10 Productivity and Food Webs in the Sea Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton ©Jeffrey S. Levinton 2001

Productivity vs biomass Biomass the mass of living material present at any time, expressed as grams per unit area or volume Productivity is the rate of production of living material per unit time per unit area or volume

Productivity Primary productivity - productivity due to Photosynthesis Secondary productivity - productivity due to consumers of primary producers

Food Chain Food chain - linear sequence showing which organisms consume which other organisms, making a series of trophic levels Food web - more complex diagram showing feeding relationships among organisms, not restricted to a linear hierarchy

Food Chain Abstraction Adult herring Phytoplankton Barnacle larvae Mollusk larvae Small copepods euphausid tunicate cladocerans amphipod sand eel Young herring arrowworm Larger copepod Phytoplankton Copepod Herring Food chain Food Web

Transfer Between Trophic Levels Transfer from one trophic level to the next is not complete: 1. Some material not eaten 2. Not all eaten is converted with 100% efficiency

Transfer Between Trophic Levels 2 Budget for ingested food (use energy units): I = E + R + G I amount ingested E amount egested R amount respired G growth (partitioned between somatic growth and reproduction)

Transfer Between Trophic Levels 3 Incomplete transfer up a food chain: Measure by food chain efficiency: E = amount extracted from a trophic level amount of energy supplied to that level Often in range of as little as 10%

Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n B = primary production P = production at highest level E = food chain efficiency N = number of links between trophic levels

Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E =.1, B = 1, n = 2,3,4 If n = 2, P = ?

Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E =.1, B = 1, n = 2,3,4 If n = 2, P = ? P = 1 x (0.1) 2 = 1 x 0.01 = 0.01

Transfer Between Trophic Levels 4 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n Let E =.1, B = 1, n = 2,3,4 If n = 3, P = ? P = 1 x (0.1) 3 = 1 x 0.1 x 0.1 x 0.1 = 0.001

Transfer Between Trophic Levels 5 Use food chain efficiency to calculate energy available to highest trophic level: P = BE n With 5 trophic levels, a change of E from 0.1 to 0.2 magnifies P by a factor of 16

Oceanic Food Webs Food webs in the oceans vary systematically in food chain efficiency, number of trophic levels, primary production

Oceanic Food Webs Food Chain Type Primary Productivity gCm -2 y -1 Trophic Levels Food Chain Efficiency Potential Fish Production mgCm -2 y -1 Oceanic Shelf Upwelling ,000

Oceanic Food Webs Food Chain Type Primary Productivity gCm -2 y -1 Trophic Levels Food Chain Efficiency Potential Fish Production mgCm -2 y -1 Oceanic Shelf Upwelling ,000

Oceanic Food Webs Food Chain Type Primary Productivity gCm -2 y -1 Trophic Levels Food Chain Efficiency Potential Fish Production mgCm -2 y -1 Oceanic Shelf Upwelling ,000

Oceanic Food Webs Food Chain Type Primary Productivity gCm -2 y -1 Trophic Levels Food Chain Efficiency Potential Fish Production mgCm -2 y -1 Oceanic Shelf Upwelling ,000

Oceanic Food Webs Note: Great potential of upwelling areas due to combination of high primary production, higher food chain efficiency, lower number of trophic levels

Oceanic Food Webs Stable, low nutrient Turbulent, high nutrient Few trophic levels Many trophic levels Open ocean, gyre centers Shelf, upwelling

Measuring Primary Productivity Gross primary productivity - total carbon fixed during photosynthesis Net primary productivity - total carbon fixed during photosynthesis minus that part which is respired.

Measuring Primary Productivity 2 Net Primary productivity most interesting: gives that part of the production available to higher trophic levels

Measuring Primary Productivity 3 Oxygen technique - Principle - relies upon fact that oxygen is released during photosynthesis CO 2 + 2H 2 O ---> (CH 2 O) n + H 2 O + O 2

Measuring Primary Productivity 4 Oxygen technique 2 - there is an addition from photosynthesis and a subtraction from respiration

Measuring Primary Productivity 5 Oxygen technique 3 - Measurement of oxygen: Winkler technique - chemical titration of Oxygen Polarographic oxygen electrode -

Measuring Primary Productivity 6 Oxygen technique 4 - Light-Dark bottle technique: Light bottle gives oxygen from photosynthesis minus oxygen consumed in respiration Dark bottle gives oxygen consumed from Respiration

Measuring Primary Productivity 7 Oxygen technique 5 - Light-Dark bottle technique: Start light and dark bottles with water sample, wait a short amount of time At end of experiment: oxygen in light minus that in dark bottle gives you gross photosynthesis

Measuring Primary Productivity 8 Oxygen technique 6 - Light-Dark bottle technique: Get change of oxygen, but need to convert to units of carbon. If phytoplankton are synthesizing sugars, multiply change in oxygen atoms by 375 to get equivalent in carbon

Oxygen technique - effect of depth

Measuring Primary Productivity 9 Radiocarbon technique - Principle: carbon is taken up by cells During photosynthesis, so if you label that carbon you can trace it as it is incorporated into cells during photosynthesis.

Measuring Primary Productivity 10 Radiocarbon technique 2 - Method: add bicarbonate to solution With phytoplankton that is labeled with 14 C

Measuring Primary Productivity 11 Radiocarbon technique 3 - Method: add bicarbonate to solution With phytoplankton that is labeled with 14 C Incubate phytoplankton in the radiocarbon Solution Then filter phytoplankton and count radiocarbon Taken up by phytoplankton, using a scintillation counter

Measuring Primary Productivity 12 Radiocarbon technique 4 - Calculation: 1.Know the amount of bicarbonate that was in container 2. Know the amount of radiolabeled bicarbonate you added and the amount that was taken up by Phytoplankton  allows calculation of amount of bicarbonate taken up in photosynthesis

Measuring Primary Productivity 13 Radiocarbon technique 5 - Correction: 14 C is taken up more slowly than much more common stable isotope 12 C. Therefore, --> need to multiply results by 1.05 to get amount in photosynthesis

Measuring Primary Productivity 14 Radiocarbon technique 6 - What you get with this measure: Carbon incorporation into phytoplankton (net photosynthesis)

Measuring Primary Productivity 15 Compare Oxygen technique with radiocarbon: Oxygen technique - used where primary production is high in estuaries, shelf Radiocarbon technique - useful where primary production is low such as open ocean

Measuring Primary Productivity 16 Compare Oxygen technique with radiocarbon 2: Oxygen technique tends to give higher estimates of primary production, perhaps because cells are leaking sugars during photosynthesis, resulting in loss of radiocarbon when cells are filtered and counted

Measuring Primary Productivity 17 Satellite Approaches: Satellites can use photometers specific to wavelength to measure chlorophyll, Seawater temperature Need ground truthing to get relationship Between chlorophyll concentration and primary production; varies with region

Measuring Primary Productivity 18 Satellite Approaches 2: Satellites can use photometers specific to wavelength to measure chlorophyll, Seawater temperature Need ground truthing to get relationship Between chlorophyll concentration and primary production; varies with region

sun Satellite Color scanner Irradiance Radiance Phytoplankton

Geographic Variation of Productivity 1.Continental shelf and open-ocean upwelling Areas are most productive 2. Convergences and fronts often are sites of rise of nutrient rich deep waters (e.g., shallow water seaward of slope 3. Central ocean, gyre centers are nutrient poor, low primary production

South Pacific North Pacific North Atlantic South Atlantic Antarctic Indian Ocean

Satellite image of world productivity, from SeaWiFS satellite

The End