Secchi Disk
Out of the blue one afternoon, I got a call from Dr. Richard Kirby, a Marine Institute fellow at Plymouth University in England. He wants to recruit volunteers for a study he and his colleagues are conducting to survey and map the seasonal and annual changes in phytoplankton worldwide. These microscopic organisms are the first link in the marine food chain and, like most sea life, have a preferred temperature range. If climate change is affecting their numbers, it would be useful to know where and by how much.
We all like projects and tinkering. Sometimes I think maybe that’s why we own boats. They keep our fingers nimble and our minds occupied. And a lot of us worry about the state of the waters in which we sail, despite the opinions to the contrary that pop up on our letters pages from time to time. So I was intrigued.
“Because the phytoplankton live at the surface of the sea, they’re being affected by rising sea temperatures due to climate change,” Kirby explained in a follow-up email outlining the Secchi Project.
To measure and quantify what is actually occurring on a global basis, Kirby and his team hope sailors and fishermen will pitch in and help collect data, since it would be tough for a handful of researchers to cover the world’s oceans on their own.
To gauge the amount of phytoplankton in a water column, one just has to measure the turbidity of the water using a simple device called a Secchi disk, which you can easily make on your own. The disk is named after Father Pietro Angelo Secchi, S.J., an astronomer who created the first disk in 1865 to measure water turbidity in the Med.
To make your own disk, cut a 30-centimeter-diameter circle out of a sheet of plywood, plastic, or metal and paint it matte white. Put enough weight on one side (Kirby suggests 200 grams, about seven ounces) to make the disk sink in seawater, and add an eye on the other side for attaching a surveyor’s tape measure. The tape costs about $18 online, or you can use a rope calibrated in 20-centimeter increments.
Out on the water, with the sun at your back, lower the disk over the side, letting it sink until you lose sight of it. Then record the depth. The researchers recommend taking readings between 1000 and 1400.
To file your report, all you need is a smartphone and the Secchi app developed by computer scientists at Plymouth University. The app uses the phone’s GPS to capture your location, then provides an easy-to-follow sequence of prompts to enter the data that Kirby and crew will track. The app either transmits the data in real time or stores it until you return to land and have Internet access again.
It’s that simple. So now you have a project for a rainy morning when you can’t get down to work on the boat. And during the season, you can justify all your sailing adventures by chalking it up to research. All for the phytoplankton.
