almost as many ways for introductions to occur as there are introductions.
But here is a list of the most well-known and documented. I found one example
of shipping water very interesting.
Several years ago 3000 Pacific oysters were shipped from California to
Woods Hole. The shipment had 2
certificates stating the oysters were parasite and disease free. That was all well and good but only 10% of
the shipment was checked which I believe is standard. After arriving at Woods
Hole, the oysters were washed and the water saved. There was a total of 29
species of algae, diatoms, protozoans, and invertebrates detected in the
water the oysters were shipped in.