Effects Of Aquaculture On Macrobenthic Community In Sansha Bay,Fujian Province

Sansha bay represents one of the most typical mariculture embayments in Chinese coasts,and there are crucial significances of investigating the effects of macrobenthic ecosystem affected by farming(including cage farming)in this area.Although a number of studies on macrobenthic ecosystem in Sansha bay had addressed,researches of investigating with massive stations,of functional feeding groups of macrobenthos and from the view of trophic ecology about the macrobenthos in Sansha bay were rare.In this paper,community structure and functional feeding groups of macrobenthos as well as trophic characteristics of numerically dominanted polychaeta,based on sampling data in August 2016,had been used to illustrate the effects of macrobenthic ecosystem affected by farming.The main results were concluded as follows.1.Community structure of macrobenthos and its relationship with the environmental variables in Sansha bayA total of 74 species belonging to six phyla were encountered and 14 environmental variables,including depth,salinity,temperature,TN,TP,were collected among four types of water(large yellow croaker farming,kelp rope farming,abalone raft farming and non-farming).The main conclusions were included:(1)The total species included annelides(48 species),arthropods(12 species),molluscs(9 species),echinoderms(2 species),nematodes(2 species)and coelenterates(1 species).The average abundance and biomass of macrobenthos were 371.34 ind./m2 and 21.82 g/m2,respectively.The average abundance and biomass of annelides were 292.68 ind./m2 and 13.06 g/m2,respectively.Heteromastus filiformis,Sternaspis scutata,Onuphis eremita,Lumbrineridae unidentified species 1 and Ophelina acuminata were numerically dominated.(2)The mean of Shannon-wiener diversity index was 2.56(ranging from 0.00 to3.51),which showed a higher diversity.The mean of Simpson index was 0.26(ranging from 0.10 to 1.00),the mean of Pielou index was 0.83(ranging from 0.00 to 0.97)and the mean of Margalef index was 0.97(ranging from 0.16 to 1.75)(3)Kruskal-Wallis test domenstrated that there were no significant differences(P>0.05)for all the above-mentioned community parameters among four types of waters,and the consequent comparison(Behrens Fisher test)results showed that only one difference was detected,which was occurred in the Shannon-Wiener diversity index between large yellow croaker farming and non-farming areas(P<0.05)(4)The cluster analysis revealed that structure of macrobenthic community in Sansha bay showed remarked spatial heterogeneity.Canonical correspondence analysis demonstrated that depth,temperature and salinity of bottom water body,and water content,silt-clay fraction,total nitrogen as well as total organic matter of sediment were main factors regulating the benthic communityIn summary,impacts of farming on the species diversity of macrobenthos were considered not remarked in Sansha bay,but there may be moderate impacts on the community structure of macrobenthos in according with classcical succession model proposed by Pearson&Rosenberg(1978)2.Functional feeding groups of macrobenthos and its relationship with the environmental variables in Sansha bayAccording to the food preferences,the macrobenthos collected in Sansha Bay were classified into four functional groups,including carnivorous group(C),omnivorous group(O),detritivorous group(D)and planktophagous group(P1).The main conclusions were listed as(1)The macrobenthic species in Sansha bay included carnivorous group(27 species),detritivorous group(25 species),omnivorous group(16 species)and planktophagous group(6 species).Compared with group C(75.91 ind./m2),group O(37.80 ind./m2)and group Pl(29.27 ind./m2),the average abundance of group D,reaching 228.35 ind./m2,was the largest.The average biomass of group C was 12.11 g/m2,higher than group D(6.19 g/m2)and group Pl(2.84 g/m2).The lowest average abundance showed by group O,which only was 0.68 g/m2.(2)Redundancy analysis showed that TP in the sediment,salinity and pH of bottom water body as well as depth were the main factors regulating the functional feeding groups of macrobenthos.In addition,TN and TP in the sediment as well as depth showed a stronger relationship with carnivorous group.An integrated dependency with environmental parameters was illustrated by detritivorous group.The salinity of bottom water showed a remarkable relationship with omnivorous group.The combination of dissolved oxygen and temperature of bottom water as well as C/N was considered as the main affectable environmental variables regulating the number of planktophagous group.The composition of functional groups of macrothos in Sansha bay differed from those in natural waters and other mariculture waters as revealed in previous studies.Although benthic functional groups in Sansha bay implied that they were located in organic matter enriched environment,the distribution patterns of the groups could not fully reflect the disturbances from fish cage farm.3.Trophic ecology of numerically dominant polychaetes in Sansha bayThe stable isotopes of five numerically dominant polychaetes(Heteromastus filiforms,Lumbrineridae unidentified species 1,Ophelina acuminata,Onuphis eremita and Sternaspis scutata)in four kinds of waters of Sansha bay were analysed.The δ13C,δ15N of the studied polychaetes had wide variations in most studied waters.One-way ANOSIM analysis showed that there was no significant difference in δ13C,δ15N among four types of water.Differences of TN and TOC of the studied species in varied waters were also rare,with the exception of those from Ophelina acuminata among different types of water.In all,the above-mentioned results demonstrated that the AOM had not remarked affected the dietary characteristics of numerically dominant polychaetes.