I collect stuff from the beach several times a year, some of it like your barnacles, but most of it live. I find porcelain crabs, pistol shrimp, tiny serpent stars, anemones, clams, chitons, limpets and more. Most have been freshly washed up on the beach after a storm and stay alive living in sponges or attached to bigger shells. I've never quarantined any of it, 85% to 90% of it survives and I've never had any issues. The small stars don't do well out of the water even when living inside a sponge. The crabs and shrimp do much better, nearly a 100% survival rate. I've been doing this for about 10 years and all 4 of my tanks have been problem free.