Marine Biology (MSCI.302)

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Problem Sets 

Problem Set #3

This problem set is due at the start of class on Wednesday, April 14th.  It is based on readings in chapter 6, Intertidal Ecology.  There are two questions, neither of which is quantitative (I hear some of you cheering).  The first should be fairly clear from your readings (it is from your book’s review questions).  The second is very much your own thinking.  Please type your answers and the combined length for both questions should be no more than two pages and no less than one (double spaced, 10 or 12 font, 1 inch margins).

1.      Why is the age structure of sessile intertidal rocky shore organisms in a given area often dominated by a single age class?  How can such a skewed age structure become established?

2.      Do you think it is likely that a single species could evolve that would dominate all zones of the rocky intertidal, from low to high?  Why or why not?  (Hint:  Consider the demands of, for example, competition, predation, wave stress, dessication stress, thermal stress, oxygen stress….   Answers such as “yes, they can if they can do everything well,” or alternatively “no, you can’t do everything well” are not acceptable.  You must specifically explain either how they could do everything well, or alternatively, what specific limitations prevent them from doing everything well.)

Problem Set #2

This problem set is due at the start of class on Wednesday, April 7th.  It is on photosynthesis and fish production in the sea and is based on a classic paper in oceanography:  Ryther, J.H. 1969. Photosynthesis and Fish Production in the Sea. Science 166:72-76.  Ryther’s early model was somewhat over-simplistic, but elegant in concept and remarkably on target.  He effectively predicted the biological cap on total ocean fisheries harvest which was not reached until the 1980s.

 

Ryther estimated the primary production rates and area of 3 oceanic provinces in order to determine the annual primary production for each.  He then estimated the trophic efficiency for each province, as well as the mean number of trophic levels leading to fish.  Combining these estimates, he was able to calculate the total oceanic production of fish.  By filling in the blanks below, you will recreate his calculations.  You may print this out, or you may simply report the blanks from each table on a separate sheet.  Regardless of which you do, you must show your work and pay attention to units!

 

1. Fill in the blank spaces for the two tables below and show your work separately.

 

Province

 

% of ocean

 

Area (km2)

Mean productivity (g C/m2/yr)

Total primary productivity

(metric tons C/yr)

Open ocean

90

326 x 106

50

 

Coastal zone

9.9

36 x 106

100

 

Upwelling areas

0.1

0.36 x 106

300

 

 

 

 

 

 

(mean productivity is primary production)

(1 metric ton = 1000 kg)

 

 

 

Province

Annual primary production from table above (metric tons C/yr)

Avg.

Trophic level

Trophic efficiency (%)

 

 

Fish production (metric tons C/yr)

Open ocean

 

5

10

 

Coastal zone

 

3

15

 

Upwelling areas

 

1.5

20

 

Total

 

 

 

 

 

 

 

 

 

(the average trophic level refers to the average trophic level of fish removed by fisheries for each province.  Trophic efficiency is the energy transfer efficiency from one level to the next for the food web in each province.)

How do you you deal with half a trophic level in the table above? – See what you can figure out.

 

 

2. In the last 2 decades, the total world fishery harvest has reached something of a plateau of between 90 and 100 million metric tons per year. 

 

a.       What percentage is that of your estimate for total fish production from the table above? 

b.      Where did that proportion go before we (humans) started taking it out?

c.       What are the consequences of our removal rates?

 

Problem Set #1

This problem set is due at the start of class on Monday, Feb 9.  It is based on readings in chapter 2 of your textbook and some sound thinking on your part. 

 

The first two questions require written answers.  Some answers may require only a sentence or two, while others will require a larger paragraph.  You are to type your answers, and I will grade them (especially the longer paragraphs) for both content (75%) and writing technique (25%).  These questions all have correct answers (they are not just opinion).  Answer each question and justify it with sound logical arguments and/or evidence from the text.  Use appropriate vocabulary from the chapter in your answer.  Don’t expect all the clues to be right next to the figures in your text – you will need to read much of the chapter for full understanding.  In terms of writing technique, I will be looking for proper sentence structure and the cohesive and logical presentation of your points.  Your answers should be concise (but not vague or incomplete)!  I am interested in the physical/chemical conditions and biological interactions behind the patterns. 

 

The third question is quantitative.  This question should be done by hand in pencil.  You must show all of your work.

 

  1. In figure 2.37 on p. 67 of your textbook, examine the figure representing the temperate North Pacific.  Explain:
    1. how is it possible to have a zooplankton peak in biomass without a phytoplankton peak?

Phytoplankton primary production rate increased, but the standing crop never increased because it was kept low by increased zooplankton grazing.

    1. why does the North Atlantic have a spring phytoplankton peak in biomass, but the North Pacific does not?

North Pacific copepods are more omnivorous, so they are already present (and living off smaller zooplankton) as the spring bloom starts to appear, at which time they switch to herbivory.  Thus, their grazing keeps the spring bloom from ever showing up as an increased standing crop.  It is a very efficient system.  In the North Atlantic, copepod nauplii respond to the spring bloom by grazing, growing, and reproducing.  They are not numerous enough to reduce the standing crop until the next generation of copepods kicks in.

 

  1. In table 2.3 on p. 69 of your textbook, examine the net primary productivity numbers in the Ocean column.  Explain:
    1. why is the most productive season for the total global ocean from July to September?

OK, stupid professor award.  I made a silly error in my thinking (duh!) and one of you called me on it after class today – Thank you!  Yes, the peak productivity does occur in the southern ocean in winter/spring (their summer/fall), but that is not the most productive season globally because low production in northern waters balances it out.  July-Sept is the most productive season globally because the southern ocean bloom is just starting and the northern ocean bloom is still at it’s peak.  Why is the northern ocean bloom more extensive in late summer rather than early?  Receding ice cover allows a larger surface for photosynthesis in late summer, along with nutrient runoff from melting ice.

    1. Why is the productivity total for mesotrophic regions 3 times larger than the value for eutrophic regions?  Doesn’t that seem counter-intuitive?

 

The table expresses production in Pg of carbon, not Pg C/km2.  Eutrophic regions are more productive per unit area, but on a global scale, they only cover a small area of the ocean as compared to mesotrophic regions.  Thus, if you sum up all the production in mesotrophic regions, it exceeds the production in eutrophic areas.

 

  1. Quantitative questions, using the values table 2.3 and data given in your textbook on pages 69 and 70 (“Primary productivity of the biosphere”).
    1. In table 2.3, the total net primary productivity for the oceans represents what surface area of ocean?  Express your answer in square km.

In the tale, total ocean productivity is 48.5 Pg of C.  On p. 70, you are told the average annual productivity for the oceans is 140 g C/m2.  The formula is:

48.5 x 1015 g C * (1 m2 / 140 g C) * (1 km2 / 1 x 106 m2) = 3.46 x 108 km2

 

    1. If oceanic primary producers utilized the photosynthetically available radiation as efficiently as terrestrial primary producers, what would the total oceanic net primary production in table 2.3 change to?  (assume nutrients are not limiting)

On p. 70, oceanic phytoplankton absorb about 7% off the photosynthetically available radiation, while terrestrial plants absorb 30%.  You can treat is as a simple ratio:

(48.5 Pg C / X) = (7 / 31), so X = 48.5*31 / 7 = 215 Pg C. 

 

Both the written and quantitative questions pointed out the need to keep track of what types of information you are after:  production rates versus standing crop, total production or production per unit area…  These differences are very important and the data mean very different things.  Always pay careful attention to units and whether numbers are comparable (you can’t compare an amount and a rate, for example).

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