Marine Ecosystems
Introduction - Photosynthesis to Chemosynthesis

Marine Ecosystem

1. Introduction
2. Phytoplankton
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
10. Coral Ecosystem

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Don's Introduction


Kelp Forest in the Monterey Bay

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Objective:  To examine the conditions leading to the abundance and distribution of life in the sea and the complex interations between the organisms that compose a food web.


Arctic Food web
Marine food web for the Arctic.
Marine food web for the Arctic.
Phytoplankton generate organic carbon through photosynthetic reactions.
Phytoplankton are eaten by the zooplankton, who are in turn eaten by fish, on up to large marine mammals. Organic carbon that settles to the sea floor is usually consumed by marine organisms there.
(Credit: Christopher Krembs, NOAA, US Department of Commerce) and
The Ocean World

Photosynthesis to Chemosynthesis

The fundamental process of life on our planet (both on land and under the sea) is governed by the incorporation of inorganic carbon into organic carbon as shown in the following chemical reaction.

6H2O + 6CO2 + nutrients + energy <=> C6H12O6 + 6O2

When the reaction is driven to right, energy is stored and carbon is incorporated into living material through either:

Photosynthesis (using solar energy)---->
Chemosynthesis (using chemical energy)---->

When the reaction is driven to the left, energy is released through:

<---Aerobic Respiration---

Photosynthesis in the ocean is largely carried out by microscopic algae that float with the ocean currents as we learned, if you were able to experience the field study of the San Francisco Bay (if you went voyage or if it was offered during your class).

diatfil1.jpg (4908 bytes)         073-03.jpg (9848 bytes)

Lower photograph is copyrighted and provided through the courtesy of Micheal Martin at the
Michael R. Martin's Phytoplankton Image Library

These microscopic plants, consisting of only a single cell, are called phytoplankton, and often considered the grasses of the sea, since they "eat the sun's energy" and form the base of the marine food web. Not only do these organisms form the base of the marine food web, but also produce nearly 70% of the oxygen in the atmosphere on our planet and, when dead, their remains sink to the seafloor to ultimately compose a significant portion of the hydrocarbons that drive the global economy.Some of these organisms produce dimethylsulfide (DMS), an important chemical compound that enhances cloud formation in our atmosphere, which in turn, impacts global climate.

During times of high nutrient levels in coastal waters and  extensive sunlight, these organisms reproduce, bloom and grow rapidly, creating "clouds" of microscopic plants which produce the green color of the sea.

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Photo on left courtesy of NASA's Athena Project - Ocean Color

Billions and billions of microscopic, single-celled algae make up the bloom shown in the picture above.

Life on our planet would clearly not be the same without phytoplankton.

ęCopyright 2017
March 13, 2017

Send to Don Reed

Department of Geology
San Jose State University

Let's learn more about marine algae or phytoplankton?