"And God said, “Let the waters swarm with swarms of living creatures, and let birds fly above the earth across the expanse of the heavens.” So God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind.
And God saw that it was good. And God blessed them, saying, “Be fruitful and multiply and fill the waters in the seas, and let birds multiply on the earth.” And there was evening and there was morning, the fifth day.
I think that at some point God, all of the holy angels, and all of the saints who have ever lived are going to fit nicely inside of a City that is 1500 miles square, or 1500 miles in all directions. Various calculations have been done that show that all of God's people who have ever lived and all the holy angels could have "mansions" on five acres of land with ceilings so high that they could have atmospheres and still there would be tons of space remaining left over inside of New Jerusalem.
So I think that we would easily all fit on a New Earth without having to forfeit the sea for the purpose of land reclamation.
He who was sitting on the Throne also said "Behold, I am making all things new". If He saw fit to make the sea creatures the first time, I can't imagine why they wouldn't be included under the "all things" umbrella, along with maybe my cat. And if He makes the fish again, they've got to have a sea to swim in.
Plus, I was hoping to have a boat on the new earth. It would be nice to have an ocean to float it on, a Caribbean to cruise it in.
So what does it mean "no more sea"?
We will enter the thousand years as a numberless multitude from every nation, every tribe, every people and language, standing before the throne and before the Lamb.
During the thousand years we will become directly acquainted with God, the angels, each other and even the lives of the lost as we assist in a feature of their judgement. Or do you not know that the saints will judge the world? Do you not know that we are to judge angels?
After the thousand years are completed, we won't be quite the same as individual peoples as we were when the thousand years began. We will all be on the same page, there won't be a division of nations.
"And they will be his people, and God himself will be with them as their God"
We will be One People, His People, and God Himself will be with us as Our God. There's no longer a diverse group of many nations, tribes, peoples and languages anymore as there were when John saw the "beast" rise up out of the "sea".
John didn't really see a literal sea that a beast rose up out of, it was the troubled "sea" of humanity, the diverse group of many nations and languages from around the world.
"And the angel said to me, “The waters that you saw, where the prostitute is seated, are peoples and multitudes and nations and languages.
But after the thousand years are finished there will be no more of these "waters", no more "sea".
"They will be his people, and God himself will be with them as their God"
"He who was sitting on the Throne also said "Behold, I am making all things new".
"And God said, “Let the waters swarm with swarms of living creatures, and let birds fly above the earth across the expanse of the heavens.” So God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind.
""Then I heard every creature in heaven and on earth and under the earth and on the sea, and all that is in them, saying:
"To him who sits on the throne and to the Lamb be praise and honor and glory and power, for ever and ever!"
Peaceful Sabbath.