From introduced species to invader: what determines variation in the success of Codium fragile ssp tomentosoides (Chlorophyta) in the North Atlantic Ocean?

The green alga Codium iragile ssp, tomentosoides (Chlorophyta) has been int roduced accidentally and successfully from Japan to many shores of the nort hern and southern hemispheres, including those of the Northeast and Northwe st Atlantic Ocean. On most European coasts, Codium occurs regularly but at low abundances in the intertidal zone and is absent from subtidal habitats. In contrast; Codium is extremely abundant in subtidal kelp beds in the Nor thwest Atlantic Ocean where it often reaches nuisance proportions. This dif ferential success cannot be accounted for by either the properties of the i nvader or by physico-chemical differences between invaded coasts. A theoret ical comparison between two regions on opposite sides of the Atlantic Ocean , i.e. Eastern Nova Scotia, Canada, and south central Britain, illustrates how the resident benthic community may determine the difference in relative abundance of Codium in subtidal habitats between northeast America and Eur ope. In this review, low floral species diversity, biological disturbance a nd facilitation by a previous species invasion are suggested as potential f actors for the establishment, success and abundance of Codium in the Northw est Atlantic Ocean, but these require testing in field experiments.