Conducting a Plankton Tow
Collecting marine plankton and magnifying these tiny and often microscopic organisms for 
observation is a wonderful educational activity for anyone interested in marine habitats and coastal marine wildlife. Marine plankton can be collected from both inshore and offshore waters using inexpensive nets constructed from everyday items as well as more expensive models sold by commercial companies.
A plankton sample collected off a pier in a harbor setting can be just as productive as one collected from a vessel many miles offshore.
Homemade nets can be constructed from every day materials like nylon stockings and metal coat hangers and are easy to use by kids of all ages. Wading in shallow water with net in hand is often a child’s first introduction to marine wildlife and coastal habitats. Catching tiny organisms and getting wet is fun and exciting. And these types of outdoor activities help children appreciate and value the animals and other type of wildlife that are part of our natural world.
Commercial plankton nets have a longer life span and are designed to collect plankton of a specific size range depending upon the size of the mesh that is used.
These rugged nets come in a variety of lengths and can filter specific types of phytoplankton and zooplankton based on their size and depth in the water column. The price range of these nets can vary significantly and is often based on the quality of the materials used and the overall size of the net. Both science supply companies and oceanographic businesses offer a wide range of plankton nets online.
With plankton net in hand, you can collect both microscopic and macroscopic organisms that form the base of the marine food chain. The species of plankton that you collect from your plankton tow will depend upon the mesh size of your net and the depth of the water column that is sampled. When the tow is complete, rinse the sides of the net with salt water to wash down any plankton that is caught in the mesh. This will help to concentrate as much sample as possible in the collection chamber at the bottom of the net. You now have a concentrated plankton sample that can be used in numerous activities and can be observed using a variety of magnifying
devices.
To the left is a plankton sample collected from a bridge close to shore and to the right is a sample collected from a vessel at sea. Both samples look like they contain cloudy or dirty water. Actually, the cloudiness of the sample is due to all the plankton that is suspended in the water sample. So cloudy water doesn’t always mean polluted water. In fact, most of the time, cloudy water means productive water!
Before examining your plankton sample, you may want to record the initial volume of your plankton concentrate. This measurement is needed if you want to determine the number of planktonic organisms per volume of seawater. To accomplish this, you will also need to know the distance of your plankton tow and the time required to complete the tow. This exercise is a great way of making math relevant and understandable to middle school and high school students.
There are many different types of equipment that can be used to
observe marine plankton. The simplest and the cheapest gear can often produce results that would wow anyone interested in the sea. An inexpensive instrument that we often use aboard Captain John Boats is called the Discovery Scope. This is a hand-held magnifier that allows you to closely observe a plankton sample that is 
contained within a plastic chamber. More expensive equipment, like stereo-microscope, can provide greater magnification but typically require electrical access to illuminate the sample from below.
To learn more about marine plankton, visit the section titled “Plankton” on the NECWA Resource page. Here you will find reference books, field guides and online resources that will help you better understand and identify marine plankton of coastal New England. When observing plankton, don’t worry about getting the ID’s correct. Just have fun discovering they wide array of amazing organisms, both single-celled and multi-celled, that comprise the base of the marine food chain and that sustain all life in our oceans.
Here are some images of plankton through the lens of a stereo-microscope.
