In the field
Water enters the Continuous Plankton Recorder (CPR) through a square aperture (1.27 cm each side), about the size of a thumbnail. It then flows down an expanding tunnel, which effectively reduces the water pressure to minimise damage to the captured plankton, and exits through the rear of the device. The movement of water past the CPR turns an external propeller at the rear of the device that operates a drive shaft and gear system, which advances the silk filtering mesh. Plankton in the water are filtered onto this constantly moving band of silk. This filtering silk meets a second band of covering silk, effectively sandwiching the plankton, and is then wound onto a spool in a storage tank containing formalin. Both phytoplankton and zooplankton are retained.
The advantage of the CPR is that it is robust and can be easily deployed and retrieved in minutes while a vessel is under way. This means that CPRs can be deployed from a range of vessels including
The CPR is fitted with a Star-Oddi recorder measuring temperature, depth, and pitch and roll of the instrument.
Detailed descriptions of the CPR device and its sampling characteristics are summarised in Richardson et al. (2006) and Hosie et al. (2003). Please click link below for full pdf download.
In the Lab
Cutting of the silk and the Phytoplankton Colour Index
The 6 m length of the plankton silk 'sandwich' is carefully unrolled and laid out on a bench. Prior to being cut, the colour of the silk is compared with the colour of a standard set of colour charts by laying the silk against a white background. This Phytoplankton Colour Index is estimated for each numbered division (sample) on the graduated silk. This index has 4 levels depending on the greenness of the silk (0: no colour; 1: very pale green; 2: pale green; 3: green). Phytoplankton Colour has proven to be a good index of phytoplankton biomass (chlorophyll) estimate fluoremetrically and from satellite (see Richardson et al. (2006) for more information). Although the phytoplankton colour assessment is done 'by eye', there is very close agreement between CPR analysts on the estimated colour of silks.
The silk is then cut into segments representing 5 nautical miles of towing distance using the ships location information to relate the plankton data from the CPR silk to a real position. The size of the segments varies slightly and is calculated depending on the speed the silk was wound through the CPR unit; 5 nautical miles is approximately equal to 5 cm.
Phytoplankton analysis (on-silk)
The covering and filtering silks are opened out with the plankton facing upwards. The filtering silk is laid on a glass plate sprayed with a little water to keep the silk moist. Under a compound microscope with a large 150 mm x 100 mm stage, twenty fields of view (295
Zooplankton analysis (off-silk)
The silk is then rinsed off into a 2 litre beaker using tap water, ensuring that all animals are removed from the silk. The zooplankton washed off the silk are then poured through a 100