The Bible says,
“Then the second angel sounded: And something like a great mountain burning with fire was thrown into the sea, and a third of the sea became blood. And a third of the living creatures in the sea died, and a third of the ships were destroyed” (Revelation 8:8-9).
The second angel sounded and what appeared to be a great mountain burning with fire was thrown into the sea. Mountains in Scripture symbolize nations or great cities, because cities were built on hills for protection.
Jeremiah 51:25 uses imagery that is similar to Revelation 8. In Revelation 8, there was a great nation and a great city that God judged, which was Rome, and any great nation or great city that opposes the church.
Therefore, even as a great burning mountain thrown into the sea has repercussions on many in the surrounding area, so one third of the sea became blood, one third of the living creatures in the sea died, and one third of the ships were destroyed.
Only a third are destroyed, because this was not the final Judgment. These trumpets announced partial judgments on the world, but they were foretastes of the final judgment.