- Species with a high number of appearances on current 'hit lists', both international and national
- Emerging threats: potential major impacts or rapid spread rates of species not currently problematic.
From these, they assigned a score of (i) spread - the number of continents already invaded, and (ii) impact: either ecological, economic and/or health. Then, they eliminated those whose genus is already represented in the top 100, or those whose value can also be 'positive' (economic, ecological or health). This leaves just 10 candidates...
I think my vote would probably go to the triffid-like Giant Hogweed Heracleum mantegazzianum, although the aquatic plants on the list also sound particularly threatening.
However, it was a surprise to find the beautiful Lionfish Pterois volitans on there - I have often admired this in large aquariums although I was aware it is not one you would easily keep at home, being rather poisonous! If this piscivorous fish becomes more widespread it's impact on populations of reef fish is anticipated to be enormous - as if there weren't enough threats to coral reefs already with climate change and coral bleaching.
