Taxonomy And Dynamic Changes Of Sessilids In Two Culture Systems Of Procambarus Clarkii

The species of order Sessilida Kahl,1933 are a group of protozoans with a cosmopolitan distribution in aquatic ecosystems,and most attach to a substrate by a stalk,a lorica or a scopula.They are speciose and numerous,and could respond rapidly to changes in environment.Procambarus clarkii Girard,1852 is one of the most important economic animals in China,and the main culture models include rice-crayfish integrated system(RC)and crayfish monoculture system(CM).The sessilids in crayfish integrated systems are insufficient studied despite the fact that they are one of the important components of these systems.Herein,a taxonomic study on epibiotic and free-living sessilids in RC and CM from Qianjiang,Jianli,Huangshi and Hanchuan is conducted.Two new species were established,and 9 known species were redescribed.The list of sessilids is as follows: Epistylis calix n.sp.,E.paravaginula n.sp.,Pseudovorticella monilata Tatem 1870,Carchesium polypinum(Linnaeus,1758)Ehrenberg,1830,Campanella sinica Wang et al.,2021,E.semiciculus Zhou et al.2019,E.hentscheli Kahl,1935,E.chrysemydis Bishop et Jahn,1941,E.chlorelligerum Shen,1980,Opercularia protecta Penard,1922,and O.nutans Ehrenberg,1831.What’s more,an investigation of dynamic changes of sessilids in RC and CM are conducted.The main results and conclusions are summarized as follows:1.These epibiotic sessilids belonged to the following genera: Epistylis,Opercularia,Carchesium,and Vorticella.The epibiotic sessilids were dominated by Epistylis species.Compared to the solitary sessilids,the colonial sessilids(e.g.,Epistylis)were more competitive,so they could always occupy more sources and became dominated.2.The sessilids showed a predilection of attachment for maxilliped,followed by pereopod,nectopod and gill.The results revealed that the distribution of sessilids in the P.clarkii were determined by the space and nutrient availability,and the morphology of site surfaces.3.In RC,the total attachment rate of epibiotic sessilids was 97.4%(150/154),the mean abundance was 478 zooid/ind.The abundance of epibiotic sessilids peaked in December2020 and 2021,with minimum values in June and July 2021.In CM,the total attachment rate of epibiotic sessilids was 84.9%(135/159),the mean abundance was 523 zooid/ind.And the abundance peaked in August 2021,with minimum values in January,May and June2021 and January 2022.The attachment rate of epibiotic sessilids in RC was higher than in CM,and the mean intensity in RC was lower than that in CM but without significance(P>0.05).4.The dynamic changes of epibiont sessilids has no significance correlation with 14 water quality factors,i.e.,p H,water temperature,dissolved oxygen,transparency,zooplankton/phytoplankton density,zooplankton/phytoplankton biomass,zooplankton/phytoplankton Shannon-Wiener diversity index,zooplankton/phytoplankton Pielou evenness index and zooplankton/phytoplankton Margalef richness index in RC(P>0.05),and only showed significant,negative correlation with water transparency(P<0.05)in CM.These results suggest that these 14 factors may not have significant effects on sessilids community.