Yahweh continues giving Ezekiel his message to Tyre. The city of Tyre continues to be described as if it were a wrecked ship. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "Cities at the sea" represents the people in those cities. Alternate translation: "The people of the cities by the sea will tremble" (See: [[rc://en/ta/man/translate/figs-metonymy]])