|Chapter 14: Biological Productivity and Energy Transfer
Primary production of organic compounds is generated mainly through algal photosynthesis, although bacteria may also produce primary organic compounds through chemosynthesis. Biological productivity is controlled primarily by availability of nutrients and sunshine. Biomass may be transferred from phytoplankton to herbivore and various carnivore trophic levels. Only about 10% of the mass taken in at one level is passed on to the next.
Upon completion of this chapter, the student should be able to:
1. Define biomass in the context of the marine environment.
2. Define primary productivity and distinguish between photosynthesis and chemosynthesis with respect to primary productivity and name locations in the ocean in which one would expect to find photosynthetic and chemosynthetic organisms.
3. Differentiate between gross primary productivity and net primary productivity and describe how the metabolic processes of photosynthesis and cellular respiration relate to gross and net primary productivity.
4. Outline the methods used to estimate primary productivity in marine environments including:
A. plankton nets
B. Gran method (= light and dark bottles)
C. SeaWiFS (Sea-viewing Wide Field-of-View Sensor)
5. Name the nutrients that limit primary productivity in marine environments.
6. Describe the sources of nutrient input into ocean systems including:
A. coastal runoff
B. river input
7. Define the compensation depth for photosynthesis and describe how it is measured.
8. Explain the relationship among the compensation depth, the euphotic zone, and the depth to which solar radiation penetrates the ocean and describe how these relationships change in coastal waters as opposed to waters of the epipelagic open ocean.
9. Explain why marine life is more abundant in coastal waters as compared with the open ocean listing all factors (biological, chemical, geologic, and physical) that affect species diversity, biomass, and the distribution of life in the ocean.
10. Detail the electromagnetic spectrum for visible light and explain the relationship between wavelength and energy, and discuss the implications of this relationship for light penetration in marine environments.
11. Describe the measurement of water clarity in aquatic systems. Explain the relationship between clarity and turbidity and describe how these concepts are related to primary productivity?
12. Discuss the relationship between the color of ocean water and the productivity level of that area.
13. Define eutrophic and discuss how eutrophication is related to nutrient input and to primary productivity.
14. List the photosynthetic organisms commonly found in marine environments, their taxonomic classification, and their preferred habitat including:
A. sea grasses (Kingdom Plantae, Division Angiospermae (or Anthophyta) – textbook uses Spermatophyta
B. cord grass, Spartina alterniflora (Kingdom Plantae, Division Angiospermae (or Anthophyta)) – textbook uses Spermatophyta
C. mangroves, Rhizophora and Avicennia (Kingdom Plantae, Division Angiospermae (or Anthophyta)) – textbook uses Spermatophyta
D. brown algae (Kingdom Protista, Division of Phaeophyta)
E. green algae (Kingdom Protista, Division Chlorophyta)
F. red algae (Kingdom Protista, Division Rhodophyta)
G. golden algae (Kingdom Protista, Division Chrysophyta)
H. diatoms (Kingdom Protista, Division Bacillariophyta)
I. coccolithophorids (Kingdom Protista, Division Haptophyta)
J. dinoflagellates (Kingdom Protista, Division Dinoflagellata or Pyrrophyta)
15. Describe the formation of a harmful algal bloom (HAB) including the causative organisms and the environmental factors that contribute to the development of HABs.
16. Compare and contrast the productivity of polar, temperate, and tropical oceans describing the physical, chemical, and geologic factors that contribute to productivity differences as a function of latitude and applying information from previous chapters.
17. Define entropy as it applies to marine systems.
18. Distinguish between a community and an ecosystem and give an example of each that you would find in a marine environment.
19. Differentiate between autotrophic and heterotrophic modes of nutrition and give an example of a marine organism that would employ each nutritional strategy.
20. Define each of the following terms that describe the position of an organism in the food chain (trophic level) and an example of a marine organism that fits the category including:
21. Distinguish among the following types of consumers in terms of the food they eat and their position on the food chain and give an example of a marine organism that would fit into each category including:
A. herbivore B. carnivore
C. omnivore D. bacteriovore
22. Define detritus and describe how detritus fits into the energy flow in a marine ecosystem.
23. Differentiate among the following types of symbiotic relationships and give an example of each including:
24. Describe the biogeochemical cycling of the following nutrients in the ocean:
25. Know the relationship between trophic level (caloric content) and the trophic transfer efficiency (gross ecological efficiency) and discuss the biological implications of a 90% energy loss between adjacent trophic levels.
