Allow Shmoop to indulge our inner Captain Obvious for a moment. Antonio's mother's last name is Luna, which is the Spanish word for moon. That's some pretty clear symbolism right off the bat, as the moon represents Antonio's mother and her people. It's no accident that they're called that.
But there's more to it than that. The moon also symbolizes what her family stands for—farming, being tied to the land, and therefore staying in one place. Antonio discovers this firsthand when he goes to work with his uncles, saying, "I learned that the phases of the moon ruled not only the planting but almost every part of their lives. That is why they were the Lunas!" (22.235-237).
And then there's Antonio's father's family—the Márez. Márez roughly means sea (mar), and like the sea (and the wind that has such an effect on the sea), the Márez clan is all about constant motion. They could hardly stay put if they tried. Antonio's father's family appears to Antonio in a dream to make this clear:
"He is a Márez," the Vaqueros shouted. "His forefathers were conquistadores, men as restless as the seas they sailed." (1.190-191)
The contrast between the Luna and Márez clans, as represented by the moon and the sea, epitomize the two forces that are pulling at Antonio throughout the novel. His father wants him to roam, his mother wants him to farm, and Antonio, as usual, is stuck somewhere in the middle.