The small sand mounds are typically found near small holes that are about the size of your pinky finger. Male and female fiddler crabs dig burrows in the sand to escape from predators. But scientists believe there may be more to the sand mounds- especially for male crabs.
Padre Island National Seashore wrote on Facebook:
"Some scientists suggest that the female fiddler might take the size of the mudballs into consideration when choosing her mate, while others suggest that it might be easier for a female to see her potential mate when he is in front of his pile of mudballs. But the majority of the science suggests that the mudballs play a significant role in defining a male fiddler crab’s territory."
The post states:
"Since fiddler crabs do most of their courting just outside of their burrow, scientists suggest that this barricade might serve as a visual deterrent to potential competitors, essentially letting them know that their territory - and the female fiddlers in it - are already spoken for."