Yes they are on the boat as required by law. However, when actually swimming they provide pool - noodles that you tuck across your chest and under the arm pits (you'll see pictures of this). Together with the wetsuit this provides enough flotation that you stay at the top of the water and are stable. If you wore a life jacket while snorkeling you'd be too high and too upright to put your face in the water. If you are not having a phobia about water, then you'll be fine. All you need to do is float and look around.
They give you a noodle to float on. Hope this helps
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