Study On The Characteristics And Diversity Of Swimming Animal Communities In The Qixing Islands

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 80 nekton species which are belonging to 3 classes,14 orders,42 families,62 genera,including 52 fishes,13 shrimps,10 crabs and 5 cephalopod.The total of the species among two seasons were varied,with 61 species in autumn and 52 species in spring.The seasonal migration is obvious by the result that only 30 species were catched in both two seasons,accounting for 37.5% of the all species.About the ecological type,42 species was belonging to warm water,38 species was warm temperature,no cold temperature species.The majority species of 58 which are offshore migration species,followed by coastal settlement species of 15 and estuarine migratory species of 7.The relative importance index(IRI)showed the result that dominant species had ten species,6 species were arised in autumn,including 3 species in ground floor,2 species in near the bottom,1 species in upper middles;4 species in spring,including 2 species in ground floor,1 species in both near the bottom and upper middles.This showed that the major species of dominant species was the ground floor species.The result of NMDS analysis showed that the standard sequence map of autumn had a certain explaining significance and the spring’s was a good sort.Cluster analysis demonstrated that 12 stations in autumn can be divided into 4 groups at the similarity level of 70%,and the stations can be divided into 4 groups at the similarity level of 60% in spring.SIMPER analysis showed that a little difference was found between the characteristic species and different species in autumn,but a big difference in spring.A significant difference was detected between 2 combinations in spring with the result of ANOSIM analysis.Two combinations were G1 and G4,G2 and G4,the P value between G2 and G4 was 0.008 that has significant difference.There were 3 combinations which had obvious difference in spring,which were G1 and G4,G2 and G3,G2 and G4.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.The evenness index which was more than 0.7 among 12 stations in autumn has 6,and 3 in spring.According to 《aquatic testing handbook》,when h’ is between 1 to 3,it shows that this sea water moderately affected by human impact.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 Qixing islands offshore.In addition,the degree of interference is more serious in spring.With the abundance curve is on the basis of biomass curve,this also displays that the species are smaller in spring.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 17 and 13 respectively.The plankton functional group was obvious dominant functional group in autumn,with its weight accounted for 62.89%,while omnivorous functional groups was a larger group in spring with no dominant functional group.The material and energy of the area were mainly transferred through the following two ways: planktons→ plankton functional group →omnivorous predator functional groups →carnivorous functional groups;plankton→ plankton functional group →nekton/zoobenthos functional feeding group →carnivorous functional groups.The Shannon-wiener diversity index(H’)of functional group ranged from 0.09~1.424,which had a positive correlation with the two factors of the species number and biomass percentage.The H’ of functional group in spring is larger than in autumn.