The Shelf Sea Ecosystem

1. The Shelf Sea Ecosystem Dr. Mark Moore Rm. 456/18 E-mail: cmm297 20th February 2003

2. Introduction • Primary production in shelf seas • Secondary production and food webs • The physics of shelf seas as a control on food web structure • Review and conclusions

3. Primary production in shelf seas Forms of phytoplankton Controls on growth: nutrients and light Cell size and succession

4. Primary production in shelf seas 1 Smallest: cyanobacteria, mainly synechococcus in coastal seas, <2m

5. Flagellates 2-20 m

6. Dinoflagellates O(100 m)

7. Diatoms (50->1000 m)

8. Primary production in shelf seas 2 Photosynthesis is reduction of inorganic carbon resulting in production of organic matter and evolution of oxygen: H2O + CO2 + light  organic matter + O2 Primary production and the growth of phytoplankton can be limited by the availability of the key resources Nutrients and Light

9. Photosynthesis is an increasing function of light and nutrients the relative availability of these resources can control the growth rate Geider et al. 1998 Limnol. Oceanogr. 43 679-694

10. Primary production in shelf seas 3 Relationship of cell size to succession In general larger cells (diatoms) are found in situations where higher ambient nutrient concentrations are found Cullen et al. 2002 pg 297-336 in The Sea Vol 12 Wiley

11. Secondary production and the food web Trophic levels The microbial loop Food web complexity Loss of energy between trophic levels

12. Secondary production and the food web 1 Transfer of energy and organic matter through the various trophic levels is called the food chain But situation is more complex, e.g. fish can be omnivorous, also the microbial loop…..

13. Secondary production and the food web 2 Bacteria and viruses and micro-zooplankton (flagellates and ciliates) can cycle organic matter through dissolved and particulate pools can act as a sink for primary production Kirchman Ed. (2000) Microbial ecology of the Oceans Wiley

14. Secondary production and the food web 3 Food webs are complex, involve multiple transfers with organisms covering wide range of size classes

15. Secondary production and the food web 4 Transfer of energy between trophic levels There is some loss of energy at each level in the food chain (web) Average efficiency is low <20%

16. Physics of shelf seas as a control on ecosystem structure Mixing, stratification and blooms at fronts Coastal upwelling and blooms Nutrient inputs to coastal waters: red tides

17. Physics of shelf seas as a control on ecosystem structure 1 Temperature Chlorophyll

18. Physics of shelf seas as a control on ecosystem structure 2 Temperature Chlorophyll

19. Physics of shelf seas as a control on ecosystem structure 3

20. Review and conclusions: from phytoplankton to fish Food webs are complex From Azam et al. 1983

21. Review and conclusions: from phytoplankton to fish When nutrients are low, favours smaller phytoplankton grazed by microzoo, microbial loop and recycling dominate As nutrients become more available, larger phytoplankton can survive, grazed by larger zoo, less trophic levels and hence higher yield to top of chain (fish)

22. Review and conclusions: from phytoplankton to fish In very general (cross system) terms, fisheries yield can be related to total primary production occurring however the number of trophic levels and efficiency of these steps governs the yield

23. Relationship of primary production and fish production in three different marine habitats