Oxygen levels in the ocean are changing globally from natural and human-induced processes. Many marine invertebrates depend on vision to find food, shelter, and avoid predators, particularly in their early life stages when many are planktonic. This is especially true for crustaceans and cephalopods, which are common prey items for other animals and whose larvae are highly migratory in the water column.
these conditions are changing due to human-influenced climate change and even pollution. Atmospheric warming is changing temperatures in the ocean as well, which decreases the mixing of well-oxygenated surface waters to deeper waters. Additionally, nearshore environments are increasingly losing oxygen in a process called eutrophication, in which excessive nutrients in the water fuel a bloom of plankton that then deplete available oxygen dissolved in the water. This can lead to die offs of fish and other marine animals. Eutrophication is often the result of coastal pollution, like runoff from agriculture or sewage.
— source scripps.ucsd.edu | May 8, 2019