Are we making a distinction between intentional and accidental introductions of non-indigenous organisms? The Zebra Mussel type of potential problem was predicted, which is why ships were supposed to empty their bilge tanks at sea and refill with sea water, but some mute-donkey of a skipper forgot and ZM infested the Great Lakes as a result. On the other hand, the intentional introduction of some organisms resulted in devestating unintended consequences, like Kudzu vines.

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"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau