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010. Marine Ecology. Energy Flow & Nutrient Cycle. Food Chains Artificial devices to illustrate energy flow from one trophic level to another Trophic Levels: groups of organisms that obtain their energy in a similar manner. Food Chains.

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slide1

010

Marine Ecology

slide3

Food Chains

  • Artificial devices to illustrate energy flow from one trophic level to another
  • Trophic Levels: groups of organisms that obtain their energy in a similar manner
slide5

Food Chains

  • Total number of levels in a food chain depends upon locality and number of species
  • Highest trophic levels occupied by adult animals with no predators of their own
  • Secondary Production: total amount of biomass produced in all higher trophic levels
slide6

Nutrients

  • Inorganic nutrients incorporated into cells during photosynthesis
  • - e.g. N, P, C, S
  • Cyclic flow in food chains
  • Decomposers release inorganic forms that become available to autotrophs again
slide7

Energy

  • Non-cyclic, unidirectional flow
  • Losses at each transfer from one trophic level to another
  • - Losses as heat from respiration
  • - Inefficiencies in processing
  • Total energy declines from one transfer to another
  • - Limits number of trophic levels
slide9

Energy Flow through an Ecosystem

sun

Food Chain

Primary

Producer

Primary Consumer

Secondary Consumer

Tertiary Consumer

zooplankton

larval fish

phytoplankton

fish

heat

heat

heat

water

Nutrients

fungi

Decomposer

slide10

Transfer Efficiencies

  • Efficiency of energy transfer called transfer efficiency
  • Units are energy or biomass

Pt = annual production at level t

Pt-1 = annual production at t-1

Et = Pt

Pt-1

slide11

Transfer Efficiency Example

  • Net primary production = 150 g C/m2/yr
  • Herbivorous copepod production = 25 g C/m2/yr

=Pcopepods

Et = Pt

Pt-1

= 25 = 0.17

Pphytoplankton

150

  • Typical transfer efficiency ranges
  • *Level 1-2 ~20%
  • *Levels 2-3, …: ~10%
slide12

Energy & Biomass Pyramids

10% efficiency

Tertiary consumers

10 J

2nd order carnivores

Secondary consumers

100 J

1st order carnivores

Primary consumers

1,000 J

Deposit feeders, filter feeders, grazers

Primary producers

10,000 J

algae, seagrass, cyanobacteria, phytoplankton

1,000,000 J sunlight

slide13

Cellular

Respiration

Feces

Growth

Energy Use By An Herbivore

slide14

Food Webs

  • Food chains don’t exist in real ecosystems
  • Almost all organisms are eaten by more than one predator
  • Food webs reflect these multiple and shifting interactions
slide16

Some Feeding Types

Many species don’t fit into convenient categories

  • Algal Grazers and Browsers
  • Suspension Feeding
  • Filter Feeding
  • Deposit Feeding
  • Benthic Animal Predators
  • Plankton Pickers
  • Corallivores
  • Piscivores
  • Omnivores
  • Detritivores
  • Scavengers
  • Parasites
  • Cannibals
  • Ontogenetic dietary shifts
slide17

Food Webs…

Competitive relationships in food webs can reduce productivity at top levels

Phytoplankton

(100 units)

Phytoplankton

(100 units)

Herbivorous

Zooplankton

(20 units)

Herbivorous

Zooplankton

(20 units)

Carnivorous

Zooplankton A

(2 units)

Carnivorous

Zooplankton A

(1 units)

Carnivorous

Zooplankton B

(1 units)

Fish (0.2 units)

Fish (0.1 units)

slide18

Recycling: The Microbial Loop

  • All organisms leak and excrete dissolved organic carbon (DOC)
  • Bacteria can utilize DOC
  • Bacteria abundant in the euphotic zone (~5 million/ml)
  • Numbers controlled by grazing due to nanoplankton
  • Increases food web efficiency
slide19

Microbial Loop

Solar

Energy

Phytoplankton

Herbivores

CO2

nutrients

Planktivores

DOC

Piscivores

Bacteria

Nanoplankton

(protozoans)

slide21

Keystone Species

Kelp Forests

slide22

An Ecological Mystery

  • Long-term study of sea otter populations along the Aleutians and Western Alaska
  • 1970s: sea otter populations healthy and expanding
  • 1990s: some populations of sea otters were declining
  • Possibly due to migration rather than mortality
  • 1993: 800km area in Aleutians surveyed
  • - Sea otter population reduced by 50%
slide23

Vanishing Sea Otters

  • 1997: surveys repeated
  • Sea otter populations had declines by 90%
  • - 1970: ~53,000 sea otters in survey area
  • - 1997: ~6,000 sea otters
  • Why?
  • - Reproductive failure?
  • - Starvation, pollution disease?
slide24

Cause of the Decline

  • 1991: one researcher observed an orca eating a sea otter
  • Sea lions and seals are normal prey for orcas
  • Clam Lagoon inaccessible to orcas- no decline
  • Decline in usual prey led to a switch to sea otters
  • As few as 4 orcas feeding on otters could account on the impact
  • - Single orca could consume 1,825 otters/year
slide28

Inquiry

  • Define keystone species.
  • What is the relationship between sea urchins and sea otters?
  • Why doesn’t a food chain illustrate what really happens in ‘who-eats-who’ relationships?
  • Why are decomposers important?
  • Why do animals that eat lower on the food chain gain more energy than a top carnivore?
  • Homework assignment: pick a ecosystem and draw a food web. (E.g. coral reef, arctic, salt marsh, mangrove, estuary, deep sea…)