Secchi Disk

Global Citizen Science – Introducing the Secchi App

Screenshots of the Secchi App
Screenshots of the Secchi App

SecchiApp2Calling all budding marine biologists!
The University of Plymouth has developed an app that let’s you directly contribute to science by recording phytoplankton densities with the aid of a simple device called a Secchi disk – which you can make at home – and their free iPhone or Android app.
Phytoplankton are tiny floating algae that soak up carbon dioxide and nutrients and use sunlight to convert them into carbohydrates, proteins and fats to grow and release oxygen at the same time. Phytoplankton is very important for climate change because when they die they settle down to the sea bed either directly or by being eaten and then pooped out by animals. This process of binding carbon dioxide from the ocean and burying it layer upon layer of sediment on the ocean floor is often called a carbon sink.
Quite apart from this phytoplankton is also the basis of the marine food chain, so almost all other ocean creatures depend on it.
But many researchers have claimed to find a decrease in phytoplankton levels. But now you can help in what may become the worlds biggest phytoplankton study and help find out what is really happening with phytoplankton worldwide.
The app shoes you how to make a simple device called a Secchi disk – basically a flat circular disk lowers into the water by a rope. You then lower thie disk down into the water until it just disappears from view and record this depth – this is the ‘Secchi depth’. So basically you are measuring underwater visability in the vertical dimension.

how a secchi disk works
The Secchi disk measures the visibility of the water column in the vertical plane and this measurement serves as a crude measure of plankton density.

This is a so-called proxy for phytoplankton density in the water – it’s not the actual measurement of phytoplankton density but a measurement that is very strongly correlated to it, because phytoplankton is the main cause of visibility levels. So by measuring the visibility we can indirectly infer how dense the phytoplankton is in the water.
The app has full instructions on how to make a Secchi disk and how to make the measurements. So if you have access to a boat, download the app, and get busy as doing some ‘citizen marine biology’!

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