000, cited by Schaffelke and Hewitt 2007). Its advantage over the native, perennial Halidrys siliqua may be due to its semi-perennial lifestyle, not having to invest in a sturdier structure for winter survival, and so is capable of more rapid growth in spring and summer (Wernberg et al. 2000). On the Isle of Cumbrae, Scotland, S. muticum was found to displace the native Dictyota dichotoma, probably through competition for light and substrate (Harries et al. 2007). In Strangford Lough, Northern Ireland, competition with the native Saccharina latissima was not seen. Instead, growth of S. muticum was slower in single-species plots, due to intraspecific competition. Disturbance and removal of the native seaweed was considered responsible for the expansion of S. muticum (Strong and Dring 2011). In the German Wadden Sea, competition with the native algae Polysiphonia nigrescens, Antithamnion plumula and Elachista fucicola, and also with settling Pacific Oysters (Crassostrea gigas) was seen. Reduced oyster settlement could affect epibenthic communities by reducing by limiting the expansion of hard substrate (Lang and Buschbaum 2010). | ||
| Economic Impact | Shipping/Boating | |
| Dense beds of Sargassum muticum were reported to interfere with the movement of small boats and to clog their intake pipes (Critchley et al. 1986). | ||
| Economic Impact | Industry | |
| Sargassum muticum was reported to clog the intakes of power plants in England (Critchley et al. 1986). | ||
| Economic Impact | Fisheries | |
| Sargassum muticum is reported to foul fishing lines and nets, and has also interfered with oyster culture and harvesting in England and France (Critchley et al. 1986). | ||
| Economic Impact | Aesthetic | |
| Large amounts of Sargassum muticum washing up on beaches, were an unpleasant feature on recreational beaches. Dense beds of Sargassum, were reported to interfere with swimming and recreational sailing. Sargassum muticum was also considered a threat to native marine biota and their habitats. A removal program was studied and organized by a coalition of local, regional, and national environmental agencies, in southern England (Critchley et al. 1986). In 1974-1975, a large campaign of hand-picking by volunteers was conducted, with about ~800 collecting trips and 31 metric tons collected. However, hand-collecting overlooked germlings and small plants. Mechanical removal, herbicides, and release of natural herbivores all proved to be ineffective. Specialized cutting machines, trawls, and suction devices were developed and tested, and found to be more effective, but would require continual annual use (Critchley et al. 1986). | ||
| Ecological Impact | Habitat Change | |
| On the Isle of Cumbrae, Scotland, canopies of Sargassum muticum support a higher abundance, but lower diversity of epifauna than the native Dictyota dichotoma, probably due to a more complex structure (Harries et al. 2007). In Strangford Lough, Northern Ireland, S. muticum has colonized large areas of bare substrate by 'stone-walking', attached to stones and shells, and moving by water motion. Invertebrate communities were altered under the canopies, and were dominated by smaller, more opportunistic species than the bare substrate (Strong et al. 2011). Sargassum muticum in this estuary was more heavily colonized by epiphytes and herbivorous amphipods than the natives, and appeared not to benefit from 'invader release' (Strong et al. 2009). In the Limfjorden, Denmark, S. muticum supports a similar epifaunal community in species composition to the native Halidrys siliqua, but supports a much higher density of fauna, especially amphipods, because of the greater size and complexity of S. muticum's thallus (Wernberg et al. 2005). | ||
| Ecological Impact | Food/Prey | |
| Sargassum muticum had faster rates of growth and decomposition than the native brown seaweed Halidrys siliquosa in the Limfjord, Denmark, resulting in higher productivity, and faster turnover of organic matter. Sargassum muticum was preferred to H. siliquosa by the major grazer, urchin Psammechinus miliaris, but grazing losses of S. muticum were small, compared to those due to decomposition (Pedersen et al. 2005; Pedersen et al. 2016). In feeding experiments in Germany, using the snail Littorina littorea, the urchin Psammechinus miliaris, and the isopod Idotea baltica, the native Fucus vesiculosus was preferred to S. muticum from Germany, but S. muticum and S. horneri, collected in Japan, were both more strongly avoided, suggesting that European populations have reduced chemical defenses (Schwartz et al. 2016). Flat Periwinkles (Littorina obtusata and L. fabalis) from English Channel sites first colonized 6-40 years ago (1970s), fed as readily on S. muticum as on native Ascophyllum nodusum, in comparison to snails from later invaded areas. This difference is suggestive of behavioral or evulutionary adaptation (Kurr and Davies 2018). In Strangford Lough, Northern Ireland, S. muticum was more densely inhabited by the amphipod Dexamine spinosa than native algae (Saccharina latissima, H. siliquosa, Fucus serratus) and more heavily grazed by the amphipod (Strong et al. 2009). In the Wadden Sea, Germany, increased abundance of the native Snake Pipefish (Entelurus aequoreus) was promoted by dense growths of S. muticum, which also supported high densities of harpacticoid copepods, food for the pipefish (Polte and Buschbaum 2008). | ||