On the co-occurrence of two exotic, invasive marine organisms: the brown seaweed Sargassum muticum (Yendo) Fensholt and the Spirorbid tube worm Janua (Neodexiospira) brasiliensis (Grube), in association with the indigenous eelgrass, Zostera marina L. and Wrack, Fucus serratus L. in the south-west Netherlands and the Channel Islands, Europe

Janua (Neodexiospira) brasiliensis, an immigrant spirorbid, has extended its range in Europe Once restricted to Portsmouth Harbour, south coast of Britain, the tubeworm has subsequently established isolated, but well-developed populations in a small saline canal in the south-west Netherlands and in an intertidal outflow channel from the Jersey Power Station at St. Helier in the Channel Islands, in Portsmouth Harbour, where J. brasiliensis was first discovered as an European immigrant species, the tubeworm is associated with another introduced organism, the brown seaweed Sargassum muticum; in the south-west Netherlands J. brasiliensis develops most prolifically upon the marine angiosperm Zostera marina, whilst at St. Helier the brown wrack Fucus serratus has become most heavily colonized. Both new sites of establishment are influenced by seasonally elevated seawater temperatures (25°C), which may be responsible for the notable, localized population developments on Z. marina and F. serratus (mean settlement densities of 29.7±2.5 and 55.1±3.5 individuals per cm2 respectively were recorded)