A rock dredge is a useful device for collecting sediment samples from a hard seabed, such as on deep coral reefs which are usually made of a hard limestone rock. A dredge is sometimes preferred over a sediment grab device because they are quite robust and can be towed over very rough ground. As well as rocks and gravel, large seabed marine life is often caught in a rock dredge making this device also useful for understanding marine wildlife diversity on the seafloor.