Discover the Ocean’s Most Ingenious Home Builders

Humans are some of the greatest builders on the planet, but we’re not the only ones. Beneath the ocean, some unlikely creatures build breathtakingly intricate structures with a variety of clever techniques and materials. Underwater homes serve many purposes: they shelter offspring, offer refuge from predators, and in some cases, support entire ecosystems. Some of these creatures even open their homes to other species. And some can even be kept in a home aquarium, where you can watch them build their homes.

1. Octopuses

Octopuses amaze people with their high intelligence. They can open jars, solve puzzles, and react with a variety of emotions. Few people realize they’re also brilliant engineers, says Jennifer Brandon, a San Diego-based oceanographer.

“They use their siphons to eject water into the sand to create a slurry, then make their burrows out of that ‘quicksand,’” Brandon says. “Some then reinforce the walls of their burrows with mucus. Many species also arrange rocks, shells, and debris into strategic barricades.”

Females are particularly meticulous about building dens for laying and tending thousands of eggs. A female will tend her eggs without eating for months until she finally dies. So, morbidly, her den is also her coffin. If that story depresses you, then here’s another: There’s actually a species called the “Gloomy Octopus” (Octopus tetricus). Australian researchers have documented that instead of being solitary lurkers as we tend to think of octopuses, dozens of them will gather and build their dens close together. Researchers have playfully dubbed these sites as “Octopolis” and “Octlantis.” And just like people living in overcrowded apartments, these octopuses have plenty of drama between them.

2. Giant Larvaceans

Though virtually invisible to the average beachgoer, giant larvaceans are some of the most remarkable architects in the sea. They look like little tadpoles, only 10 millimeters or so long, but they construct immense, transparent balls of mucus as much as a meter wide to filter food from the sea. A single larvacean can filter tens of gallons of seawater every hour. When the mucus structure becomes clogged—typically within a day—the animal abandons it and makes a new one. These discarded “houses” sink to the ocean floor, taking with them organic material like a care package from above for bottom-dwelling species to eat.

Giant larvaceans play a complicated role in pollution management in the ocean. By sending carbon-rich particles of organic matter down to the deep sea, they help remove it from layers of the ocean near the surface, where it would stay in more active circulation and contribute to climate change. Instead, it gets buried under silt at depths where the water doesn’t circulate as much. The same is true of microplastics, but the picture in that case is more complicated.

“These fast-sinking houses are one way microplastics are getting to the deep sea,” Brandon says. “More plastic in the ocean could clog their filters faster and make them work harder to get to their real food.”

And while it can seem beneficial to reduce the amount of microplastics in the upper ocean where there are more species in the human food chain, we don’t know yet how introducing these pollutants to the deep ocean will affect the fragile and largely unexplored ecosystems there.

3. Mantis Shrimp

Mantis shrimp are industrious burrow builders. Found in tropical and subtropical seas, they use their specialized appendages to scrape, flick, and compact material. Some line their burrows with mucus or reinforce walls with pebbles, allowing them to control interior temperature and oxygen flow. These burrows aren’t just temporary shelters—they serve as nurseries, storage areas for prey, and protective retreats from larger predators.

The architecture of their burrows is tailored to their hunting style. “Spearer” species dig narrow, vertical tunnels that allow for quick ambushes from below. “Smasher” species often build U-shaped or winding burrows with multiple entrances. They can punch hard enough with their claws to break the shells of other species. In fact, the acceleration of their punch is nearly as fast as a bullet! As if all this undersea engineering skill weren’t enough, Carrie Tyler, Professor of Marine Conservation at the University of Nevada, says that they also have an astonishing ability to keep them from wandering off and forgetting where their home is.

“Mantis shrimp have a homing behavior called path integration that allows them to find their way back to their burrows,” Tyler says. “They continuously monitor their heading relative to the position of their burrow so they don’t get lost.”

4. Coral

Coral is created by innumerable tiny polyps that together are some of nature’s most ambitious architects. Each tiny animal builds a hard limestone skeleton made of aragonite, a form of calcium carbonate extracted from seawater. Over centuries, colonies of polyps grow, die, and build upon themselves, forming coral reefs that stretch for hundreds of miles. Sometimes they reach close enough to the surface to accumulate sand and debris and become islands. The Great Barrier Reef, the world’s largest living structure, is even visible from space!

These reefs support around 25% of all marine species while covering less than 0.2% of the ocean floor. They serve as breeding grounds, hunting territories, and protective havens for countless fish, mollusks, crustaceans, and other sea creatures. Reefs also help shape ocean currents, absorb wave energy, and protect coastal communities from storms and erosion. One strategy humans use to help ocean life is to create artificial reefs by deliberately sinking cleaned and prepared structures such as boats and even old subway cars in carefully selected areas, providing surfaces for coral and other marine life to colonize. In recent years, large areas of coral have died in a process called “bleaching” that is the result of temperature changes in the ocean, not the chemical balance of the water.

