Think of the first expression as idiomatic. It is expressive - the animals feel comfortable in the ocean. If you have just managed to buy a very small, simple flat in downtown Shanghai to live in, you might say: "This flat/apartment may not be very big or luxurious, but to me, it's home." The second sentence is correct but does not feel as natural as the first. As a neutral statement, you could say: "All these animals live in the ocean," or more scientifically, "The ocean is the natural habitat for all these animals."