In the intertidal zone, one of the inhabitants of sandy beaches is the scavenging ghost crab Ocypode. These small crabs live inside of burrows they dig themselves, where they hide when a predator comes near by. Their incredibly fast disappearance is the reason they got the name "ghost crab." They were very active when we saw them digging new homes, hiding from us, going up and down the beach looking for something to eat (and we also saw them feeding).
The very characteristic "sand-balls" left behind are pellets, which is sand filtered by them while looking for microorganisms. They are very important because they clean the beaches of organic debris. It is always great to enjoy the little things that life has to offer.