Scientists are reporting a decline in oxygen-rich waters throughout the world. Causes for the decline vary from place to place but may involve climate change and increasing discharges of tainted water. In Puget Sound, low oxygen levels can occur naturally or due to eutrophication from human-caused pollution. In this five-part series, we describe the critical nature of oxygen to Puget Sound sea life. Scientists are finding that changes in oxygen levels can lead to physiological adjustments, shifts in predator-prey relationships and other repercussions throughout the food web.

As observed in Hood Canal, low-oxygen conditions can upend the lives of Dungeness crabs trying to stay alive. Levels of dissolved oxygen can alter predator-prey relationships for a multitude of species, affecting populations throughout the food web. Part two of our series "Oxygen for life" examines a crab case study.

In time, lower dissolved oxygen worsened by climate change could increase the abundance of rare species in Puget Sound while putting populations of more common species into a tailspin. Part three of our series "Oxygen for life" looks at how warmer waters will gradually make it harder for many sea creatures to breathe. 

How do excess nutrients trigger low oxygen conditions in Puget Sound and what do those conditions mean for the species that live here?