I can second this.
I was attempting to build a structure high up over the ocean ((lukewarm?) above level 200. Took a jump, and as the surface came in view the ocean was literally covered in dolphins. Abandoned project in the area due to lag. Dolphins spawn too readily as it is, but this was crazy. Wish they were simply persistent spawns from the world seed...about the same as horses. HINT: Making dolphins ridable would suit this, and of course you can separate fantasy from reality by giving an achievement for dolphin riding called "Don't ever do this for Real!"
View after wiping out a section of gravel. No Gravel in inventory or on ground
So you are not supposed to get gravel with a fortune shovel?
How is that "works as intended"?
Superflat waterworld with additional stone (64) and less water (30) also lack ocean mobs (fish), only drowned. Subterranean ocean monuments are created with structures on, dry, but with elder guardians.
update to 25w02a set Hard to effectively Peaceful...somehow. Game setting/file is still Hard, but behavior is Peaceful.