Environmental Impacts Of Mariculture On Sedimentary Variables And Polychaete Community Structure In Sansha Bay,Fujian Province

Sansha Bay is one of the most typical mariculture bays in the East China Sea,and there are remarked significances to study the environmental effects of aquaculture in this area.There already existed a number of studies addressed in this problem,but the existed studies had some shortcomings,such as not enough sampling stations,limited environmental factors,lack of statistical analysis,and so on,which maybe affect the scientificity of conclusions.In this study,we intended to trace environmental impacts of farming activity through analysis the spatial differences of 9 sedimentary variables(?¹⁵N,?¹³C,TOC,TN,TP,AVS,C/N ratio,water content and silt-clay content)and polychaete community structure among four kinds of waters?large yellow croaker cage farming,abalone raft farming and kelp rope farming waters and non-farming water?based on data collected from 10 cruises?monthly cruises from May 2009 to January 2010,one cruise in August 2016?.Upon this,the following main contents were included.1.Spatial variability of typical sedimentary variables and their implication for mariculture effectsIn the 4 kinds of waters?non-farming,large yellow croaker farming,abalone raft farming and kelp rope farming?,we established a total of 41 sampling stations,and 1cm surface sediment samples were collected to analyse spatial distribution characteristics of nine environmental parameters(?¹⁵N,?¹³C,TOC,TN,C/N ratio,TP,AVS,water content and silty clay content).The main conclusions were drawn as follows.?1?Kruskal-Wallis test showed that there were no significant differences?P>0.05?for all the above parameters among 4 types of waters,and the consequent?Behrens Fisher test?comparison results also showed that only occasional differences were detected,including the ?¹⁵N and ?¹³C in abalone aquaculture and reference stations,silt-clay content in seaweed farming and reference stations?P<0.05?.?2?Principal component analysis?PCA?showed that the studied variables can be divided into 4 categories?Eigenvalue>1?,and the main components explained the variation?87.7%?.Among them,PC1 was mainly composed of TOC,TN,water content and silt clay content with the maximum interpretation?44%?.PC2 was mainly composed of ?¹⁵N,?¹³C and TP?20.2%?.PC3 was mainly composed of C: N ratio,and the amount of interpretation is 12%.PC4 was mainly composed of AVS,the amount of interpretation was 11.6%.?3?PCA and Cluster clustering results had similar results,sampling stations were randomly distributed which did not correspond to the differences in the farming activities.?4?The above results showed that aquaculture activities had no significant impact on the benthic environment.However,considering the farming methods and the large aquaculture production in Sansha Bay?large yellow croaker production was 1.28 × 105 t in 2014?and correlation calculation?unpublish data?,it is considered that the farming waste is still the main source of organic matter and nutrients,meanwhile the regional topography and hydrological conditions,such as broad tidal flats,high water exchange ability may be the important reasons for the ceasing of excessive accumulation.2.Temporal and spatial variation characteristics of Polychaeta community structure and their response to aquaculture activitiesA total of 20 sampling stations in three types of waters?non-farming,seaweed farming,and large yellow croaker cage farming?were designated in the prriod May 2009 to January 2010?9 cruises?.In the August of 2016,an addition cruise was conducted,which included 41 stations in four types aquaculture waters?non-farming,large yellow croaker farming,abalone raft farming and kelp rope farming?.Sediment samples were collected using a box,based on which polychaete animal samples were obtained,and consequently analysed the characteristics of community structure to reveal the spatial differences.We used cluster?division of community?,ANOSIM?communities differences test?and SIMPER?key components different communities?analysis to study the impacts of aquaculture on polychaete community structure.Additionally,canonical correspondence analysis?CCA?was conducted to study the relationship between community composition and typical environmental factors.The main results were as follows:?1?In the cruises of 2009-2010,the abundance in cage farming and non-cage farming waters were 124.84 ind./m²,184.54 ind./m² and 2.37,respectively.In the cruise of 2016,polychaete community in the cage farming water had advantages in the number of species,abundance and biomass and Shannon-Wiener diversity index compared to those in other types waters,which were 47,346.20 ind./m² and 20.12 g/m²,respectively?only abundance was slightly lower than that in abalone farming area?.A comparision of community structure of large yellow croaker cage farming waters between two sampling period showed that the number of species in 2016 cruise was less than those in 2009-2010 cruises?41 species vs.65 species?,abundance and biomass were approximately twices of that in 2016?346.20 ind./m²>180.54 ind./m²,20.12g/m²>8.67g/m²?,and diversity index H' was significantly higher in former than in latter?2.37>1.54?.But there were no significant difference in the 6 typical communities parameters in different aquaculture waters?P>0.05?based the data sets of May 2009 to January of 2010,and the August of 2016.?2?Two-way ANOSIM analysis showed that there was no significant differences in polychaete community structure in 2009-2010 cruises?R=0.05,P>0.05?.Take the community with highest similarity?cruise in the May of 2009,22% similarity?as an example,cluster analysis showed that cage farming and non-cage farming stations were evenly distributed in the two communities which implicated no significant difference?R= 0.009,P>0.05?.However,polychaete community in the August of 2009,with the lowest similarity?15%?,could be divided into two communities which could represent cage farming and non-cage farming stations.Significant differences between the communities could be confirmed by one-way ANOSIM analysis?R=0.601,P<0.01?.Subsequent SIMPER analysis showed that there were differences between species composition in the two communities.Cluster analysis showed that polychaete community could be divided into three communities at 30% similarity level in the August of 2016.Though SIMPER analysis showed that there were differences considering the key species composition among the three communities,diffrerent waters stations were evenly distributed those communities.These indicated that cage culture did not have a significant impact on polychaete community structure.3.Relationship between the polychaete community and environmental factors in Sansha BayBased on the data in cruise of the June of 2009,CCA analysis showed that pH?F=4.72,P<0.01?and water depth?F=4.01,P<0.01?and dissolved oxygen?F=2.28,P<0.05?were key environmental factors regulated polychaete distribution pattern in Sansha Bay.However,polychaetes community in 2016 cruise showed that Depth?F=2.07,P=0.01?and TOC?F=1.78,P=0.04?were the key environmental factors affecting polychate distribution in Sansha Bay.