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Subarctic Pacific lower trophic interactions: production-based grazing rates and grazing-corrected production rates



Subarctic Pacific lower trophic interactions: production-based grazing rates and grazing-corrected production rates



PICES Scientific Report ember; 32: 8-15



The work Dr. Selph proposes would be an excellent characterization of short-term ecosystem variation, going far beyond just the chlorophyll data available in earlier studies. The flow cytometry data can be available in real-time to help us track where we are in the cycle as observations go forward. It is essential to effective 'reactive' planning during the cruises that most aspects of our results be progressively evident as we generate them, rather than emerging at some meeting a year or more after the observations at sea. An intriguing aspect of work in the central Gulf of Alaska is that the specific composition of the algal flora is different on every visit one makes, as shown by Beatrice Booth's work in SUPER (Subarctic Pacific Ecosystem Research). Phytoplankton are always predominantly picoplankton and nanoplankton (mostly less than 7[long dash]8 [mu]m), but the dominant cells can be coccoid chlorophytes, any of the divisions of small flagellates, or even small diatoms. We cannot fully understand what is happening without knowing what sorts of algae are operating around us; we cannot just measure chlorophyll. We are likely to see transitions in phytoplankton composition, although we may not be able to explain such transitions when they occur. However, they should be documented. In this regard, Dr. Nicholas Welschmeyer proposes in the next essay to do 'CHEMTAX' high-performance liquid chromatography (HPLC) work on a twice daily basis aboard ship, with regularly posted results. That would provide another dimension to the picture. It will be essential that growth rates of phytoplankton be estimated by up-to-date, reliable techniques that take full account of the impact of microheterotrophs in incubation bottles. This is important, in part, because the trophic link from pico- and nanophytoplankton to protozoan grazers initiates transfer to larger organisms: copepods, euphausiids, fish, squid, and mammals. Nicholas Welschmeyer has developed a dilution technique using carbon-14 which seems ideally suited to high-nitrate lowchlorophyll (HNLC) situations and thus to the core problems to be studied by OECOS. At the Workshop he discussed these methods (and some other aspects of an approach to subarctic Pacific ecology).

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