2. The material in this slide show is provided free for educational use only. All other forms of storage or reproduction are subject to copyright- please contact the National Marine Aquarium The slide show was designed and produced for the NMA by STEP, the Science Training & Education Partnership T raining & S cience E ducation P artnership www.national-aquarium.co.uk www.step-up-to-science.com

3. Plant growth in the oceans: Resources and controls

4. Plant growth Resource limitation Summary Grazing control

5. Plant growth Resource limitation Summary Grazing control

6. These tiny, single-celled plants grow simply by dividing into two new cells The most important plants in the ocean are phytoplankton

7. If the conditions are good for growth, the number of cells will double each day

8. DAY 1 1 cell

9. DAY 2 2 cells

10. DAY 3 4 cells

11. DAY 4 8 cells

12. Population (number of cells) Starts with one cell, one cell division per day

13. This growth is exponential, and is described by a model of the type: where N is number of cells and t is time, and the constant k is related to the doubling time:

14. DAY 30 535 million cells The exponential model is obviously correct in describing the process of continuous cell division, but it predicts an unrealistic ever-increasing biomass

15. In reality, there is a limit to the amount of phytoplankton biomass that a habitat will support, so the rate of population increase starts to decline

16. This logistic model is more complex, but makes a more realistic prediction Starting population Equilibrium population Rate constant Time

17. Plant growth Resource limitation Summary Grazing control

18. What can limit phytoplankton growth? Too little light Lack of materials to build new cells

19. WATER OXYGEN CARBOHYDRATE CARBON DIOXIDE LIGHT STEP Like all plants, phytoplankton algae grow by photosynthesis They build complex organic materials from carbon dioxide and water, using light as an energy source

20. Light decreases as you go deeper into the ocean

21. The decrease in light with depth is also described well using an exponential model, this time a decay: Light at depth ‘z2’ Light at depth ‘z1’ Absorption coefficient Difference in depths

22. Photosynthesis is dependent on light

23. There is more photosynthesis where water is clear than where it is turbid Depth (metres) Photosynthetic rate

24. Too dark for growth surface 100 m 500 m 1000 m 3500 m Enough light here for growth

25. So phytoplankton will grow well when they are close to the surface... … but phytoplankton that are deeper down will not receive enough light for growth

26. The light available for phytoplankton is controlled by a number of different environmental factors

27. Phytoplankton production Phytoplankton biomass LIGHT ENERGY

28. Phytoplankton production Phytoplankton biomass TurbidityWeather Ocean circulation Ice coverClimate Incident solar radiation Mixed layer temperature Average light in surface mixed layer Wind mixing

29. In addition to light, phytoplankton need a wide range of chemical elements to build organic material

30. Carbon is the most abundant element in organic material However, carbon is in plentiful supply in the surface oceans Carbon dioxide is readily soluble in water, and can diffuse in from the atmosphere

31. Other elements are needed to build phytoplankton biomass Some elements are required in large amounts, whilst others are needed only in minute quantities

32. These elements are usually called nutrients Nutrients needed in large amounts include nitrogen, silicon and phosphorus

33. CHEMICAL NUTRIENTS Phytoplankton production Phytoplankton biomass TurbidityWeather Ocean circulation Ice coverClimate Incident solar radiation Mixed layer temperature Wind mixing Average light in surface mixed layer

34. Again, there are complex environmental controls on the amount of nutrients available to phytoplankton

35. Phytoplankton production Phytoplankton biomass TurbidityWeatherIce coverClimate Incident solar radiation Mixed layer temperature Nutrient availability Wind mixing Ocean circulation Chemical nutrient supply Biogenic regeneration Average light in surface mixed layer

36. Trace elements are elements that are needed in very small amounts Many are metals, such as iron, zinc and cobalt. They may form parts of enzymes, so that trace elements can be important controls on growth and uptake of nutrients

37. Phytoplankton production Phytoplankton biomass TurbidityWeatherIce coverClimate Incident solar radiation Mixed layer temperature Nutrient availability Wind mixing Ocean circulation Chemical nutrient supply Biogenic regeneration Trace elements Average light in surface mixed layer

38. Plant growth Resource limitation Summary Grazing control

39. So far, we have looked at controls on phytoplankton growth rates

40. Removal of phytoplankton is an important control on both biomass and production

41. BIOMASS LOSSES Phytoplankton production Phytoplankton biomass TurbidityWeatherIce coverClimate Incident solar radiation Mixed layer temperature Nutrient availability Wind mixing Ocean circulation Chemical nutrient supply Biogenic regeneration Trace elements Average light in surface mixed layer

43. Herbivorous animals that graze phytoplankton are small, ranging in size from fractions of a millimetre to a few centimetres These animals grow and reproduce rapidly, so that their population increases fast when phytoplankton biomass increases This means that grazing is an effective control on phytoplankton

44. The overall picture of control on phytoplankton involves many factors, often inter-related

45. Sedimentation TurbidityWeatherIce coverClimate Incident solar radiation Mixed layer temperature Average light in mixed layer Nutrient availability Wind mixing Ocean circulation Chemical nutrient supply Biogenic regeneration Trace elements Phytoplankton production Phytoplankton biomass Grazing

46. Plant growth Resource limitation Summary Grazing control

47. Cell division gives rapid population increase Phytoplankton does not increase exponentially in nature You have seen that -

48. Light decreases with depthPhotosynthesis is determined by light, so decreases with depth and turbidity You have seen that -

49. Chemical nutrients are also important for phytoplankton growth Grazing by herbivores can control the abundance of phytoplankton You have seen that -

50. Sedimentation TurbidityWeatherIce coverClimate Incident solar radiation Mixed layer temperature Average light in mixed layer Nutrient availability Wind mixing Ocean circulation Chemical nutrient supply Biogenic regeneration Trace elements Phytoplankton production Phytoplankton biomass Grazing

51. NOTES for USERS The material in this slide show is designed to support the teaching of science at Key Stage 1 A full description of the slide show, and linked activities for students, can be found on the National Marine Aquarium (NMA) web-site: Teachers are free to amend the slide show in whatever way they feel fit, or to use slides in other contexts. However, please note that neither the NMA nor the designers will accept responsibility for modifications, and original material remains copyright of the NMA Individual images used in the slides are copyright of NMA or STEP, except where acknowledged separately The slides have been set up to display as A4 landscape format. If they are incorporated into other slide sequences with different display settings, change in aspect ratio and text location will occur The slide sequence contains the minimum of effects and transitions. However, there are some automated animations, and teachers will wish to make sure that they are familiar with the sequence before use in class Use the PowerPoint notes viewer to obtain additional information for some slides www.justaddh2o.tv www.national-aquarium.co.uk