Burrow morphology of ghost crab Ocypode stimpsoni on Ikarashi beach, Niigata, Japan

Abstract

Lack of evidence prevents an understanding of how ghost crabs create burrows underground. For the reconstruction of ichnogenetic stages in the burrows of ghost crabs, we report on how the burrows of the ghost crab Ocypode stimpsoni from the foreshore and backshore on Ikarashi beach, Niigata, Japan are created. Plaster casting of the burrows reveals detailed morphology with bioglyphs on the burrow wall. The casts of burrows show a variety of morphologies, such as J-and Y-shapes. Based on the burrow ichnogeny, J-shaped burrows were well constructed at a shallower level of the waterline underneath the beach, occasionally creating a second opening of the burrow. In turn, Y-shaped burrows were constructed at a deeper waterline, thereby recycling and reburrowing the deepest part of the J-shaped burrow. As a result, the total depth of Y-shaped burrows tends to be larger than that of J-shaped burrows. The depth and mean diameter of the burrows range from 3.3–37.6 cm and 9.28–31.54 mm, respectively, and the depths are apparently shorter than those on a Pacific beach. The lines of evidence suggest that the morphological features of burrows in Ikarashi beach are attributed to a smaller difference in tidal level in the Sea of Japan, where the available space for burrows ought to be limited by the waterline under the ground.