The sentence reads: "The plan underscores rehabilitation of threatened wildlife species including inland aquatic, coastal and marine ecosystems..." The word "including" is used to introduce examples or specifics within a broader category, making it the most appropriate choice.
"Gathering" implies the act of collecting, which does not fit the context of specifying ecosystems.
"Counting" refers to numerical assessment, which is not appropriate in this case.
"Mixing" refers to combining things, which does not align with the context of specifying ecosystems for conservation.