1: Underwater islands

2: (deep) Grand reef

Same

1- Underwater islands

2- doesn't make sense cuz the only biome with a lost river entrace that has leviathans is the northern blood kelp zone, but it only has 1 Ghost Leviathan, the deep grand reef has no leviathans, the bulb zone also only has 1 leviathan, the mountains don't have a creature with a special ability, unless the Reaper Leviathan grab counts

I’m generalising the entire grand reef biome, there are ghosts and sea Treaders, which are 2 leviathan class creatures.

So the second biome is actually 2 biomes?

No

Grand reef and deep grand reef can just be classified as ‘the grand reef’

The deep grand reef is just the lower part of the grand reef

The grand reef is the opening to the deep grand reef

The deep grand reef is an opening to the lost river

What are the Grand Reef caves then?