You can definately sub white sesame seeds if you briefly toast them first (in a flat, dry saute pan on high heat for maybe a minute or two), but DON'T try to to sub kelp for wakame.

Kelp is a thin toasted seaweed that is meant to enhance the flavor of food in much the same way as salt. If you try to rehydrate it, it just become gummy and gluey (which can be a fabulous attribute when using it in batters for Okonomiyaki because it dissolves almost completely), but wakame is an actual sea vegetable that only comes to life once it's been rehydrated.

There are other seaweeds out there if you can't find wakame, and the best way to determine if they'd work as a substitute is to determine how processed they are. Nori and kelp are heavily processed...chopped, dried, put back together. Kinda like the "Spam" version of seaweed. You want seaweed that's gone through nothing mroe than harvesting and drying.

Kryssa

I'd bet that you will be able to find these at most Japanese grocery stores

you live in seattle and cant find wakame and black sesame seeds? c'mon..