Hypoxia is the scientific term for low oxygen content. The waters near the bottom of Oregon’s Nearshore ocean along with other areas off the Pacific Northwest are becoming more hypoxic over time. The fraction of the waters that are inshore of 200 m (656 ft) that were hypoxic from 1950 to 1980 during the summer upwelling period was about 2% and has increased to about 24% in 2009-2018. It was calculated to 56% in 2021 due the strong and prolonged upwelling that year. The hypoxia is caused by blooms of phytoplankton that make oxygen when they are alive in the surface waters, but that decompose when they die and fall to the sea floor. That decomposition by microbes consumes oxygen in the water and can make it hypoxic, especially in areas where the bottom water stays in place and is not flushed out quickly. Areas of hypoxia have been called “dead zones”, because dead fish and invertebrates have been found in these areas, but as explained above it is a bit of a misnomer since hypoxia is caused by the surface waters being so productive in producing phytoplankton that is at the base of the food web. These low oxygen levels directly affect the fish and invertebrates that live in these areas who need the oxygen in the water to breath. The effects and response differ by species. Some move out of the area if they are able to, but some cannot and may die in extreme events.
This video provides an overview of hypoxia and its effects on our marine resources as well as people as well as some of the research work that is being done.