Secchi App: Tracking Phytoplankton with the Push of a Button [GUEST POST]

Help scientists monitor the phytoplankton population in oceans with a secchi disk and the secchi app.

Want more marine-themed citizen science projects? We’ve got you covered!

Screen shot of the secchi app
Screen shot of the secchi app

Marine ecosystems, like all ecosystems, are made of complex food webs. At the base of the marine food web are the phytoplankton. Phytoplankton are very important, as they are responsible for about half of all photosynthesis on the planet; they absorb half of the carbon dioxide in the atmosphere and produce half of the oxygen we breathe. Global warming and climate change are unfortunately putting phytoplankton numbers in danger, as phytoplankton populations are negatively affected by warming waters. When the water warms, it creates layers of temperature, so there is less cycling of nutrients than in more mixed waters.

To track these changes, a team of scientists led by Dr. Richard Kirby at Plymouth University, have created a mobile app called the Secchi App.  The app, along with a homemade secchi disk, can be used to measure the turbidity of the water.   These measurements give an estimate of the amount of phytoplankton in the water, and the app attaches GPS information to the data.  Users must select their GPS location first and then input the Secchi Depth. If you are far out to sea the app will  store your data until you get a network connection, when you will be prompted to submit your data to the database; you can decline until later if you are connected to a roaming network.

Testing the waters with a white secchi disk.
Testing the waters with a white secchi disk.

Using a Secchi disk is very straightforward: a 30-cm white disk is attached to a 50 meter-long fibreglass tape measure and lowered into the water until it just disappears from sight, then the depth of the disk below the surface is recorded (this is called the ‘secchi depth’). For the app, there are no restrictions on what the secchi disk can be made from, as long as it’s painted white, weighed down with a 200 gram weight or heavier depending on the disk material (it is important the disk sinks vertically), has a diameter of 30 cm, and is kept clean for maximum visibility. The ideal time to collect data is between 10 in the morning and 2 in the afternoon. Users also have the option to input the temperature of the water, take a photograph, add notes, and input their boat name. These details, especially the temperature, would help scientists understand the context of the Secchi depth even more.

Dr. Kirby says this app is for “seafarers  and scientists.” [1]  Anyone with a boat, a secchi disk, and a phone can participate. Since the ocean is too large for data collection by one team, they need your help. Collecting and inputing data for the Secchi app takes less than five minutes, which gives users the opportunity to collect multiple data points in a small amount of time.

When users send their measurements to the database, scientists like Dr. Kirby can use them to accurately predict the productivity of phytoplankton in the ocean. When you use the secchi app and send your data, you are helping scientists track of the number of phytoplankton in the ocean. Their numbers affect the abundance of all organisms in the food web above them. Since phytoplankton are such an important part of the marine food web, their numbers affect the populations of many other species. Participants are helping to track phytoplankton as well as many keystone species. You could be a part of something much larger.

Editor’s Note: The bottom image has been changed to show a white marine secchi disk, which is the proper disk for this type of project. In addition, the quote from Dr. Kirby has been referenced appropriately.  We apologize for the errors.

[1] From FAQ section.

Plankton Pundit
How to make a Secchi disk (Page 5 of guide)

Image credits: Dr. Richard Kirby

Albany Jacobson Eckert is working toward a BS in Marine Vertebrate Biology at Stony Brook University. She hopes to conduct oceanographic research in the near future. Her blog,, is geared toward promoting scientific literacy and explaining concepts behind recent scientific headlines.

Categories: Citizen Science, Ecology & Environment, Nature & Outdoors, Ocean & Water