Small craters on the seabed are not likely to last long. However, one things underwater archaeologists have encountered is that submerged objects will often have areas around them dug out by the current. Basically, what happens is as the current encounters the object and is forced to go up over it, that causes the water right next to the object to become turbulent, which can push sediment away from the object. In archaeological terms, that allows later material to be deposited, which is why stratigraphy is of little use in underwater archaeology, even though it is of critical importance by land.
In terms of this situation, if there is a depression next to the recorder casing, it could indicate the direction in which the local currents tend to flow, and the depression was excavated by turbulent water from the current being forced over the recorder casing.