Pelagic Food Chain

Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Pelagic Food Chain: Summary Pelagic Food Chain: Summary • The food chain concept • More realistic: food web – An attempt by scientists to – Still very oversimplified make a simple model of the – Can be verified by extreme complexity of biological measurements communities • Observe gut contents • Illustrate simple principles • Use isotopes to track flow – Goal of constructing a budget of of organic carbon • Production at each trophic level – Even at this level, • Who eats what calculations of – Also understand how these production & efficiency properties change over time get complex quickly and location 1 2 Garrison Fig. 14.1, p. 334 Garrison Fig. 13.6, p. 310

Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Pelagic Food Chain: Summary Pelagic Food Chain: Summary • Example of a food web model derived from research – Puget Sound pelagic zone • Large number of organisms (but still not all) • Based on gut contents – Weight of arrow shows proportion of produc- tion following that path • How we derive simpler “food chain” model • Highlight “dominant” species & trophic pathways 3 4 Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Pelagic Food Chain: Summary Pelagic Food Chain: Summary • The main • What determines which organisms are found chain: in which environment? Evolution • 4 Birds & whales – Example: • 3 Baitfish • Anchovy & sardine dominant baitfish off California • (2.5) Carnivorous • Herring & sand lance dominant baitfish off Washington zooplankton • Why? Not entirely clear – Side branches – Herring prefer cooler water not leading to – Differences in types of zooplankton & fish feeding adaptations? higher levels – Example: • 2 Copepods & • Mackerel dominant feeder on baitfish off California krill – Prefer warmer water • 1 Phytoplankton • Salmon off Washington

5 6 – Prefer cooler water & need rivers

Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Productivity in Ocean Zones Pelagic Food Chain: Summary • Comparing 3 general types of environments • 3 factors that determine food-chain productivity

– Again a great simplification NOTE: Biomass used here as differences in different environments – Based on productivity an indicator of productivity – Primary productivity • Types defined in Sverdrup textbook • Subject of next lecture – Upwelling zones – Trophic efficiency • Argued to reflect dispersal of food supplies – Coasts • Predators expend more energy to obtain dispersed prey – Open ocean – Number of trophic levels • My modification • Size of primary producers – “Coasts” lumped – Small phytoplankton: more trophic levels to grow a fish big enough with temperate & subpolar open ocean to harvest • Size of harvestable fish 7 – “Open ocean” includes only low latitudes 8 – Small fish harvestable near shore, big fish far from shore Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Comparing Food Chains Comparing Food Chains • Upwelling vs. (low-latitude) open ocean • In (low-lat) open ocean, phytoplankton small – Remember Peruvian – Microflagellates & cyanobacteia case is unique – So herbivores small (Protozoa microzooplankton) – More typical – Copepod- & krill-sized zooplankton are carnivores upwelling has – 1 extra trophic level to reach that harvest from size of ZP 3rd trophic level • Also Copepods & krill some Copepods & krill Microzooplankton from 4th Large diatoms Microflagellates & cyanobacteria

9 10

Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Oceanography 101, Richard Strickland Lecture 26 © 2006 University of Washington Comparing Food Chains Comparing Food Chains • In (low-lat) open ocean, small fish are mostly • Result: 2 extra trophic level in (low-lat) open not economically harvestable ocean vs. (typical non-Peru) upwelling – Poor market value: Flying fish filets? • Combines with lower efficiency in open ocean – Great distances boats must travel to harvest – These two factors illustrated in these pyramids • Must harvest predators of small fish – For 1000 arbitrary units of PP (primary – 1 extra productivity) trophic – But PP

level to Copepods & krill is 10-20 Copepods & krill reach times harves- Copepods & krill Microzooplankton higher Copepods & krill Microzooplankton

table Large diatoms Microflagellates & cyanobacteria in Large diatoms Microflagellates & cyanobacteria

11 size fish 12 upwelling