Studies Of Ecological Characteristics Of Food Zooplankton And Estimation Of Secondary Production In Sansha Bay And Xinghua Bay, Fujian Province

Sansha Bay is situated in northeast coastal area of Fujian Province with good water quality and rich aquatic resources.It is also the spawning ground of large yellow croaker;Xinghua Bay is situated in middle part of coastal area of Fujian Province,which is also the biggest bay and important mariculture base in Fujian Province.Zooplankton is an important part of marine ecosystem and also the secondary production in food chain.Food zooplankton,whose species composition and quantity distribution are closely related to fishery,is the direct or indirect diet of economic aquatic animals.There were limited reports on the zooplankton in Sansha Bay and Xinghua Bay and systematic studies on the food zooplankton as well.This study established 12 stations respectively in Sansha Bay(119°43′30″E¹19°58′00″E,26°38' 30 " N²6°44' 30 " N) and Xinghua Bay(119°17' 30 " E¹19°25' 00 " E,25°18' 30 " N²5°23' 30 " N).Based on the seasonal data from 4 cruises,respectively,on February,May,August and November,2007,the species composition,biomass,abundance and seasonal variation of food zooplankton,with their secondary production,P/B rate and conversion efficiency are analyzed in the two bays.The important results are as follow:1.The ecological characteristics of food zooplankton in Sansha Bay and Xinghua Bay.82 species of food zooplankton were identified in Sansha bay.Among them there are 35 species of copepods,5 species of amphipodas,4 species of decapods,3 species of chaetognaths,3 species of urodeles,2 species of Isopods,2 species of mysidaceans,2 species of ostracods,2 species of cumaceans,1 species of euphausiacea,1 species of polychaete,19 types of pelagic larvas and 3 species of benthic copepods.Copepod is the most important dominant group in Sansha Bay. The proportion of abundance is high during all seasons.The second group is pelagic larvas,whose abundance varies greatly with the seasons.It reaches the highest in summer,the lowest in winter.The mean value of biomass in Sansha Bay is 94.52 mg·m^-3,which is 90.21%of total zooplankton biomass.The mean value of abundance is 665.36 ind·m^-3,which is 97.79%of total abundance.The biomass and abundance in spring and autumn are greater than those in summer and winter.The distribution of biomass and abundance both showed different features with seasonal variation.77 species of food zooplankton were identified in Xinghua Bay.Among them there are 32 species of copepods,3 species of amphipodas,5 species of decapods,2 species of chaetognaths,3 species of urodeles,1 species of Isopods,3 species of mysidaceans,4 species of ostracods,1 species of cumaceans,1 species of euphausiacea,1 species of polychaete,19 types of pelagic larvas and 2 species of benthic copepods.Like the Sansha Bay,copepods is also the most important dominant group in Xinghua Bay.The proportion of abundance is high during all seasons.The second most important group is pelagic larvas,whose abundance varies greatly with the seasons.It reaches the highest in summer,the lowest in winter.The mean values of biomass and abundance in Xinghua Bay differ from those in Sansha Bay.In Xinghua Bay,the mean value of biomass is 183.24 mg·m^-3, which is 60.88%of total zooplankton biomass.The mean value of abundance is 1187.52 ind·m^-3,which is 96.93%of total abundance.Biomass and abundance both reach the greatest in spring,then decline progressively to the smallest of the whole year in winter.The distribution of biomass and abundance both showed different features with seasonal variation.Analysis results show that water temperature and runoff are major influencing factors for the species composition,temporal and spatial variation of food zooplankton in the two bays. 2.The estimation of secondary production,P/B rate,conversion efficiency for food zooplankton in Sansha Bay and Xinghua Bay2.1 The secondary production of food zooplankton in Sansha Bay and Xinghua BayThe average individual secondary production of food zooplankton in Sansha Bay is 2.045μgC·ind^-1·d^-1.The secondary production of food zooplankton in sea area is 11.924 mgC·m^-2·d^-1,which reaches the highest in autumn,second highest in summer,lowest in winter.The average individual secondary production of food zooplankton in Xinghua Bay is 1.568μgC·ind^-1·d^-1.The secondary production of food zooplankton in sea area is 11.924 mgC·m^-2·d^-1,which reaches the highest in spring,the second highest in summer and lowest in winter.The results show that the secondary production of food zooplankton in the two bays are related to factors including individual size,life cycle,sea water temperature,stability of water body,etc.2.2.The P/B rate of food zooplankton in Sansha Bay and Xinghua BayThe P/B rate is 0.082 in Sansha Bay and 0.089 in Xinghua Bay.Both of them reach highest in summer,the second highest in spring and lowest in winter.P/B rate is negatively correlated to individual mean dry weight of food zooplankton and is positively correlated to water temperature.2.3.The conversion efficiency of food zooplankton in Sansha Bay and Xinghua BayAccording to historical data,the conversion efficiency of the primary production to the secondary production is 36.17%in Sansha Bay and 21.01%in Xinghua Bay.It reaches the highest in autumn and lowest in winter in Sansha Bay, but does the highest in spring and lowest in summer in Xinghua Bay.The conversion efficiency is closely related to the abundance of nutrients.