Ecosystem is a type of Structure. Structure is related to River. River is related to Current. 
Seize is a synonym of Take. Take is a synonym of Undergo. Undergo is a synonym of Experience. Enjoy is a type of Experience. 
Ecosystem --IsA--> Structure <--RelatedTo--> River <--RelatedTo--> Current 
Seize <--Synonym--> Take <--Synonym--> Undergo <--Synonym--> Experience <--IsA-- Enjoy 