Abstract
Between 2005 and 2012, 61 marinas and harbours around the English coast were surveyed to record the occurrence of non-native species (NNS) of sessile invertebrates. From these surveys, geographic distributions are described for eight species of ascidians, six bryozoans and five other species. A mean of 6.7 sessile invertebrate NNS per site (range 0–13 species) was recorded. At the 43 sites on the English Channel coast, the mean was 7.8 NNS per site, and all of the ten English sites that had ≥ 10 NNS were in the western or central region of the Channel coast. Ten sites on the Channel coast surveyed in 2004 were re-visited at least once in 2009 or 2010, and the mean number of sessile invertebrate NNS had increased from 6.0 to 7.6 species per site. Combining data from all visits in 2005–2012 for the sites surveyed in 2004, the mean number of NNS recorded per site rose to 9.2. Very rapid rates of spread along the English coast and beyond are inferred for the erect bryozoan Tricellaria inopinata d’Hondt & Occhipinti Ambrogi, 1985 and the ascidian Corella eumyota Traustedt, 1882. At least five recently arrived species that were limited to a small number of sites in 2012 are expected to increase markedly in geographic range and prevalence: the ascidians Asterocarpa humilis (Heller, 1878), Botrylloides diegensis Ritter and Forsyth, 1917, and Didemnum vexillum Kott, 2002; and the bryozoans Schizoporella japonica Ortmann, 1890 and Watersipora subatra (Ortmann, 1890). Rapid assessment surveys of marinas and similar sites proved to be an effective means of documenting the arrival and spread of NNS over a relatively wide geographic range and of distinguishing different rates of progression.
Highlights
A substantial proportion of marine non-native species (NNS) are sessile organisms that live attached to solid substrates, and NNS are often very prominent in the fouling biota of artificial coastal structures (Glasby et al 2007; Floerl et al 2009; Marins et al 2010; Mineur et al 2012)
The low percentage (2.6%) of species first records generated during the final fifteen minutes at 11 Solent marinas in December 2009 suggests that a one-hour search of a site is generally adequate to detect the target species present
Salinity recorded as single readings on generally infrequent visits to sites showed very little correlation with NNS diversity at the sites, and is little mentioned in our account
Summary
A substantial proportion of marine non-native species (NNS) are sessile organisms that live attached to solid substrates, and NNS are often very prominent in the fouling biota of artificial coastal structures (Glasby et al 2007; Floerl et al 2009; Marins et al 2010; Mineur et al 2012). Ports and harbours are important sites for the primary introduction of NNS carried by international shipping, while smaller commercial vessels and leisure boats are believed to be effective agents of subsequent secondary spread (Wasson et al 2001; Minchin et al 2006; Murray et al 2011). Floating docks or pontoons in ports, harbours, and marinas provide solid surfaces with the distinctive feature of continuous submersion at a constant, shallow depth, and are remote from the seabed and its predators. Such surfaces support an abundant fouling biota and appear to favour NNS (Neves et al 2007; Glasby et al 2007; Dafforn et al 2009). Marinas are an increasingly common component of developed shorelines and offer opportunity for the cost-effective survey of species’ distributions along coasts, their pontoon walkways providing ready access from the surface to submerged fouling biotas, irrespective of the state of the tide
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