Alien species are species present outside their native range, usually through no fault of their own. Their accidental or deliberate introduction is largely down to human activities. The numbers of alien species such as alien seaweeds are increasing all over the world due to the increase of worldwide exchanges such as maritime traffic and the aquaculture and aquarium trade. Invasive species can have a harmful effect on human health and ecology.
Human activities are responsible for non-native species introduction, which is one of the major aspects of globalisation, and the increase in international maritime trade has considerably facilitated this phenomenon.
Alien species are considered as a major threat to marine biodiversity. Due to their capacity to alter the composition of ecosystems, as well as the negative consequences of carrying parasites and pathogens, their economic impact should also not be underestimated.
Alien species are the hitchhikers of the seas
In regards to seaweeds, the aquaculture and the global market of edible molluscs are recorded as a significant transmitter, since they frequently house live organisms fixed on their shells. Among alien species, invasive species are those that have a harmful economic, human health and/or ecological impact.
The Mar Piccolo of Taranto in the Mediterranean Sea in Southern Italy, a coastal semi-enclosed basin, is the third hotspot of species introduction in the Mediterranean, through maritime traffic and aquaculture. It has therefore been continuously monitored for early detection of any new introduction since the Eighties.
In a study published in Botanica Marina, researchers confirm that temperature and salinity monitoring in the Mar Piccolo of Taranto region could provide a first estimation of the invasive potential of an alien species soon after its introduction.
Here, populations of two invasive or potentially invasive alien seaweeds, the Japanese cold-temperate brown seaweed Undaria pinnatifida (the Wakame of Asian cooking) and the tropical red seaweed Hypnea cornuta have been studied to detect their possible impact on local biodiversity as well as on economic activities.
After a period of expansion, Undaria pinnatifida disappeared ten years after its introduction. In contrast, Hypnea cornuta continuously spread in the basin and has increased in biomass since its introduction.
This different behaviour was explained by comparison of their natural optimum salinity and temperature ranges with those registered in the Mar Piccolo. In conclusion, the basin seems too salty and too warm for U. pinnatifida, and not too cold for H. cornuta. To date, notwithstanding its considerable spreading, H. cornuta has not provided any negative impact.
The study highlighted that once the natural ranges of temperature and salinity of an alien species is known, the monitoring of these parameters in the recipient region can provide a first estimation of its settlement potential soon after its introduction.