Our Changing Oceans

Oceans are the largest heat sink on the planet, absorbing 90% of the excess heat caused by climate change⁴. As our ocean temperatures rise, warmer-water species are extending their range and becoming more prevalent further north along the Pacific coast. Invasive species such as Sargassum horneri, a marine alga, thrive under more moderate ocean temperatures⁵. As ocean water temperatures increase, oxygen also becomes less soluble in our oceans. As a result, ocean warming has reduced oxygen concentrations in the California Current by 20% from 1980 to 2012⁶. Oxygen is important in the ocean for the same reason it is on land—plants and animals require oxygen to survive.

Reduced oxygen concentrations have a wide range of impacts on marine life, including decreasing the quality and quantity of suitable habitat, reducing growth rates, interfering with reproduction, increasing susceptibility to disease, and even blinding some marine species. Market squid, rock crabs, and many other important species that comprise our local fisheries experience vision impairment as they travel through low oxygen zones during vertical migrations. If dissolved oxygen concentrations continue to decrease in Southern California waters, the survival of these oxygen-sensitive creatures could be impacted due to increased difficulty in finding food and avoiding predators.

Unusually warmer winter ocean temperatures may have also facilitated the spread of sea star wasting disease in 2013-2014, a syndrome that decimated many species of sea stars at Channel Islands National Park and Marine Sanctuary, including sunflower sea stars, which are now functionally extinct in California. Sunflower sea stars are keystone predators in kelp forest ecosystems as they help regulate purple urchin populations and ultimately prevent overgrazing of kelp. Urchin populations have boomed across Northern and Central California since sunflower stars disappeared, devouring wide swathes of kelp and other seaweeds and threatening this vital ecosystem. Warmer waters have also been linked to increased spread of withering syndrome in black abalone, an iconic endangered species of marine snail found in the park.

large starfish on rock with kelp — Two sunflower stars cling to the side of a boulder in a rocky reef environment.
Dave Witting

We depend on the oceans, so we have a responsibility to protect them. The oceans absorb the extra carbon dioxide people emit when they burn fossil fuels which alters the chemistry of the oceans. This is called ocean acidification. Since the start of the industrial revolution, the ocean has absorbed roughly 30% of the carbon dioxide that people generate through industry and agriculture⁷. Ocean waters off the Pacific coast have become 40% more acidic since 1750⁸, impacting many sea-dwelling species. The change in chemistry is reducing the amount of calcium carbonate in the ocean. Just as humans need calcium to build their bones, many sea creatures such as abalone, oysters, clams, and mussels, need calcium carbonate to build their skeletons and shells. As a result of this ocean acidification, we are seeing sea creatures’ shells and skeletons become thinner and more brittle. Since shelled organisms are essential throughout the marine food chain and are vital to our economy, these changes can threaten hatcheries and impact both marine life and the people who depend on them.

Due to kelp’s speedy growth rate, these algae are extremely proficient at removing dissolved carbon dioxide from our oceans. In fact, 200 million tons of carbon dioxide are being sequestered by macroalgae such as giant kelp every year⁹. Declines in kelp forests will further decrease the effectiveness of this natural carbon sink from mitigating the impacts of climate change.

rays of sunlight coming through a kelp forest — NPS/ Scott Gabara

Now that we know about ocean warming and acidification, it’s important to rethink our use of fossil fuels and act collectively to inspire new approaches and civic programs to solve climate change.