Marine and Coastal Systems: Resources, Impacts, and Conservation
I. Central Case: Collapse of the Cod Fisheries
A. No fish had more impact on human civilization than the Atlantic cod.
B. This abundant groundfish (fish that feed on the bottom of the ocean) was a dietary staple in cultures on both sides of the Atlantic.
C. Cod provided the economic engine for many communities along coastal New England and Canada.
D. After decades of technologically advanced fishing techniques harvested many mature breeding adults, the cod populations in the Atlantic “crashed.”
E. Government officials in Canada, followed by U.S. officials, closed fishing areas to all commercial fishing. In most of the areas, the cod have not rebounded.
1. It is believed that cod remain limited because the former prey of adult cod are now competing for food with and even eating young cod before they can mature.
2. A bright spot in the story is that areas of the Georges Bank are recovering due to elimination of destructive practices such as trawling. Some other species are recovering such as Ocean Scallops. There is evidence that young cod are beginning to appear as well.
II. The Oceans
1. The study of the physics, chemistry, and geology of the oceans is called oceanography.
2. Oceans influence global climate, teem with biodiversity, facilitate transportation and commerce, and provide us resources.
A. Oceans cover most of Earth’s surface.
B. The oceans contain more than water.
1. Ocean water is salty because the ocean basins are the final repositories for water that runs off the land.
2. The salinity of ocean water generally ranges from 33 to 37 parts per thousand (ppt), varying from place to place because of differences in evaporation, precipitation, and freshwater runoff from land and glaciers.
3. Seawater also contains nutrients such as nitrogen and phosphorus that play essential roles in nutrient cycling.
4. Another aspect of ocean chemistry is dissolved gas content, particularly the dissolved oxygen upon which gill-breathing marine animals depend.
C. Ocean water is vertically structured.
1. Water density increases as salinity rises and as temperature falls, giving rise to different layers of water.
2. The waters of the surface zone are heated by sunlight each day and are stirred by wind.
3. The pycnocline is the region below the surface zone in which density increases rapidly with depth.
4. The deep zone of the ocean lies beneath the pycnocline and is not affected by wind and sunlight.
5. Oceans help regulate Earth’s climate by absorbing and releasing heat to the atmosphere.
D. Ocean water flows horizontally in currents.
1. The ocean surface is composed of currents—vast, riverlike flows driven by density differences, heating and cooling, gravity, and wind.
2. Currents transport heat, nutrients, pollution, and the larvae of many marine species.
E. Vertical movement of water affects marine ecosystems.
1. Upwelling is the vertical flow of cold, deep water toward the surface, bringing nutrients from the bottom.
2. Downwelling transports warm water rich in dissolved gases downward, providing oxygen for deep-water life.
F. Seafloor topography can be rugged and complex.
1. Parts of the ocean floor are just as complex as the terrestrial portion of the lithosphere.
2. In the bathymetric profile, gently sloping continental shelves underlie the shallow waters bordering continents.
3. Most of the seafloor is flat, but there are volcanic peaks, reefs, and deep trenches.
4. Oceanic zones differ greatly, and some support more life than others.
a. The well-lit top 10 meters, called the photic zone, contains nearly all of the oceans’ primary productivity.
b. Between the ocean’s surface and the floor are the pelagic habitats.
c. On the ocean floor is the benthic area.
III. Marine Ecosystems
A. Open-ocean ecosystems vary in their biological diversity.
1. Much of the ocean’s life is concentrated near the surface in areas of…