Test 2 Key: Life in the Ocean

Test is graded out of 120 points (6 questions, each 20 points)
   90 – 100% = A
   80 – 89%  =  B
   70 – 79%  =  C
   60 – 69%  =  D
   below 60  =  F

Please answer any 6 of the 8 questions below, providing as much relevant detail as possible.  If appropriate, you may supplement your answer with a diagram or sketch.  Please cross out the answer space for any questions that you do not want graded; otherwise the instructor will grade the first 6 questions with answers.

 1.  How does the penetration of light (or lack of it) affect life in the ocean?

A complete answer addresses these points:

- Only a narrow band of the electromagnetic spectrum penetrates ocean water, and that is visible light

- Different wavelengths of light penetrate to different depths, with Red penetrating the least and blue penetrating the greatest.  The greatest number of different wavelengths and the greatest amount of light is in the euphotic zone, the upper 70 meters of water.

- Blue light penetrates the farthest, but this is only to about 600 m, by 1000 m depth there is no more light penetration

- Organisms in shallow tropical waters show the most variety of colors, whereas organisms in the deep ocean show the least variety of colors

- Where colors are available and visible, animals make use of them as identifiers, warnings, camoflage, and mating displays

- Photosynthetic pigments absorb different colors (red, blue) better than others, and consequently phytoplankton can harvest light at different depths

2.  The ocean maintains a fairly constant pH, and yet the surface waters tend to be slightly more alkaline (basic) and the deep waters tend to be slightly more acidic.  Why is this?  What process is maintaining the pH balance?

A complete answer addresses these points:

- The average pH of ocean water is about 8, but this is a dynamic average, as it is constantly maintained largely by biological processes.  These processes form the “biological pump” and are:

a) Respiration (CO2 exhaled, oxygen absorbed, drives pH to acidic conditions)
Carried out by organisms at all depths (surface, mid water, ocean bottom)

b) Photosynthesis (O2 produced, CO2 absorbed, drives pH to alkaline conditions)
Carried out in surface water by phytoplankton and photosynthesizing bacteria (and macroalgae).

- A pH diagram would be helpful here

- The surface ocean water is the only place where oxygen can enter the ocean (via photosynthetic processes and through absorbtion from the atmosphere, and thus, is slightly more alkaline than the deep ocean, where oxygen is used up in respiration processes that produce CO2, which produces more acidic conditions.

3.  Why are there so few large carnivorous predators in the ocean?

A complete answer addresses these points:

- There are relatively few large carnivores in the ocean compared to all other trophic levels because the energy needed to maintain these animals is enormous.  Energetically speaking, they are very expensive. 

- A trophic pyramid diagram would be helpful here.

- The trophic pyramid can be considered as biomass or numbers of organisms

- The trophic pyramid shows how the primary producers or autotrophs (phytoplankton & photosynthetic bacteria) are the base of the food chain, produce the energy for the other organisms, and represent the greatest biomass. 

- From primary consumers (zooplankton) upward through secondary and tertiary consumers, the energy transfer is only about 10%, which means enormous loss (90% at each step) in energy.  This “lost” energy is consumed in heat loss, and maintenance of the organism. 

- Therefore, a single tuna or swordfish or shark represents an enormous investment of energy, much of which is lost on the way “up the trophic pyramid”.

- Some large predators are more energy efficient, and feed at a much lower level in the trophic pyramid.  Whale sharks, for example, predate upon zooplankton, as do baleen whales (e.g., krill).

4.  What is the “base of the food chain” or “base of the trophic pyramid”?  What do these organisms do?

A complete answer addresses these points: 

- The phytoplankton, nanoplankton and picoplankton(photosynthetic bacteria) form the base of the food chain for most of the ocean, exceptions to this are the chemosynthetic bacteria of the hydrothermal vents.

- Although microscopic, these organisms are powerhouses of the ocean. They convert sunlight, carbon dioxide and water into glucose molecules and oxygen (photosynthesis).  (Some, the chemosynthetic bacteria, convert hydrogen sulfide, carbon dioxide and water into glucose molecules and sulfuric acid, without the aid of sunlight.)

- Collapse or drop in population of the autotrophic organisms would be a matter of serious concern for ocean life.  Important in serving as food, in supplying oxygen, and also in drawing down CO2 in the atmosphere and surface water (e.g., coccolithophore blooms, diatom blooms)

- Conversely, massive blooms of these autotrophic organisms can also be a concern.  (e.g., Dinoflagellate blooms (red tide, shellfish poisoning)

- Blooms stimulated by nutrient loading, such as fertlizer/sewage runoff from rivers/estuaries

5.  Symbiotic relationships are important in ocean communities, and are especially noticeable in coral reefs.  How do symbiotic relationships affect coral reef development?

