| Our country has vast ocean and is characterized with long and tortuous coastline,which supplies prominent natural conditions for the development of marine economy.However,with the advancement of industrialization and urbanization in coastal areas,local coastal areas are facing multiple problems,such as habitat destruction,fishery resources decline,and biodiversity decrease,which threat the safety of our ecosystem and the sustainable development and utilization of biological resources.As an important component of marine ranching,the artificial reef has been demonstrated to be capable of mitigating pressures on the coastal ecosystems and enhancing fishery yield.To estimate the performance of the artificial reef in improving the habitat and resources,and elucidate the mechanism of ecosystem functioning,comparisons between the artificial reef and the adjacent natural reef in the offshore of Yantai were carried out in terms of community structure,trophic structure and energy flow,and the main contents and conclusions are as follows:(1)To ascertain the potential difference of demersal fishery community composition among natural and artificial reefs and adjacent sand bottom area in the nearshore of Yantai,four seasonal fishery investigations were undertaken from May 2018 to February 2019.In total,45,45 and 35 species were collected at the natural reef,the artificial reef and the sand bottom area all year round.Marked difference on species richness was not detected between the natural reef(30.8±5.7)and the artificial reef(25.8±3.4),both of which showed greater species numbers than the sand bottom area(18.3±1)significantly(Kruskal-Wallis test,p<0.05).Besides,CPUE(catch per unit effort)were much higher at both reef types than at the sand bottom area at each season(ANOVA,p<0.05),while the natural reef displayed higher CPUE values relative to the artificial reef in spring and summer(ANOVA,p<0.05).The CPUE of dominate species varied spatially,especially for Fat Greenling Hexagrammos otakii and Korean rockfish Sebastes schlegelii,where the artificial reef displayed an apparent advantage over other two areas in terms of CPUE.On the indices of bio-diversity,Shannon-Wiener diversity index(H?)displayed a pattern as:the natural reef(H?=2.39)>the artificial reef(H?=1.96)>the sand bottom area(H?=1.76).The natural reef displayed a higher Pielou evenness index(J=0.83)than the artificial reef(J=0.74),and no significant difference was observed between each of reef areas and the sand bottom area(J=0.79).No significant difference on Magalef species richness index(D)was detected within two reef types(2.97 and 2.91 for the natural and artificial reefs,respectively),and a relative lower D value was calculated in sand bottom area(D=2.19)(ANOVA,p<0.05).ANOSIM results showed that community structures differed notably among three areas,owing to that the abundance and distribution of dominate species spatially.To summary,the artificial reef in the nearshore of Yantai can support local demersal fishery yields,especially for reef-associated fishes.However,the biodiversity and community complexity of the artificial reef was at a lower level when compared to the adjacent natural reef.(2)To have a knowledge of the restoration of the food web of artificial reefs in the nearshore of Yantai,the trophic structure and trophic flow at the artificial and the nearby natural reef(as the reference)was characterized and compared,with biotic and abiotic samples,including primary producers,macrobenthos and fish were collected,together with the inclusion of the stable isotope method.Totally,we collected 18 algae species(15 and 18 for the artificial and natural reefs,respectively),and Chrysymenia wrightii displayed the highest biomass by dry weight at both reef types(208.52±181.4 g m-2 accounting for 31.81%of the total algae biomass and 162.62±211.68 g m-2accounting for 28.96%,at the natural and artificial reefs,respectively),followed by Ulva pertusa(101.55±82.64 g m-2 accounting for 5.9%and 94.86±91.72 g m-2 accounting for 15.64%,at the natural and artificial reefs,respectively).In addition,we totally sampled 36 macrobenthos(30 and 36for the artificial and natural reefs,respectively),and the macrobenthos at each reef type could be clustered into five trophic groups,namely filter-feeder,ominivore,detritivore,shellfish killer and grazer,according to the clustering analysis on their stable isotopic characteristics.Based on the contribution of nutrition sources to macrobenthos calculated by Mix SIAR model,we found that macrobenthos groups was fueled by same basal organic matter at either reef type,though the contribution varied from the natural to the artificial reefs.Moreover,33 fish species(26 and 33 for the artificial and the natural reefs,respectively)were collected in total,and they could be clustered into five trophic groups,namely generalist,benthivore,planktivore,Decapod feeder and piscivore,at each reef type as well.The qualitative diet analysis revealed that the diet sources were similar for specific fish group within two reef types,but the proportion of dietary composition would be distinct spatially for this group.By establishing general food web models from basal resources up to fishes at each reef type,we identified five same main food chains spatially,which were two pelagic pathway based on POM and three benthic pathway based on either Chlorophyta or a mixture of microphytobenthos,POM and Chlorophyta.To summarise,an artificial reef ecosystem that has been established for 5-10 years in the nearshore of Yantai can support principal trophic structure and trophic pathways similar as its natural counterparts,even though magnitudes of pathways differed within two reef ecosystems.(3)To assess the habitat quality of artificial reefs as alternative habitats of natural reefs supplied to reef predatory fishes and elucidate the mechanism of their coexistence at reef area,a case study of two common reef-associated predatory fishes in the north of Chinese sea,Fat Greenling H.otakii and Korean rockfish S.schlegelii were investigated based on the comparative analyses of both diet composition and trophic niche.The gut content analysis(GCA)showed that H.otakii preyed primarily on Decapod and Amphipod,while S.schlegelii exhibited higher dependence on fish(Blinniidae and Gobiidae).Overall,there were greater prey richness and diversity at the natural reef relative to the artificial reef.With stable isotopic analysis(SIA)in conjunction with Mix SIAR complementing the GCA,both spatial and interspecific difference were revealed on the food partitioning of H.otakii and S.schlegelii as well,evidencing the disparities identified from the GCA,confirming the habitat-specific effect on the prey availability for both reef-associated fishes.Additionally,comparisons on trophic niche breadth and niche overlap indicated higher trophic diversity but relatively greater food partitioning degree for both species at the natural reef than at the artificial reef.The food partitioning was also the main reason of their coexistence at both reef types.Our results suggest artificial reefs may harbor a prey assemblage different from natural reef but can support large populations of predatory reef-associated fishes and accommodate their coexistence,despite that the composition and supply of prey species varied spatially.(4)Ecopath models at both the artificial reef and the natural reef in the nearshore of Yantai were established,by using practical survey data,together with relevant references,in order to make comparisons on energy flow characteristics within two different reef ecosystem.The result showed that the total system throughput was lower at the artificial reef(6455.47 t·km-2·year-1)than at the natural reef(9490.48 t·km-2·year-1),suggesting the relative small scale of the former system compared to the latter.Based on the model output,function groups were clustered into five trophic levels at both habitat types,with energy occupied by medium and lower trophic levels outweighed others.Moreover,algae and phytoplankton are two important energy sources,whereas the detritus pathway dominates the whole trophic pathways.The mean energy transfer efficiencies at the natural reef and the artificial reef systems were 10.56%?10.21%,which were similar to the Lindman efficiency(10%),reflecting that two types of reef systems performed well.Total primary production(TPP)/Total respiration(TR)at the natural reef and the artificial reef were 1.49 and 1.93,which implied that there's still gap on maturity between the artificial and the natural reefs.Nevertheless,both the Connectance index(CI)and System Omnivory Index(SOI)were slightly higher at the artificial reef relative to the natural reef as well as other systems at the parallel latitude,suggesting that the artificial reef has had has relatively complicated inter-species relations and high level stability at present. |
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