Food Webs as Fuel for the Ecosystem

The idea that all parts of life are interconnected is an ancient motif found in mythology, religion, art, and science. It’s also a concept central to a recent report on the importance of food webs to the health of the Columbia River Basin ecosystem. As lead report author Dr. Robert J. Naiman puts it, “food webs fuel that ecosystem,” underpinning the productivity and resiliency of the basin’s fisheries.

The three key areas of concern: whether the system can produce enough of the right food at the right times to maintain thriving populations of native fishes; the effects of non-native species on food supply; and the proliferation of contaminants and chemicals in the watershed.

Until now, the Council, NOAA Fisheries, tribes, and other state agencies haven’t really focused attention on changes to food webs, assuming that conditions have been relatively favorable and stable. But as the ISAB report indicates, changes to the basin’s food webs are widespread and appear to be affecting the aggregate carrying capacity of the river to produce wild fish.

“The question of the carrying capacity of the river was something we hadn’t really considered before,” says Naiman. “Are we overlooking the impact of competition for food between native fish and hatchery fish and other non-native species?”

The report was undertaken by the Council’s Independent Scientific Advisory Board in late 2009 to help understand the role of aquatic food webs in the basin and how they affect native fish restoration efforts. The Council’s fish and wildlife program strives to establish and maintain an ecosystem that sustains an abundant, productive, and diverse community of fish and wildlife.

The impact of massive annual releases of juvenile fish from hatcheries appears to be taking a toll on stocks of wild fish. About 130 - 150 million hatchery salmon and steelhead are released each year, and according to the report, “The thousands of metric tons of food used to raise them, as well as the hundreds of thousands of metric tons of natural foods required to maintain them in the river, affect the capacity of the Columbia River to support naturally produced native fishes.”

Added to this is the proliferation of non-native plants and animals, creating so-called “hybrid” food webs. According to Naiman, “There are so many non-native creatures that are part of the system now; realizing the magnitude of their impact is a new reality.”

“While not completely clear, it sure looks like we may be exceeding the carrying capacity of the river, and that was a big surprise.”

The growing presence of contaminants in the river system is another enormous factor affecting the health of food webs. “We were stunned by just how much is in the watershed,” says Naiman. “These chemicals, from pesticides to personal care products to medicines, disproportionately affect food webs, especially the small, but essential organisms at their base. We know so little about them, yet they could be a lynchpin in whether or not restoration actions succeed.”

For Naiman and his associates on the report, the ultimate message is clear. “We’re at a turning point, and we need to understand that 10 or 20 years from now, there is a high probability that we may be looking at a vastly different ecosystem. We need to ask ourselves if the restoration actions in place now will still be viable, and will they still make sense.”