Community Structure And Biodiversity Of Nekton In Eastern YuHuan And Adjacent Offshore Area

In this paper,we studied the nekton species composition,the two quarter turnover rate,ecological type,dominant species,community structure,diversity,the degree of interference,and functional group diversity.There are 62 nekton species which are belonging to 15 orders,33 families,51 genera,including 37 fishes,14 shrimps,8 crabs and 3 cephalopod.The total of the species among two seasons were varied,with 51 species in autumn and 41 species in spring.The seasonal migration is obvious by the result that only 30 species were catched in both two seasons.About the ecological type,28 species was belonging to warm water,34 species was warm temperature,no cold temperature species.The majority species of 43 which are offshore migration species,followed by coastal settlement species of 10 and estuarine migratory species of 9.The relative importance index(IRI)showed the result that dominant species had 3 species were arised in autumn,and 1 species was arised in spring.This showed that the major species of dominant species was the ground floor species and near the bottom species.The result of NMDS analysis showed that the standard sequence map of two seasons had a certain explaining significance and the spring's was a good sort.Cluster analysis demonstrated that 12 stations in every season can be divided into 2 groups.The offshore sea area is one group and the outer sea area is another group.ANOSIM analysis showed that there were extremely significant differences in the spring and autumn groups.Diversity index analysis indicates that the two seasonal nekton diversity was at a medium level and the range and mean of the diversity index in autumn was slightly larger than that in spring.This be affiliated to with the species number and the evenness.The number of species in autumn is more than spring and the species of 12 stations is more even than spring.ABC curve analysis showed that the W value of two seasons were close to 0.This result indicated nekton community was in moderately interference in Yuhuan offshore area.In addition,the degree of interference is more serious in autumn.Two season's nekton functional group composition had no variety,which all can be divided into 7 functional feeding group and this showed that the functional group structure is stable.The plankton functional group was primary in both autumn and spring,which had 12 and 10 respectively.The omnivorous predator functional group was obvious dominant functional group in autumn and spring.The material and energy of the area were mainly transferred through the following two ways: planktons ? plankton functional group ? omnivorous predator functional groups ? nekton functional groups;plankton ? plankton/zoobenthos functional group ?nekton/zoobenthos functional feeding group ? nekton functional groups.The Shannon-wiener diversity index(H')of functional group ranged from 0.427~1.631,which had a positive correlation with the two factors of the species number and biomass percentage.The H' of functional group in autumn is larger than in spring.