One of the simplest biological samplers, zooplankton nets are made in a wide variety of styles and sizes. The two nets in the MARMAP Bongo vertical-haul net system shown here each have a mouth diameter of about 25 cm.
The historic roots of plankton sampling reach back to the early 19th century when Thomson invented a net he used to sample crab and barnacle larvae. From this simple collecting device has evolved an astounding array of instrument types and collecting strategies for sampling in an immense and often hostile environment. The history of nets and their use in collecting zooplankton from the world's oceans, continental shelves, coastal embayments, and freshwater bodies are almost as varied as the subjects zooplankton biologists have undertaken to study. An account of the tools that have been employed to collect zooplankton has been recently prepared by Wiebe and Benfield (2000), and provides a description of standard sampling methods. Wiebe and Benfield provide a chronological listing of the instrument systems and categorized systems presented in the text.
When sampling plankton, an investigator is attempting to answer two questions in a quantitative way: 1) What living plankton organisms does the sea contain at a given time?
2) How does this material vary from season and from year to year? In the early history of ocean sampling, an assumption was made that plankton were evenly distributed in the oceanic waters and because of this one could take small samples which would be representative of large oceanic areas (if the volume of water filtered by the net could be determined exactly and providing some of the organisms caught by the net would not escape through the net mesh). This premise was tested in a variety of ways by many investigators, and many of the sources of error associated with sampling plankton by nets and with counting methods to analyze the samples were identified.
Ultimately the research community recognized that there were large scale spatial variations in the concentration of planktonic forms. This spatial variability led to a reassessment of sampling that produced the tools we use today.
The Bongo net was invented in the mid-20th century. Today, bongo nets are available both in opening/closing and non-closing form. However, the most commonly used net is a non-closing MARMAP Bongo Net, developed around 1980.
How It Works
A pulley with a 19 mm diameter chain or cable is used to lower the nets into the water column. A collecting bucket, attached to the cod-end of the net, is used to contain the zooplankton sample. Finally, when the net is retrieved from the ocean, the collecting bucket can then be detached and easily transported to a laboratory.
Very simple to operate
Nets do not open and close
Aquatic Research Instruments
Nets only: $50-160 each, depending on length and mesh size
Stainless steel ring frame: $200-300
Collecting buckets: $40-60 each
Chain/cable, 19 mm. diameter
Some descriptions modified from: Wiebe, Peter H. and Benfield, Mark C., From the Hensen Net Toward 4D Biological Oceanography; Woods Hole Oceanographic Institution, Woods Hole, MA 02543; Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA 70803; 20 March 2001.
Harris, R.P.; Wiebe, P.H.; Lenz, J.; Skjoldal, H.R.; Huntley, M. Zooplankton Methodology Manual, Academic Press, London/San Diego, 2000.