26. Distinguish among a food chain, a food web, and a biomass pyramid.
27. Describe the role of microorganisms in the marine environment.
Demonstration and activities:
Using models of Earth and Sun, demonstrate the variation in insolation with latitude and season
Review areas of open ocean upwelling (use global winds)
- The Blue Planet: Seas of Life (BBC Video), 2001, one hour each episode
- Life of Earth (BBC Video, David Attenborough), one hour each episode
- Origins of Life (Ventura), 2002, 75 minutes
- The Living Sea (Image Entertainment), 2000, 40 minutes
I. Primary productivity
A. Photosynthetic productivity
1. Gross primary productivity
2. Net primary productivity
3. New production
4. Regenerated production
B. Measuring primary productivity
1. Plankton nets (trap organisms)
2. Gran method (oxygen concentration)
3. Chlorophyll levels (SeaWiFS)
C. Availability of nutrients
1. Nitrate, phosphorous, iron, silica as examples
2. Main source: river runoff
D. Availability of solar radiation
1. Compensation depth for photosynthesis
2. Euphotic zone
E. Margins of oceans
1. Nutrients available
F. Light transmission in ocean water
Electromagnetic spectrum: solar radiation is mainly visible wavelengths
2. Ocean selectively absorbs longer wavelength of visible light
3. Secchi disk
Ocean color influenced by turbidity and photosynthetic
5. Ocean color related to primary productivity
II. Photosynthetic marine organisms
1. Shallow seawater, e.g., eelgrass, surf grass, mangrove
B. Macroscopic algae
1. Generally in shallow seawater, most fixed to seafloor
2. Classified by color: brown, green, red
C. Microscopic algae
a. Golden algae: diatoms and coccolithophores
b. Dinoflagellates: red tide (harmful algal bloom, HAB)
III. Regional productivity
A. Biological pump: organic matter from euphotic zone to sea loor
1. Thermocline (pycnocline) barrier to vertical mixing
2. Prevalent subtropical gyres
B. Polar oceans
1. Arctic productivity controlled primarily by sunlight
2. Antarctic productivity greater due to upwelling
3. Isothermal—no barrier to mixing
C. Tropical oceans
Productivity low (sufficient sunlight, scarce nutrients,
2. Equatorial upwelling
3. Coastal upwelling
4. Coral reefs
D. Temperate oceans
Combination of sunlight and nutrient availability—strong
2. Winter productivity low
3. Spring productivity higher until nutrients used up
4. Summer productivity low
Fall productivity higher until sunlight lessens as winter
IV. Energy flow
A. Flow into marine ecosystems
1. Biotic community plus environment
2. Producers (autotrophs)
3. Consumers and decomposers (heterotrophs)
a. Herbivores, carnivores, omnivores, bacteriovores
V. Biogeochemical cycling
A. Matter is cycled from one chemical form to another by life
1. Production, feeding, decomposition, dissolution
B. Carbon, nitrogen, and phosphorous cycles
1. Carbon readily available
2. Nitrogen and phosphorous limit primary productivity
3. Redfield ratio: 105:15:1 (C:N:P)
4. Carbon cycle: uptake of CO2 by algae and plants, return of C through respiration and decomposition
5. Nitrogen cycle: uptake by algae and plants, consumption by animals and microbes, released as dead matter and fecal matter
Complicated by nitrogen-fixing and denitrifying
6. Phosphorous cycle: uptake by algae and plants, consumption by animals and microbes, released as dead matter and fecal matter
Bacteria (one step) convert organic phosphorous to
7. Nitrogen is most likely the limiting nutrient, especially in temperate ocean
Silicon cycle: limiting for organisms that use silicon for
tests and shells
VI. Feeding relationships
A. Trophic levels
1. Chemical energy transferred by feeding
B. Transfer efficiency
1. Usually inefficient
2. Gross ecological efficiency averages about 10%
C. Food chains, food webs, and the biomass pyramid
Food chain: linear, primary producer, herbivore,
carnivore, top carnivore
Food web: branching: top carnivores feed on different
3. Biomass pyramid: number of individuals and total biomass decrease in successive trophic levels
a. Organisms increase in size
D. Microbes also consume primary producers
1. Phytoplankton exudates
2. Phytoplankton munchate
3. Zooplankton excretions
4. Cyanobacteria fix nitrogen, important producers in oligotrophic open ocean
5. Viruses are parasitic
End of chapter questions and exercises:
1. Gross primary production is the total amount of organic matter produced by photosynthetic organisms over a certain amount of time. Net primary production is the gross minus the amount of organic matter used by phytoplankton themselves. It is the net that is available for consumers.
2. Most nutrients enter the ocean through river runoff. Coastal waters generally have more nutrients because they are closer to source (rivers). If one of the nutrients is lacking (e.g., iron), then primary productivity is low. Life is concentrated closer to coasts because of the availability of nutrients (rivers).
3. Photosynthetic autotrophs need sunlight for energy. In polar oceans, sunlight does not penetrate deep into the oceans during winter (dark). In the tropics, sunlight does penetrate deep into the ocean during the year, but nutrients are scarce. The thermocline prevents vertical mixing and inhibits recycling of nutrients between surface ocean (euphotic zone) and deeper ocean.
