Lecture 3 - Marine Food Webs & Limits to Fisheries Production

Question 1

How can global production be estimated?

Answer 1

Estimate global primary production and determine which fraction of it is transferred to fish stocks to calculate fisheries productivity

Question 2

Primary production (definition)

Answer 2

The production of organic materials from inorganic components

Question 3

What are the most common primary producers in the ocean?

Answer 3

Phytoplankton

Question 4

What are the 2 main limiting factors for primary production in the ocean?

Answer 4

1) Light

2) Nutrients

Question 5

Sufficient light for net photosynthesis occurs only in the top 1)___ of the oceans, only 2)___% of its volume

Answer 5

1) ~150 meters

2) 2%

Question 6

1)___ and 2)___ are usually depleted in 3)___ and must be replenished from 4)___

Answer 6

1) Nitrate
2) Phosphate
3) surface waters
4) below

Question 7

Mixed layer (definition)

Answer 7

The surface layer of the ocean with relatively uniform temperature and salinity, mixed by windstorms

Question 8

Pycnocline (definition)

Answer 8

Zone of rapid change in water density that marks the bottom of the mixed layer and acts as a barrier to water mxing

Question 9

What determines water density?

Answer 9

1) Temperature

2) Salinity

Question 10

What are the 3 major types of ecosystems?

Answer 10

1) Open ocean gyres
2) Coastal/continental shelves
3) Upwelling zones (coastal and equatorial)

Question 11

Coastal/Continental shelves have ___ primary production

Answer 11

high

Question 12

Why are coastal/continental shelves sites of high primary production?

Answer 12

They are not deep, so nutrients return more easily.

Question 13

Open oceans/gyres have ___ primary production

Answer 13

low

Question 14

Why are open oceans/gyres sites of low primary production?

Answer 14

They are very deep, so nutrients are easily to to depth and nutrients slowly mix back to the surface

Question 15

Coastal upwelling results in very ___ primary production

Answer 15

high

Question 16

Why is coastal upwelling in Pacific ocean basins seasonal?

Answer 16

Winds due to the monsoon

Question 17

Equatorial upwelling is a site of ___ primary production

Answer 17

high

Question 18

Trophic level (defintion)

Answer 18

The position of an organism (bottom to top) in a food web

Question 19

Food chain (definition)

Answer 19

A linear arrangement showing transfer of energy and materials

Question 20

___ reflect the complex nature of trophic interactions

Answer 20

Food webs

Question 21

All organisms feed ___

Answer 21

selectively

Question 22

What determines the optimal range of prey?

Answer 22

1) Sensory mechanisms and thresholds for detecting prey
2) Physical constraints on contact (encounter) frequency
3) Minimum size that can be effectively captured/handled
4) Maximum size that can be effectively captured/handled

Question 23

What constraints are predators under when prey are too small?

Answer 23

1) Detection

2) Retention effort

Question 24

What constraints are predators under when prey are too large?

Answer 24

1) Capture efficiency

2) Handling problems

Question 25

Predator length/Optimal prey length = ?

Answer 25

~10

Question 26

True or false. Terrestrial food webs are less size structured than marine food webs.

Answer 26

True, primary producers are large and herbivores span the entire size spectrum

Question 27

Which is more productive, oligotrophic or eutrophic marine environments?

Answer 27

Eutrophic

Question 28

Why is there regional variation in food web length?

Answer 28

Nutrient supply dynamis and the size of primary producers

Question 29

Why do small phytoplankton have a competitive advantage in low nutrient environments?

Answer 29

Nutrients are taken up across the cell membrane of phytokplankton and smaller plankton have a greater surface area to volume ratio, making them better nutrient sponges

Question 30

Surface area equation

Answer 30

4 x pi x r^2

Question 31

Volume equation

Answer 31

4/3 x pi x r^3

Question 32

Why are long food webs observed in the gyres?

Answer 32

The gyres are low energy, low nutrient (oligotrophic), and deep. Small phytoplankton dominate, serving as the small consumer base for the longer food webs.

Question 33

Why are short food webs observed in upwelling and high energy systems?

Answer 33

These environments are high energy and high nutrient (eutrophic). Large phytoplankton dominate, serving as the larger consumer base for the longer food webs.

Question 34

There is proportionally greater 1)___ biomass in more productive regions. Thus, these systems have proportionally 2)___ fisheries yield.

Answer 34

1) top trophic level

2) greater

Question 35

Ecological efficiency (EE) factor (defintion)

Answer 35

The proportion of energy, weight, or carbon consumed and subsequently available to the next trophic level of consumption

Question 36

EE must take into account 1)___, 2)___, and 3)___

Answer 36

1) growth efficiency
2) losses to lower trophic levels
3) losses to the same trophic level

Question 37

What is the value of EE according to summary studies?

Answer 37

~10%

Question 38

What % of energy consumed is lost to metabolism or excretion?

Answer 38

85%

Question 39

What % of energy consumed is lost to growth?

Answer 39

15%

Question 40

Calculation for fish production

Answer 40

Fish production = PP x EE^Trophic level

Question 41

What is the current estimate of maximum sustainable yield?

Answer 41

100-200 mmt/yr

Question 42

Eutrophic (definition)

Answer 42

(of a lake or other body of water) rich in nutrients and so supporting a dense primary producer population

Question 43

Euphotic zone (definition)

Answer 43

Layer closer to the surface that receives enough light for photosynthesis to occur

Question 44

Oligotrophic (definition)

Answer 44

Relatively low in plant nutrients and containing abundant oxygen in the deeper parts