Lecture 13- Marine food webs

Question 1

What is the big difference in primary producers on land and in the sea?

Answer 1

-on land they are large (trees) -in the seas they are unicellular (phytoplankton)

Question 2

How does a food chain work?

Answer 2

-1. Phytoplankton 2. Herbivorous zooplanktin 3. carnivorous zooplankton 4. small fish 5.larger fish 6- seal 7. killer whale

Question 3

What is the difference if trophic levels on land and in the sea?

Answer 3

-on land usually up to 3 or 4 -in the sea can reach almost 7(not really)

Question 4

What do all organisms need to grow and thrive?

Answer 4

-energy -electrons -carbon (plus associated nitrogen, phosphorus and sulphur)

Question 5

What are autotrophs?

Answer 5

-synthesize their own complex carbon compounds.

Question 6

What are phototrophs? (subdivision of autotroph)

Answer 6

-such as phytoplankton use energy from sunlight plus carbon dioxide and water to synthesize complex carbon compounds

Question 7

What are chemotrophs? (subdivision of autotrophs)

Answer 7

-use energy from inorganic chemical compounds, such as methane, hydrogen sulphide, or reduced iron plus carbon dioxide or some organic carbon to synthesize complex carbon compounds

Question 8

What are mixotrophs?

Answer 8

-are organisms that can use energy from both sunlight and chemical compounds.

Question 9

What are heterotrophs?

Answer 9

are organisms that must eat other organisms to obtain complex carbon compounds. Some are able to use sunlight or inorganic compounds for energy, others must use organic carbon compounds for energy. People are heterotrophs that get complex carbon compounds and energy from other organisms.

Question 10

What are bacteroivores?

Answer 10

-eat bacteria

Question 11

How do we determine food web structure?

Answer 11

• Stomach content analyses (traditional) - Stable carbon and nitrogen isotope analysis -observation (put camera on)

Question 12

Who are the primary producers in the sea? (trophic level 1)

Answer 12

-phytoplankton (autotrophic)

Question 13

Who are the primary consumers in the sea? (trophic level 2)

Answer 13

-zooplankton

Question 14

Who are the secondary consumers in the sea? (trophic level 3)

Answer 14

-predatory zooplankton

Question 15

Who are the tertiary consumers in the sea? (trophic level 4)

Answer 15

-filter feeders

Question 16

Who are the 4th, 5th and 6th level consumers?

Answer 16

-predators

Question 17

What are the 3 characteristics of marine food webs?

Answer 17

• Marine food webs are complex •Species may alter levels in a food web at different life cycle stages •Consumers often feed at multiple levels in a food web

Question 18

Who are the primary producers?

Answer 18

• phytoplankton, seaweeds, plants (sea grass), chemotrophic bacteria

Question 19

How much do the diatoms contribute to ocean primary productivity?

Answer 19

• contribute about 60 per cent of the primary productivity in the oceans. - 200,000 different species diatoms ranging is size from micrometres to millimetres

Question 20

How much do the Coccolithophores (haptophytes) contribute to ocean phytoplankton biomass?

Answer 20

• contribute about 15 per cent of the average oceanic phytoplankton biomass to the oceans.

Question 21

What types of zooplankton are the primary consumers?

Answer 21

-Single-celled animals such as ciliates or amoeboids that never grow large. -Copepods about 7500 species, extremely abundant. Biomass ∼ 0.8 and 2.0 billion tons -Shrimp e.g. Krill, ∼ 500 million tons in the southern ocean -Larval forms of barnacles, molluscs, fish, and jellyfish, all of which grow to be much larger animals

Question 22

What types of filter feeders are the secondary consumers?

Answer 22

-Shrimp and krill. -Immature stages of larger animals such as jellyfish and fish. -Small planktivorous fish such as sardines, anchovies, mackerel and herring,highly abundant and a principal target of modern fisheries. -Some whales (e.g. blue whale)

Question 23

What types of carnivores are the tertiary consumers?

Answer 23

=Jellyfish = Cephalopods (squid and octopus). -Predatory fish= enormous diversity

Question 24

What sort of predators are the 4th, 5th and 6th level consumers?

Answer 24

1.Large predatory fish such as sharks, tuna, and mackerel. 2.Marine mammals - seals, walruses, dolphins 3.Birds such as pelicans, albatross, penguins and skua. 4.Jellyfish Cephalopods (squid and octopus). Predatory fish - enormous diversity 5.People, the dominant top predator.

Question 25

Are animals ever in one trophic level?

Answer 25

-only phytoplankton are exactly level 1 -the rest usually on a scale as they eat thing on their level etc. -whales about level 2

Question 26

What are the two reasons why energy transfer through the food chain is inefficient?

