In situ video and fluorescence analysis (VFA) of marine particles: applications to phytoplankton ecological studies.

Abstract

Phytoplankton consists of microscopic single-celled microalgae which transform, through the photosynthesis process, inorganic substances into organic biomass readily available to secondary consumers. Due to their role of primary producers, microalgae represent the basis of the marine food web. Phytoplankton is composed of a very high number of species that can be classified by functional groups (e.g., diatoms, dinoflagellates), size classes [pico-plankton (<2 µm), nano-plankton (2-20 µm), micro-plankton (> 20 µm)], or pigment composition (fucoxanthine, phycoerytrin, Chl a). In coastal areas, spatial and temporal variability of the phytoplanktonic community is very high and dependent on hydrographical conditions and physical processes. An increase in observation capacities is required to improve our knowledge of phytoplankton ecology and community patterns. Most of the environmental studies on phytoplankton ecology have used standard laboratory microscopic observations (Utermöhl 1958) to identify, enumerate, and classify phytoplankton species. This routine methodology is time-consuming and remains limited in comparison to the spatio-temporal resolution of physical/chemical sensors used during oceanographic in situ measurements. Thus, the need for automatic in situ methods giving relevant information on the plankton community structure has been clearly expressed by the scientific community.In situ video and fluorescence analysis (VFA) of marine particles: applications to phytoplankton ecological studies. AbstractRecent advances in laser and video technologies have enabled single particles to be visualized in aqueous solution. Here, we describe a new instrument enabling the analysis of the fluorescence signatures of marine particles directly in seawater: the Video Fluorescence Analyser (VFA). A field of view is produced inside a measurement chamber by a laser beam at 473 nm that illuminates a shallow region, 3500 µm deep. Individual cells or particles in this field appear as individual spots of light, which are clearly resolved by video against a dark background. The method can resolve particles ranging from 6 µm to several millimeters. The camera is equipped with mobile optical filters: band-pass filter, 520-580 nm, for phycoerythrin visualisation and high-pass filter, > 600 nm, for Chlorophyll a pigment. These filters are remotely controlled and displaced in front of the CCD camera, allowing imaging and discrimination between fluorescent particles. We report here experimental procedures and calibrations performed in the laboratory with phytoplankton cells (Dunaliella tertiolecta, Karenia mikimotoi, Pseudonitzschia australis) and calibrated fluorescent beads. Image analysis processing enabled particle counts, measurements, and size classification. The auto-fluorescence of individual particles was also tested in situ during a field cruise. In relation to other sensors, the VFA allowed particle enumeration and discrimination and detecting spatial variability of the phytoplankton size spectra in relation to hydrolog...

Distribution and dynamics of two species of Dinophyceae producing high biomass blooms over the French Atlantic Shelf

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Scaling Up From Regional Case Studies to a Global Harmful Algal Bloom Observing System

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A new transportable floating mesocosm platform with autonomous sensors for real‐time data acquisition and transmission for studying the pelagic food web functioning

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