8. Distribution of Life in the Sea

Marine Ecosystem
1. Introduction
2. Chemosynthesis
3. Carbon in the Sea
4. Carbon Cycle
5. Conditions for Life
6. Limiting Nutrients
7. Nutrient Distribution
8. Life in the Sea
9. Food Webs

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Coccolithophorid, a marine algae (phytoplankton)

Primary productivity is defined as the rate at which biomass is produced by photosynthetic and chemosynthetic organisms in the form of an organic substance.

Microscopic plant life,  at the base of the marine food web, is the primary food and energy source for the marine ecosystem. Phytoplankton convert nutrients into plant material by using sunlight with the help of the green pigment, chlorophyll.

The green pigments, caused by chlorophyll in the plants, absorb light, and the plants themselves scatter light.

Together, these processes change the color of the ocean as seen by an observer looking downward into the sea. Very productive water with a high concentration of plankton appears blue-green (as you learned at the aquarium).

Very pure water appears deep-blue, almost black. Believe it or not, the crystal clear, blue water that you associate with Hawaii is largely devoid of marine life, except near the islands.

The islands of Hawaii are similar to an oasis of life, surrounded by an oceanic desert.


Diatom, a marine algae (phytoplankton)

From space, variations in ocean color can be measured with sensitive instruments.

Ocean and land plants are green because of the chlorophyll in plant cells.  Chlorophyll-a absorbs mainly blue-violet and red and reflects green;  a second form of chlorophyll, chlorophyll-b, absorbs mainly blue and orange and reflects yellow-green. Satellite instruments measure the amount of reflected light of different wavelengths.

The amount of reflected light at different wavelengths allows scientists to estimate the productivity of Earth's land masses and oceans.

We can therefore use ocean color to identify regions of high primary production by measuring the amount of chlorophyll, the green pigment in plants, with satellites.

Since the rest of the marine animals follow the food, then by mapping the distribution of chlorophyll, we also map the distribution of organisms in the sea, both plant and animal.

Using the map below and the one in your handout,

  • draw HHHH in regions of high primary productivity (anything above 0.2 on the scale) and

  • LLLL in regions of low primary productivity (less than 0.2)

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Let's examine of high primary productivity:

1.  Coastal regions because of the very high amounts of nutrients shed from the continents.

2. East side of ocean basins - coastal upwelling is common here largely because of wind direction (from pole to equator) and the cold eastern boundary currents weaken the density layering as a result of ocean temperature allowing cold deep waters, with their reservoir of nutrients, to be transported to the surface by upwelling.

3. Polar regions - cold waters in these areas absorb high amounts of gas (CO2 and O2) both of which allow life to flourish.   Significant upwelling in these regions provides nutrients to the surface waters (once again the cold nature of the surface layer allows deep water to easily mix upwards by upwelling).

4. Equatorial regions - ocean waters diverge (move away on both sides of equator related to the change in the direction of the coriolis effect), nutrient-rich deep waters move upward to fill the void caused by the divergence of surface waters.

Low Productivity (magenta colors)

Notice how the regions of the main circular current gyres (circular surface currents) are marked by low productivity and that these regions occupy the vast majority of the ocean basins.  These are regions of downwelling, which removes nutrients from the surface waters and therefore severely limits the amount of life in these regions of the ocean.

Nutrients, which ultimately control the number of organisms in the sea, have many effects, including controlling the distribution of marine life


©Copyright 1999
July 28, 2015
Send to Don Reed

Department of Geology
San Jose State University

How does marine life interact in predator-prey relationships?