Study on the function of carbon transport by heterotrophic dinoflagellates

硅藻在深海固碳中起着重要的作用，即生物泵。硅藻水华的命运在很大程度上受到细胞下沉、作为硅藻食草动物粪便颗粒下沉或上层再矿化的影响。为了了解这种命运，人们对摄食硅藻的大型浮游动物进行了大量的研究。另一方面，另一种硅藻摄食者异养甲藻的生物学和生态学是有限的，甲藻在固碳中的作用也是未知的。在本研究中，我们研究了甲藻对硅藻的捕食及其在固碳中的作用，发现了4种摄食硅藻的异养甲藻，如Gyrodina sp.。，产于亚北极太平洋的裸子藻和裸子藻属。它们在微型浮游动物群落中的贡献一般较低。，而且经常缺席。硅藻开花站生物量最高。异养DIN…的贡献在Oyashio地区，更多的鞭毛虫数量达到微型浮游动物总数的20%，碳生物量的60%。在西次北极环流的中心区域，它们在非水华状态下的贡献率为10%，在水华期间增加到50%(20.1mggm；-3)。这表明异养甲藻的动态很大程度上依赖于硅藻密度。观测到的最大摄食率为532mgc m^&lt；-3；d^&lt；-1。数学模拟表明，在西亚北极环流硅藻水华期间，异养甲藻有可能吞噬所有硅藻的产量。放牧对碳素运输的重要性在很大程度上受甲藻初始细胞密度和捕食者密度的影响。在甲藻初始密度较低或捕食者密度较高的情况下，甲藻的生物量在1-4周的一般持续时间内不足以影响硅藻水华。因此，当桡足类的生长期开始早于硅藻水华的开始时间时，对甲藻的选择性取食会减少种群规模。这些结果表明，春季的硅藻、碳和营养动态受到食物网组成的重要影响。本研究揭示了异养甲藻的生态特征及其对碳和生物元素循环的影响，这一点以前知之甚少。然而，由于它们的丰度在水平和时间上有很大的变化，因此在食物网动态和生物地球化学循环中的作用仍然不清楚。我们需要进一步研究异养甲藻的生理和生物学特性，以建立包括甲藻在内的生态系统模型，并了解它们在生态系统和生物地球化学循环中的作用。较少

Diatoms play an important role jn the carbon sequestration to the deep sea, i.e., biological pump. The fate of diatom bloom is largely influenced by the cell sinking, sinking as faecal pellet of diatom grazer, or remineralization in the epipelagic layer. In order to understand the fate, many studies on the macrozooplankton feeding on diatoms has been carried out. On the other hand, biology and ecology of the other diatom feeder, heterotrophic dinoflagellates, are limited, and the role of the dinoflagellates on carbon sequestration is unknown. In this study, we investigated on the diatom grazing by dinoflagellates and the role on carbon sequestration.We found 4 diatom-feeding heterotrophic dinoflagellates, such as Gyrodinium sp. , in the genus of Gyrodinium and Gymnodinium in the subarctic Pacific. Their contribution in microzooplankton assemblage is generally low. , and often absent. The high biomass was observed in the diatom blooming station. The contribution of the heterotrophic din … More oflagellates reached 20% of total microzooplankton in number in the Oyashio region and 60% in the carbon biomass. In the central region of the western subarctic gyre, their contribution was 10% in weight at the non-bloom status, and it increased to 50%(20.1 mgC m^<-3>) during the bloom. These indicate that the dynamics of the heterotrophic dinoflagellates is largely dependent on the diatom density. The maximum ingestion rate observed was 532 mgC m^<-3> d^<-1>.The mathematical simulation showed that the heterotrophic dinoflagellates had potential to graze down all the diatom production during diatom bloom in the western subarctic Gyre. The importance of the grazing on the carbon transport is largely influenced by the initial cell density of the dinoflagellate and the predator density. In the case of the low initial density of the dinoflagellates or high predator density, the biomass of the dinoflagellates does not reach to high enough to impact the diatom bloom within the general duration of the event of 1-4 weeks It is suggested that the selective feeding of copepods on the dinoflagellates decrease the population size when the timing of copepod growth period initiate earlier than the diatom bloom. These results indicate that the diatom, carbon and nutrient dynamics in spring are crucially influenced by the food-web components.This study demonstrate the ecological characteristics of the heterotrophic dinoflagellates and their influence of carbon and biogenic elemental cycling which are little know previously. It is, however, still unclear the roles on the food-web dynamics and biogeochemical cycling due to their large horizontal and temporal variations in their abundance. We need further studies on physiological and biological characteristics of the heterotrophic dinoflagellates in order to develop the ecosystem model including the dinoflagellate and to understand their role in the ecosystem and biogeochemical cycling. Less