Open Oceans: Pelagic Ecosystems

1. Open Oceans: Pelagic Ecosystems

2. Bacterioplankton

10. Elements of an Ecosystem Approach • What are the components? • What are the special environmental challenges? • What are the special adaptations? • How do we understand form & function? • What are the controlling processes? • What are the important patterns?

11. Pelagic System Components • The area of open water of oceans, including the entire water column away from the bottom substrates • Nutrients and salts • Plankton • Nekton

12. Dimensions of Variation for Plankton • Size: virus (2 x 10-7 m) to jellyfish (0.2 m) • Energy processing & nutritional modes • photosynthetic (phytoplankton) • heterotrophic, ingestive (zooplankton) • heterotrophic, absorptive (mycoplankton) • infective (viroplankton) • Life history variation • permanent residents • transient members of the plankton community

13. Phytoplankton Diatoms Foraminifera Dinoflagellates

14. Coccolithophores

15. Coccolithophore bloom, English Channel 20 km

16. Mixture of groups producing a “bloom” Baltic Sea 1 Coccolithophores 2 Diatoms 3 Eukaryotic picoplankton

17. Diversity of form

18. Zooplankton: protista

19. Zooplankton: crustacea

20. Copepod

21. Zooplankton: larvae

22. Challenges • Maintaining access to nutrients, light, & resources • Avoid being food for larger consumers

23. Adaptations for maintaining position • Use water movements • Convection cells (from diurnal cycles in heat) • Langmuir convection cells from wind

24. Langmuir patterns in the Galapagos

25. Adaptations for maintaining position • Affect buoyancy • Use lighter ions for osmotic balance (e.g., use chlorides rather than sulphates) • Develop flotation organs (gas, oils, fats) • Manipulate resistance (use viscosity) • “parachute” morphology • elaborate appendages

26. Global scale patterns of pelagic productivity

27. What are controlling processes? • Primary Productivity • Different estimates of productivity • Gross Primary Productivity • Net Primary Productivity • Standing crop • and Grazing Rates

28. What is “productivity”? • primary productivity is defined as the total quantity of carbon fixed by autotrophs • a rate expressed as grams of carbon fixed per square meter of sea-surface per unit of time • gross primary production is the total amount of organic matter produced by autotrophs • net primary production is the energy remaining after respiratory needs have been met • NPP = Gross Primary Production - Respiration

29. Questions to consider • Why should we care about patterns of biological productivity in oceans? • What are the spatial patterns of productivity? • What mechanisms promote or limit productivity?

30. Why should we care about productivity? • Photosynthetic activity in oceans created current O2-rich atmosphere • Plankton form ocean sediments & fossil fuels • Plankton are a critical part of “carbon pump” that influences atmospheric CO2 • Phytoplankton form the base of food webs and associated biological diversity • Limits to productivity may limit the amount of harvestable biomass from ocean ecosystems

31. Measuring Primary Productivity: Data • Standing crop methods • Chlorophyll concentration (water extraction, satellite) • Cell counts (flow cytometers) • Rate measurements • Light-dark bottle method • Carbon-14 uptake • Advantages & disadvantages

32. chlorophyll density & temperature

33. Link between producers & grazers

34. Measuring Primary Productivity: Inferences • Simple models integrate different parameters to estimate rates of productivity • Model components (Field et al. Science 281:237-240) • chlorophyll concentration • water depth in photic zone • fraction of water column where photosynthesis is light-saturated • surface temperature

35. Results of productivity model

36. Some patterns • average primary productivity in the oceans is ~50 g C/m2/yr • 300 g C/m2/yr considered relatively high rate of primary productivity  • low rates of primary productivity typically 20 to 30 g C/m2/yr