Deep-sea fish community structure strongly affected by oxygen and temperature

In a new study, researchers from Scripps Institution of Oceanography at the University of California San Diego and the Monterey Bay Aquarium Research Institute (MBARI) took advantage of the natural oceanographic gradient in the Gulf of California to study the effects of variable oxygen levels and temperatures on demersal fish communities — fish that live on or near the seafloor. They determined that in regions containing very low levels of oxygen (7 ?mol/kg of oxygen or less), fish diversity declined dramatically. For comparison, oxygen concentration at the ocean surface is usually between 200 and 300 ?mol/kg. This has implications for the future of deep-sea fish communities in the face of climate change. In the study, published on March 5 in Marine Ecology Progress Series, the researchers conducted surveys in three different regions in the Gulf of California. The gulf’s unique seafloor geography provides dramatically different environmental conditions within a relatively short distance. In the north, deep seawater temperatures are relatively warm with high oxygen levels while in the south, the deep sea is colder and extremely oxygen poor. “It’s really rare to find such large differences across such a small spatial scale,” said lead author Natalya Gallo, a marine ecologist and postdoctoral research associate at Scripps Oceanography. “This lets us pick apart some of the environmental factors that affect the types of fish communities we see, making this a really great study system.”

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