Under the wet sand along beautiful shorelines, just beneath our feet during beach strolls, there lies an entire ecosystem. The mole crab (also known as a sand crab or sand flea) is a small but mighty sea creature that lives just below the surface of the sand.
When thinking of a sand flea, the first thought that comes to mind is probably not pleasant. After all, fleas are not the most welcomed guests in any room. Despite this unpleasant first impression, these creatures can be endearing with their quirky habits and harmless nature.
Dive deeper into the small world of the mole crab.
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Habitat
Less than one inch long, mole crabs are small yet durable ocean creatures. These animals live in colonies within the swash area (the area on the beach where the waves wash over the sand) of the intertidal zone on tropical and subtropical beaches. The intertidal zone is no picnic for its inhabitants. Constant waves crash over this zone and can move around things in its path. Tides also change as the day progresses, so mole crabs are tasked with following the tides to stay in the wet swash zone of the sandy beaches. This means that entire mole crab colonies move up and down the swash zone as the tide shifts every day—talk about hard work and perseverance.
Appearance
These sand fleas are barrel-shaped creatures equipped with tough, brown-speckled armor that blends into their sandy surroundings. Their exoskeleton acts as protection from oncoming waves. Underneath they have five leg-like appendages and a short tail-like appendage known as a telson (the perfect tool for digging) that they hold into their body when bracing for impact. These features allow them to float around in the tidal waves and land safely somewhere new. Mole crabs also typically have eyes on short stalks and feathery antennae that are used for filter feeding.
Feeding
Mole crabs use their appendages to their advantage in the swash zone, the beach area where waves wash up, employing their legs to back up and burrow their bodies just beneath the surface of the sand. Some species leave their protruding eye stalks above the surface so they can watch for oncoming food (although they’re so tiny it would be quite difficult to spot them from above). Mole crabs are filter feeders, meaning they take advantage of the water moving around them to feed. As the tides roll in, mole crabs release their antennae and use these feathery tools to filter food like kelp, plankton and detritus. The crabs then pass their antennae over their mouths to release the gathered mixture of sand and nutrients.
Reproduction
These tiny creatures have a relatively short lifespan of about two to three years. When mating, males will sometimes attach themselves to females, becoming semi-parasitic until they eventually outgrow the area. Females are typically larger than males and carry orange eggs ranging as many as 45,000 on their undersides. That’s a lot of mole crabs.
Predators
For these small sand fleas, the crashing tidal waves aren’t their biggest threat. Many seabirds love to walk along the shore and search for mole crabs hiding just beneath the surface of the sand. Other species of crab and some fish also feed on these tiny sand fleas. Mole crabs face their hungry predators constantly which means their ability to hurriedly burrow into the dense wet sand is highly necessary for their survival. Against a predator, these tiny crabs’ best defense is a swift tide rolling in which allows the crab to quickly disappear into the sand.
Despite looking like a creepy crawly, mole crabs are harmless to humans and don’t bite or sting. So, unless you are part plankton, you have nothing to worry about. Their filter feeding techniques and tough exteriors render them amazing tenants of the intertidal zone and fascinating ocean animals that make the word “flea” seem less daunting. These creatures have their own little ecosystem right below our feet, unbothered as we walk along the sand above them. Perhaps on your next walk on the beach, you can shift your attention to the sand where you just might see a tiny sand hole fit for a mole crab.
Want to learn more about the weird and wonderful animals of the sea? Check out our Ocean Conservancy Wildlife Library to explore more fascinating creatures beneath the surface of our ocean.
The post Meet the Mole Crab appeared first on Ocean Conservancy.
Ocean Acidification
Dr Heidarzadeh’s TV interview with SkyNews on the massive M7.7 Panama earthquake on 9 October 2026
Dr Heidarzadeh’s TV interview with SkyNews on the massive M7.7 Panama earthquake on 9 October 2026. Click here for the full story.
Dr Heidarzadeh’s TV interview with SkyNews on the massive M7.7 Panama earthquake on 9 October 2026
Our ocean is an incredibly vast and mysterious place. And there is no place where that is more evident than the deepest ocean area in the world: the legendary Mariana Trench. Located east of the Philippines, the Mariana Trench lies in the Mariana Archipelago in the western portion of the North Pacific. The greater area of the Mariana Trench Marine National Monument is made up of more than 95,000 square miles of ocean. Beneath these waters lie incredibly complex aggregations of submerged islands and volcanoes … and of course, an astoundingly massive trench.
Dive in with us to have your biggest questions answered about the famed Mariana Trench.
How deep is the Mariana Trench?
The deepest part of the Mariana Trench, known as Challenger Deep, is almost 36,000 feet below the ocean’s surface. For context, Mount Everest is about 29,000 feet above sea level, so the Mariana Trench is about 7,000 feet deeper than Mount Everest is tall. For one more comparison, the RMS Titanic lies at a depth of about 12,500 feet below sea level. The Challenger Deep is in waters nearly three times deeper than this ship’s final resting place.
