United States Geological Survey scientists have found that a cooling in Pacific Ocean temperatures ed to increases in ecologically threatening phytoplankton blooms m San Francisco Bay, California. The declining temperatures took place off the coast of California between 1999 and 2004. The occurrence of these blooms is surprising because such blooms are normally associated with increases n the amount of nutrients, such as nitrogen and phosphorus, entering estuaries from such sources as wastewater treatment plants and agricultural fields. In this case, the bay's phytoplankton blooms occurred during a period of decreasing nutrient concentration and inputs.
The scientists discovered the effects of the cold Pacific temperatures by using biological and water-quality data collected over twenty-five years. The colder temperatures caused changes in the types, abundance, and migration patterns of marine life into the San Francisco Bay from coastal ocean waters. For example, marine life, such as fish, shrimp, and crabs, migrated to the warmer waters thot are found in the bay.
The migrations increased the numbers of predators such as bay shrimp and Dungeness crabs that eat filter feeders, such as clams. Clams can filter large quantities of phytoplankton from the bay's water, which can prevent phytopldnklon blooms. With the increase in predators, there wds d corresponding
decrease In clam populations and an increase in phytoplarkton.
