Taxonomic And Ecological Studies On Epibiotic Diatoms In Typical Intertidal Habitats

As an juncional zone of ocean and terrestrial ecosystem,intertidal habitat is an important area of marine biodiversity research.The zone includes mangrove forest covered by mangrove plants,mudflats,sandbeach,rock foreshore without or little plants and other habitat types.Among them,mangrove forest is a typical unique tropical and subtropical marine intertidal habitat which has rich biodiversity and high primary productivity.However,there were several reports on diatoms living on abiotic substrates in various intertidal habitats,epibiotic diatom on biotic substrates has been widely ignored and underestimated.In fact,they may play an important role in biodiversity and productivity of intertidal benthic organisms,especially epidiatoms on the biological substrates of mangrove forests,which are typical habitats in the intertidal zone.The characteristics of species diversity and ecological role of the epidiatoms are an important scientific issue to be systematically studied.In this paper,we collected samples of different common biotic substrates from benthic areas of typical intertidal habitats in China,such as mangrove plants,associated plants and benthic animals,and collected samples of abiotic substrates and water samples for comparison.Light microscopy(LM)and Electron microscopy(EM)were used to observe the morphology,species identification,taxonomic systematics and floristic study of epidiatoms living on the substrates.We analyzed the species composition,morphological characteristics,attachment forms and spatial and temporal distribution characteristics of epidiatoms in typical intertidal benthic habitats in China,and discussed species diversity,taxonomic and ecological characteristics of epidiatoms and their important roles in intertidal ecosystems.The main results are as follows:1.A total of 130 species(including 13 varieties)of epidiatoms,belonging to 63 genera,18 families,9 orders and 2 classes,were identified from various biotic substrates and some abiotic substates in these five intertidal typical zones.The Centricae class includes Discoidales,Biddulphiales,Triceratiales and Paraliales,with a total of 7 families,17 genera and 31 species.The Pennatae class includes Naviculales,Bacillariales,Diatomales,Achnanthales and Surirellales,with 11 families,46 genera and 99 species.This study fully described the morphology characters,ecology habitats and geography of 130 species of epidiatoms,and attached LM and/or EM photos of every species.2.The analysis of epidiatom species composition shows that the number of epibiotic diatoms belonging to Discoidales Schütt,Naviculales Bessey and Bacillariales Hendey are richness,showing 26 species,29 species and 33 species,respectively,which account the total for 67.7%.Among them,the most richness is Nitzschia(16 species),then Tryblionella,Simonsenia and Achnanthes,showing 6 species,5 species and 4 species,respectively.3.There are differences existing in the diversity of epibiotic diatoms on different substrates.A total of 105 species,belonging to 48 genera,15 families and 2 classes,8 orders,were identified during the annual seasons and monthly epidiatom samplings investigation in Jiulong Estuarine Mangrove forest in Zhangzhou,Fujian.There are 40 species of epidiatoms from mangrove seedlings,41 species from Ishige okamurai,34 species from Suaeda australis,31 species from mangrove fallen leaves,23 species from Cyperus malaccensis Lam.,22 species from Enteromorpha prolifera Muller J.Agardh and mangrove leaves,and 21 species from Caloglossa leprieurii(Mont.)J.Ag.4.There are geographical differences of epidiatoms on biotic substrates in the five typical intertidal habitas,and the species and commnunity structures of epidiatoms varied in different mangrove areas.The analysis on the species composition characteristics of diatoms identified on various substrates and the relationships with substrates from mangrove forest in Jiulongj iang Estuary,Zhangzhou,Fujian were carried out.The results showed that 20 species of diatoms existed on various substrates respectively,which indicate that these species show less preferences towards substrates.While some identified epidiatoms only found in some specific biotic substrates,which indicate that the diatom have preferences and specificities to some biotic substrates,such as Halamphora bistriata Stepanek&Kociolek,Nitzschia dissipata(Kützing)Rabenhorst,Simonsenia delicatula Mikhailov&Makarova,Tryblionella acuminata Smith,and Tryblionella compresa(Bailey)Poulin