Review –Seasonal cycle –spatial variation Food web and microbial loop Eutrophic vs. Oligotrophic food webs Biological pump

Phytoplankton biomass Zooplankton biomass Nutrients Relative increase Mixing Stratified Light Temperature Annual cycle in N. Atlantic Spring bloom Fall mini- bloom

Primary production and its seasonal cycle vary greatly in space Chl a from SeaWIFS satellite

Atlantic Ocean Pacific Ocean Temperature South pole Equator North Pole Mixed layer is deeper in Atlantic than in Pacific Depth (m)

Video of mixed layer with wind mixing (go to 8:21)

Latitudinal variation in seasonal cycles driven by variation in irradiance 90 o N = N. Pole 60 o N ~Anchorage,AK 30 o N ~N. Florida 0 o N = Equator [Also Irradiance]

Annual cycles in other regions Try this on your own: Draw the vertical profiles of temperature and light and the critical depth for each region as we did in class for the North Atlantic. Phytoplankton biomass Zooplankton biomass

Chisholm, 2000 Biological Pump Photosynthesis Respiration Sinking Remineralization

On average, predators are ~10x bigger than prey Hansen et al ESD = Equivalent Spherical Diameter

What’s in a liter of seawater? 1 Liter of seawater contains: 1-10 trillion viruses 1-10 billion bacteria ~0.5-1 million phytoplankton ~1,000 zooplankton ~1-10 small fish or jellyfish Maybe some shark, sea lion, otter, or whale poop *The bigger you are, the fewer you are This basking shark can filter ~25,000 L seawater per day!

phytoplankton zooplankton fish Assume a trophic transfer efficiency of 10% Biomass Efficiency 0.1 Trophic transfer efficiency = fraction of biomass consumed that is converted into new biomass of the consumer

Traditional view of simple food web: Small things are eaten by (~10x) bigger things Size (μm) 20,000 2, Heterotrophs Autotrophs

Have to add heterotrophic bacteria, heterotrophic protists, and autotrophic bacteria Size (μm) 20,000 2, Heterotrophs Autotrophs

Bacteria absorb organic molecules leaked by microbes and phytoplankton. This creates a microbial “loop.” 20,000 2, Size (μm) Heterotrophs Autotrophs Dissolved organic matter Microbial Loop

Chisholm, 2000 Zoom in on food web Photosynthesis respiration

Phytoplankton are eaten by zooplankton

Plankton size structure is important Diatoms, dinoflagellates Coccolithophores, cyanobacteria

Importance of microbial loop depends on environmental conditions. Microbial loop

Definitions Eutrophic environments have high nutrient concentrations and high productivity. Coastal upwelling regions and estuaries are Eutrophic. Oligotrophic environments have low nutrients and low productivity. Subtropical gyres (open ocean) are Oligotrophic. It takes a lot of mixing or a big nutrient influx to make an environment eutrophic. Stratified systems eventually must become oligotrophic.

Diatom bloom in Barents SeaClear water over Great Barrier Reef Eutrophic -coastal -estuaries -upwelling -high latitudes Oligotrophic -open ocean -central gyres

In eutrophic systems, large phytoplankton (diatoms) dominate and more biomass goes directly to large plankton and fish. Temp. Depth D cr Microbial loop is less important

Temp. Depth D cr In oligotrophic systems, small phytoplankton (e.g. cyanobacteria) dominate and biomass goes through more levels of plankton to get to fish. Microbial loop is key

Open Ocean Tuna Carniv. Fish Carniv. Plankton Herbiv. Plankton Phytoplankton 5 Levels 10% Efficiency Coastal Ocean Carniv. Fish Carniv. Plankton Herbiv. Plankton Phytoplankton 4 Levels 15% Efficiency Upwelling Zone Anchovies Phytoplankton 2 Levels 20% Efficiency Oligotrophic Eutrophic

Draw biomass spectrum here

Area% of ocean area Total Plant Production Transfer Efficiency Trophi c Levels Estimated Fish Production (x10 9 metric tons carbon per year) (x10 6 metric tons per year) Open Ocean %54 Coastal Ocean %429 Upwelling Zones %246

Open oceanCoastal ocean Upwelling zones =10 9 metric tons C per year =10 6 metric tons fish per year 5 Trophic levels 10% Efficiency 4 Trophic levels 15% Efficiency 2 Trophic levels 20% Efficiency

Chisholm, 2000 Photosynthesis respiration Food-web structure affects the export of carbon to deep ocean

How does organic matter get to the bottom of the ocean? Dead cells and fecal pellets (plankton poop) sink. Big ones sink faster. Dissolved organic matter, pieces of gelatinous animals etc. stick together and form bigger “marine snow” that sinks. Organic debris is collectively known as Detritus.

Bigger plankton sink faster. They also have bigger, faster-sinking fecal pellets. Marine snow Large plankton and their fecal pellets Small plankton and their fecal pellets

In eutrophic conditions, there are more, larger particles that sink into deep ocean. Temp. Depth Large fecal pellets Large Marine snow D cr

In oligotrophic conditions, there are fewer, smaller particles that sink more slowly into deep ocean. Temp. Depth D cr small fecal pellets

Eutrophic vs. Oligotrophic summary EutrophicOligotrophic Mixed layerMore mixing Cooler More stratified Warmer Nutrients High concentration Newer Low concentration More recycled PlanktonLargerSmaller ParticlesLarger Faster-sinking Smaller Slower-sinking Carbon ExportMoreLess