“Recent discoveries show that seawater is not in direct contact with the growing skeleton, as was previously thought,” Tyler says. “This means that corals are able to regulate their internal ion concentrations, even as oceans acidify, and that to save coral reefs we should lower the temperature, not increase water pH.”

In other words, newly growing coral has a thin layer of living tissue around it that insulates it from ocean chemistry, but not from rising temperatures. As with so many areas of environmental catastrophe, climate change is a primary culprit.

5. Tube Worms

Many marine worms build elaborate tube-shaped dwellings from sand, shell fragments, minerals, or mucus. These serve not just as protective homes but also as the base of unique ecosystems, supporting bacteria that convert chemical energy into food in a process known as chemosynthesis. In the deep sea, especially around hydrothermal vents, giant tube worms form towering colonies that shelter a wide range of life. Hydrothermal vents are able to support life in conditions of low light, high pressure, and extreme heat from scalding water jetting into the frigid cold of the deepest seas. Studying them has broadened scientists’ ideas of where extraterrestrial life might thrive and where to look for it, even in the most extreme and contradictory environments.

6. Pistol Shrimp and Goby Fish

Pistol shrimp are among the ocean’s loudest animals. They each have an oversized claw that they snap so hard it makes a bubble that, at very close range, pops at 210–218 decibels—louder than a gunshot! They’re small, though, so to the human ear, when many shrimp snap at once, it still just sounds like faintly sizzling bacon. But the combined noise is still sometimes enough to interfere with sonar and underwater communication. Tyler says that either claw can become the primary weapon.

“Like a crab, if a pistol shrimp loses or damages its larger claw, it will regrow it,” Tyler says. “The new claw will be smaller, and the undamaged remaining claw will grow and become the larger, snapping claw.”

Pistol shrimp have poor vision, but they have a unique partnership with goby fish. The gobies stand watch at the entrance. When danger approaches, they dart inside the burrow, signaling the shrimp to do the same. In return, the shrimp allows the goby to sleep in the burrow at night and, in some species combinations, lay their eggs in the burrow. The shrimp will even seal up the burrow entrance at night to keep both species safe and cozy inside until morning. Check out what this relationship looks like in this award-nominated video.

7. White-Spotted Pufferfish

The white-spotted pufferfish (Torquigener albomaculosus), found off Japan and parts of the western Pacific, is famous for its elaborate courtship displays. To attract a mate, the male uses only his fins to carve large, intricate circles—up to six feet wide—into the sandy sea floor. These geometric “underwater mandalas” feature precise ridges and valleys, later decorated with shells and coral fragments.

Each nest takes about a week to complete and serves two purposes: impressing females and creating a fine, soft environment for egg development. If a female approves of the symmetry and scale—indicators of the male’s fitness—she lays her eggs in the nest’s center. After the eggs hatch, the male abandons the nest and builds a new one the next season. Be sure to watch this video—it’s so fascinating that you’ll want to share it with others.

Which Ones Can Be Pets?

Brandon says only a couple of these home-building sea creatures can thrive in a saltwater tank.

“The only ones I would recommend having at home would be an octopus and a goby fish,” Brandon says. “Mantis shrimp can be kept in tanks, but you have to house them in bulletproof glass because their claw punches are so strong. Pistol shrimp may also be able to crack aquarium glass.”

Coral is also popular with saltwater aquarium enthusiasts, though they need carefully monitored conditions, and some species are easier for beginners than others. Cynthia Traxler, founder of ForgedBySalt, says that in over 20 years of keeping a saltwater reef aquarium, one of her favorite experiences was hosting a pistol shrimp and watchman goby duo. Of the two, pistol shrimp are harder to find and don’t live as long. It took Traxler about 2 years of searching before she was able to find a pair. After the shrimp died, the goby actually carried on with the tunnel-building as best it could. Her verdict?

“I would highly recommend this experience to any saltwater aquarium enthusiast! The relationship between these creatures is constantly entertaining,” Traxler says. “They are easy to keep and very peaceful. Keeping this pair was one of the most enjoyable experiences in my time with the hobby.”

Weird and Wonderful

Isn’t it amazing to realize how many weird and wonderful things are in the ocean? Many of these are creatures and behaviors we never learned about in school, because in many cases, they’ve only been studied in detail since we were in school. There’s no telling how much more there is to discover. And as we learn about them at A-Z, we’ll delight in delighting you with their stories.

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