Biodiversity Studies Of Epiphytic Organisms On Seaweeds And Their Litter

Seaweeds are important primary producers in the coastal waters,providing diverse habitats and substrates for a variety of epiphytes,and increasing the biodiversity of coastal ecosystems.In order to understand the epiphytic biodiversity on “living” seaweeds in the Nanao sea area of Shantou,Guangdong Province,epiphytic biome on different types of seaweeds and the characteristics of the marine organism community structure were investigated in October 2019 and 2020.Laboratory experiments compared the bacterial community structure succession in the litter decomposition process of Gracilaria lemaneiformis and Gracilaria lichenoides to explore the bacterial diversity in the litter decomposition process of the “dead” Gracilaria seaweeds.The main results are as follows:(1)Field surveys showed that the total richness and shannon diversity index of epiphytic biome on seaweads were higher than that in the seawater.The Shannon diversity index of epiphytic eukaryote on seaweeds was significant higher than that in the seawater(p<0.05).The dominant genera between epiphytes on seaweeds and organisms in the seawater were different.Syedra,Harpacticus and Symbiodinium were dominant genera in epiphytic eukaryote,and Exiguobacterium and Psychrobacter were dominant genera in epibacteria.In the seawater,Parvocalanus and Navicula were dominant genera,and the dominant genus of bacteria was HIMB11.Results show that seaweeds increase the biodiversity of coastal ecosystems.The diversity of epibacteria on seaweeds was significant higher than that of eukaryotes(p<0.05).Aeromonas,Psychrobacter and Acinetobacter were the core microbiome of epibacteria.The prediction of functional composition indicates that the dominant species of core bacteria group were mainly related to amino acid transportation and metabolism,energy production and conversion,cell wall synthesis,and signal transduction of seaweeds.(2)The laboratory simulation experiment of the seaweed litter showed that the epibacteria had obvious community succession during the decomposition of the litter.Proteobacteria was the dominant group of epibacteria in the early stage of decomposition of G.lemaneiformis litter(0days,10 days).Bacteroidetes was the dominant group of epibacteria after 20 days of litter decomposition.Firmicutes was the dominant phylum of epibacteria after 35 days of litter decomposition.The dominant group was re-successful into Proteobacteria after 55 days of litter decomposition.The richness and diversity of litter-epibacteria OTUs increased first and then decreased.The shannon diversity index of epibacteria OTUs on G.lemaneiformis litter decomposed for 20 days was the highest.Carboxylicivirga of Bacteroides and Desulfovibrio of Proteobacteria were the keystone bacteria in the whole succession process.The epibacteria in the whole decomposing process of G.lemaneiformis litter preferred positive symbiosis and showed an interdependent relationship.The richness and relative abundance of the litter-epibacterial OTUs on G.lemaneiformis and G.lichenoides showed the similar trends at the phylum level.Desulfovibrio was the dominant epibacteria of G.lemaneiformis and G.lichenoides litter which belongs to sulfate-reducing bacteria.There was no significant difference in the complexity and diversity of the epibacterial community structure between G.lemaneiformis and G.lichenoides litter(p>0.05).Results shows that when the environment is similar,the alpha-diversity and community complexity of epibacterial OTUs on different species of litter show the same trend.