The Second Vial

The Second Vial
Sea Turns to Blood
And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea.
Rev 16:3 KJV
Sounds like "The Second Trumpet" (8:8).
It could be that the apostle is referring to the Mediterranean Sea.
In any case, the sea does not just become red—it becomes as blood such as that from a dead man—turbid, reeking and corrupt. The vile concoction kills every fish, water mammal and anything else that’s lurking beneath the waters.

Without life in the waters, the entire ecosystem is upset. Birds who feed on seafood will starve to death. Predators who feed on the birds will die. Fishermen will go broke, and some entire who depend on the sea for livelihood will fall into deep financial depression.