Fronts, jumps and secondary introductions suggested as different invasion patterns in marine species, with an increase in spread rates over time

Abstract

Not all introduced (invasive) species in a region will spread from a single point of introduction. Longdistance dispersal or further introductions can obscure the pattern of spread, but the regional importance of such processes is difficult to gauge. These difficulties are further compounded when information on the multiple scale process of invasive species range expansion is reduced to one-dimensional estimates of spread (e.g. km yr 21 ). We therefore compared the results of two different metrics of range expansion: maximum linear rate of spread and accumulation of occupied grid squares (50 Â 50 km) over time. An analysis of records for 54 species of introduced marine macrophytes in the Mediterranean and northeast Atlantic revealed cases where the invasion process was probably missed (e.g. Atlantic Bonnemaisonia hamifera) and suggested cases of secondary introductions or erratic jump dispersal (Dasysiphonia sp. and Womersleyella setacea). A majority of species analysed showed evidence for an accumulation of invaded sites without a clear invasion front. Estimates of spread rate are increasing for more recent introductions. The increase is greater than can be accounted for by temporally varying search effort and implies a historical increase in vector efficiency and/or a decreased resistance of native communities to invasion.

Occupation, body size and sex ratio of round goby (Neogobius melanostomus) in established and newly invaded areas of an Ontario river

“…Shortdistance migration from high-density areas into lower-density marginal habitat, followed then by further range expansion from the marginal habitat has been suggested in at least two other studies (Ray & Corkum, 2001;Bergstrom et al, 2008), and may also occur from areas of low density present at the edges of the range. Invasive species can exhibit complex range expansion processes which in some cases have been studied in depth; for example, the flat bottom sea star (Asterias amurensis; Dunstan & Bax, 2007), cane toad (Phillips et al, 2008;Llewelyn et al, 2010), and marine macrophytes (Mineur et al, 2010); however, the particular mechanisms of round goby range expansion are still largely unknown. In our study, the downstream segment is disconnected from the CORE area whereas the upstream segment is almost immediately adjacent (Fig.…”

European seaweeds under pressure: Consequences for communities and ecosystem functioning

“…The large majority of introductions occurred after the mid20th century. Many species have been observed only a few times, with a very restricted distribution, while more than 54 species have been spreading more or less extensively (Mineur et al, 2010a). These 54 species therefore fall into the category of "invasive" species (Colautti and MacIsaac, 2004).…”

“…On a European scale, spread rates of invasive species have been shown to have been increasing over the course of the last century, accelerating the frequency of secondary introduction events (Mineur et al, 2010a). Also, increasing survey effort involving the use of molecular approaches is facilitating the detection of such species, either newly introduced, or already established.…”

“…Cumulative total number of introduced seaweed species observed on Atlantic shores of Europe, the Mediterranean Sea and the Macaronesian region (Azores and Canary Islands), over the last centuries (period 1800--2005) (data compiled fromMineur et al, 2010a).…”

Four new exotic red seaweeds on European shores

“…Gruet 1976;Pérez et al 1981;Cabioc'h and Magne 1987;Stegenga 1997;Verlaque 2001). Most of these species are still currently spreading along north-eastern Atlantic and Mediterranean shores, with observations regularly made in new localities (Mineur et al 2010a). In the present note, we report the occurrence of four species of macroalgae observed for the first time in Europe and believed to have been introduced with human activities.…”