That is commonly called rockweed (Fucus vesiculosis). The pockets of air that you want to pop are what keep the the rockweed afloat. When I am swimming in the ocean, I like to gently pick up one of these clumps of rockweed and shake it to see what creatures may be hiding in it. Sometimes you may find little bitty zooplankton trying to make their way to adulthood.
Click here to learn how seaweed is used for in our daily lives.
Image (c) Educational Technology Clearinghouse of the University of San Francisco.