I kept a Long Island Sound tank for many years.
I also used to have an Urchin collecting and selling business with Sound urchins. (Urchin Searchin Ent.) I would collect about 50 a day using SCUBA. They are pretty hard to kill unless as you found out, you heat them up.
They really don't even require acclimation more than a few minutes. I used to feed them a head of lettuce every day and once I had to many so I put 24 of them in my reef where they all decided to spawn at the same time. What a mess but nothing died.
You can keep small blowfish, starfish, pipefish, seahorses, sea robins, hermit, green and fiddler crabs.
Those Sound tanks are really interesting.
I still use Sound water in my reef and collect it behind my house.