Effects Of Different Environmental Factors On Biological Characteristics Of Harmful Algae (Scrippsiella)

Scrippsiella species widely distribute along China Sea and formed harmful blooms many times.To understand the forming mechanism of harmful algal blooms(HABs),we researched environmental factors effects on some biological characteristics of Scrippsiella species in this paper in order to supply bases for prevention of HABs.Resting cysts play an important role in the life cycle of some dinoflagellates,which are considered to be one of the initiation factors of algal blooms.We described the types and morphological diversity characters of Scrippsiella trochoidea cysts both from in situ sediment samples and induced in different cultural conditions in the present research.Scrippsiella trochoidea cells were maintained in f/2 and f/2-N separately at 20℃and 12:12 L:D cycle.After 14 days and 8 days,the resting cysts were observed in two different media respectively.After 30 days,the cultures were preserved at darkness,and 4 types of resting cysts were found in another 90 days,They are as follows:ⅰ,Spherical to ovoidal cyst(25 to 39μm long) covered by sparse or numerous calcareous attachment(1 to 4μm length),calcareous surface,,ⅱ,Spherical cyst(29 to 35μm diameter) with non-calcareous surface attachment,calcareous surface.ⅲ,Spherical to ovoidal cyst(29 to 35μm long) without any surface attachment,calcareous surface.ⅳ,Spherical cyst(24 to 35μm diameter) without any surface attachment,organic surface.The first type cysts are the most common,percentagewise,which are 77.70%and 95.18%respectively in two different cultures.The cysts from sediments primarily comprise the first type which have calcareous attachment and the infrequent forth type which has organic wall without any attachment.The reasons why Scrippsiella trochoidea cysts produced at culturing have many morphologies and the four types have different percentages as well as the morphologies of cysts from sediments were dicussed in this paper.Compared these cysts produced at culturing with the cysts from sediments would supply the bases that the field Scrippsiella trochoidea cysts have many morphologies.Scrippsiella irregularis is a new species identified in 2007.We found that low nutrient concentration could induce cysts production and high temperature and salinity were suited for cells growth in culturing.The life history of Scrippsiella irregularis has asexual stages or sexual stages,the former relate to the single vegetative cell to form two vegetative cells by binary fission,the latter is that gamete mates to yield zygote with two longitudinal flagella and the zygote also can divide to produce two vegetative cells.Scrippsiella irregularis temporary cyst is formed by morphologic changes of vegetative cell,and the temporary cyst can germinate to release vegetative cell when environmental conditions are comfortable.The contact statuses of cells are different between vegetative cell division and zygote division.The sexual stages in life history of Scrippsiella irregularis were studied and that results help to reinforce the amount of dinoflagellate species with sexual reproduction as well as supply the base for better understanding Scrippsiella irregularis by researching life history of Scrippsiella irregularis.