The following materials are exerpts from the California Coastal Commission's California Coastal Resource Guide, which can be ordered from University of California Press by calling 1-800-822-6657.
California's nearshore waters provide a rich and varied habitat for a diversity of marine life; vast numbers of algae, invertebrates, fish, seabirds, and mammals inhabit these shallow waters, which overlie a gently sloping region called the continental shelf. Where the shelf drops off to the deep sea floor, the open ocean begins; in contrast to the espectilly rich nearshore waters, the open ocean is much less fertile, gradually becoming less productive farther from shore. The fertility of nearshore waters depends upon patterns of oceanic circulation that supply the nutrients necesary to support life.
Beneath the waters of the Pacific Ocean lies a topography as varied as that found on the continents. Alnog some shorelines, such as the Atlantic coast, the continental shelf is broad, but on the geologically active California coast, the shelf is very narrow, often no more than four or five miles wide. All along the California coast, the continetnal shelf and slope are etched by submarine canyons. Created by a series of complex processes, submarine canyons continue to be carved by sporadic turbidity currents--waterfalls of sand, gravel, and muddy sediments. Longshore transport along the shoreline carries beach sand and sediments into the submarine canyons, where they are then swept to the deep sea floor.
The oceans are in constant motion due to wind-driven currents. The California current, carrying water cooled by its passage through the northern latitudes, flows southward along the shore from the Washington-Oregon border to Southern California. This basic current is modified by seasonal variations in wind direction that give California's nearshore region its three more or less distinct "oceanic seasons." Beginning in March, prevailing westerly winds, combined with the effects of the earth's rotation, drive surface waters offshore. These waters are replaced by deep, cold water that flows up over ht econtinental shelf to the suface, carrying with it disolved nutirents from the decay of orgainic material that had sunk to the ocean floor. This process, known as upwelling, is restricted mainly to west coasts of continents, and is responsible for the high productivity of California's nearshore waters.
The upwelling period continues until September when northwesterly winds die down and the cold upwelling begins to sink. This period, characterized by relatively high surface temperatures, is known as the oceanic period, and last through October.
In winter, changes in atmoshpheric conditions over the Pacific Ocean bring southwesterly wind to the Califonia coast. In respone to these winds, a northward surface current begins and flows along the coast inland of the California Current. This current called the Davidson Current, generally lasts through February, when the prevailing winds shift again and the cycle begins anew.
Every few years this pattern is disrupted by a phenomenon known as El Nino. The El Nino baths nearshore areas in unusually warm, nutrient poor water from the south, which affects coastal food webs and causes phytoplankton production to drop, fisheries to decline, seabirds to starve, and marine mammals to temporarially stop breeding.
Phytoplankton, the basis of almost all ocean food webs, thrives under normal nearshore summer conditions. Nutrient rich waters, combined with long sunlight days, causes the phytoplankton to "bloom." The resulting abundance of phytoplankton causes herbivorous and carnivorous zooplankton populations to expand. Common members of the zooplankton communities include protozoans, jellyfish, copepods, krill, mollusk larvae, and arthropod larvae. These zooplankton provide food for fish which are in turn eaten by birds and mammals.
In addition to phytoplanton supported communities, lush growths of algae flourish in California's nearshore waters. The kelp forest is a diverse and complex community that occurs along much of the California coast. Kelp forests are composed of dense stands of large brown algae, predominately giant kelp, with an understory of various red and brown algae. Giant kelp is one of the fastest growing plants known; growing an average of 10+ inches a day in spring, a frond of kelp may eventually reach a height of over 250 feet. The fronds, anchored on the rocky sea floor by strong holdfasts, grow upwards towards the surface, bouyed by their gas-filled floats.
Kelp forests provide food and shelter for an array of organisms. The kelp blades and holdfasts are home to invertbrates, while anemones, abalones, sea stars, urchins, and sea cucumbers live on the rocky bottom of the forest. Kelp beds are also home to fish such as the blacksmith, kelp bass, and several species of rockfish and surfperch. Sea otters live in the canopy, feeding on the abolone, sea urchins, and other invertebrates they catch on the bottom, and harbor seals forage the kelp beds for fish.
The upwelling process that occurs in nearshore waters does not occur in the open ocean off the California coast. As a result, the vast open ocean is less abundant. Because food is less abundant here, pelagic fish must be able to travel great distances to find prey. Plankton-feeding fish that range from nearshore waters into the open ocean include Pacific herring and northern anchovy; predators include species of marlin, tuna, mackerel, and salmon, as well as squid. Many whales and porpoises also feed in the open ocean.
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