To prevent floating microclimates such as floating flora and shrog nests from being completely overpowered, there's a few rules I've been going by for use of them for transport to different landmasses. Following this guideline will hopefully prevent unrealistic overuse of these convenient microclimates.

Landmass-Unrestricted: Microclimate Ecology
A species which is directly part of the ecology of a floating microclimate can go basically anywhere where the microclimate is present. Basically, this species is expected to be living in the microclimate itself.

While this is unrestrictive for the landmasses the species has access to, it takes an extra generation for their lineage to go inland, as they will have all 3 flavors taken up by the ocean, coasts, and beach (or wetland).

Examples: A blood-sucker that lives inside the nests of seafaring shrews, an arboreal herbivore which lives and feeds from floating mangroves

Special exception: Flora that are reasonably expected to be intentionally spread via seeds in a seafaring shrew's nest don't have to include the ocean biomes, as they never "live" in them. I used this exception for the fuzzpile, the wood and berries of which were used readily as building material (and in the latter case as food) by the Seashrog, allowing it to move inland immediately.

Biome-Unrestricted: Likely Transport Events
A species which is very likely to be incidentally transported by the microclimate may spread to another nearby landmass. It doesn't live in the microclimate, but goes on and survives accidental trips often enough to cross short stretches of ocean. This technically breaks the biome rules, but this transport method is a precedented exception.

This is biome-unrestricted because the only required biomes are the beach or wetland where the floating microclimate overlaps with the species' normal range. The species may go inland immediately. However, this is restricted to landmasses that are very close to one another, analogous to Beta's flyways in distance.

Examples: A small creature lays its eggs in a seafaring shrew's nest because its babies feed on rotting flora, a perching creature nests in the mangroves sometimes and gets carried off after storms

Genus Groups
Floating microclimates are great free explanations for global genera. But try not to get too carried away! While missing mesofauna niches are always good to fill, when it comes to larger organisms, it's good to avoid visually homogenizing every landmass with the same kind of tree.

Reminder
As fun as it is to have your species be literally everywhere, this isn't really necessary and is frankly a lot of work, especially if you plan to make descendants for each landmass! Trust me, making so many shrogs has been a lot of labor and sore hands and I'm still not done, not to mention the ideas I have for kakonats and more. Keeping the lineage contained on one or two landmasses is less work and has less risk of causing any mass-homogenization, and you have more time to focus on making just one robust localized lineage. (I know some of you have been worried about islands sinking, but don't worry--while I can't give details on the week 27 map, it's been known since before the limbo that there won't be any more of that insane sea level rise).

There's also limited space in both shrew nests and floating mangroves that must be considered. Looking at a seashrog nest in particular, it's already a bit crowded--that 10 meter wide bowl contains two adult shrogs and their offspring, piles of food and nest material, a shailnitor, multiple cleaner and false cleaner borvermids, some stowaway harmblesses, a small breeding population of kakonats, and possibly a shorelance or two. Minus one shrog, there might be a pirate waxface and her babies literally on top of all that. There are probably still some niches open, but after a certain point, I think the shrogs are gonna start kicking out some of the stowaways.

This isn't to say that you should never use floating microclimates! Just please be mindful of the ecology you're messing with and how much work you're making for yourself.