Feeding behavior of the ocypodid crab Macrophthalmus japonicus and its effects on oxygen-penetration depth and organic-matter removal in intertidal sediments

Abstract

This study examined the poorly understood feeding behavior of the ocypodid crab Macrophthalmus japonicus in the field to explore its effects on oxygen-penetration depth (OPD) and organic-matter removal from intertidal sediments. An in situinvestigation was conducted on an upper mud flat in the mouth of the Han River estuary, on the western coast of Korea. The behavior of M. japonicus and variation in the OPD within its habitat were surveyed and contents of organic materialssuch as organic carbon (OC), organic nitrogen (ON) and δ15N in its feeding pellets were compared as contrasted with non-feeding sediments during the daytime ebb in summer. We continuously recorded the surface activity of the crab during two main feeding periods and during a resting period, when the crabs remain immobile on the surface. Feeding periods exceeded 1 h crabs fed on sediments more actively during the first feeding period (45 pseudo-pellets individual