Pharos to Collect Scientific Data Between the Falklands and South Georgia

Pharos to collect scientific data between the Falklands and South Georgia

Designed by Sir Alister Hardy the continuous plankton recorder (CPR) was initially trialed in the Southern Ocean during the Discovery expeditions (1925-1937) to quantify the amount of Antarctic krill present. Over the next few years Hardy modified the design to sample plankton and its simple design has remained unchanged since 1948. Deployed worldwide the CPR is a robust, reliable and effective way of collecting plankton samples and it has been used to collect one of the longest running marine biological data series in the world.

In its stainless steel housing the CPR can be towed in rough weather behind large vessels up to speeds of 25 knots. Water containing plankton just below the sea surface enters the CPR through a small aperture at the front of the device and is filtered between two fine silks. The internal mechanism is driven by an impeller that causes the silk to be spooled onto a reel in a storage tank containing fixative (formalin) for preserving the plankton until it can be analysed. The silks are marked every 10 nautical miles and using the tow log, including GPS positions, it is possible to record where along the survey route the plankton was collected from.

Samples are analysed at the Sir Alister Hardy Foundation for Ocean Science (SAFHOS) in Plymouth. Silks are initially examined visually for their colour with the degree of “greenness” of the silks being an indicator of any phytoplankton blooms. Closer examination under a microscope allows counts and species identification to be conducted on all types of phytoplankton and zooplankton.

This March saw the first tow of the CPR off the PV Pharos between the Falkland Islands and South Georgia. As the Pharos left Stanley the CPR was deployed off the back of the vessel and plankton was continually sampled for the entire 750nm journey (with one change of internal cassette mid way) until the vessel entered into Cumberland Bay. The CPR will be deployed every other month on the same route to gather seasonal data on plankton species composition and abundance allowing any interannual changes in the biomass or makeup of the plankton community to be identified. It will also give information on changes in plankton communities across the Polar Front. As plankton forms the basis of the food chain this information can also be examined in relation to fluctuations in fish, seabird and marine mammal numbers.

To coincide with the first deployment of the CPR between the Falklands and South Georgia and to celebrate the life and work of Sir Alister Hardy a set of four stamps have been released. An image of the CPR showing both the external and internal mechanisms is on the 60p stamp. Working at his microscope on the feeding strategy of North Sea herring, Sir Alister Hardy is portrayed on the 70p stamp. As well as a prominent marine biologist, Hardy was also a talented painter and his watercolour (painted from the RRS Discovery when she was at Grytviken) of “A busy day at the whaling Station” is shown on the 95p stamp. The £1.15p stamp depicts the RRS Discovery, Captain Scott’s first Antarctic vessel, and the ship used for many scientific investigations of the Southern Ocean including both plankton sampling and studies of the benthic (sea floor) fauna.

Thanks to the Captain and crew of the Pharos and Bernard Meehan (Fisheries officer) for the smooth deployment of the CPR and to all at SAFHOS for their work in getting this project underway and in advance for analysing the plankton samples. Photograph courtesy of David Allen.