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.
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!
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.