This explanation says,
the target which 脅【おびや】かす threatens is not a person but abstract things such as a society, a nation, a status, peace, happiness and the like.
Is the reading of this sentence therefore the following?
豊【ゆた】かな海【うみ】が、ごみに脅【おびや】かされています
The rich ocean is threatened by garbage.
豊【ゆた】かな rich
脅かす【おどかす】 threaten
脅かす【おびやかす】 threaten
https://www.asahi.com/articles/ASPCV5W3SPCKTZNB00F.html?iref=comtop_Opinion_01