sea snakes breed and will have a go at biting anything. They frequently come on land to lay eggs. Luckily they have such a small head that if you present it with a fist it will have problems biting although some divers say that they can open their jaws enough to bite a table top. That size is unlikely to be encountered close inshore. Push it away with an open hand and it will bite you on the skin between the fingers.
They are extremely poisonous.