Sharks are key to the health of our oceans and climate

Above: Blue sharks inhabit the open ocean, completing long migrations and diving to depths greater than 3,280 feet.

Our oceans have a direct impact on regulating Earth’s climate and are the planet’s largest absorber of atmospheric carbon. As our climate warms, maintaining their ecological balance and resilience is critical to withstanding extreme climatic events.

Superpower: strategic predators

Sharks that inhabit coastal waters ultimately protect and enhance what is known as “blue carbon”—carbon stored in oceans. These remarkable animals will patrol and hunt in coral reefs and seagrass meadows, or even scavenge the sea floor looking for dead matter. When sharks target plant-eating fish, they can positively impact the marine carbon cycle. This predatory behavior limits the potential of the prey fish to excessively eat ocean vegetation, like seagrass meadows and kelp forests, that are crucial for carbon absorption through photosynthesis. Seagrass can capture atmospheric carbon 35 times faster than tropical rainforests and store huge amounts of carbon for decades.

As apex predators, sharks fundamentally shape and maintain their ecosystems. They’ve been around for over 400 million years—before trees first laid down roots—making them one of Earth’s greatest survivors. More than 530 species of shark help protect the delicate balance of marine ecosystems, benefiting oceans and the climate.

For example, tiger sharks help flourishing seagrass meadows by keeping populations of sea cows in check. They also prevent overgrazing from sea turtles and other prey species, resulting in more evenly distributed seagrass. And in coral reef ecosystems, sharks will prey on herbivorous coral reef fish, enhancing the carbon-capturing and storage abilities of the coral reef ecosystem.

Sharks protect carbon stores in marine ecosystems not only by preying on herbivorous fish but also by simply causing grazing fish to disperse and reduce their foraging efforts. By reducing the amount of foraging behavior and activity that agitates the sediment on the ocean floor that actively stores carbon, sharks reduce the potential for any loss of stored carbon disturbed by fish movement.

Superpower: carbon movers and shakers

Many shark species migrate thousands of miles over their lives, and they help cycle and redistribute nutrients throughout marine ecosystems.

Sharks swim throughout the different ocean layers, performing vertical migrations that mix nutrient- and oxygen-rich deep water with nutrient-poor surface waters, helping to oxygenate them and enhance their productivity. This aids creatures living in the ocean’s surface water, like phytoplankton, by getting the nutrients they need to be more productive. Like plants on land, phytoplankton can pull carbon dioxide from the atmosphere and produce oxygen.

Sharks also transfer nutrients through their fecal matter. Grey reef sharks in shallow reef ecosystems supply multiple pounds of nitrogen daily to their habitats. Sharks that live in the open ocean, like hammerheads, makos, and more, are also important contributors to this effort. But in addition to the fertilizing effect their fecal matter can have on carbon-storing marine vegetation or phytoplankton, the feces itself also directly contains carbon and stores it at the bottom of the ocean floor when it sinks.

When animals on land die, the carbon stored in their bodies is released into the atmosphere. But when ocean creatures die, their bodies—and the carbon in them—sink to the bottom, becoming carbon reservoirs for thousands of years. Carbon makes up about 10%-15% of a shark’s body, so this cycle is particularly important for larger marine animals.

The real villains in this story

In recent decades, shark populations have been hard hit and are declining considerably, with more than a third of all shark and ray species now threatened with extinction. They are among the most endangered marine animals—mainly because of overfishing and harmful fishing practices. A study of 18 oceanic shark and ray species found that overfishing has led to a 71% reduction in their numbers globally since 1970.

The loss of top and medium predators like sharks can have cascading effects on the ocean ecosystems, leading to imbalances such as booms in prey numbers, an overabundance of herbivore fish, and the potential destruction of carbon-storing underwater habitats. In coral reefs, reduced shark populations can increase other dominant predatory fish that prey on the fish that eat algae, decreasing species diversity and increasing algae blooms that ultimately suffocate reefs. 

The climate crisis also has the potential to further decimate shark numbers. Warming waters push fish populations into newer areas, disrupting the availability of food where they should commonly be found. Blue sharks are harmed by warming waters; they don’t dive as deep in warmer areas with low oxygen levels, which leaves them vulnerable to getting caught in fishing gear. More sharks, rays, and other large marine fish—along with large ocean animals like whales and dolphins—means more carbon is stored in their bodies. However, overfishing directly reduces this carbon storage with each life lost.

The enduring hero

Ecosystems with healthy shark populations are more productive and thriving than those without. They are also more resilient to change and maintain ecosystem balance. Sharks have been around for hundreds of millions of years and have survived five major mass extinction events, outliving dinosaurs. Their resilience and role in our oceans are unmatched. But this value can go unnoticed when sharks are cast as fear-inducing aggressors stalking our oceans. In reality, they are curious guardians patrolling and protecting the precious balance of their ocean home. People and the planet need them, and we must protect them and reframe their story.

Learn about other wildlife climate heroes.