Phytoplankton sinking is an important property that can determine community composition, affecting nutrient and light absorption in the photic zone, and influencing biogeochemical cycling via material loss to the deep ocean. To date, the difficulty in exploring the sinking processes is partly due to methodological limitations in measuring phytoplankton sinking rate. However, in the last decade, works have illustrated various methods based on some non-invasive and low perturbing approaches (laser scanner, video-microscopy, fluorescence spectroscopy). In this study, we review the methods for sinking rate estimation and describe the Plankton Tracker, a novel integrated system to investigate in vivo the dynamic sinking behavior of phytoplankton. Plankton Tracker is composed of a long-distance objective and a video-microscopy facility coupled with a specifically developed image analysis system (Plankton Tracker Elements). Diatoms and dinoflagellates were individually-tracked. By processing recorded videos and images, sinking traits (e.g. trajectory length and complexity, sinking velocity, turning angle) were obtained simultaneously with morphological traits (e.g. linear dimensions). We also applied a Biased Correlated Random Walk model to sinking traits. Particularly, we found linear motion in the colony-forming Thalassiosira sp. and sinusoidal reorientation in the dinoflagellate Scrippsiella acuminata. We found complex suspension dynamic of the large Coscinodiscus sp. In this view, the Plankton Tracker approach is likely to provide more insights towards the exploration of dynamic sinking behavior in phytoplankton.

浮游植物下沉是一项重要属性，可以决定群落组成，影响光区的养分和光吸收以及通过物质流失到深海影响生物地球化学循环。迄今为止，探索沉没过程的困难部分是由于测量浮游植物沉没率的方法学局限性。然而，在过去的十年中，工作已经说明了基于一些非侵入性和低干扰方法（激光扫描仪，视频显微镜，荧光光谱法）的各种方法。在这项研究中，我们回顾了沉没率估算方法，并描述了浮游生物追踪器，这是一个新颖的集成系统，可在体内研究浮游植物的动态沉没行为。浮游生物追踪器由长距离物镜和视频显微镜设施以及专门开发的图像分析系统（浮游生物跟踪器元件）组成。单独跟踪了硅藻和鞭毛藻。通过处理录制的视频和图像，可以同时获得下沉特征（例如轨迹长度和复杂度，下沉速度，转弯角度）以及形态特征（例如线性尺寸）。我们还将偏相关随机游动模型应用于下沉特征。特别是，我们在形成菌落的Thalassiosira sp。中发现了线性运动。和鞭毛状正鞭毛虫的取向。我们发现了大型Coscinodiscus sp。的复杂悬浮动力学。按照这种观点，浮游生物追踪器方法可能会为探索浮游植物的动态沉没行为提供更多的见解。