Upon cross referencing this with my IRL subnautica maps. And applying a compass to it. And also referencing the depth. I can confirm that this is the spare reef.
It's completely harmless. Just stay away from the dunes Northwest of the reef (EXTREMELY DANGEROUS) you'll also encounter the blood kelp trench northwest of it (dangerous and leading to the lost river) and the grand reef South of it (highly dangerous. Beware the ghost leviathan lurking there) if you head west you'll find the Sea Treader's path, don't go too far or you'll reach the dead zone and be swarmed be ghost leviathans.
The sparse reef. it is completely safe, the only threat are bleeders, and there is some pretty good loot and stuff down there. i recommend to explore the wreck and the alien sanctuary down there. it also shares borders with the grand reef on the west, the floating island on the west but above sea level, the blood kelp trench on the east, the dunes on the northeast, and the sea treaders path on the north.
And, as @Kaden103 mentioned earlier, DO NOT GO TO THE DUNES. IT IS A COMPLETE WASTE OF TIME AND SEAMOTHS, PLUS THERE IS NOTHING THERE TO HELP YOU WITH THE STORY AND GAME PROGRESS.
