What does Revelation 8:8 mean?

This verse tells what happened when the second angel blew his trumpet. Something like a great mountain burning with fire splashes down into the sea. This colossal object may be a meteor. The first trumpet referred to a rain of hail, fire, and blood. Some suggest the first trumpet will be a kind of meteor shower, preceding an even more disastrous event as described here. The reference to "sea" is distinct from the fresh water resources of earth, such as lakes and rivers. Those will be affected in a later trumpet judgment.

Perhaps this judgment falls upon the Mediterranean Sea, which is under control of the beast described in Revelation 13:11–18. Though only described later, at this point in the tribulation this end-times figure will already have arrived. The beast, who controls commerce in the tribulation period, will experience a great financial loss under this second trumpet judgment, because a third of the sea becomes blood. Once again, this judgment recalls what happened when Pharaoh refused to let the Hebrews leave Egypt. Exodus 7:14–22 reports that the Lord commanded Moses to tell Aaron to take his staff and stretch his hand over the waters of Egypt so they would become blood. Moses and Aaron obeyed the Lord and the Nile turned to blood. Just as God punished Pharaoh in this way for his suppression of the people of Israel, even so he will punish the beast for suppressing those who refuse to worship the Head of the Revived Roman Empire.