There are probably a lot of upstream areas left for the rest of us to research.
My "boss" is from Oahu. So we go there to visit her family.
Been all over the habitats there and Kauai.
Maui and the big island are next on the list.
With 30-40ft waves on the northshores, not a good time to go snokeling however. Maybe when it's more mellow. Looked like CA coast during winter storms, just a lot warmer water, sharper reefs and rocks. I use to think CA waters where(and are extremely dangerous) when you get big surf, but the rocks are not nearly as bad and the fools here are smarter than the dimwits that try and surf there.
Best place in the USA to drown.
Hiker got killed when we where there also, fell 400ft trying get some stuff he lost. Common sense. Tourist often lack that. Evolution at work I figure.
It's hardly the safe place some think of it.
But offers a lot of nice aquatic plant materials and sediments, wood, rock, etc. Locals who get out and hike/enjoy nature tend to have good common sense however.
They have mosses in a few streams growing well, most of the mosses and ferns on the pali
likely will do well, particularly the ones at the highest elevations of these two islands as well as Molokai and the western mountains on Maui.
Careful where you get the stuff, make sure you leave no trace and respect the land. State parks are kapu, private property etc. I think locals are fairly good there, but tourist could use a good "beating". This is true most places, Florida, CA etc, but city folks that rarely ever go out to the country tend to have some troubles here and there.
Just be smart and careful what you do and where the items are taken from.
We have road side piles of Manzanita, but one guy went to the state park and nabbed some stuff in full view of park ranger.