Lecture 13- Marine food webs Flashcards Preview

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Flashcards in Lecture 13- Marine food webs Deck (52):

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

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


How does a food chain work?

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


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

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


What do all organisms need to grow and thrive?

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


What are autotrophs?

-synthesize their own complex carbon compounds.


What are phototrophs? (subdivision of autotroph)

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


What are chemotrophs? (subdivision of autotrophs)

-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


What are mixotrophs?

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


What are heterotrophs?

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.


What are bacteroivores?

-eat bacteria


How do we determine food web structure?

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


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

-phytoplankton (autotrophic)


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



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

-predatory zooplankton


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

-filter feeders


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



What are the 3 characteristics of marine food webs?

• 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


Who are the primary producers?

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


How much do the diatoms contribute to ocean primary productivity?

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


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

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


What types of zooplankton are the primary consumers?

-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


What types of filter feeders are the secondary consumers?

-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)


What types of carnivores are the tertiary consumers?

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


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

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.


Are animals ever in one trophic level?

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


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

-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.


What is the equation of budget for ingested food?

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


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

minority of the ingestion


Why is some food egested?

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


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

-Majority is used for respiration


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

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


What is the growth efficiency?

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


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



Why are food chains oversimplifications?

-consumers often feed at multiple levels in a food web


What is food chain efficiency?

(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


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

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


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

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


What is the maximum catch fisheries can catch per year?

-100 million tons

- based on phytoplankton productivity in the oceans

-it is correct

-now catch abut 90


What are the three main marine planktonic food chains?

1. Oceanic system 2. Coastal 3.Upwelling


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

•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


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

•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


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

•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


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

-fewer trophic levels are more efficient


What is bottom-up control of a food chain?

-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)


What is top-down control of a food chain?

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


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



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

-4 or 5


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

1)Trophic hypothesis 2)Food chain stability hypothesis


What is the trophic hypothesis?

-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


What is the food chain stability hypothesis?

-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


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

-there is ∼ 1000 times more plant biomass (phytomass) than animal biomass (zoomass).

-About 18% of plant biomass is eaten by land animals.


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

-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.