The octopus most likely won't go after the brine shrimp and they have almost no nutritional value. Can you get some live shrimp? You can order from aquaculturestore.com, or if really desperate you can get freshwater ghost shrimp from your local LFS. Freshwater shrimp are not as nutritious as salt water shrimp but it could tide you over until you can order live salt water shrimp. You can also try frozen, raw shrimp (it will be gray instead of pink). Your octopus may not be interested in eating an arrow crab. Good luck!