only found on mangrove leaves;Navicula gregaria Donkin,Gomphonema lagenula Kützing,Cocconeis mascarenica Riaux-Gobin&Compere,and Rhopalodia constricta(Brébisson)Krammer only found on Enteromorpha prolifera.The same phenomenon showing the species diatom composition on varies substrates appear in the other four typical intertidal habitats.5.Based on the observation and the analysis of molecular sequences,we observed and described a new genus Chinia Gao,Lin,Chen&Witkowski Gen.nov.,and two new species Chinia longhaiensis Gao,Lin,Chen&Witkowski sp.nov.,Microcostatus Witkowskii Lin,Gao&Chen.The typical characteristics of the genus Chinia are as following:the valves are obviously wavy and uneven,the raphe canals are slightly eccentric and perforated,the copulae are perforated,which belongs to simonsenioid-type raphe canal,is supported by sparse infundibulum-like portulae,which are separated by large fenestrae.The valves also have hymenate areolar occlusions and the raphe lacks a central nodule.The typical features of Chinia longhaiensis are as following:small cell,plate-like plastids and obvious 3-8 fenestrae,uneven valves,transapical striae composed of irregular areolae with small hymenate.The apices are acutely rounded,with portulae connecting the raphe cannal and the internal cells.The raphe canal is ornamented with lace-curtain-like siliceous deposits,and equipped with two or three spinules at the poles.The typical features of Microcostatus Witkowskii are as follows:Conspicuous nonperforated conopeum in the central area of the valves.The depressions in the axial area show clearly tranverse microcostae.The striae are continuous under the conopeum from the sternum towards valve margin.Raphe in the internal is straight and the central ends slightly deflected unilaterally.Poorly developed helictoglossae are present in distal ends.The external central raphe ends slightly expanded and deflected to the same side.The distal ends hooked and bent to the opposite side of the central ends and continuous onto the mantle.Based on the analysis of molecular sequence evolution,the genus was classified into Naviculales and Sellaphoraceae,but not belonged to Naviculaceae.6.Twelve Chinese new recorded species were observed and described as well:Amphora insulana Stepanek&Kociolek,Hyalosira tropicalis Navarro,Licmophora remulus(Grunow)Grunow,Cocconeis mascarenica Riaux-Gobin&Compere,Cocconeis subtilissima Meister,Astartiella persica Ashworth,Planothidium mathurinense Riaux-Gobin&Al-Handal,Simonsenia aveniformis Witkowski,Gomes&Gusev,Nitzschia rhopalodioides Hustedt,Tryblionella compressa(Bailey)Poulin,Tryblionella cf.confusa Bertolli&Torgan and Tryblionella persuadens(Cholmnoki)Cavalcante,Tremarin&Ludwig.7.The ecology habitats of epidiatoms are compared,the results show that most of epibiotic diatoms are benthic attached species.However,some planktonic species such as Thalassiosira minima Gaarder,Thalassiosira weissflogii(Grunow)Fryxell&Hasle,Cyclotella atomus Hustedt,and Cymatodiscus planetophorus(Meister)Hendey existed on the substrates,which indicate that these species may both have plantonic and attached habitats,and may live temporarily on the substrates by tidal action.At the same time,some freshwater species existed as well,like Discostella stelligera(Cleve&Grunow)Houk&Klee and Luticola ventriconfusa Lange-Bertalot,which show that mangrove area exist freshwater injection from estuary,and these species have certain adaptability to salinity changes.8.Comparison of attachment morphology of diatoms on different biotic substrates show that there are three main types of common attached types of biotic epidiatoms,showing attachments by glial membrane,pad and stalk;and different attached types of epidiatoms exist on different biotic substrates.In this study,we focused on the research of the epidiatoms on biotic substrates from intertidal typical mangrove habitats in China,and collected some abiotic substrates.We systematically investigated the species diversity characteristics on the biotic substrates from intertidal zone,discovered the new diatom genus,species and Chinese new records,which enriched the diversity and area records of marine diatom in China.It will provide the important data base for Chinese marine biological diversity especially the biodiversity research in the intertidal ecosystem and coastal ecological environment investigation and monitor.It has important theoretical and practical significance on diatom species diversity research,and to explore the ecology position of marine diatoms in marine ecosystems.