The nonnative organisms are introduced to new aquatic ecosystems in option "D" which is migration.
What is an aquatic ecosystem?
An aquatic ecosystem is an ecosystem in and encircling a body of water, indifferent to land-based terrestrial ecosystems.
Aquatic ecosystems have communities of organisms that are dependent on each other and on their environment.
Thus, migration is not a way that nonnative organisms are presented to new aquatic ecosystems related to trade.
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