Feeding behavior of an ocypodid crab Macrophthalmus japonicus associated with daily exposure during ebb tide and its effects on vertical oxygen profiles and organic matter removal in intertidal sediments

Abstract

The objective of this study is to elucidate the feeding behavior of an oxypodid crab, Macrophthalmus japonicus, the most dominant macrofauna in Korean mud flat, and to clarify its role in organic matter mineralization on the intertidal sediments. Feeding behavior of the crabs was recorded on video tape for 10 hours of the daytime ebb on a Han river tidal flat in the west coast of Korea. Temporal variations of oxygen penetration depth from the surface sediments and Chl a concentration in the sediments were measured with 2 hour intervals at both the mud sediments with a natural crab density and the defaunated sediments. Carbon and nitrogen concentrations, C/N ratio and N were compared between the non-feeding sediments and feeding pellets harvested by oxypodid crabs. Macrophthalmus japonicus showed different feeding activities with air temperature and it affected oxygen penetration depth from the surface by probing the substratum with chelae. They were mainly fed on benthic diatoms and organic carbon and nitrogen concentrations of the feeding pellets were reduced down to 60% due to their feeding. It was calculated that organic carbon and nitrogen were mineralized at the rate of 1.89 mmol C m-2 h-1 and 0.24 mmol N m-2 h-1. C/N ratio increased to 18% in feeding pellets compared with that of non-feeding sediments. These results suggest that carbon mineralization rate by the feeding of Macrophthalmus japonicus comes up to 5ments. Feeding behavior of the crabs was recorded on video tape for 10 hours of the daytime ebb on a Han river tidal flat in the west coast of Korea. Temporal variations of oxygen penetration depth from the surface sediments and Chl a concentration in the sediments were measured with 2 hour intervals at both the mud sediments with a natural crab density and the defaunated sediments. Carbon and nitrogen concentrations, C/N ratio and N were compared between the non-feeding sediments and feeding pellets harvested by oxypodid crabs. Macrophthalmus japonicus showed different feeding activities with air temperature and it affected oxygen penetration depth from the surface by probing the substratum with chelae. They were mainly fed on benthic diatoms and organic carbon and nitrogen concentrations of the feeding pellets were reduced down to 60% due to their feeding. It was calculated that organic carbon and nitrogen were mineralized at the rate of 1.89 mmol C m-2 h-1 and 0.24 mmol N m-2 h-1. C/N ratio increased to 18% in feeding pellets compared with that of non-feeding sediments. These results suggest that carbon mineralization rate by the feeding of Macrophthalmus japonicus comes up to 5