>

and the residents of the Republic of Crimea who do not want to be slaves of the Kiev regime, as under the Communists, who are they?
What kind of armaments do you imagine Ukraine having that could make a harbour unusable? 
They might be able to take out a few warehouses, maybe a bit of rail or if they hit the harbour with everything they have a pier.
You need some serious tonnage to make a harbour unusable. Like nuke scale tonnage and even that would probably only make the harbour unusable due to radiation. It's like trying to sink a piece of land. >

Send in divers and plant mines? >

Damage a ship, or maybe two? Before the harbour is cleared by Russian divers. Not at all a bad idea if the Ukrainians have the means. But it will in no way make the harbour unusable. >

It would not endear the residents of Crimea to Ukraine if it ever regained the territory. And I don’t think Ukraine’s military situation is at all desperate enough for such a move. >

Ukrainians aim to retake Crimea . Blowing up the bridge between Russia and Crimea have caused a collapse of Russian Logistic . They can't supply the troops in Crimea and southern front ( due to rail there being in range of Ukraine weapons ) to be in any figthing shape . 
They even made sure the bridge is just partially damaged to allow Russian forces and sympathizers to have a retreat option like in other operations . >

This is the answer - blow the fucking bridge. With it gone, the Port becomes very limited in functioning since all the supplies for the port come across the bridge. It would also make Russia's position in the south untenable. >

They already did . A truck blow up a while back on the bridge making it too structurally weak to move a train on it . 
Without rail transport  , Russians can't supply their troops in dependable fashion since they lost most of their military trucks early in the war and had to commandeer civilian ones . And transport ships make too much of an easy targets for most weapons including drones and missiles . >

Same question as why they would ask for cluster bomb munitions, something that would tax their rebuilding efforts after blowing up Russians- what's to lose? Pootin has not waged war against a cogent enemy, he has acted in pissy-pants temper tantrum missile barrage after barrage of retribution, trying to wipe out the people he can't conquer. So what if Sevastopol is destroyed in the attack? Mariupol? Crimea? At this point, the whole country will have to de-mine, dig out, and rebuild; Ukraine is the people and the dotted lines across the earth are just markers in a bloodbath against a dying asshole.