Diatom aggregation in the sea: mechanisms and ecological implications
Diatom aggregation in the sea: mechanisms and ecological implications
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DOI：
10.1017/s0967026202003657
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发表时间：
2002-04
影响因子：
2.4
通讯作者：
D. Thornton
中科院分区：
文献类型：
--
作者：
D. Thornton
海洋雪是海洋的一个普遍特征，也是通过海洋生态系统输送能量和营养物质的一个重要媒介。硅藻聚集体是海洋雪的主要来源，它们在水华期间形成，在较小程度上通过底栖生物膜的再悬浮形成。在硅藻聚集体中常见的属是：菱形藻属、角毛藻属、管藻属、细柱藻属、短丝藻属和海丝藻属。大多数实地考察都局限于北方有限的几个地点。为了量化硅藻聚集的全球影响，有必要在更广泛的领域进行实地考察，特别是在南半球。当粒子碰撞并粘在一起时，聚集体就形成了。水体中的碰撞受到湍流、不均匀沉降和动物摄食的影响，而硅藻的粘性受到胞外聚合物（EPS）的影响。实验室实验表明，硅藻产生更多的EPS营养限制下，虽然很少有人知道不同的营养限制如何影响EPS的数量和组成以及随后的粘性。EPS在环境中形成三个库：细胞涂层、可溶性EPS和透明外聚物颗粒（TEP）。有必要调查池的EPS之间的非生物和生物过程的转换动力学，以及这些转换如何影响聚集体的浓度和结构。解聚过程在很大程度上被忽视了，尽管它们在确定水柱中聚集体浓度的动态方面与聚集一样重要。硅藻聚集体作为将碳和其他营养物质从透光层运输到海底的一种手段，其地球化学意义已得到充分证实。然而，团聚体的内部生物地球化学尚未得到很好的了解。聚集体含有厌氧微网站和进一步的工作是必要的，以确定聚集体是否是显着的汇氮在水柱通过厌氧反硝化。已经提出了几个假设来解释硅藻聚集在该领域，但其中许多是有缺陷的，因为提出的机制和适应性解释需要自然选择在种群水平上运作，而不是基因或个体。
Marine snow is a ubiquitous feature of the ocean and an important agent in the transport of energy and nutrients through marine ecosystems. Diatom aggregates, which form during blooms and, to a lesser extent, by the resuspension of benthic biofilms, are a primary source of marine snow. Genera commonly found in diatom aggregates are: Nitzschia, Chaetoceros, Rhizosolenia, Leptocylindricus, Skeletonema and Thalassionema. Most fieldwork has been restricted to a limited number of locations in the Northern Hemisphere. To quantify the global impact of diatom aggregation there is a need to conduct fieldwork in a wider range of areas, particularly in the Southern Hemisphere. Aggregates form when particles collide and stick together. Collisions in the water column are affected by turbulence, differential settlement and animal feeding, whereas diatom stickiness is affected by extracellular polymeric substances (EPS). Laboratory experiments have demonstrated that diatoms produce more EPS under nutrient limitation, although little is known about how limitation by different nutrients affects the quantity and composition of EPS and subsequent stickiness. EPS form three pools in the environment: cell coatings, soluble EPS and transparent exopolymeric particles (TEP). There is a need to investigate the dynamics of conversion between the pools of EPS by both abiotic and biological processes and how these conversions affect aggregate concentration and structure. Processes governing disaggregation have been largely overlooked, although they are as important as aggregation in determining the dynamics of aggregate concentrations in the water column. The biogeochemical significance of diatom aggregates as a means of transporting carbon and other nutrients from the euphotic zone to the seabed is well established. However, the internal biogeochemistry of aggregates is not well understood. Aggregates contain anaerobic microsites and further work is required to establish whether aggregates are significant sinks for nitrogen in the water column through anaerobic denitrification. Several hypotheses have been proposed to explain diatom aggregation in the field, but many of these are flawed because the mechanisms and adaptive explanations proposed require natural selection to operate at the level of populations rather than genes or individuals.