What is the meaning of "Domu Yoshevei Iy"?
Rashi: Mourn and sit silently, residents of islands. Refer to 23:2:2:1.
Radak: Residents of islands, be silent and sad, for the city of your commerce was destroyed.
Radak, from Targum Yonasan: Domu is to be broken. Also Tzidon was on the sea.
Malbim: The verse depicts that Tzidon mourns over Tzur, for Anshei Tzidon had great damage; they had wealth and trade in Tzor. The Navi tells them to be silent, especially the traders of Tzidon. You will be full of overseas commerce. Your loss from Tzor will be filled doubly!
What is the meaning of "Socher Tzidon Over Yam Mil'uch"?
Rashi: Merchants of Tzidon, who cross seas, used to fill you (islands) with all merchandise. Now that Tzur will fall, also Tzidon will fall with it. They were close to each other, within a journey of one day.
Radak: The singular applies to the Klal, like "va'Yhi Li Shor va'Chamor" (Bereishis 32:6), "Ki Im ha'Sus Asur veha'Chamor Asur (Melachim II, 7:10), "Ko Someru l'Ish Yavesh Gil'ad" (Shmuel I, 11:9) and similar verses. Mil'uch refers to Tzor; you were filled with merchandise.
Malbim: Tzidon was near Tzor; it was not esteemed at all during the serenity of Tzor. All Tzor fell, all the business was moved to Tzidon, and it became very rich, until Nebuchadnetzar conquered it.