While it is true that building a city under the ocean would be easier than going to Mars, going to Mars isn’t going to stop oceanographic research. One does not cancel out the other. It’s not like we are pulling out funds from researching the ocean so we can go to Mars. There are things still to be discovered under the sea. There are things still to be discovered in space. Both will go on because we have billions and billions of people and some people like studying the oceans and some people like studying space!