Intentional introductions of commercially harvested alien seaweeds.
The two main drivers for intentional introductions of commercial macroalgae are (1) increasing global demand for macroalgae and macroalgal products, and (2) increasing need for alternative and sustainable livelihoods among coastal communities in less-developed countries (particularly to reduce degradation of coral reefs) and in the less-developed rural areas of more-developed countries. The macroalgal species that form the basis for commercial aquaculture (mainly Saccharina japonica (J.E. Areschoug) C.E. Lane, C. Mayes, Druehl et G.W. Saunders, Porphyra species, Undaria pinnatifida, Kappaphycus alvarezii, and Gracilaria species) are thus the ones most likely to be intentionally introduced to other places. The highest-profile cases of ''invasive'' macroalgae have mainly resulted from unintentional introductions, particularly via shipping. Two cases are species important commercially for aquaculture, U. pinnatifida and K. alvarezii, although the global spread of U. pinnatifida beyond Asia has been caused mainly by shipping. K. alvarezii has been intentionally introduced to many countries for aquaculture and has been reported as invasive in one locality in Hawaii; however, more recently it has emerged that Eucheuma denticulatum is in fact the main culprit at this locality. While environmental problems from intentional introductions have been few compared with those from unintentional introductions, it does not appear that commercial species are, as a group, inherently any more or less risk-prone than most unintentionally introduced species. Only a minority of alien species may ever become invasive, but it is difficult to predict which will become pests. In principle, international norms allow states to intentionally introduce exotic species for commercial purposes, provided that environmental threats can be avoided. In practice, the burden of proof and duty of care about environmental threats and protection of biodiversity is nowadays much higher than before. States cannot take it for granted that alien species may be introduced; new proposals should follow formal risk assessment and monitoring processes that are science-based, and should be strongly justifiable in terms of ability to provide expected economic benefits.