Calculating the future of the California Current Ecosystem

This is the twelfth and final in a yearlong series of stories showcasing the research that the Ocean Protection Council supported in partnership with California Sea Grant, with funding from Proposition 84.

Few places in the world’s oceans are as biologically productive as the California Current Ecosystem (CCE), which, as the name implies, lies off California’s coastline, from British Columbia to Baja California, Mexico. Seasonally, cold waters filled with nutrients feed krill, squid, and sardines, among other species. These are in turn consumed by other species, from birds to fish to marine mammals. 

Unfortunately, this region is also suffering some of the world's fastest-recorded declines in dissolved oxygen. Scientists worry that this could eventually lead to a major ecological disruption by narrowing the available habitat for species that need oxygen. To understand that potential future, a team of researchers—supported by funding from the Ocean Protection Council—decided to look at the CCE’s past.

The team, led by Curtis Deutsch, a geoscientist at Princeton University, noted that the seasonal upwellings of cold water already cause short-term declines in oxygen, a condition known as hypoxia — and that species’ ongoing response to these hypoxic conditions may help us understand how they’ll fare in the future. The CCE is a well-studied area, with robust long-term ecological datasets; the team decided to combine this accumulated data with models that predict the impacts of climate change. 

The process required several steps: first, biologists need to understand the temperature-dependent hypoxia tolerance of the species in question. What kind of habitat can they use, in other words? Second, using “hindcast” models — which look backward, rather than forward — the team determined how much these species’ habitats have varied historically, due to season changes. Next, based on climate change projections, the researchers determined how increased hypoxia (and warmer water) will increasingly constrain habitat. Ultimately, the team aimed to have the developed framework adopted by resource managers and agencies. 

In addition to Deutsch, the team included Brad Seibel, a biologist at the University of South Florida, and Martha Sutula, the head of the biogeochemistry department at the Southern California Coastal Water Research Project, a public agency that applies scientific research to aquatic ecosystem management. The project resulted in multiple journal articles, including a 2022 paper in Global Change Biology that included Deutsch as a co-author. By 2100, the paper notes, changes to the CCE will impact biological processes in many species, with some metabolic rates increasing by as much as 25%. The changes will be most severe in the north, where the impacts of climate change are projected to be more pronounced. The shallow waters along the inner continental shelf will be heavily impacted too, since the species at these depths tend to be more sensitive to changes.

The authors identified two species for which they had combined temperature and oxygen sensitivities, northern anchovy and Alaska pink shrimp. Warmer temperatures will drive metabolic rates upwards for both species — and the decreasing oxygen levels will limit their energy. This means that the southern edges of both species’ current ranges, where water is warmer, will no longer be viable habitat; their ranges are expected to shift northward — which, given that these are both commercially harvested species, has key implications for fisheries and economies. 

Everywhere the researchers looked in the CCE and for every taxon they studied, they found some changes. And, they note, “such changes are highly unlikely to be restricted to the suite of species examined here, and can reasonably be expected to occur across species yet unstudied. Such widespread change will, over time, cause substantial changes in ecosystem structure and function.”