Bacterivory in Oceanic Environments: Relative Importance ofthe Heterotrophic Microbial Loop

浮游小型浮游动物在海洋食物网中的作用已在野外工作中进行了粗略的探索。小而脆弱的生物很难在野外条件下分离和研究。研究它们作用的一种方法是比较大相径庭的海洋环境的食物链。这项研究计划的目标是确定通过营养稀少和营养丰富的海洋群落，特别是细菌生物量的消费者，通过微生物循环进行碳转化的相对重要性。有待检验的假设是，与沿海生态系统相比，海洋生态系统中异养微生物，即细菌和原生动物消耗和呼吸的初级生产力固定的碳总量所占的比例更大。初级生产力、细菌生产力和生物活性将在北大西洋西部的三次巡航期间在一个沿海地点和一个马尾藻海地点进行测量。细菌碳的产生总量和初级生产的百分比将在这些海洋环境中确定，并与切萨皮克湾和葡萄园湾两个浅海环境中的微生物碳转化模式进行比较。大型原生动物和微型动物常见物种的大小分级和单细胞分离研究；将使用放射性标记的自然细菌进行等氮类，以确定这些群落中细菌生物量的主要消费者。海洋中产生的许多碳是以微生物的形式存在的，这些微生物太小了，看不见，也很容易操纵。近年来，人们清楚地看到，这些生物对从两极到赤道的海洋食物链至关重要。评估微生物重要性的一种方法是比较它们在几种不同环境中的生长速度，并检查哪些生物能够以微生物为食。这项研究将测量几种类型的微生物在不同环境中的生长速度，这些环境包括相对贫穷的马尾藻海和相对肥沃的乔治海岸。它还将识别哪些生物体消耗细菌。人们的期望是，微生物生产在马尾藻海的食物链中比在乔治海岸地区重要得多。

The role of pelagic microzooplankton in food webs of the sea has been explored sketchily in field work. Small, delicate organisms are difficult to isolate and study in the field situation. One method of studying their role is to compare food chains of widely different marine environments. The goal of this research program is to determine the relative importance of carbon transformation through the microbial loop of an oligotrophic and euptrophic oceanic community, including especially the consumers of bacterial biomass. The hypothesis to be tested is that a greater percentage of the total amount of carbon fixed by primary productivity is consumed and respsired by heterotrophic microorganisms, i.e. bacteria and protozoa, in oceanic ecosystems than in coastal ecosystems. Primary productivity, bacterial productivity, and bactivory will be measured at a coastal site and a Sargasso Sea site during three cruises in the western North Atlantic. The total amount of bacterial carbon produced and the percentage of primary production that this bacterial carbon represents will be determined in these oceanic environments and compared to the patterns of microbial carbon tranformation in two neritic environments, Chesapeake Bay and Vineyard Sound. Size fractionation and single cell isolation studies of common species of larger protozoa and microm;etazoa will be performed using radiolabelled natural bacteria in order to identify the primary consumers of bacterial biomass in these communities. %%% Much of the carbon produced in the sea is in the form of microorganisms too small to see or easily manipulate. In recent years it has become clear that these organisms are quite crucial to the food chain of the seas from the poles to the equator. One way to evaluate the importance of the microorganisms is to compare their growth rates in several different environments and to examine which organisms are able to feed on the microorganisms. This study will measure rates of growth of several types of microorganisms in contrasting environments, the relatively impoverished Sargasso Sea and the relatively fertile Georges Bank. It will also identify which organisms consume the bacteria. The expectation is that microbial production is much more important in the food chain of the Sargasso Sea than it is in the Georges Bank area.