|Abstract: ||由於浮游植物的體型分佈和海洋碳循環之間有著密切關係，本研究之目標是想要了解除了被捕食及沉降作用之外，競爭環境中的營養鹽是否也控制了海洋中浮游植物的體型大小。實驗上使用基隆沿岸海域所分離的骨藻 (Skeletonema costatum CH0128) 和聚球藻 (Synechococcus spp. CH0129)，進行單獨培養、混合培養、以及加入攝食者之競爭培養，觀察兩藻種在不同濃度的營養鹽組合和有無攝食者存在之生長情況。藉由各自在單獨培養下所得到的生長曲線，以Monod公式為理論進行迴歸後，得到骨藻和聚球藻的Ks，依序為0.02 f和0.002 f (f為f培養基配方中的營養鹽濃度)，而最大生長率 (µmax) 為1.62和1.04 day-1；再求得各自在單獨和競爭培養下的生長率及所能達到的承載量，利用生長率競爭百分比 (µcomp﹪) 及承載量競爭百分比 (Kcomp﹪) 與營養鹽濃度的關係來判斷同時存在對彼此相互的影響。無論是在實驗室或野外培養，隨著營養鹽濃度的下降骨藻在競爭中會變得較佔優勢，其生長率競爭百分比均接近100﹪，而聚球藻則是在高營養鹽的狀況下較佔優勢，並具有較高的生長率競爭百分比；在承載量競爭百分比方面，聚球藻是在高營養鹽環境中表現較佳，然而對骨藻來說，在所有培養中均未受到聚球藻的影響，承載量競爭百分比都在95﹪以上，唯一的例外出現在實驗室中的f/20相對濃度下，此時骨藻的承載量競爭百分比降至1﹪。總括來說，隨著水中營養鹽濃度的降低，骨藻競爭力會強於聚球藻，而攝食者的存在會造成聚球藻數目的減少。根據這些結果，推測在富含營養鹽的海域攝食作用的確會抑制聚球藻的生物量，而使矽藻有機會發展成優勢藻種，但在營養鹽貧瘠的開放性大洋，雖然骨藻和聚球藻會因為環境中營養鹽的多寡而有競爭的現象，但這類海域聚球藻佔優勢的事實並非因為聚球藻是競爭中的贏家，而是因為沉降作用使矽藻無法在有光層中累積。|
Due to the close connection between phytoplankton size distribution and marine carbon cycle, the goal of this study is to understand whether competition of nutrients, as compared with predation and cell sinking, also controls the size distribution. Experimentally, a diatom (Skeletonema costatum CH0128) and a cyanobacteria (Synechococcus spp. CH0129) were isolated from costal area of Keelung, and were used in a series of incubations with different nutrient concentrations. The population growth of these two phytoplankton was monitored when they were incubated separately, jointly, or with the existence of predators. Using Monod’s equation as a regression model, the Ks’s of S. costatum and Synechococcus spp. were estimated as 0.02f and 0.002f (the relative nutrient concentration is expressed as a fraction of the f-media); the µµax’s were estimated 1.62 and 1.04 day-1, respectively.By the comparison of maximum growth rate and carrying capacity between incubations with and without the competitor, a growth rate competition ratio (µcomp%) and a carrying capacity competition ration (Kcomp%) were constructed to judge their mutual influences in the same environment. In both lab-prepared media and natural seawater, S. costatum became more dominant with the decrease of nutrient concentration, and its µcomp% was close to 100%. Synechococcus spp. CH0129 dominated high nutrient environment and has higher µcomp%. Synechococcus spp. CH0129 also has better Kcomp% ratio at high nutrient concentrations. However, S. costatum did not feel the influences from Synechococcus spp. in all incubations, and almost all Kcomp% ratio of S. costatum were higher than 95%. The only exception was observed in the f/20 media, in which Kcomp% of S. costatum decreased to 1%. In conclusion, the competitive ability of S. costatum is better than that of Synechococcus spp. at low nutrient concentrations, and the existence of predator can effectively decrease the abundance of Synechococcus spp. Based these results, predation apparently controls Synechococcos spp. biomass in high nutrient environment, which let diatoms dominate in such locations. On the other hand, although nutrient competition still occurs in the oligotrophic open ocean, the dominance of Synechococcos spp. is due to cell sinking of diatoms which prevented diatoms to accumulate in the euphotic zone.