Loud voices in heaven had proclaimed that “the kingdom of the world has become the kingdom of the Lord and of his Christ” (Revelation 11:15). The “world” includes not just land/earth but also the sea—as was illustrated by the mighty angel planting his two feet on sea and land respectively (Revelation 10:2). So it is to be expected that the dragon would direct his diabolic frustration not just to the “land” part of earth but also to the “sea” part.
12 Therefore, rejoice, O heavens and you who dwell in them! But woe to you, O earth and sea, for the devil has come down to you in great wrath, because he knows that his time is short!”