April 2025
Sharks have long been portrayed as terrifying predators of the deep, but really, they are essential guardians of the ocean. Despite their fearsome reputation, these apex predators play a crucial role in maintaining the delicate balance of marine ecosystems. Sharks contribute in ways that might surprise you, from regulating prey populations to keeping coral reefs thriving. In this article, we'll explore five key ways sharks help keep our ocean healthy, including in your national marine sanctuaries, and discuss why healthy shark populations are vital for the future of all marine life.
1. Sharks Keep Fish Populations in Check
Sharks are often misunderstood, but they play a crucial role in keeping ocean ecosystems healthy. As apex predators, they help maintain balance by preying on sick, weak, or overabundant animals—including fish, marine mammals, and other ocean life. This natural population control prevents any one species from growing too large and throwing the ecosystem out of balance.
When shark numbers decline, the ripple effects can be dramatic. For instance, in areas where sharks have disappeared, populations of mid-level predators like groupers have surged. These fish, in turn, consume smaller herbivores that normally graze on algae. Without enough of these plant-eating fish, algae can quickly take over coral reefs, making it harder for corals to grow and recover from stress like storms or warming waters.
By keeping prey populations in check, sharks indirectly support biodiversity and help protect critical habitats like coral reefs. Their presence ensures no single species dominates the food web—an essential part of ocean health. Protecting sharks helps preserve this delicate balance, supporting life from the tiniest fish to the largest marine mammals, and safeguarding the future of our planet’s blue heart.
2. Sharks Help Ocean Habitats Thrive
Sharks do more than just regulate prey populations—they help protect some of the ocean’s most important and productive habitats: coral reefs, kelp forests, and seagrass meadows.
As apex predators, sharks help keep grazer and mid-level predator populations in check. This top-down control is especially important for coral reefs, where too many mid-level predators (like groupers) can reduce populations of herbivorous fish. Without enough herbivores to graze on algae, reefs can become overrun with algae, making it difficult for corals to grow and recover. By keeping the food web balanced, sharks indirectly support the conditions coral reefs need to stay healthy and resilient.
In kelp forests, sharks help maintain ecosystem stability in a similar way. When shark populations are healthy, they reduce pressure from predators that feed on sea urchins—a major grazer of kelp. This helps keep urchin populations in check, preventing them from overgrazing and clearing out large sections of kelp. The result is a thriving kelp forest that provides food, shelter, and breeding grounds for a wide variety of marine life.
Sharks also play a key role in protecting seagrass meadows. Their presence influences the movement of grazers like sea turtles and dugongs, who feed on seagrass. Instead of lingering in one area and overfeeding, these animals tend to move more often when sharks are nearby, giving seagrass time to regrow. This natural “grazer rotation” helps preserve seagrass beds—critical habitats for juvenile fish, invertebrates, and other marine species.
By helping to balance the food web, sharks support the health of these essential habitats. And when coral reefs, kelp forests, and seagrass meadows thrive, so do the countless species that depend on them.
3. They Strengthen Fish Genetics
Sharks play a vital role in keeping fish populations healthy and resilient. As skilled predators, they tend to target weak, sick, or aging individuals—removing those less likely to survive and reproduce. This natural form of selection strengthens fish populations over time by allowing the fittest individuals to thrive and pass on their genes.
By culling the sick, sharks also help prevent the spread of disease and genetic defects within schools of fish. In some cases, the act of fleeing from sharks even helps fish shed parasites, as their scales rub together or against surfaces—an unexpected benefit of predator-prey dynamics.
Without sharks, these natural checks would be lost. Unhealthy or disease-prone fish could multiply unchecked, weakening the population as a whole and disrupting the delicate balance of marine ecosystems. Protecting sharks helps ensure the long-term health, diversity, and sustainability of ocean life.
4. Sharks Help Maintain Biodiversity
Sharks are more than just top predators—they shape the behavior and distribution of marine animals throughout the ocean. Their presence creates a "landscape of fear," influencing where prey species move and feed. This natural regulation prevents any one species from dominating an area, allowing multiple species to coexist and reducing the risk of habitat destruction.
Sharks help maintain a balanced ecosystem where biodiversity thrives by keeping marine populations in check. Studies suggest that healthy shark populations contribute to overall ecosystem function and can even enhance resilience to environmental disturbances. When sharks are removed, food webs can become unbalanced, leading to cascading effects that weaken the entire ecosystem. Protecting sharks means protecting the stability of marine environments, ensuring that ocean life remains biodiverse, adaptable, and resilient in the face of change.
5. Sharks Contribute to Coastal Economies
Healthy shark populations support thriving coastal economies, especially through ecotourism. In many parts of the world, people travel specifically for a chance to see sharks in their natural habitat while diving or snorkeling—an experience that generates millions of dollars annually for local communities, dive operators, and tourism businesses.
Shark tourism doesn’t just boost income; it also builds awareness and leverages support for a healthy ocean. Many dive operators partner with scientists or participate in citizen science programs, collecting valuable data on shark behavior, populations, and habitats. This hands-on involvement strengthens public support for marine protection while contributing to real research.
Sharks in Your Sanctuaries
Sharks are essential to maintaining the health and balance of ocean ecosystems, playing a crucial role in regulating marine populations, helping habitats thrive, and supporting local economies through ecotourism. Despite their importance, sharks face growing threats from things like habitat loss and the global demand for shark products. To help protect these important marine species, the United States has some key shark management measures place, such as the Magnusen-Stevens Act.
National marine sanctuaries, which are managed for sustainable, compatible use and responsible recreation, also benefit shark populations by providing safe, relatively undisturbed habitats where they can feed, breed, and migrate. For example, the remote, healthy coral reefs of Papahānaumokuākea are uniquely dominated by large numbers of apex predators, including carnivorous sharks, jacks, and snapper.
National marine sanctuaries also offer great opportunities for researchers to study and monitor shark feeding and migration patterns. For example, Dr. Nancy Foster Scholar, Grace Casselberry is studying the interactions between great hammerhead sharks (Sphyrna mokarran) and Atlantic tarpon (Megalops atlanticus) in Florida Keys National Marine Sanctuary. When a shark snatches a fish that an angler is fighting on their fishing line before it can be landed, this interaction is called a "shark depredation" event. Depredation has a negative impact on the livelihoods of fishing guides. Casselberry’s research suggests that anglers can use fishing gear that will allow them to land tarpon faster, thus reducing fight times and the opportunity for depredation.
On the U.S. West Coast, Greater Farallones National Marine Sanctuary and Monterey Bay National Marine Sanctuary serve as vital habitats for great white sharks, and researchers at Monterey Bay White Sharks have been using electronic tags to observe their movements and locate hot spots for shark feeding allowing them to gain insights into factors that alter the distribution and availability of their prey within the greater California Current Ecosystem.
By supporting responsible fishing practices, regenerative tourism, and scientific research, we can all help support healthier shark populations in your national marine sanctuaries and a healthy ocean for future generations.
Claire Mullin is a communications intern for NOAA’s Office of National Marine Sanctuaries and student at the University of Oregon.
Rachel Plunkett is the content manager and senior writer/editor at NOAA’s Office of National Marine Sanctuaries