Biological invasions

The ecological impacts of aquatic invasive species are a growing concern for coastal zone management and conservation. The French Channel-Atlantic coasts are no exception, mainly because of international shipping practices and aquaculture. France is even the European country most colonized by introduced species of macroalgae. The cost-benefit analysis of invasion management is not straightforward, even though the exploitation of several living resources is based on the invasive characteristics of these species (for example, molluscs and macrophytes in aquaculture). The oyster Crassostrea gigas is considered a nuisance species in the Wadden Sea or Australia, where it supplants native oysters, while it is the subject of a major exploitation in France at the same time. In addition, there are many historical cases showing that an invasion initially “under control” is not necessarily permanent, even after several decades. Understanding the interactions between human activities, the functioning of ecosystems and global change is therefore essential in order to establish new management options. New approaches need to be developed to prevent any inadvertent introduction and limit the side effects of ongoing invasions.

The impacts of the ongoing global changes are not conducive to optimism. Thus, the French Atlantic coast is confronted with at least three major environmental changes:

● the average annual temperature of seawater is rising steadily (about 1.5 ° C over the past 25 years),

● there is a very clear positive trend of the North Atlantic Oscillation (NAO),

● there is a drastic decrease in freshwater inputs due to climate change and concomitant changes in human activities on watersheds (eg increased irrigation for agriculture). The “marinating” of estuaries near ports leads to an increase in the potential risks of invasion by new marine species, while global warming favors the establishment of subtropical exotic species (for example the harmful dinoflagellates of the genera Ostreopsis and Gambierdiscus in the Bay of Biscay). By definition, species invaders are able to adapt to their new environment and are best placed to cope with global changes. What about native species that are not used to such environmental changes? Although climate change is progressive, will all species (native and invasive) adapt or will we observe a global homogenization of flora and fauna?