Coastal Upwelling Changes Affect Marine Animal Growth, Reproduction

Marine animals off the California coast are experiencing short-term slumps in growth and reproduction, and new research suggests that the phenomenon could be linked to an increasing variability in the strength of coastal upwelling currents, which work to supply nutrients to a number of crucial ecosystems in the region.

According to the NOAA, upwelling is when wind blows across the ocean and pushes water away. This surface water is then replaced by deeper waters, which are rich in important nutrients. This phenomenon, which typically occurs along North America's west coast, allows phytoplankton to bloom - a major food source for fish, seabirds and marine mammals, according to researchers at the University of Texas at Austin.

The new study indicates that the California coast has seen winters with extremely low rates of upwelling for at least 60 years, resulting in slower growth in the region's fish as well as lower reproductive rates among local birds.

"Our study underscores the fact that California is a place of high coastal upwelling variability," lead study author Bryan Black said in a statement. "You have to keep that in mind if you're managing a fishery - for example, you can't plan for every year being moderate or reliable. There are a lot of ups and downs."

To reconstruct the past 600 years of upwelling along the California coast, researchers examined tree ring growth from blue oak trees within the region - a specimen that is particularly sensitive to climate shifts that are associated with upwelling.

Comparing the data from the tree rings with other local biological factors, they learned that poor upwelling is connected with a decrease in biological productivity. Luckily, because the region's birds and fish are quick to bounce back from these events, the increased variability of upwelling strength has not led to long-term declines.

Researchers are not blaming climate change for this upwelling phenomenon, but they have their suspicions.

"This is consistent with what we expect from climate change, but at this point, we can't attribute it to that. This is something we need to continue watching to see how climate variability plays out in the coming years," Black said.

The findings were published in the journal Science.