Job opportunity Falkowski lab seeks aquarist/ undergraduate assistant for the coral lab! If interested, contact Frank Natale:

Review –Competition for nutrients –Light –Critical and Compensation Depths Seasonal cycle and spatial variation Food web and microbial loop Eutrophic vs. Oligotrophic food webs Biological pump

μ max1 = μ max2 K s1 <K s2 Sp. 1 wins except at very high nutrients μ max2 > μ max1 Equal K s Sp. 2 wins, but not by much at low nutrients μ max2 > μ max1 K s1 <K s2 At low N, Sp. 1 wins At high N, Sp. 2 wins Species 1 Species 2 Nutrient Concentration N Specific Growth Rate μ Competition for nutrients Max growth rate (a constant) Half-saturation constant (a constant)

Light attenuates with depth. Longer wavelengths have greater absorption by particles and attenuate more with depth. Too much light damages cells and reduces photosynthesis (photoinhibition). depth Irradiance 5

Compensation & Critical Depth

Definitions Autotrophs get their carbon and energy from inorganic sources. Phytoplankton are autotrophs because they get their carbon from CO 2 and energy from light. Heterotrophs get their carbon and energy from pre-formed organic matter. Zooplankton are heterotrophs because they get carbon and energy by eating phytoplankton.

Protists - single cells Size range: 1 to 1000 μm Life span: days to ~week Crustaceans Size range: 0.01 to 10 cm Life span: weeks to years Gelatinous animals Size range: mm to m Life span: months to ~year Some marine heterotrophs (Zooplankton) krill copepods salpsjellyfish ciliates dinoflagellates Copepods are the most numerous multicellular marine animals!

Seasonal evolution of mixed layer

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

Draw seasonal cycle of temperate and light profiles with critical depth here

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)

Nutrient limitation varies among oceans Mixed layer is deeper in Atlantic than in Pacific Remineralized nutrients accumulate in deep water, transported by ocean conveyer belt

Atlantic vs. Pacific spring bloom Winter: Deep mixed layer, Production shuts down Spring: Phytoplankton bloom Zooplankton - slow to catch up Winter: Shallower mixed layer, Continuous low production Spring: Phytoplankton bloom Zooplankton - right there to eat the bloom! Phytoplankton biomass Zooplankton biomass

Spring in the Arctic is darker & colder than winter at mid-latitudes 90 o N = N. Pole 60 o N ~Anchorage,AK 30 o N ~N. Florida 0 o N = Equator [Also Irradiance]

Seasonal cycle varies with latitude Lalli & Parsons Nutrients [Nutrient]Light Winter Spring Summer Autumn Winter Light Latitude

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

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 million 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, autotrophic microbes 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

Chisholm, 2000 Zoom in on Biological Pump 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 SeaTransparent L. Tahoe Eutrophic -coastal -estuaries -upwelling 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

AreaTotal Plant Production Transfer Efficiency Trophic Levels Estimated Fish Production (x10 9 metric tons carbon per year) (x10 6 metric tons per year) Open Ocean 3910%54 Coastal Ocean 8.615%429 Upwelling Zones %246

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

How does food-web structure affect 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