Lecture 3 - Marine Food Webs & Limits to Fisheries Production Flashcards
How can global production be estimated?
Estimate global primary production and determine which fraction of it is transferred to fish stocks to calculate fisheries productivity
Primary production (definition)
The production of organic materials from inorganic components
What are the most common primary producers in the ocean?
Phytoplankton
What are the 2 main limiting factors for primary production in the ocean?
1) Light
2) Nutrients
Sufficient light for net photosynthesis occurs only in the top 1)___ of the oceans, only 2)___% of its volume
1) ~150 meters
2) 2%
1)___ and 2)___ are usually depleted in 3)___ and must be replenished from 4)___
1) Nitrate
2) Phosphate
3) surface waters
4) below
Mixed layer (definition)
The surface layer of the ocean with relatively uniform temperature and salinity, mixed by windstorms
Pycnocline (definition)
Zone of rapid change in water density that marks the bottom of the mixed layer and acts as a barrier to water mxing
What determines water density?
1) Temperature
2) Salinity
What are the 3 major types of ecosystems?
1) Open ocean gyres
2) Coastal/continental shelves
3) Upwelling zones (coastal and equatorial)
Coastal/Continental shelves have ___ primary production
high
Why are coastal/continental shelves sites of high primary production?
They are not deep, so nutrients return more easily.
Open oceans/gyres have ___ primary production
low
Why are open oceans/gyres sites of low primary production?
They are very deep, so nutrients are easily to to depth and nutrients slowly mix back to the surface
Coastal upwelling results in very ___ primary production
high
Why is coastal upwelling in Pacific ocean basins seasonal?
Winds due to the monsoon
Equatorial upwelling is a site of ___ primary production
high
Trophic level (defintion)
The position of an organism (bottom to top) in a food web
Food chain (definition)
A linear arrangement showing transfer of energy and materials
___ reflect the complex nature of trophic interactions
Food webs
All organisms feed ___
selectively
What determines the optimal range of prey?
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
What constraints are predators under when prey are too small?
1) Detection
2) Retention effort
What constraints are predators under when prey are too large?
1) Capture efficiency
2) Handling problems
Predator length/Optimal prey length = ?
~10
True or false. Terrestrial food webs are less size structured than marine food webs.
True, primary producers are large and herbivores span the entire size spectrum
Which is more productive, oligotrophic or eutrophic marine environments?
Eutrophic
Why is there regional variation in food web length?
Nutrient supply dynamis and the size of primary producers
Why do small phytoplankton have a competitive advantage in low nutrient environments?
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
Surface area equation
4 x pi x r^2
Volume equation
4/3 x pi x r^3
Why are long food webs observed in the gyres?
The gyres are low energy, low nutrient (oligotrophic), and deep. Small phytoplankton dominate, serving as the small consumer base for the longer food webs.
Why are short food webs observed in upwelling and high energy systems?
These environments are high energy and high nutrient (eutrophic). Large phytoplankton dominate, serving as the larger consumer base for the longer food webs.
There is proportionally greater 1)___ biomass in more productive regions. Thus, these systems have proportionally 2)___ fisheries yield.
1) top trophic level
2) greater
Ecological efficiency (EE) factor (defintion)
The proportion of energy, weight, or carbon consumed and subsequently available to the next trophic level of consumption
EE must take into account 1)___, 2)___, and 3)___
1) growth efficiency
2) losses to lower trophic levels
3) losses to the same trophic level
What is the value of EE according to summary studies?
~10%
What % of energy consumed is lost to metabolism or excretion?
85%
What % of energy consumed is lost to growth?
15%
Calculation for fish production
Fish production = PP x EE^Trophic level
What is the current estimate of maximum sustainable yield?
100-200 mmt/yr
Eutrophic (definition)
(of a lake or other body of water) rich in nutrients and so supporting a dense primary producer population
Euphotic zone (definition)
Layer closer to the surface that receives enough light for photosynthesis to occur
Oligotrophic (definition)
Relatively low in plant nutrients and containing abundant oxygen in the deeper parts
