Diel vertical migration of the copepod Calanus sinicus before and during formation of the Yellow Sea Cold Bottom Water in the Yellow Sea

To understand the effects of the Yellow Sea Cold Bottom Water （YSCBW） on the diel vertical migration （D- VM） of the copepod Calanus sinicus, we surveyed vertical distribution of C. sinicus at a fixed station in the Yellow Sea before （spring） and during （summer） formation of the YSCBW. Cold water （〈10℃） was observed in the bottom layer when the water column was thermally stratified in summer, but the water column was thermally well-mixed in spring 2010. Samples were collected from five different layers at 3-h intervals using an opening-closing net. Adult females （1-155 ind./m3） showed a clear normal DVM pattern throughout the entire water column in spring, whereas adult males did not migrate. DVM of copepodite V （CV） individuals was not clear, but the maximum abundance of CI-CIV occurred consistently in the upper 10-20 m layer, where there was a high concentration of chlorophyll-a （Chl-a） （0.49-1.19μg/L）. In summer, weak DVM was limited to cold waters beneath the thermocline for adult females （〈30 ind./m3）, but not for adult males. The maximum abundance of CI-CIV also occurred consistently in the subsurface layer （20-40 m） together with high concentrations of Chl-a （0.81-2.36 μg/L）. CV individuals （1-272 ind./m3） moved slightly upward noc- turnally to the near-surface layer （10-20 m）, where the average temperature was 25.74℃, but they were not found in the surface layer （0-10 m; 28.31℃）. These results indicate that the existence of the YSBCW affected food availability at depth and the vertical temperature distribution, leading to variation in the amplitude and shape of stage-specific vertical distributions （CI to adults） in C. sinicus before and during the formation of cold waters in the Yellow Sea during the study period.

The Community Structure of Macrozoobenthos and Its Temporal Change on the Gapo Artificial Tidal Flat in Masan Bay, Korea

This study was conducted to get some basic information on the community structure of macrozoobenthos and its temporal change at 3 sites on the Gapo artificial tidal flat within Masan Bay from March 2002 to April 2004 when 8 years passed after the construction. The Gapo artificial tidal flat was constructed by filling the dredged contaminated sediments of MasanBayfrom 1990 to 1993. The surface sediment consisted of fine particles, but the grain size at the tidal flat has changed from mud to muddy sand by adding coarse particles for manila clam aquaculture by local fishermen from 2002. A total of 35 faunal species including 23 species at the upper tidal flat, 28 species at the lower tidal flat and 30 species in the tidal channel were collected during the study period. Polychaete worms were the most dominant fauna in species number and total faunal density, but mollusks were the most dominant in biomass. There was a specific species composition along tidal level. At the upper tidal flat, Prionospio japonicus, Sigambra tentaculata, and Neanthes succinea were dominant and at the lower tidal flat, N. succinea, P. japonicus, Corophium sinensis, and Ruditapes philipinarum were dominant while S. tentaculata, Paraprionospio coora, and C. sinensis were dominant at the tidal channel. In the feeding guild composition of the community, the surface deposit feeder (SDF) was the most abundant functional group followed by carnivores. The abundance and biomass showed a seasonal fluctuation;they decreased during summer seasonal and recovered in autumn. The Benthic Pollution Index (BPI) reflecting the trophic composition of macrozoobenthic community at each site remained in a very low level during most study period, which indicates the macrobenthic community of the Gapo artificial tidal flat has been in a disturbed environmental condition. The MDS plots also indicated that the species composition has changed seasonally and a large change in it was shown from spring to summer at all three stations. These results indicated that the benthic community in the constructed mud flat area has not reached on a stable structure until the spring of 2004 for 10 years after the artificial tidal flat construction.