Sunday, January 15, 2012
Our Ocean Backyard: Fertility Food Chains and Fish by Gary Griggs
The waters off the coast of California are some of the most biologically productive on the planet because of the process of upwelling, which is most pronounced in the spring and early summer. During these months, winds from the northwest dominate along the California coast, and help drive the offshore California Current southward.
The surface waters of the ocean, however, are also influenced by the Earth's rotation. This process, known as the Coriolis effect, causes surface currents in the northern hemisphere to be deflected ninety degrees to the right of their direction of movement. As a result, the surface waters off California tend to move offshore in the spring and early summer, and are replaced by bottom waters through upwelling.
This deeper water is typically rich in nutrients, such as nitrates and phosphates, from the decomposing organic matter that is constantly sinking to the sea floor.
The combination of the nutrients, which serve as fertilizer, and the exposure to the longer days and sunlight of spring and summer, lead to enhanced photosynthesis or blooms of the phytoplankton, which are the small floating algae. These microscopic plants, such as diatoms, are in turn fed on by the zooplankton, or the small floating animals such as krill.
The growth of the small plants and animals serve as the base of the food chain that provides for all of those marine animals higher up the food chain, the fish, sea birds, and marine mammals.
Coastal upwelling also influences weather patterns. Along the northern and central California coast, upwelling lowers sea surface temperatures and increases the frequency of summer fog. The cold surface waters chill the overlying humid air so that saturation occurs and fog forms, just like the condensation of moisture that occurs on a glass when you bring an ice cold drink outside on a warm day.
Globally, upwelling regions only constitute about 0.1 percent of the total surface area of the oceans, but these regions account for an astonishing 95 percent of the global production of marine biomass, and about 21 percent of the world's fishery landings. The major upwelling areas occur off the west coast of continents. In addition to California, these include the rich fishing grounds off Ecuador, Peru and Chile, and off northwest Africa.
The fertile waters offshore California have been fished for as long as there have been humans occupying the coast. Native Americans stayed close to shore, fishing in the bays, estuaries and tide pools.
The Chinese, Japanese, Italians, Azoreans, Portuguese, and others who came later, all discovered different resources they could harvest from the near shore waters. At different times over the past 150 years these included abalone, albacore, anchovies, crabs, salmon, sardines, sea otters and sea urchins, shrimp, squid, rockfish, whales and just about everything else that had any value to humans.