February 2025
Love is in the air this Valentine's Day, but beneath the surface of the ocean and Great Lakes, partnerships thrive year-round. These relationships, known as symbiosis, involve two different species living together, often to the benefit of one or both. Symbiosis takes many forms: mutualism (where both benefit), commensalism (one benefits, and the other is unaffected), and parasitism (one benefits at the expense of the other). Across America's National Marine Sanctuary System, there are countless examples of these fascinating partnerships that keep biodiversity booming and ecosystems thriving. Let's dive in and explore nine remarkable "matches made in the ocean."
Giant Clams and Zooxanthellae in National Marine Sanctuary of American Samoa
Known as faisua in the Samoan language, giant clams are native to the South Pacific and Indian Ocean, like in National Marine Sanctuary of American Samoa. Inhabiting warm coastal waters and lagoons, these large clams and tiny algae, called zooxanthellae, have formed a mutually beneficial bond, similar to that of coral and their symbiotic algae. Zooxanthellae live inside the tissues of giant clams, providing them with nutrients through photosynthesis. In return, the clams offer the algae a safe place to live and access to sunlight by positioning themselves in well-lit areas of the reef. Together, they create a vibrant, colorful display that not only supports their survival but also contributes to the health of coral reef ecosystems. Small giant clams (Tridacna maxima) are found on the reefs throughout National Marine Sanctuary of American Samoa, with particularly high densities around the Ta'u sanctuary unit. The highest density of clams in American Samoa has been observed within the lagoon at the Rose Atoll National Wildlife Refuge within the Rose Atoll Marine National Monument.
Honu (Green Sea Turtle) and Cleaner
Fish
in Hawaiian Islands Humpback
Whale National Marine Sanctuary
In the waters surrounding the Hawaiian Islands, green sea turtles (Chelonia mydas) – or honu – regularly visit “turtle cleaning stations.” At these underwater spas, the turtles rest peacefully while convict tangs (Acanthurus triostegus) and other reef fish nibble away parasites and dead skin. This mutually beneficial relationship keeps the turtles healthy and the fish well-fed. Beyond benefiting individuals, these cleaning stations play a vital role in maintaining reef health by reducing parasite loads and promoting biodiversity. This underwater teamwork highlights the importance of symbiosis in creating vibrant and balanced marine ecosystems.
Come along and explore with green sea turtles as they take you on a Sanctuaries 360 adventure around Hawaiian Islands Humpback Whale National Marine Sanctuary!
Canada Geese and Beavers
in Mallows
Bay-Potomac River National Marine Sanctuary
Mallows Bay-Potomac River National Marine Sanctuary, known for its historic shipwrecks, also serves as a home to Canada geese (Branta canadensis) and beavers (Castor canadensis), two species that form an unexpected partnership. Beavers construct intricate dams and lodges, creating sheltered wetlands that attract various species. Canada geese often nest on top of these lodges, benefiting from the elevated, protected locations to keep their eggs safe from predators and flooding. While the beavers don't gain much in return, they don't seem to mind the feathered roommates. This commensal relationship helps maintain a thriving wetland ecosystem, benefiting countless other species in the sanctuary.
Enjoy a Sanctuaries 360 scenic paddle through the Mallows Ghost Fleet.
Decorator Crabs and Anemones
in
Cordell
Bank National Marine Sanctuary
The cold, nutrient-rich waters of Cordell Bank National Marine Sanctuary off California's coast are home to decorator crabs, crafty crustaceans that create their own camouflage. These crabs attach pieces of anemones, sponges, algae, and other materials to their shells, blending seamlessly into their surroundings to avoid predators. Anemones and sponges often benefit from this relationship by being transported to new areas with strong currents where they can access more food and grow. This mutualistic partnership highlights how resourcefulness and teamwork go hand in hand beneath the waves.
Can you find the decorator crab in this Sanctuaries 360 video?
