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Lecture 39: MATTER AND ENERGY TRANSFER IN MARINE ECOSYSTEMS

Powerpoint Lecture Slides

Ecosystems
Producers, Consumers, Decomposers
Trophic levels
Food chains and food webs
Efficiency of energy flow
-- biomass limits and trophic pyramids

FOOD RESOURCES OF THE OCEANS- INTRO
World fish catch
Distribution of fishing areas


MARINE ECOSYSTEMS

Food needed for...

1. matter (for growth and reproduction)
2. energy (for metabolic processes)

Ecosystem: Community of plants and animals ... interactions between organisms and environment permit efficient matter and energy transfer.

Producers, Consumers, Decomposers: Categories of interrelated organisms in an ecosystem.

Primary Producers: . autotrophic plankton (bacteria)
Consumers: . heterotrophic animals

Primary consumers: herbivores
Secondary and higher-level consumers (carnivores, predators)

Decomposers: . heterotrophic bacteria (and fungi)

Derive matter and energy from excrement and dead tissue
Completes the cycle of matter (nutrients) to producers

TROPHIC RELATIONSHIPS
-- TROPHIC LEVELS, FOOD CHAINS, AND FOOD WEBS

"Trophic relationships" describe what an organism eats, and who eats it
= producer-consumer relationships.

Energy and matter pathways in a simple food chain

trophic levels:

4 top predator
3 carnivore
2 herbivore
1 autotroph

Example: simple food chain of herring in a coastal area:

trophic levels:

4 herring
3 carnivorous zooplankton
2 herbivorous zooplankton
1 phytoplankton

Energy and matter pathways in a more complex food web. More descriptive of marine trophic relations.
Adult herring -- different levels, different food organisms.
Food webs more stable than simple food chains -- greater variety of food organisms.

ENERGY TRANSFER BETWEEN TROPHIC LEVELS

o Matter (organic substances, CO2, O2, nutrients) cycled continuously between producers, consumers and decomposers.

Examples: Cycles of P and N

o Energy flows in one direction:
Sun --> producers --> consumers --> decomposers

Energy utilization is not very efficient

o 1% of available solar energy is utilized by marine phytoplankton
o Most of the energy "fixed" by producers or eaten by heterotrophs (70-90%) is used by them for life processes or expelled as unusable waste heat.
o Remainder (10-30%) maintains biomass and is available to consumers at next highest trophic level.

Biomass at each trophic level is controlled by efficiency of energy transfer

--> Trophic Pyramid
o Lowest trophic level: high biomass; many small producers
o Highest trophic level: low biomass; few, large animals

Examples of trophic-level efficiencies:

Herring in coastal regions
Anchovy in coastal upwellings
Tuna in open ocean

Implications for harvesting marine fish as food resource:
Yield of harvest depends on trophic efficiency and trophic level harvested.

FOOD RESOURCES OF THE OCEANS

World fish catch increased 4-fold from l950 to l990

1953 23 * 106 metric tons
1970 68 * 106 metric tons
1990 86 * 106 metric tons

Types of animals harvested:

88% fin fish
8% shell fish
4% crustaceans

Use of the harvest:

60% for human consumption
40% for oil, fishmeal for livestock and poultry
Importance to human diet:
1% of total food production
12% of total animal protein

Distribution of fishing areas controlled by:
1. Primary productivity -- rapid nutrient replenishment
2. Trophic structure ...
... number of trophic levels is low
... efficiency of energy transfer in food chain is high

Open Ocean Areas
o Fisheries in upwelling zones in equatorial and polar oceans
-- nutrient supply to surface waters.
o But the harvest is fin fish (e.g., tuna) from high on an inefficient food chain.

Coastal Areas
o Nutrient supply and regeneration is good -- vertical mixing, runoff.
o Harvest both pelagic fish (herring) and bottom fish (cod, hake, haddock in northern waters)
o Shorter, more efficient food chain -- less energy expended by consumer organisms because of the higher population density of phytoplankton.

Upwelling Areas -- west coasts of Americas and Africa
o High primary productivity.
o Harvest small, fast-growing, phytoplankton-eating species that travel in dense schools, and are easy to catch: anchovies, sardines.
o Short, very efficient food chains.


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