Population Dynamics And Toxin Production Of Dinophysis Species In The Coastal Waters Of Qingdao

Food poisoning incidents caused by diarrhetic shellfish poisoning (DSP) toxins occurred frequently in coastal countries around the world. Presently, there is no DSP report in China, but DSP contaminated shellfish has been frequently detected in China, which should be paid more attention by relevant administrative agencies. A lot of previous studies found that toxic species in genus Dinophysis were the main source of DSP in shellfish. Although Dinophysis spp are widely distributed in the coastal waters of China, knowledge on Dinophysis spp is quite limited due to the difficulties in culturing Dinophysis species, and the low cell densities presented in seawater under normal condition. Most of the studies on Dinophysis spp. are confined to the morphological description of the species recorded, researches on the eco-physiological characteristics, toxin production and genetics of Dinophysis spp. are not carried out. In the current study, we selected the coastal waters of Qingdao, where contaminated shellfish and distribution of Dinophysis spp. have been reported, to study the species composition, population dynamics and toxin production status of Dinophysis spp. From 2009 to 2010, phytoplankton samples were collected periodically from the fixed stations to identify the species of Dinophysis by morphological features and single-cell PCR analytical results. Cells of each Dinophysis species were counted under microscope to study the distribution pattern and population dynamics of Dinophysis species. Meanwhile, LC-MS methods were established to analyze the toxin composition and content in hand-picked Dinophysis cells and concentrated phytoplankton samples.The results of morphological observation combining with single-cell PCR anlaysis found 3 Dinophysis species in the coastal waters of Qingdao, D. aucminata species complex, D. rotundata and D. fortii. Populations of Dinophysis spp. showed an obvious seasonal dynamics. From 2009 to 2010, investigation results at Zhongyuan Wharf of Tuandao Bay indicated that D. acuminata species complex was the major Dinophysis species in the phytoplankton communities, and it appeared mainly from April to September, with the highest cell density around 800 cells/L. D. rotundata appeared later than D. acuminata species complex, mainly from August to September, with much lower cell density around 100 cells/L. From Mar. 2010 to Feb. 2011, investigation in coastal waters of Qingdao foundd that Dinophysis species presented mainly from May to August at the surface water and distributed mainly at the entrance and outside the Jiaozhou Bay, and in the eastern part of the Bay. The distribution area was the largest in July. In the sea area with deep water outside and at the entrance of the Bay, cell density of Dinphysis at the bottom layer often exceed that at the surface. The maximum cell density of D. acuminata species complex in the sea area at the entrance and outside the bay appeared in June, and the highest value of cell density of 1.98×103 cells/L was found at D3 station (36o04N,120o23E). The maximum cell density of D. acuminata species complex inside the Bay appeared in July, with the value of more than 200 cells/L. D. rotundata in the coastal waters of Qingdao started to appear from May, but the cell density remained low until August when it became dominant in Dinophysis populations in most of the studied area. D. fortii was seldom observed in the coastal waters of Qingdao during the whole year, which appeared only at the entrance and in the eastern/southeastern part of the Bay in July at very low cell density.To study the toxin production status of Dinophysis species, toxins in hand-picked Dinophysis cells as well as samples of concentrated phytoplankton were analyzed with the LC-MS/MS methods. Toxins were detected in all the 3 species of Dinophysis in the coastal waters of Qingdao. In 2010, PTX2 was found in all the 3 species of Dinophysis, and the toxin content in a single cell was the highest in D. fortii, followed by D. acuminata speices complex and D. rotundata. Content of PTX2 in cells of D. acuminata species complex varied significantly during the investigation period from April to September, and was relatively high at early April and early July. OA, DTX1 and PTX2 were detected in the isolated cells of D. acuminata species complex collected from Zhongyuan Wharf of Tuandao Bay on Apr.25 in 2009, which was different from those cells collected in 2010. The average toxin content in a single cell is 2.54 pg for OA, 4.04 pg for DTX1 and 1.73 pg for PTX2, respectively. OA, DTX1 and PTX2 were often found in the concentrated phytoplankton samples, and the toxin composition and content changed in different season. From Apr. 2010 to Fre. 2011 at Zhongyuan Wharf of Tuandao Bay, PTX2 was the major toxin component, the content of which was extremely higher than OA and DTX1, except for early April, when the content of OA and DTX1 was the highest. The content of PTX2 showed two peaks at late June and middle August respectively, with the highest value of 595 pg/m~3 at late June. Besides early April, the content of OA and DTX1 showed another small peak in August, but were both below 15 pg/m~3. The content of PTX2 in concentrated phytoplankton samples correlated well with the cell density of Dinophysis acuminata, whereas no relation was found between the content of OA & DTX1 and cell density of Dinophysis spp.. Except for the south part of the Jiaozhou Bay in February, toxins were detected from all the investigated area during the whole year. PTX2 was the dominant toxin component. The maximum content of PTX2 in all the stations appeared from June to August. The highest content of PTX2, 7488 pg/m~3, was recorded at June in C3 station inside the Bay. The concentration of OA & DTX1 was relatively low, and the value was between 0 to 100 pg/m~3. In some samples, gymnodimine(GYM), spirolide 1 (SPX1) and toxins suspected to be dinophytoxin 2 (DTX2) and PTX2 seco acid (PTX2sa) were also detected.In summary, the current study found three Dinophysis species in the coastal waters of Qingdao, D. aucminata complex, D. rotundata and D. fortii. Toxins including OA, DTX1 and PTX2 were detected from the Dinophysis species. All these toxins were detected in the phytoplankton samples collected in the coastal waters of Qingdao, and the cell density of D. acuminata species complex correlated well with the PTX2 content of the phytoplankton samples, suggesting that D. acuminata species complex might be the source of PTX toxins in the phytoplankton samples. This is the first report concerning the population dynamics and toxin production status of Dinophysis species in China. Results from the the current study provide a better understanding for the formation and potential impacts of of Dinophysis blooms, and offer a scientific basis for the adimistration agencies to inspect and prevent the poisoning incidents caused by toxic Dinophysis spp..