Effects of activities of an oxypodid crab, Macrophthalmus japonicus, 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 removal from the intertidal sediments. The crab’s feeding behavior, variations of oxygen penetration depth and Chl a concentration in their feeding substratum, and the removal rate of organic carbon and nitrogen in their feeding pellets were investigated during the daytime ebb on a mud flat of the Han river estuary, Korea. The activity pattern of Macrophthalmus japonicus was relatively dependent on both air temperature and their size, and oxygen penetration depth was affected by their activities of probing the substratum with chelae for feeding and movement. Organic carbon and nitrogen concentrations of the feeding pellets decreased down to 60% due to their feeding. It was calculated that organic carbon and nitrogen were removed at the rate of 1.89 mmol C m-2 h-1 and 0.24 mmol N m-2 h-1, respectively. C/N ratio increased to 18% in feeding pellets compared with that of non-feeding sediments. Depletion of 15N in the pellet (5.99 permil) compared to that in the sediment (7.21 permil) further implied that the crab removed N in the sediment. Overall results indicated that carbon removal by the feeding of Macrophthalmus japonicus was comparable to 50% of anaerobic C mineralization in the sediments, and the crabs feed on ni. The crab’s feeding behavior, variations of oxygen penetration depth and Chl a concentration in their feeding substratum, and the removal rate of organic carbon and nitrogen in their feeding pellets were investigated during the daytime ebb on a mud flat of the Han river estuary, Korea. The activity pattern of Macrophthalmus japonicus was relatively dependent on both air temperature and their size, and oxygen penetration depth was affected by their activities of probing the substratum with chelae for feeding and movement. Organic carbon and nitrogen concentrations of the feeding pellets decreased down to 60% due to their feeding. It was calculated that organic carbon and nitrogen were removed at the rate of 1.89 mmol C m-2 h-1 and 0.24 mmol N m-2 h-1, respectively. C/N ratio increased to 18% in feeding pellets compared with that of non-feeding sediments. Depletion of 15N in the pellet (5.99 permil) compared to that in the sediment (7.21 permil) further implied that the crab removed N in the sediment. Overall results indicated that carbon removal by the feeding of Macrophthalmus japonicus was comparable to 50% of anaerobic C mineralization in the sediments, and the crabs feed on ni