Summary
In the mid 1920’s, Sir Alister Hardy developed a radical new method for sampling plankton continuously, rather than taking spot samples using conventional plankton nets. The CPR was first used in Antarctic waters during the 1925-27 Discovery expedition, and has been used successfully for 70 years to monitor plankton in the North Sea and North Atlantic Ocean. Sixty-five years later the CPR returned in Antarctic waters when the Australian Antarctic Division initiated a CPR survey of the Southern Ocean on RSV Aurora Australis south of Australia and west to Mawson. The objectives are to study regional, seasonal, intra-annual and long term variability in zooplankton abundance, species composition and community patterns, as well as the abundance and distribution of krill larvae produced annually. The monitoring of zooplankton is a valuable addition to the vertebrate predator based CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) Ecosystem Monitoring Programs established around Antarctica, especially in relation to studies of natural and climatic induced variability. Zooplankton have much shorter lives, usually one or two years, and a faster population turnover than vertebrate predators. They are closer to the start of the food chain and are expected to respond more rapidly to change. The survey covers a large area from 60° E to 160° E, and south from about 48° S to the Antarctic coast - an area of more than 12 M square kilometres. Tows are conducted throughout the shipping season, normally September to April, but occasionally as early as July (midwinter). The large area and temporal scale means that it is difficult to separate temporal and geographical variation in the data. Hence, CPRs are now also towed on the Japanese icebreaker Shirase in collaboration with the Japanese Antarctic program. Shirase has a fixed route and time schedule, travelling south on 110° E in early December and north on 150° E in mid March each year and will serve as an important temporal reference for measuring long term interannual variability and to help interpret the Australian data. Since 1990, over 80 tows have been made providing over 35,000 nautical miles of records. The most successful seasons to date have been the 1997/98, 1999/00 and 2000/01 austral summers with 20, 31 and 26 tows, respectively. The 1999/00 season included a unique, near simultaneous three ship crossing of the Southern Ocean along 25° 30' E, 110° E and 157° E. Typical CPR tows show very high abundance of zooplankton in the upper 20 m of the permanent open ocean zone between the sea ice zone and the subAntarctic Front. This is an area thought to be oligotrophic. Appendicularians, small calanoid and cyclopoid copepods dominate the plankton. By comparison the surface waters of the sea ice zone has low species diversity and abundances. Zooplankton data, and hence distribution patterns, can be time and geo- coded to GPS data, environmental data collected by the ships' underway monitor system, e.g. fluorometry, water temperature, salinity, and meteorological data.