Permalink : http://hdl.handle.net/2115/72086

JaLCDOI : 10.14943/bull.fish.68.3.43

KEYWORDS : Appendicularia;Arctic;Larvacea;Oikopleura vanhoeffeni;population structure

The horizontal and vertical distributions of the appendicularian community and the population structure of dominant species in the southeastern and northern Bering Sea shelf and the Chukchi Sea were studied during the summer of 2007. The feeding impact was also calculated and the results were compared with those found in 1983-1996. Oikopleura vanhoeffeni was the dominant species in this region and stage I specimens with small tail lengths ( : TL < 2 mm) dominated the population. The mean daily clearance rate was 16.4 ml ind.−1 day−1, which corresponded to a population daily clearance rate in the water column of 0.003-25.5% day−1. The dominance of stage I and specimens with a small TL suggest that the main spawning of O. vanhoeffeni occurred before summer in 2007. Large-sized individuals (TL > 14 mm) dominated in 1983-1996 and, considering the generation length of O. vanhoeffeni (ca. one year), the main spawning of O. vanhoeffeni would not have occurred before summer from 1983-1996. In 2007, O. vanhoeffeni are considered to have spawned earlier because newly recruited small individuals are more abundant. Recently, the timing of the sea ice retreat is becoming earlier in this region, and the fastest ice-free timing was reported in 2007. Earlier sea ice retreat may induce an altered timing of primary production and other biological phenology. Thus, the early spawning of O. vanhoeffeni in 2007 may result in the dominance of smaller specimens observed in that year.