Asexual reproduction occurs when a piece of a sponge breaks off and grows into a new individual. This is known as fragmentation.
Sexual reproduction occurs when two sponges release their sperm and eggs into the water. The sperm swim to the eggs and fertilize them. The fertilized eggs then develop into larvae. The larvae swim for a period of time before settling down and growing into new sponges.
So, sea sponges can both live birth (asexual reproduction) and lay eggs (sexual reproduction).