Distribution and Population Structure of the Galatheid Crab Shinkaia crosnieri (Decapoda: Anomura: Galatheidae) in the Southern Okinawa Trough

Abstract

The spatial distribution around hydrothermal vents, population structure, and relative growth parameters of the galatheid crab Shinkaia crosnieri were examined. Surveys were done by the Shinkai 2000 on the Hatoma and Dai-yon Yonaguni Knolls in the southern Okinawa Trough. On the Hatoma Knoll, S. crosnieri inhabited areas (temp. 4.0-6.2[degree]C) about 0.2-2 m away from the active vent (temp. 301[degree]C). In the outer area of the habitat of S. crosnieri (temp. 3.0-3.7[degree]C), dense beds of Bathymodiolus mussels occurred and aggregations of Alvinocaris shrimp were observed. In this survey, 248 specimens of S. crosnieri were collected. Small, probably just post-metamorphic juveniles and large, mature adults co-occurred. Chelipeds of males were proportionally larger than those of females, while abdomens of females were proportionally larger than those of males. Larger chelipeds in males are thought to have evolved through male-male competition for females, and wider abdomens in females are thought to be related to the attachment of fertilized eggs to the abdominal appendages.