How do we collect plankton samples?

When it comes to collect plankton samples, there are different options, all relying on technologies, it all depends on what you want to study.

If the purpose is to study micropalaeontology, working on fossils specimens, from decades to million years, we use drilling systems. With this device, we can access the sediment accumulated over time, constituting the sediment floor. To learn more about it, you can check this article.

Its cone shape helps to guide the plankton and concentrate it in the container at its tip. There is a valve at the end, to allow or not the particles to pass into the sampling bottle. Usually, the net is towed by a boat, laying horizontally, during an amount of time determined in the protocol. After collecting the plankton (or other particles that may be studied in the surface ocean, e.g. plastic debris) in the sampling bottle, we analyse it using microscope and binocular. The plankton net is carefully cleaned between each sampling to avoid contamination.

Another method to collect plankton (or particles in general) is sediment traps. This method is used when we want to estimate a vertical particles flux over time (usually plankton, but can also be microplastics for example).

The sediment traps can be placed at different depth, either relying of the sea floor (usually in coastal environments) or attached to a buoy holding it from the surface (usually in the open ocean). They are usually left for a year, and collected before being returned to the same location for long-term monitoring. The sinking particles from the surface to the deep ocean are trapped in the bottles, and each bottle (=each sample) corresponds to a define amount of time, at a define location, at a defined depth and a defined surface (= the surface of the funnel). From these data, we can qualify and quantify the Marine snow, i.e. the plankton organisms sinking to the seafloor after their death. 

October 2024

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