Ciguatera Environmental Monitoring Methodology

Objectives of this tutorial

This tutorial provides a set of tools and advices useful for the implementation of a environmental surveillance of microalgae associated with ciguatera poisoning.

Assembly, deployment and collection of window-screen devices (or artificial substrates)

Window screens (WSs) are cheap, simple-in-design and easy-to-use passive sampling devices for benthic dinoflagellate cells.
These videos detail how to assemble, deploy and collect WS devices in the field :

Macroalgal samplings (natural substrates of dinoflagellates associated with ciguatera)

This video details how to sample macroalgae 

Processing and preserving window-screen and macroalgal samples  

The videos below detail the methods of processing and fixing window screens and macro-algae samples, depending on the nature of the analyzes for which they are intended. 

Identification and enumeration of dinoflagellate cells using light microscopy

LIST OF EQUIPMENT REQUIRED

  • 1 light microscope equipped with  x10, x20, x40, x100 lenses
  • 1 Sedgewick Rafter counting chamber or, alternatively, microscope slides and coverslips
  • 1 micropipet (P1000) and appropriate tips
  • 1 hand tally counter

SAMPLE OBSERVATIONS UNDER THE MICROSCOPE

  1. Invert the tube sample several times to allow cell resuspension
  2. Pipet 1 mL of sample  and load it onto the counting chamber using a micropipet
  3. Examine the sample under the light microscope
  4. Count the cells by scrolling the counting chamber from right to left and top to bottom, covering the whole observation field 
  5. Refer to the toxic dinoflagellates ID tutorial for an accurate identification of the different species of ciguatera-related benthic microalgae present in the sample (Download tutorial – pdf)
  6. Perform at least 3 countings per sample to allow determination of mean cell density values

NB: if Sedgewick Rafter counting chamber are unavailable, countings can be carried out on 100 µl sample volumes using microscope slides and coverslips

Assessing dinoflagellate cell abundance in samples

Estimate cell number in macroalgal samples

Download excel spreadsheet with corresponding formulas

Estimate cell number in window-screen samples

Download excel spreadsheet with corresponding formulas

Learn more about Benthic dinoflagellate sampling methods

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