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Neocalanus spp. and the Structure of the Pelagic Ecosystem in the Subarctic Pacific Ocean

Neocalanus spp. and the Structure of the Pelagic Ecosystem in the Subarctic Pacific Ocean. M. Dagg, Louisiana Universities Marine Consortium H. Liu, Hong Kong University of science and Technology S. Strom, Western Washington University. Surface Mixed layer Thermocline

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Neocalanus spp. and the Structure of the Pelagic Ecosystem in the Subarctic Pacific Ocean

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  1. Neocalanus spp. and the Structure of the Pelagic Ecosystem in the Subarctic Pacific Ocean M. Dagg, Louisiana Universities Marine Consortium H. Liu, Hong Kong University of science and Technology S. Strom, Western Washington University

  2. Surface Mixed layer Thermocline Permanent halocline 0 m N. plumchrus/flemingeri zone 35-45 m N. cristatus and E. bungii zone 100-120 m data from Mackas, D.L., H. Sefton, C. B. Miller and A. Raich. 1993. Vertical habitat partitioning by large calanoid copepods in the oceanic subarctic Pacific during spring. Prog. Oceanogr. 32: 259-294.

  3. May 1984 - 10 stations: mean abundance = 152 CVs / m3 (from Mackas et al. 1993)

  4. June 1987 – mean abundance = 204 ind / m3 (from Mackas et al. 1993)

  5. (from Levitus World Ocean Atlas 1994)

  6. Chlorophyll concentration: < 5 mm = 0.577 mg l-1 5-20 mm = 0.143 mg l-1 > 20 mm = 0.051 mg l-1

  7. Chlorophyll concentration: Clearance rate: < 5 mm = 0.577 mg l-1 -0.068 L cop-1 d-1 5-20 mm = 0.143 mg l-1 0.088 L cop-1 d-1 > 20 mm = 0.051 mg l-1 0.208 L cop-1 d-1

  8. are there enough copepods in situ to structure the nano- and pico-food web in the eastern subarctic Pacific?

  9. Concentration of N. plumchrus/flemingeri CV = 25 - 500 m-3 Clearance rate on large particles (> 20 mm) = 0.2 – 2.0 L cop-1 d-1 For 200 copepods m-3 and 1 L cop-1 d-1 = 200 liters d-1 m-3 (0.2 d-1)

  10. Other considerations: top down effect by N. flemingeri/plumchrus • growth rates of large diatoms in this Fe limited system are 0.2 - 0.5 d-1 • growth rates of large ciliates and dinoflagellates?? • other copepodid stages must contribute also

  11. Conclusions Neocalanusflemingeri and N. plumchrus exert a strong structuring effect on the food web of the N. Pacific Ocean, driving the food web towards a small-cell dominated system by: removal of large cells (diatoms and microzooplankton) cascade effect that stimulates small cells

  12. Conclusions Neocalanusflemingeri and N. plumchrus exert a strong structuring effect on the food web of the N. Pacific Ocean, driving the food web towards a small-cell dominated system by: removal of large cells (diatoms and microzooplankton) cascade effect that stimulates small cells • These effects are strongest: • at low food concentrations when copepod clearance rates are highest, and • under nutrient or food limiting conditions when growth rates of prey are reduced

  13. The END

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