Writing in the March 10 issue of the journal Nature, the authors conclude that some highly productive regions of the ocean are much more vulnerable to agricultural runoff than was previously assumed.
The study is based on satellite imagery of Mexico's Gulf of California, also known as the Sea of Cortez-a narrow, 700-mile-long stretch of the Pacific Ocean that separates the Mexican mainland from the Baja California Peninsula. The area is a hotspot of marine biodiversity and one of Mexico's most important commercial fishing centers.
"Biological productivity in most of the world's oceans is controlled by the supply of nutrients to the surface water," wrote the authors, who are all affiliated with Stanford's School of Earth Sciences. "The Gulf of California contains some of the highest nutrient concentrations in the oceans and sustains highly elevated rates of biological productivity."
In the gulf, wind-driven upwellings regularly bring nitrogen and other nutrients from the seafloor to the surface, stimulating the rapid reproduction and growth of microscopic algae called phytoplankton. These algal blooms are natural events that benefit life in the gulf by generating tons of phytoplankton-a major source of food for larger organisms.
But some phytoplankton species produce harmful blooms, known as red or brown tides, which release toxins in the water that can poison mollusks and fish. Excessively large blooms can also overwhelm a marine ecosystem by depleting oxygen in the water. Scientists suspect that many harmful blooms are artificially fueled by fertilizer runoff from farms, which