夏期の小櫃川河口干潟(盤洲干潟)における表被水中の十脚甲殻類幼生

抄録

Occurrence of planktonic decapod larvae (Crustacea) in covering water at a station on the tidal-flat off Obitsu River estuary, eastern coast of the Tokyo Bay, central Japan, was investigated during 16-17th August of 2010. Samples were obtained by vertical hauls of a Marutoku net (mouth diameter 45 cm, mesh size 330 μm) from the bottom to the surface. Nineteen taxa of decapod larvae, including 8 taxa identified to species level, were occurred. These decapod larvae consisted of the species that benthic populations are distributed around the Obitsu River estuary, such as salt-marsh crab Chiromantes dehaani, salt-marsh ghostshrimp Laomedia astacina, sand-flat ghostshrimp Nihonotrypaea japonica, and sand-flat crabs Scopimera globosa and Philyra pisum. The abundance of each taxa excluding P. pisum was very low during the daytime (1-6 inds. m^<-3>), but high in the nighttime (1-470 inds. m^<-3>), largely reflected by change of abundance of N. japonica (maximum 470 inds. m^<-3> at 22 : 00). The abundance of P. pisum was positively synchronized with water level (3-36 inds. m^<-3>). Most larvae collected in this survey are in first zoeal stage that should be newly hatched from adult. A small number of megalopae and juveniles (N. japonica and unknown Brachyura) occurred mainly during the nighttime suggesting revolving larvae with diel migration between water column and seabottom.