Biodiversity

A number of Burmese pythons have been found on Key Largo, and a few in the Lower Keys.  However, there is as yet no evidence of a breeding population anywhere in the Keys.  Because pythons regularly escape or are released from captivity, it can be diff
In some places, yes, but under several constraints. Specifically, importation of live snakeheads and their interstate transport is prohibited. Many states prohibit possession of snakeheads, and several of those states have done so for decades.
Asian carp of all types have white, firm, mild flesh, which is excellent table fare, but all Asian carp also have intramuscular bones in the filets that many people find undesirable.
Most snakeheads will avoid contact with humans. However, when guarding their eggs or young, they can become aggressive if approached.
Dead snakeheads--on ice or frozen--can be imported for food purposes to any state except those where importation or possession of dead snakeheads is illegal.
Many studies show that bighead and silver carp substantially change ecosystems where they have been introduced.
Although claims of their mobility have been greatly exaggerated, several species of snakeheads are able to wriggle overland from one body of water to another, particularly if the ground is wet.
Zebra mussels do not have many natural predators in North America. But, it has been documented that several species of fish and diving ducks have been known to eat them. 
Yes, it is not unusual for salt marshes to experience dieback in small patches in some years. However, these areas are usually less than an acre or so in size and generally regenerate the next year or over the next several years.
Northern snakeheads were purposefully introduced and established into Japan in the early 1900s.