Answer 26

-Due to loss of energy through: 1.uneaten proportion of a given trophic level (escape, unpalatability or unavailability) 2.Inefficient conversion. Some proportion of food is not ingested and sinks from the water column to decompose. Another fraction is ingested but not converted to growth.

Question 27

What is the equation of budget for ingested food?

Answer 27

I=E+R+G -I = amount ingested -E = amount egested -R = amount consumed in respiration -G = amount partitioned between somatic (body) growth and reproduction

Question 28

How much is G (growth ) of the ingested food (I)?

Answer 28

minority of the ingestion

Question 29

Why is some food egested?

Answer 29

-Not all food can be assimilated, so some is egested

Question 30

What is the majority of (I) ingested food used for?

Answer 30

-Majority is used for respiration

Question 31

What are the factors leading to incomplete transfer of energy up a food chain?

Answer 31

-Growth is a minority of the ingestion -Not all food can be assimilated, so some is egested -Majority is used for respiration

Question 32

What is the growth efficiency?

Answer 32

-the proportion of assimilated food used in growth - usually 10% but can be as high as 35-40%

Question 33

How much kg of plankton do you technically need for one 3600kg killer whale to exist?

Answer 33

-

Question 34

Why are food chains oversimplifications?

Answer 34

-consumers often feed at multiple levels in a food web

Question 35

What is food chain efficiency?

Answer 35

(E) defined as the amount of energy extracted from a trophic level divided by the amount of energy supplied to the trophic level • can be used to estimate potential fish production at the top of the food chain

Question 36

What is the equation to estimate the potential fish production at the top of the food chain?

Answer 36

P= BE to power n -P = production of fish -B = biomass of phytoplankton -E = food chain efficiency -n = number of links between trophic levels

Question 37

What can small change in E (in the potential fish production equation) mean?

Answer 37

-can make large changes in overall fish production i.e. change from 0.1 to 0.2 would increase fish production 16 times

Question 38

What is the maximum catch fisheries can catch per year?

Answer 38

• 100 million tons
• based on phytoplankton productivity in the oceans
• it is correct
• now catch abut 90

Question 39

What are the three main marine planktonic food chains?

Answer 39

1. Oceanic system 2. Coastal 3.Upwelling

Question 40

What is the setup of the oceanic system (marine planktonic food chains?

Answer 40

•Low annual primary productivity ∼ 50 g C m-2 yr-1 •5 trophic levels •Food chain efficiency ∼ 10% •Fish production ∼ 0.5 g C m-2 yr-1

Question 41

What is the setup of the coastal (marine planktonic food chain)?

Answer 41

•Annual primary productivity ∼ 100 g C m-2 yr-1 •3 trophic levels •Food chain efficiency ∼ 20% •Fish production ∼ 340 g C m-2 yr-1

Question 42

What is the setup of the upwelling area (marine planktonic food chain)?

Answer 42

•High annual primary productivity ∼ 300 g C m-2 yr-1 •1.2 -2 trophic levels •Food chain efficiency ∼ 20% •Fish production ∼ 36000 g C m-2 yr-1

Question 43

What is the relationship of trophic levels and food chain efficiency?

Answer 43

-fewer trophic levels are more efficient

Question 44

What is bottom-up control of a food chain?

Answer 44

-effects of fluctuations of a species at a given trophic level on the levels above (e.g. phytoplankton bloom driven by influx of nutrients which drives increases in zooplankton and fish)

Question 45

What is top-down control of a food chain?

Answer 45

-regulation of a lower trophic level due to predation (e.g. cod predation on shrimp in the north Atlantic ocean)

Question 46

How can top down control vary with different number of of trophic levels?

Answer 46

-

Question 47

What is the most common number of trophic levels in a marine food chain?

Answer 47

-4 or 5

Question 48

What are the two hypotheses about what determines the length of food chains?

Answer 48

1)Trophic hypothesis 2)Food chain stability hypothesis

Question 49

What is the trophic hypothesis?

Answer 49

-there are a maximum no. of trophic links through which energy can travel due to food chain efficiency. i.e. the number of trophic levels are controlled by bottom-up processes related to energy flow

Question 50

What is the food chain stability hypothesis?

Answer 50

-longer food chains are inherently unstable. i.e. if changes occur at one level, they will be propagated to other levels, which may prevent stable food chains from becoming too long

Question 51

What is the biomass distribution among trophic levels in a terrestrial system?

Answer 51

• there is ∼ 1000 times more plant biomass (phytomass) than animal biomass (zoomass).
• About 18% of plant biomass is eaten by land animals.

Question 52

What is the biomass distribution among trophic levels in a marine system?

Answer 52

-In the open ocean, the biomass pyramid is inverted. Animal biomass is 30 times larger than primary producer biomass. Most ocean plant biomass is eaten by the ocean animals.