Oxygen loss in the warming waters of the California Current System (CCS) is projected to lower the region’s Metabolic Index – the temperature-dependent ratio of oxygen supply to species’ metabolic demand – to below critical levels, limiting the habitats available to marine species living there, according to a new study.
Inadequate oxygen availability could force the northern anchovy – a fish that many other species in the ecosystem rely on for food – from CCS waters, resulting in its local extinction.
The findings add to a growing body of evidence that oxygen loss caused by rising temperatures will shift the future distributions of marine species, compromising their ability to weather climate change.
Evan Howard and colleagues note that scientists can better grasp how climate change will alter ecosystems by identifying species limited by simple constraints such as oxygen availability. As climate change warms the world’s oceans, it rapidly depletes dissolved oxygen, lowers pH, and changes species distributions.
Scientists must identify how species have responded to climate stressors in the past to predict how marine ecosystems will change in the future. With its combination of diverse species, naturally low oxygen levels and pH, and strong year-to-year and decade-to-decade natural climate variability, the CCS is an ideal testing ground for new hypotheses.
Combining observational datasets with ocean model simulations, Howard et al. used the Metabolic Index to provide evidence that oxygen fluctuations in the CCS are historically linked to habitat availability, and to demonstrate an approach to evaluate marine species responses in regions faced with oxygen loss.
The researchers predicted that future habitat limitations will vary based on the depth of a species’ range, with oxygen- and temperature-sensitive organisms living less than 200 meters below the surface facing much greater habitat losses than those that dwell below 400 meters.