Evan Gallagher, UW Department of Occupational and Health Sciences
Shallin Busch, NOAA Ocean Acidification Program and NOAA Northwest Fisheries Science Center
Meg Chadsey, Washington Sea Grant
Andy Dittman, NOAA Northwest Fisheries Science Center
Paul McElhany, NOAA Northwest Fisheries Science Center
Chase Williams, University of Washington, Seattle
Washington Sea Grant-funded researchers studied the effects of ocean acidification (OA) on two ecologically and economically important species of local fishes: coho salmon and sablefish. They exposed fish to three levels of pH: Puget Sound’s current pH (7.8), the expected pH in 50 years (7.5), and the expected pH in 100 years (7.2). Then, they measured how the fish respond to important odors via behavioral analysis, electro-olfactograms and electro-encephalograms. The researchers focused on impacts to the fishes’ sense of smell because it is crucial to both species for identifying food and avoiding predators, and is additionally essential to salmon for navigating back to their home rivers to spawn.
As the oceans absorb an increasing amount of atmospheric carbon dioxide, the water chemistry is acidifying. While ocean acidification (OA) has been shown to harmfully impact several marine organisms native to the Pacific Northwest, including oysters, the effects of OA on local fishes have largely gone unstudied. The olfactory responses to food and predator odors under current and projected pH conditions of two important native species–coho salmon and sablefish–are considered in this study.
While there were no changes in response to a food odor between different pH levels for sablefish, coho salmon avoidance behavior toward predators decreased as the pH decreased, indicating ocean acidification negatively impacts coho olfaction. RNA sequencing of the olfactory tissues revealed extensive disruption in the expression of genes involved in neuronal signaling within the olfactory bulbs of salmon that were exposed to elevated carbon dioxide, with lesser impacts on the gene expression in the olfactory rosettes. This indicates the smell impairment stemmed not from the cohos’ noses, but from how their brains process smell.