It could be ingrown hairs or a minor rash.
If you have open skin, the salt might sting a bit. It's only been a day...just wait for it to go away! It's not exactly normal to have this and isn't common whenever anybody goes for a swim in the ocean. Just take it easy, stay out of the water, shower properly and put some lotion on it if it itches. If it gets worse over the next 3 days, see a doctor.
This'll probably cause no ongoing problems!
If it happens again once you go for another swim, consult a doctor so you can definately tell what these are.