Blue Planet Society: Studying the phytoplankton with citizen science

The phytoplankton in the sea, and the plankton food web they support, underpin the rest of the marine food chain (see: The importance of plankton). Living at the surface of the sea the plankton are particularly sensitive to changes in sea surface temperature, both directly through the effects of temperature upon their physiology, and indirectly through the effects of temperature upon the physics of the water column. As sea surface temperatures increase due to current global warming evidence is mounting that the phytoplankton are reacting to this change in their habitat, and this calls for more research to understand (see: What’s happening to the oceans’ phytoplankton?).

Phytoplankton: These microscopic cells begin the marine food chain. They are so numerous they account for 50% of photosynthesis on Earth.

One new project that is specifically designed to enable you to help add to our knowledge of the Oceans’ phytoplankton is the citizen science Secchi Disk study www.secchidisk.org. This study combines a 150 year-old piece of equipment invented by the Pope’s astronomer with modern smartphone technology to help collect data on the phytoplankton from oceans around the world. So, what is a Secchi Disk and how does the project work, and most importantly, how can you take part?

The Secchi Disk is a plain white, 30cm diameter disk attached to a tape measure and weighted from below. It is one of the simplest and oldest pieces of marine scientific equipment.

Firstly, just what is a Secchi Disk ? Long before modern navigational aids, when sailors just had a compass, the sun and the stars to rely upon, they knew that either the colour of the water or its clarity could provide information about their location, for example the Sargasso Sea is particularly clear while neighbouring waters are less so. To help sailors determine water clarity they would lower a white object, often a disk, over the side of the ship and watch it disappear from sight; the quicker it disappeared from sight the lower was the water clarity. Until 1865 this technique was relatively, informal. In 1865 Pope Pius IX tasked Alessandro Cialdi the commander of the Papal navy to determine the currents in the Mediterranean Sea. Cialdi asked the Pope’s Astronomer Pietro Angelo Secchi, to formalize the method of using a white disk to help determine the currents by measuring their changing clarity. A scientific paper on the currents in the Mediterranean sea was written and from then on the white disk became known as a Secchi Disk, and it has been used as a standard and simple way to measure water clarity ever since. Unchanged for decades, a Secchi Disk is a plain white disk 30 cm in diameter that is attached to a tape measure and weighted from below. When the disk is lowered into the water from the side of a boat the depth at which it just disappears from sight is noted and is called the Secchi Depth.

When lowered vertically into the water the depth below the surface at which the Secchi Disk disappears is called the Secchi Depth and this measures water clarity. In water over 25m deep and over 1km from shore, the main determinant of water clarity is the phytoplankton.

Away from estuaries and coasts the main determinant of water clarity is the amount of phytoplankton in the water column. Consequently, marine biologists have used the Secchi Depth to measure phytoplankton since the Secchi Disk’s ‘invention’ in 1865. Now, with evidence to suggest the phytoplankton in the world’s oceans are changing due to climate change, and because of their important role in the marine food chain and the Earth’s carbon cycle, we need to know if, how and why they are changing. Even though we can now obtain remote estimates of phytoplankton from satellite measurements of ocean colour, in situ measurements are still fundamental and scientists still use Secchi Disks. However, there are simply too few scientists to survey the world's oceans as well as we would wish. This is where sailors, acting as citizen scientists, can help science by making and using a Secchi Disk. By collecting Secchi Depths from around the world, from now and into the indefinite future, any seafarer can help grow the database of Secchi Depth measurements to give a much bigger time series in terms of its temporal and spatial extent.

Dr Richard R Kirby created the citizen science Secchi Disk study in 2013 to enable any seafarer to help collect data to understand the affect of climate change on the phytoplankton.

So how can citizen scientists get involved ? Anyone who goes to sea can take part, whether you are a sailor with your own yacht, a crew-member, or are on a charter sailing holiday, or you are an angler, a diver or a fisherman. All you need is a Secchi Disk and the free Secchi app installed onto your smartphone or tablet. The Secchi app is available as a native app for iOS and Android phones and also as a Web app (Secchi Web) for Windows devices (Secchi Web also runs on iOS and Android). The Secchi Disk is a DIY element to the project. A Secchi disk can be made from any material, such as a white plastic bucket lid or a piece of plywood painted white. Offcuts of 3-5 mm white Foamex that you can often obtain from printers work very well. Attached to an inexpensive fibreglass tape measure with a weight hanging below, the Secchi Disk is lowered vertically into the seawater (you need to use sufficient weight to make the disk sink vertically, which will depend upon the disk material), and the Secchi Depth is noted. The quicker the Secchi Disk disappears from sight the smaller the Secchi Depth and the more phytoplankton there is in the water. Simple!

Once the Secchi Depth is determined, you use your smartphone and the free Secchi app to obtain the GPS location and to enter the Secchi depth - a network connection isn’t required for this. The Secchi App will store the data on the phone and the Secchi Disk project receives the data as soon as network connectivity is regained. Anyone can follow the data collected on the project map. The aim of the project is to chart the seasonal and annual changes of the phytoplankton from now and into the future. It is a long-term project that carries on indefinitely. Seafarers may measure the Secchi depth at the same place regularly, or occasionally, or they may take measurements from different places as they travel. The more sailors that take part the better the coverage of the oceans, and the more remarkable and useful the citizen science Secchi Depth database will become.

I’ll now reveal my vested interest in this blog since I am the leader of the Secchi Disk project. Often, we look back and wish we had already started monitoring something about the natural world - if only we had started measuring 'x' some years ago. In terms of the phytoplankton there really is no time like the present to start growing the Secchi Depth database and this is why I created the Secchi App and this citizen science project. Since its launch in 2013 the project has gone from strength to strength. Already it is the world’s largest marine citizen science study with data from every ocean. In 2014 there was a Secchi Disk 'first' when Jimmy Cornell’s grand-daughter Nera measured a Secchi depth from the Northwest Passage, which has only recently become navigable due to global warming. Whether sailing in coastal waters or cruising across oceans, families find the project particularly useful as an educational addition to being on the water. This year small boat fishermen joined the study, as they are fully aware of the importance of understanding the phytoplankton that underpins all fisheries.