NEWPORT, Ore. – Scientists have long known that wind-driven “upwelling” during the spring and summer along the Pacific Coast is critical for bringing deep, nutrient-rich water to the surface and fertilizing plankton blooms that form the base of the marine food web.
But a new study suggests that mini-pulses of upwelling that occur in February may be just as important in creating ideal ocean conditions in the California Current system for species from rockfish to seabirds.
“These small pulses of upwelling may kick-start the production cycle and extend the growing season,” said Bryan Black, an Oregon State University researcher based at OSU’s Hatfield Marine Science Center in Newport, Ore. “We’ve found amazing synchrony in the growth rates of fish and reproductive success of seabirds – and both of these top-level predators corroborate the importance of February upwelling.”
Black’s latest study, comparing rockfish growth with seabird reproductive success, was published this month in NRC Research Press.
Black is a dendrochronologist, who applies tree-ring dating techniques to the study of marine organisms. Many long-lived fish accumulate analogous annual growth rings in their otoliths – or ear bones – allowing scientists to estimate their age. Many clams and other bivalves also lay down rings on their shells.
In addition to estimating age, scientists also can compare the size of the rings and tell something about the environmental conditions that year. Generally, large growth rings – whether on a clam, in a tree, or on a fish otolith – means that conditions were good.
“You can’t look at the rings on a single clam or tree and draw any significant conclusions,” Black said. “But when you examine dozens of individuals, and compare them with other species, the results are amazing.”
In his latest study, Black teamed with seabird ecologist Bill Sydeman at the Farallon Institute for Advanced Ecosystem Research, and NOAA researchers Steven Bograd, Isaac Schroeder and Peter Lawson to compare growth-ring chronologies of splitnose rockfish (Sebastes diploproa) and yelloweye rockfish (Sebastes ruberrimus) with egg-laying dates and fledgling success of two species of seabirds – common murres and Cassin’s auklets.
Focusing on the years from 1972 through 1994, they found that when sufficient February upwelling occurs, growth rings were much more likely to be wide in the fish, and reproductive success high for the seabirds.
The team also found that over the past 60 years, wintertime upwelling was distinct from spring/summer upwelling.
“Statistically, they’re completely unrelated,” Black said. “And that’s important because some biological processes, like rockfish growth and seabird reproductive success, are ‘tuned’ to winter climate and will show different patterns from biological processes ‘tuned’ to summer climate.
“In short,” Black added, “seasonality is critical to understanding climate response.”
The next step in the team’s research is to collaborate with terrestrial ecologists to show similar climate responses on land.
“Already we see that high-elevation tree-ring chronologies in the Cascades relate surprisingly well to rockfish growth and seabird reproductive success,” Black said. “All of that is due to their sensitivity to climate in the winter – a time of the year when the ocean and atmosphere are particularly well-coupled.”