Continuous Plankton Recorder Survey (CPR Survey)

The Continuous Plankton Recorder (CPR) is a marine sampler that is towed behind volunteer ships of opportunity at speeds of up to 20 knots and samples at a depth of 7 m below the surface. Plankton have been sampled on routes crossing the North Atlantic and NW European shelf seas using a consistent methodology since 1958. The CPR unit is a metal casing in the shape of a 1 m torpedo that houses a roll of silk which automatically rotates using a geared propeller system. The seawater enters the front aperture where plankton and small particles are captured onto the rotating silk, which has a mesh size of 270 µm. This silk is stored in 4 % buffered formalin to preserve the sample until microscopic analysis at the laboratory in Plymouth. The silk is cut into pre-defined sections that represent one sample and equate to 10 nautical miles of tow. Phytoplankton and zooplankton are identified and counted at different stages of the microscopic analysis: semi-quantitative count of phytoplankton across 20 fields of view per sample, quantitative count of all zooplankton >= 2 mm (these are picked off the silk for identification), and semi-quantitative traverse count of all zooplankton < 2 mm. For a more in-depth description of the sampling methodology please refer to Richardson et al. (2006). CPR monthly abundance counts from 1958 to 2017 are available from the following open access data portal: https://data.cprsurvey.org/datacatalog/.