ベンケイガニ

In this paper the authors reported on the hibernation, habitat and parasitic animals of marsh crabs during the hibernating period. Most of the surveys were carried out at the Umi-river from 18th of September, 1965 to 30th of April, 1966. 1. They described on the correlation between the shape of hibernating nest holes and the individual numbers in the nests, and also on the temperature in the nest hole during the hibernating period. 2. It was decided that the preparatory period for the hibernation was from the end of September to the middle of November, and that the beginning time for the hibernation was the end of November to the early part of December. 3. The awakening period after the hibernation was subdivided into the following three stages. a) The preparatory stage for the awakening after the hibernation was from the beginning to the end of February. In this stage the behaviour of crabs was restricted only in the nest hole. b) The preparatory stage for the activity was from the first half of March to 20th of April. The diameter of home range in this stage was less than 10 meters. c) The active stage was after 20th of April. The diameter of home range extended to more than 30 meters, and in this stage the important changes occurred in population construction because of abandoning their nest holes. 4. They reported on the relation between the activity of crabs and the lowest atmospheric temperature after the preparatory stage for activity, and pointed out that the activity of crabs might be also influenced by the factor of moisture corresponding with the tidal level and fine or rainy day. That is, when the temperature was low, the activity of crabs decreased even in the springtide, and when the ebb-tide came, the activity decreased even in the adequate temperature. But the activity of crabs increased in rainy and warm day in spite of the ebb-tide. The above-mentioned three factors, i.e., the lowest temperature, spring or ebb-tide and rain or shine, have a great influence upon the activity of crabs after the preparatory stage for activity. 5. To survey the horizontal distribution crossing to the stream of rivers, the belt-samplings were tried. The crabs hibernated mainly at the reed marsh, but their hibernating places were selected by the soil texture, especially the amount of retained water and the diameter of soil grains even at the same reed marsh. 6. The vertical distribution along the stream of the river was discussed. Of the three marsh crabs, Sesarma (Parasesarma) erythrodactylum Hess, Sesarma (Holometopus) dehaani H. Milne Edwards and Sesarma (Sesarma) intermedium (de Haan), S. (H). dehaani was the strongest species for high salinity of both brackish and fresh waters. But the others became weak in order of S. (P.) erythrodactylum, S. (S.) intermedium against the high salinity, inversely S. (S.) intermedium was stronger than S. (P.) erythrodactylum against the fresh water. 7. In the examination of the marsh crabs for the parasites, Nematoda (gill), Copepoda (gill) and Trematoda (gill and intestine) were found out as the animals of internal parasitism.