The Atlantic marsh fiddler crab. These creatures are colonial, often living and feeding in massive clusters. Despite being small in stature, their burrows are extensive and play an important role in regulating the turnover of nutrients in the mud and aerating marsh sediments. Males can be easily identified by a distinct patch of blue on the top of their shell, along with an impressive enlarged claw. Fiddler crabs are most active during low tide when they leave their burrows to feed on algae and other organic matter.