Connected by climate

Fish bones and tree rings reveal ecological see-saw
A section from a 53-year-old splitnose rockfish (Sebastes diplopra) otolith shows annual growth rings. (Photo courtesy of Bryan Black)

A section from a 53-year-old splitnose rockfish (Sebastes diplopra) otolith shows annual growth rings. (Photo courtesy of Bryan Black)

Fish bones aren’t exactly the most prized portion of the catch of the day. Encountering a nearly translucent sliver in a grilled fillet is at best an annoyance and at worst a choking hazard. But for one Oregon State University researcher, certain fish bones are immensely valuable.

Bryan Black, an associate professor at OSU’s Hatfield Marine Science Center, is using the otoliths – or ear bones – of Pacific rockfish to reveal the effects of climate change at sea and on land. By measuring the tiny growth increments in fish otoliths, Black has learned that marine and forest ecosystems are joined at the hip. When exposed to the same climate conditions, they respond in synchronous but different ways. Winter climate, he has also found, may have far greater effects on these systems than researchers had previously guessed.

As a dendrochronologist, or tree-ring analyst, working in Pennsylvania, Black came to Hatfield in 2003 when he saw a job advertisement calling for someone who could apply growth increment science to fish otoliths. These bones grow outward from a core, forming annual growth increments similar to those of trees. Though Black had not been trained in marine science, he was enthusiastic to learn how forestry techniques could be applied to ocean ecosystems.

“It was quite a learning curve to begin with,” Black says. “Coming from understanding forests and forest ecology and learning to apply that to marine ecosystems took a lot of learning about marine ecology, but it was exciting at the same time.”

Otolith Library

Once Black mastered the marine knowledge he needed and began studying growth increments on rockfish otoliths, he discovered a connection between ocean, climate and forest that would prove essential to understanding a broader climate story. As with trees, larger growth increments in otoliths indicate a more favorable growing season. After analyzing increments in a collection of otoliths catalogued over the last several decades, Black found that rockfish growth was correlated with climate. During years when rockfish flourished, he discovered, winter climate was characterized by persistent high-pressure weather systems between Hawaii and the West Coast. (see graphs and map below)

A core taken by Bryan Black from this large Douglas-fir near Cape Perpetua will be dated and its rings compared with those of other trees as well as geoducks – the Northwest’s largest bivalve. Such comparisons allow scientists to study climate change in new ways (photo courtesy of Bryan Black, OSU)

A core taken by Bryan Black from this large Douglas-fir near Cape Perpetua will be dated and its rings compared with those of other trees as well as geoducks – the Northwest’s largest bivalve. Such comparisons allow scientists to study climate change in new ways. (Photo courtesy of Bryan Black)

“After developing these growth chronologies I found that they were very sensitive to what happened in the winter months,” Black says. “Climate in the winter seemed to be determining how well these fish grew throughout the year, and I think that’s because if you get favorable climate in the winter you get an early start to the growing season.”

The high-pressure systems that Black noted were encouraging winter upwelling along the coast, a process in which wind drives nutrient-rich water toward the ocean surface, effectively jump-starting the growing season. What made this connection to winter climate particularly interesting, he says, is how it also shows up in tree rings. Black combined the rockfish and climate data with tree-ring chronologies. As the data came together, he realized that rockfish and trees along the West Coast were reacting to the same forces but with opposite results. While the high-pressure systems created favorable conditions for rockfish, the systems blocked moisture flow to the forest, causing drought and producing poor growing seasons for trees.

500-Year Record

Once Black had established the relationship between trees, rockfish and winter climate, he began to expand his data, joining knowledge of marine and terrestrial systems to better understand both. He used networks of tree-ring chronologies, many of which extended for more than 500 years, to illustrate conditions of the past and provide context for understanding modern climate patterns.

“You can use the trees to tell us how this winter pattern has varied over the past several centuries, which is much longer than any instrumental record can provide,” Black says. “It’s really underscoring the importance of these distinct seasonal patterns and that, especially for this winter pattern, the marine and terrestrial systems are both affected. We’re using these chronologies to tell us about this history.”

By learning how climate has varied in the past and understanding its effect on growing seasons, Black hopes to determine how ecosystems have been affected by climate variation as well as by human presence, and how they might respond in the future. In addition to increasing our understanding of the sensitive relationships between climate and terrestrial and marine systems, he says further knowledge would have practical value for fisheries to predict expectations for growing seasons and set catch limits.

“Before you can forecast any effects of climate change, you have to understand how climate affects these systems right now,” Black says. “That’s where I come in, to try to tie these climate and ecosystem patterns to the environment and human influence where possible.”

Global Network

This magnified slice of a geoduck shell clearly shows incremental growth rings used by scientists to analyze sea surface temperatures (Photo courtesy of Bryan Black, OSU).

This magnified slice of a geoduck shell clearly shows incremental growth rings used by scientists to analyze sea surface temperatures. (Photo courtesy of Bryan Black)

Now, Black is sharing his methods with other researchers. Together, he and his colleagues are applying tree ring chronology methods to study the growth increments in the otoliths of different fishes as well as other species, such as bivalves, which have growth increments in their shells. By collaborating with researchers around the world, from Alaska to Europe and Australia, they hope to establish chronologies for diverse marine systems and compare them across broad regions. The goal is to learn about the effects of climate patterns on global marine and terrestrial systems.

“There is a huge network of tree ring chronologies that has been developed all over the world and it is a leading indicator of forest responses to climate and climate change,” Black says. “I think the same could be done in marine systems as these chronologies are developed. I find it very exciting to contribute something that is of practical and ecological importance to understanding how these systems function.”

The figure named "Terra_reconstruction" is: A) Relationship among wintertime sea level pressure off the coast of western North America, tree growth in central and southern California, and sea level measured at San Francisco (an especially long instrumental record in comparison to sea level pressure). B) Full history of wintertime sea level pressure from tree-ring data, including 95% confidence intervals (gray shading). The reconstruction extends back in time to 1507 AD, providing a 500-year record of wintertime climate variability important to marine and terrestrial ecosystems. (Graphs courtesy of Bryan Black)

Figure A shows the relationship among wintertime sea level pressure off the coast of western North America, tree growth in central and southern California, and sea level measured at San Francisco (an especially long instrumental record in comparison to sea level pressure). B shows the full history of wintertime sea level pressure from tree-ring data, including 95% confidence intervals (gray shading). The reconstruction extends back in time to 1507 AD, providing a 500-year record of wintertime climate variability important to marine and terrestrial ecosystems. (Graphs courtesy of Bryan Black)

The map shows correlations between winter sea level pressure off the coast of western North America and 1) northerly winds, where positive correlations indicate flow from the north, 2) winter precipitation on land, and 3) tree-ring chronologies in western North America (note: the larger the tree symbol, the stronger the correlation with winter sea level pressure). In summary, high pressure off the west coast of North America mean more north winds, which favor marine productivity as well as drought on land, which reduces tree growth. (Map courtesy of Bryan Black)

The map shows correlations between winter sea level pressure off the coast of western North America and 1) northerly winds, where positive correlations indicate flow from the north, 2) winter precipitation on land, and 3) tree-ring chronologies in western North America (note: the larger the tree symbol, the stronger the correlation with winter sea level pressure). In summary, high pressure off the West Coast of North America means more north winds, which favor marine productivity as well as drought on land, which reduces tree growth. (Map courtesy of Bryan Black)

 

Leave a Reply


+ three = 6