4. Coastal oceans usually have plenty of nutrients because they are close to sources of nutrients. Areas of coastal upwelling have very high biological productivity.
5. Deeper ocean water is blue-green because the shorter wavelengths of the visible part of the electromagnetic spectrum (solar radiation) penetrate deepest.
6. The main kinds of macroscopic algae are brown algae (Phaecophyta), green algae (Chlorophyta) and red algae (Rhodophyta).
Brown algae: generally grow in shallow seawater (maximum 30 m), range in size up to 30 m long, common species are kelp and sargassum
Green algae: most common in freshwater: most marine species are intertidal or grow in shallow bays, range in size up to 30 cm, common species are sea lettuce and sponge weed
Red algae: most abundant and widespread; grow in water up to 100 m (a red alga has been observed growing at a depth of 268 m); range in size up to 3 m; more than 4000 species
7. Golden algae include diatoms and coccolithophores. Diatoms make boxlike tests of opaline silica. Diatom tests can accumulate on the seafloor (under areas of surface ocean upwelling) and create siliceous ooze (diatomaceous earth). Diatoms are important geologically because they indicate past areas of upwelling. Coccolithophores make tests of multiple calcareous plates and are important contributors to calcareous ooze.
8 Great abundance of dinoflagellates in seawater is called a red tide. The genus Ptychodiscus kills both fish and shellfish and is common from April to September in the Northern Hemisphere. The genus Gonyaulax contains a toxin that can be concentrated in the tissue of shellfish without killing them. Eating contaminated shellfish can cause paralytic shellfish poisoning.
9. A biological pump takes organic matter from the euphotic zone and stores it on the seafloor in the form of organic sediments. It is called a pump because this process of production, decomposition, and settling takes carbon dioxide, for example, from the euphotic zone and “locks” it into deep-sea sediments. Only about 1% of the organic matter resists decomposition to settle on the seafloor.
10. Biological productivity is controlled primarily by availability of nutrients and sunshine. Polar oceans show little vertical change in temperature with depth because there is little variation in the seasons—it is cold most of the time. Because the water is so cold, there is little or no thermal stratification and vertical mixing of water is enhanced. Thus, nutrient-rich deeper water can move upward to the sunlit (summer) regions. Productivity is limited by sunlight (no productivity in winter).
Tropical oceans also show little seasonal variation in temperature--it is usually warm all year. Thermal stratification is strong with a permanent thermocline that inhibits vertical mixing. Productivity is limited by the availability of nutrients (sufficient sunshine exists throughout the year.
Temperate oceans show significant seasonal variations in temperature. During the winter, thermal stratification may be minimal and surface water may be rich in nutrients as a result of vertical mixing. Productivity is low, however, because little sunlight enter the oceans because of the low angle of the Sun. As the Sun rises in the sky during spring, sufficient sunlight penetrates seawater to cause a spring bloom of phytoplankton. Increased solar radiation creates thermal stratification (seasonal thermocline) that inhibits vertical mixing (and nutrient replenishment). Low biologic productivity occurs during the summer. Cooling of water in the fall weakens the seasonal thermocline, and vertical mixing again provides nutrients to surface water to cause a fall bloom of phytoplankton.
11. Productivity is higher in tropical oceans where nutrients are recycled through equatorial upwelling and coastal upwelling. Coral reefs tend to retain the few nutrients present and recycle nutrients locally.
12. Energy flow through a biotic community is one-directional. Solar energy is converted to chemical energy, which is used to maintain and sustain life. Matter, in contrast, is recycled through a biotic community. Phytoplankton creates organic matter that is consumed by other life-forms. Dead organic matter and waste products sink through seawater and are dissolved and decomposed.
13. Symbiosis types:
Commensalism: less dominant life-form benefits from
relationship without harm to host, or dominant life-form
Mutualism: both life-forms benefit without harm to either one
Parasitism: one life-form (parasite) benefits at the expense of the other life-form (host)
14. The average efficiency of energy transfer is 10% between trophic levels. Phytoplankton mass required: 10,000 g. Killer whale, third level carnivore: 1 g killer whale (trophic level 5); trophic level 4, 10 g; trophic level 3, 100 g, trophic level 2, 1000 g, trophic level 1 (phytoplankton), 10,000 g. The diagram would resemble Figure 14-25. If efficiency rate were half, then phytoplankton mass required would double (20,000 g). If efficiency rate were double, then 5000 g of phytoplankton required.
15. A top carnivore that eats a variety of organisms (food web) is less likely to starve if any one of the food sources decreases in abundance. If the top carnivore fed on only one organism, any adverse change in that one population would detrimentally affect that top carnivore (single food chain).