Answer: D. migration
Aqua culture is the phenomena for rearing fish and other aquatic organisms with high commercial value for food production. Non- native organisms are added in an ecosystem in order to raise their number keeping in mind the availability of food for them. For creation of new aquatic ecosystem cargo ship hulls, recreational boats, organisms escape from the aquariums can be useful as these methods are non- natural and they are disturbing the original productivity and stability of ecosystem by introducing nonnative organisms to new aquatic ecosystem. But migration is a natural phenomena in which non-native organisms move to other habitat in search for food and habitat required for survival.