A complete answer addresses these points: 

- Symbiosis (includes mutualism, commensalism, parasitism) is the key to biodiversity in the reef community.

- Of particular importance is the mutualistic relationship between zooxanthellae algae and colonial corals.  The algae live internally in the coral polyp tissue, and supply the coral polyp with oxygen, a waste product from photosynthesis.  In return, the coral polyp supplies the algae with CO2 and nitrogenous waste products, and protection. 

- The extra oxygen is valuable to the coral polyps, which secrete a calcium carbonate outer layer that ultimately forms the great coral reefs themselves.  This symbiotic relationship is very tight-in temperature stressed corals, when temp goes to high, the algae are expelled from the corals (this called bleaching), and if they are not reabsorbed within a short time (days) the coral polyps begin to die. 

- Diagram of coral-zooxanthellae symbiotic relationship would be helpful here.

- Other examples of symbiosis include the relationship between certain fish and shrimp with anemones, which have stinging cells.  Immunity to the stinging cells gives these organisms a safe place to live (in among the anemones) and in return, they protect/clean the anemones.   

6.  What is a “trophic community”?  Discuss 3 different kinds of trophic communities in the ocean.

 A complete answer addresses these points:

- Trophic communities are populations of all species living in a particular habitat sharing a common base of the trophic pyramid-we discussed

- Chemosynthetically based communities, the hydrothermal vents, where bacteria use hydrogen sulfide, carbon dioxide and water to produce glucose and sulfuric acid.  The higher organisms living around these vents have bacteria inside and around them, which supply them with their energy-many have no digestive system at all.  (e.g., tube worms, clams)

- Photosynthetically based communities, such as the open ocean, blue water communities, where phytoplankton, nanoplankton and picoplankton form the base of the trophic pyramid, and produce glucose and oxygen from carbon dioxide, water and sunlight.  These are the most diverse in terms of numbers of species.

- Detritally based communities, such as the deep ocean floor, in the aphotic zone, where no light penetration occurs.  The base of the trophic pyramid is formed by the rain of detrital (decomoposing organic material) from the surface.  Organisms here have adapted to a highly pressurized life in the cold and dark, and have features such as very slow metabolisms, long life spans, and bioluminescent properties. 

7.  The Maximum Sustainable Yield (MSY) and the Exclusive Economic Zone (EEZ) are terms that have developed in the late 20th century.  Why are these terms now in place, and why does Hugo Grotius’ concept of Freedom of the Seas no longer work?

A complete answer addresses these points:

- Grotius’ 17th century development of what became known as the Law of the Freedom of the Seas grew out of a view that the ocean itself was inexhaustible in resources, and that it could not be owned by any one country.  It was simply a matter of defending your ability to go get what you wanted from an inexhaustible supply. 

- However, as human populations grew and as fish harvesting technology improved, a series of fisheries collapses occurred (e.g., herring, sardines, cod, for example).  In the 20th century, these collapses took on international importance.Iceland vs Grt Britain-boundary set at 20, 50, then 200 miles for Icelandic cod fishery home waters

- International response-everybody set up a 200 mile EEZ, U.S. has its own concept of EEZ, which is not only continental waters but all territories as well (e.g., Guam, American Samoa, etc.)

- The EEZ is still not enough to protect fisheries-they can be fished out by the very countries that own them.  The MSY was developed to protect remaining fisheries from collapse and to assure their future survival.  A maximum amount of fish removable without causing damage to the reproductive stock needed for the next generation is determined, and a limit is then placed (and enforced) on how many fish can be removed in one season from a fishery.

8.  For many organisms in the ocean, the rhythm of the tides governs major aspects of their lives.  Give 3 examples of how the tidal cycle affects life in the sea.

Here are 4 cases discussed in class, others are potentially acceptable:

- Tidal cycle & horseshoe crabs-Spring Tide full moon in May-June triggers spring mating of horseshoe crabs on sandy beaches of eastern north America, eggs placed just under sand to incubate, will hatch and be carried out to sea in another spring tide, new moon phase.

- Grunion-small fish with mating behavior tied to spring tide in early summer.  The “Grunion Run” is well known in California waters, where buckets of the fish are gathered during a new moon spring tide. 

- Reproductive timing of spore release by marine macroalgae in rocky coasts-Fucus for example, will release spores in spring tides to reach maximum numbers of other Fucus populations along the rocky coastline

- Stratification of rocky intertidal communities into those that live at the low tide level, those at the intertidal level, those at high tide level.  Rocky coastlines are areas of tremendous competition.  The daily tidal cycle results in rocky communities with parts completely exposed (and baked in the sun) to other parts experiencing complete submersion.  The consequence is stratification of populations by tidal zone.