mbanders

In the ocean, meanwhile, things are different. One thing is that saltwater is not as strongly desiccating as pure salt. Obviously, saltwater has a higher concentration of water than pure salt does. Saltwater can definitely still desiccate any objects that do still have a higher concentration of water than the saltwater has, pulling the water out of them; but it can’t do so as strongly as pure rock salt can.

But the other thing is that ocean animals have an internal saltiness that ensures that salt water won’t dry them up. The internal saltiness of sea snails is equal to the external saltiness of the seawater. The sea snail doesn’t dry up in salt water, because it was never about the presence of salt, so much as it was about the relative difference in water content between salt and snail.

Source: 

https://www.quora.com/If-you-can-kill-a-garden-snail-with-salt-why-do-sea-snails-not-die-in-saltwater

More explanations to widen your understanding of this profound question:

https://answers.yahoo.com/question/index?qid=1006040208799

http://www.seaslugforum.net/find/17594

I hope I have been very helpful this day with you question, I hope I have provided the right answers. Keep learning and never stop being curious, you have a whole life ahead of you young man. Peace.