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Detritivorous fishes are abundant and widely distributed in tropical coral reefs,involving a number of process of reef ecosystem including detritivory and removing sediments from epilithic algal matrixes(EAM).While lack of exact food spectrum may lead to ignore the some hidden interactions with benthic community,as well as the possible ecological impacts on coral reefs.In this study,we collected dominant detritivorous fish Ctenochaetus striatus(Quoy and Gaimard,1825)from reefs with different benthic covers,e.g.high coral cover reefs(HC),moderate coral and high short algal turfs(SATs)cover reefs(IC),and reefs with low coral cover and high cover of long algal turfs or macroalgae(LC),in the South China Sea and analysed the stomach contents of C.striatus using high-throughput sequencing.The stomach contents sequences of C.striatus was dominated by algae(relative read abundance,RRA > 80.0%),and some algal species was firstly detected to genus levels,e.g.dinoflagellates Symbiodinium and Prorocentrum.But the macroalgae and filamentous algae species,e.g.Rhodophyta,Chlorophyta Ochrophyta,detected in this study might come from the debris or early settlements of these algae instead of mature living state.The presence of C.striatus and their stomach content sequences showed obvious correlation with benthic condition in different reefs.The high RRA of macroalgae and filamentous algae detected in the stomach contents of C.striatus often associated with the presence of macroalgae in both of HC and LC reefs,and the abundance and biomass of C.striatus of these reefs was lower than IC reefs.The biomass of C.striatus showed a significant correlation with the coverage of SATs(P < 0.05),and with the temporary loss of coral cover and the increase of SATs cover,the sequences and diversity of microalgae(mainly dinoflagellates)in the stomach contents of C.striatus tended to be abundant(RRA 13.5–36.5%).Even dietary composition derived from RRA might has its potential limitation on providing precise quantilative data,the stable isotope analyses and conservative presence/absence of sequencing data also showed similar variable feeding activities in different reefs.These results indicated that C.striatus could remove microalgae this may be an important process on coral reefs,but also that C.striatus could be influenced by benthic conditions as its biomass and feeding microalgae abundance was often associated with SATs cover.Considering the widely distribution and high abundance of C.striatus in tropical reefs,the potential changes of such detritivorous fish in the functional status and possible ecological impact with moderate coral degradation should be considered and further investigated.