Species introductions, diversity and disturbances in marine macrophyte assemblages of the northwestern Mediterranean Sea

In the process of species introduction, the traits that enable a species to establish and spread in a new habitat, and the habitat characteristics that determine the susceptibility to introduced species play a major role. Among the habitat characteristics that render a habitat resistant or susceptible to introductions, species diversity and disturbance are believed to be the most important, It is generally assumed that high species richness renders a habitat resistant to introductions, while disturbances enhance their susceptibility. In the present study, these 2 hypotheses were tested on NW Mediterranean shallow subtidal macrophyte assemblages. Data collection was carried out in early summer 2002 on sub-horizontal rocky substrate at 9 sites along the French Mediterranean coast, 4 undisturbed and 5 highly disturbed. Disturbances include cargo, naval and passenger harbours, and industrial and urban pollution. Relationships between species richness (point diversity), disturbances and the number of introduced macrophytes were analysed. The following conclusions were drawn: (1) there is no relationship between species introductions, diversity and disturbance for the macrophyte assemblages; (2) multifactorial analyses only revealed the biogeographical relationships between the native flora of the sites.