I really wouldn't want to be that lead ship of the Russian landing convoy. I assume the Ukrainian Navy would have laid sea mines outside Odessa while they still had the ability. If you notice the landing ship convoy, the lead ship is clearly the smallest so as to mitigate potential losses, or it is a minesweeper which are smaller ships. Below is a newly launched minesweeper of the Russian Black Sea fleet. They also tend to be very slow and very soft targets. The one below has a fiberglass hull so as not to be magnetic.
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Edit: I wouldn't rule out a naval invasion just because the Russians haven't quite made it to the city from the North. A supporting paratroop drop would be very doable as Odessa is not far from Crimea. Also the risks are lower because they are at most only a few days from being linked with the Russian forces in the East. If the sea landing fails, the paratroopers won't be stranded for long, and if the sea landing fails, well, Odessa has put substantial resources in preparing for a beach landing and I am unsure how many resources they would have to defend against an air assault.
It is a difficult situation for Odessa. Russia simply has more resources to throw at them. They have three means of attack against Odessa, and they only need one to work. No matter what, the fighting will be intense as paratroopers and marines cannot retreat, and soon the Ukrainian forces in Odessa won't be able to retreat either.
I don't think they will invade Odessa very soon, they will leave it till the end and focus on clearing the Donbas front first. That victory will be decisive, and will sap the morale of troops in places like Odessa.
What they will do though is to keep applying pressure and the threat of invasion in order to pin down Ukrainian forces there, preventing them from going to support the main local front that is about 50 mi east in Nikolaev.