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Cutting and allocation of CPR samples After a CPR has been towed, it is returned to the laboratory at SAHFOS in its container. The CPR sampling mechanism is unloaded and the plankton filtering silk is carefully removed and labelled. The process of marking the silks and cutting them into samples takes place once a week. The filtering silk is unwound and an indelible pen is used to mark the positions of the samples on the silk. Each labelled sample represents 10 nautical miles of the route towed - this is approximately 3 cubic metres of water filtered. The samples are distributed to the CPR analysts using a computer generated random selection process. |
Marking and cutting the CPR samples |
The stages of the CPR sample analysis
procedure
The CPR analysis method has remained unchanged since the 1950s,
and underpins the database design (refer to Warner and Hays, 1994,
for a detailed methodology). Analysis is carried out using
binocular and light microscopes.
1. Phytoplankton Colour Index (green-ness index).
This has remained unchanged since 1946. Once the silk is unrolled
on the cutting table the colour is compared by eye with the colour
of a set of specially prepared colour standards by laying the silk
against a white background. The colour estimates are related to the
numbered divisions of the graduated silk and subsequently to the
samples when the silk has been cut. This process remains a
subjective estimate of the amount of green colour on the CPR
silks.
Identification and counting of plankton
i. Phytoplankton
The CPR sample has two parts: the filtering silk and the covering
silk. During analysis for phytoplankton, 20 fields of view of the
filtering silk are examined. The number of fields is recorded in
which each genus, species or variety is observed. Strict
observation protocols are followed. Phytoplankton are identified to
different taxonomic levels depending on the organism.
ii. Zooplankton "Traverse"
The filtering and covering parts of the silk are laid out under
the microscope and a complete traverse of both sides is carried out
which equates to examining 1/49th of the 10 mile sample. All
organisms seen are counted and identified during the traverse.
Strict criteria that relate to counting organisms are adhered to
when examining the silks. Numbers of organisms are later converted
to categories for entry into the database.
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iii. Zooplankton "Eyecount"
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'Eyecount' analysis under the microscope |
