Distribution features of zooplankton in the Zhejiang coastal waters

Zooplankton is the secondary producer of the ocean.The variation of its variety and quantity has a direct impact on or even control the primary productivity as well as the biomass of fish and other marine animal resources.It plays an important role in the food web of the sea.Though many studies on the zooplankton of the East China Sea are known,most of them were large scale studies covering the whole East China Sea,or small scale studies for the estuaries or the inner bays.Few studies were carried out near the forbidden fishing line.In summer and autumn,2003 and 2004,the species composition,quantitative distribution,dominant species and community structural characteristics of the zooplankton during spring tide and neap tide were studied at 37 stations in Zhejiang coastal waters(27°05′~30°54′N,121°04′~123°19′E),along the 50 m isobath(the outside sea area near the forbidden fishing line with stations P1-P20) and the 10 isobath inside sea area,with stations 1-17).234 species were identified in the studied waters,which belong to 19 groups including 66 species of Copepoda,42 species of Medusae,13 pelagic mollusks,13 Amphipod,13 Chaetognath,9 pelagic polychaeta,9 Mysidacea,6 Ostracoda,6 Sergestidae,5 Tunicata,4 Cumacea,4 Euphaussids,3 Cladocera,30 groups of pelagic larva and some others.The mean biomass of the zooplankton was 289.9±43.4 mg/m3 in inside sea area,258.9±73.6 mg/m3 during spring tide,320.8±47.3 mg/m3 during neap tide;318.9±49.8 mg/m3 in outside sea area,390.5±89.1 mg/m3 at spring tide,247.2±41.4 mg/m3.The mean abundance was 751.2±138.4 ind/m3 in inside sea area,531.8±94.4 ind/m3 during spring tide and 971.5±253.2 ind/m3 during neap tide;816.8 ±137.2 ind/m3 in outside sea area,1 041.0±243.8 ind/m3 during spring tide,and 592.5±111.8 ind/m3 during neap tide.In this investigation,it was found that Copepoda had the most contribution to the mean abundance,and next were Chaeognath,Medusae,Tunicata and pelagic larva.They were the main groups of the zooplankton.There were 15 species with dominance0.02 in the investigative zone.9 species and 10 species were identified respectively for inside and outside sea area,among which Diphyes chamissonis,Calanus sinicus,Euchaeta marina and Sagitta enflata were the dominant species,whose abundance makes up 60% of total abundance of zooplankton.As to different tidal levels and latitudes,the community structure index of zooplankton didn't change obviously.The community structure was good with higher richness,diversity index and evenness index and lower simplicity index.The indexes amplitude varied greatly(the species from 16 to 55,the richness 1.73~6.77,simplicity index 0.06~0.54,diversity index 1.67~4.51,evenness index 0.33~0.87),which indicates the instability of community structure.According to the ecological habit and distribution feature of the zooplankton,the studied area may be divided into five ecological groups,which were named inshore low salinity species,alongshore warm-temperature species,inshore warm-water species,eury-warm water species and tropical oceanic species.Moreover,the inshore warm-water and eury-warmwater species were principle groups in the area.