Hawaiian Monk Seal and Green Sea
Turtle
in Papahānaumokuākea Marine National Monument
In the pristine waters of Papahānaumokuākea Marine National Monument, Hawaiian monk seals (Monachus schauinslandi) and green sea turtles (Chelonia mydas) share a unique and indirect relationship. While not a traditional symbiotic partnership, they are sometimes found snuggling together on beaches! Throughout the Hawaiian archipelago, the Hawaiian monk seal spends about two-thirds of its time at sea. However, this pinniped also loves to sunbathe, sometimes “hauling out” onto the beach for days at a time to soak up some rays and rest. Green sea turtles sure can relate—they have been observed basking on the sand for up to 48 hours at a time, helping this cold-blooded reptile regulate its body temperature. In the ocean, monk seals often forage for food in areas where green sea turtles graze on seagrass, together keeping these habitats healthy and productive.
Manta Rays and Remoras
in Flower Garden Banks National Marine Sanctuary
In the waters of Florida Keys and Flower Garden Banks national marine sanctuaries, manta rays and remoras form a partnership that's both functional and fascinating. Remoras, also known as suckerfish, attach themselves to manta rays using a suction disk on their heads. This hitchhiking behavior allows the remoras to save energy while traveling and access food scraps left behind by the rays. In return, remoras help keep the manta rays clean by eating parasites and dead skin—keeping them healthy and their bodies smooth and aerodynamic as they swim. This mutualistic relationship demonstrates how even the largest creatures in the ocean can benefit from teamwork.
Whales and Seabirds
in Stellwagen Bank National Marine Sanctuary
Stellwagen Bank National Marine Sanctuary, located off the coast of Massachusetts, is a hotspot for a diverse array of seabirds and whales—especially humpback whales. These two very different animals team up to feed in a fascinating display of symbiosis. When whales lunge-feed on schools of small fish, they push the fish toward the surface, where seabirds are waiting to swoop in and catch an easy meal. While the seabirds benefit more directly, the whales experience little to no impact from their feathered companions. This commensal relationship demonstrates how one species's hunting technique can create opportunities for others in the food web.
Deep-Sea Anglerfish
in Monterey Bay National Marine Sanctuary
In the dark depths of Monterey Bay National Marine Sanctuary, female deep-sea anglerfish (Melanocetus spp.) rely on bioluminescent bacteria housed in a specialized light organ called the esca. These bacteria emit light, which the anglerfish use to attract prey in the pitch-black environment. The relationship is mutualistic: the bacteria gain a safe habitat and nutrients from the anglerfish, while the anglerfish benefits from an effective hunting tool. This glowing partnership showcases the ingenuity of life in the deep sea.
In some species of anglerfish, the males, which are significantly smaller than the females, exhibit a form of parasitism by permanently attaching themselves to the female's body. In this dynamic, the male provides sperm to the female while relying entirely on her for nutrients and survival. This parasitic relationship ensures reproduction in the vast and sparsely populated deep sea, a testament to the extreme adaptations of life in this environment.
Sharks and Shipwrecks
in Monitor National Marine Sanctuary
While this might not be a true symbiotic relationship (because the shipwrecks themselves are not a living organism), shipwrecks can sometimes create structure in parts of the ocean with low relief, concentrating fish and sharks in the vicinity of the wreck. Like other shipwrecks in the area off the coast of North Carolina, the wreck of the Civil War ironclad USS Monitor has become an oasis of life for the marine species in this region. Thanks to its unique position at the confluence of the Labrador Current and the Gulf Stream, the ecology on this wreck is both diverse and abundant. Sand tiger sharks (Carcharias taurus) are one of the many species that call Monitor National Marine Sanctuary home.
Check out all of the sand tiger sharks in this Sanctuaries 360 dive adventure of one of our nation's most historic shipwrecks, USS Monitor.
A Celebration of Connections
From the wetlands of Mallows Bay to the coral reefs of American Samoa, symbiotic relationships are vital to the health and balance of freshwater and marine ecosystems in your National Marine Sanctuary System. This Valentine's Day (and every day), let's celebrate the incredible partnerships found in nature—proof that even in the wild, cooperation and connection are at the heart of survival. Whether it's a fish cleaning a sea turtle or geese nesting on a beaver dam, these matches made in the ocean remind us of the beauty and complexity of life beneath the waves and the importance of biodiversity.
Rachel Plunkett is the content manager and senior writer/editor for NOAA's Office of National Marine Sanctuaries
Make sure you follow Wildlife Viewing Guidelines when you're out enjoying nature. Or explore the 50 Ways to Love Your Oceans and Coasts you can put into practice every day!