This was my first thought in response to this thread as well. There are many threads on the forums discussing the pros and cons of common names but when it comes down to it in situations like this it’s very helpful to have something. You just need to do an internet/literature search and find any evidence that anyone is using a common name for that taxon, make sure the name is distinct for that taxon, and then you can add it and include a link to the source.
But I’m not sure if I understand the context or marine taxonomy well enough to tell if that’s actually the solution here. I looked through the Aquatic Park project and found this observation where it sounds like you have a couple species of yellow sponges but because “yellow sponges” is not a taxonomic category you can’t identify them lower than phylum Porifera.
You also mentioned “nori” which based on an internet search usually refers to edible seaweed in the red algae genus Pyropia. But based on my limited knowledge of seaweeds it’s possible that people are also harvesting species of green or brown algae which they still call “nori”, but on iNat you might have to go all the way up to “plants” or “life”?
In these cases I think what you are asking for is functionality like what these feature requests are asking for:
Create taxon field functionality analogous to observation fields
Attach non-taxonomic qualities to species for searchability
Since that doesn’t exist now (and is unlikely to), @spiphany’s earlier post has the best available options.