Any advice on how to handle this? I'm working on the script for a graphic novel (web comic) about mermaids, and I feel like there's some major aspects of their physiology and culture that needed to be spelled out early in the story... but I can't figure out how to work it in without it feeling like a tacked on author's note. There aren't any humans in the story. Things about their culture effect what's happening in the plot, but they have no reason to discuss or think about those things, because not only do they already know about those things, they don't really know about any alternatives. It's just The Way Things Are. I suppose part of my trouble is with the medium. I think it'd be a little easier with the omnipresent narration you have in novels. Maybe.
You'll want to show the culture through events like a festival or through their every day lives. Things that you may not be able to show, have someone explain it to a child that doesn't know yet or discuss it with someone who disagress with the way things are. You says they have no reason to discuss their culture, but there will be those who'd disagree with aspects and think that their lives could be much better. Once upon a time women had no rights, they were expected to stay at home and look after the children, but that's not the case now, because there where those who disagreed (it may still be in some place though).
This is exactly what I had decided to do in my fantasy story, to show their culture and make it more real!
When I started my urban fantasy I had trouble writing. I finally came to realize this was because I had basically shoehorned in a human character to act as a stand-in for the reader. And I did this because it was expected. The writing picked up when I dropped her and focused (first-person) on the ghoul MC and her dealings with other supernatural creatures. It was a little strange at first, as since this was first-person (I don't like third-person) the MC did not stop to think "I am ghoul" no more than you think "I am a human being" on a regular basis. Or at least I do not. Now in fairness I took a bit of a cop-out. The opening scene has the character blasted with a shotgun (through a wooden door) and fly off a porch. Then she gets back up, pissed that her new shirt is ruined as her innards form back into place. That's the most outrageous thing that happens for a couple chapters, but establishes that she is not human from the start. My point being don't add a character if you don't want them there or feel they are needed just because the audience supposedly needs a surrogate.
Read, again, what you wrote, here: "...There aren't any humans in the story..." Now, take it into context with the rest of your post. See the problem? There are never any humans in any story - There are only "Characters." That's where you are disconnecting with writing this story. Don't try to write it as a Safari or a Travel Guide. Write it as a story and then, only when you have fleshed it out enough, should you think about things to tackle both before and during Revision.
I had a similiar problem in a current wip. I tried to write it by including a human that had no knowledge of the world they got sucked into. It ended up feeling cliched and forced. I scrapped it. Instead I did as someone mentioned above. I showed the reader the culture through actions and events, and a small dose of backstory when necessary.