Due to its enormous size, the Mariana Trench has at times been affectionately nicknamed the Grand Canyon of the ocean. This is certainly a picturesque image, but don’t let the mammoth size of this U.S. national terrestrial park fool you into thinking the Mariana Trench matches its size. The trench’s footprint is estimated to be 120 times larger than the Grand Canyon’s, and to reach the bottom of Challenger Deep, you’d need to descend through almost six Grand Canyons stacked on top of each other before you’d reach the seafloor.
Oh … and did we mention it’s five times wider than it is deep? It’s about 43 miles wide!
What is Challenger Deep, and how long would it take to reach it?
Challenger Deep is the deepest point of the Mariana Trench. Fewer than 30 people have ever journeyed to this area. The trek below the surface is long, dark and time-consuming, and it’s not an expedition considered lightly by scientists and explorers.
The first people to descend into the depths of this area in 1960 were oceanographers Jacques Piccard and Don Walsh, and it took them close to five hours to reach Challenger Deep. Since then, more advanced submersibles have been created, but it still takes two to four hours for modern vessels to reach such depths. For example, explorer and filmmaker James Cameron reached the seafloor in a little more than 2.5 hours in the first documented solo submarine dive to the area, and it took oceanographer Dr. Dawn Wright about four hours in 2022. It is crucial that these submersibles descend slowly and steadily beneath the surface, as the immense water pressure compounds with every mile a submersible descends. Speaking of pressure …
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What is the water pressure at the bottom of the Mariana Trench?
If you thought the depth of the Mariana Trench was its only jaw-dropping feature, think again. Water pressure is one of the most important factors affecting deep-sea life. In the ocean, pressure increases by one atmosphere for every 33 feet (10 meters) of depth. One atmosphere (a unit of measurement for pressure equivalent to average air pressure at sea level) is equal to about 14.7 pounds per square inch (PSI), which is the approximate standard atmospheric pressure at sea level. If you were to convert atmospheric pressure into weight, one atmosphere is about the weight of a bowling ball. Stay with me, friends.
If a vessel were to dive 2,000 feet below the surface, the pressure would equal that of 60 bowling balls stacked atop every square inch of that submersible. But 60 bowling balls is simply nothing compared to the pressure in the Mariana Trench. The atmospheric pressure at the depths of Challenger Deep is equal to about 16,000 PSI. That pressure is about the same as the weight of an entire full-grown elephant on every square inch of a submersible!
Need a more extreme comparison? If a human were to be placed at the bottom of the Mariana Trench, the pressure would be equal to that of 50 jumbo jets piled on top of a person!
Do any animals live in the Mariana Trench?
The depths of the Mariana Trench come with immense pressure and extreme darkness, but somehow, life finds a way to survive. Organisms that live at an extreme depth, like that of Challenger Deep, have to be highly adapted to low temperatures (typically just above freezing), high pressure and virtually no light at all.
Species found in the depths of the Mariana Trench might look vastly different from animals from other ocean depths because their anatomy has been refined to thrive in harsh conditions. At such great depths, these animals typically depend on chemosynthesis (using nutrient-rich waters being pumped out of hydrothermal vents) or descending detritus (dead matter that has fallen from higher parts of the ocean) for food, such as whale falls. Just a handful of these animals include species of octopuses and squids, sea cucumbers, amphipods, sea jellies, shrimp, sea worms and some wild-looking fish!
In 2025, more than 7,000 new species were discovered in the Mariana Trench, including the hadal snailfish (Pseudoliparis swirei). This is the deepest-dwelling fish currently known to science. Now, the fish has been dubbed “the Mariana snailfish.”
How was the Mariana Trench formed?
The process by which the Mariana Trench was created is a geologically fascinating one known as subduction. On the Earth’s surface, there are thin plates that cover the planet’s mantle, which is made of molten rock. If two of these plates collide, one pushes down into the Earth’s mantle while the other is pushed over the bottom plate. When this happens, a trench is formed from the drag of the bottom plate. This process can sometimes create incredibly strong earthquakes. The plates that forged the Mariana Trench’s creation are estimated to be up to approximately 180 million years old.
This trench was unknown to scientists until 1875. It was then that a team of explorers on the HMS Challenger measured the depth of the sea by simply lowering a weighted rope into the water. They were baffled when they measured that first portion of the seafloor to be five miles below the surface. And so was born the origin of some of the most daring deep-sea explorations known to mankind to date.
Is the Mariana Trench protected?
The Mariana Trench is in waters off Guam and the Mariana Islands. The region is protected from some human activities under its status as a marine monument. The creation of the Mariana Trench Marine National Monument signified that international, national and local leaders all recognize the importance of protecting this area.
However, just because the region is protected does not mean it’s not vulnerable to modern threats to ocean health. Plastic bags have been spotted in the Mariana Trench during several expeditions, highlighting the far-reaching impact of the marine debris problem. No corner of our ocean is safe from the ever-present threat of plastic pollution. The reality of a changing climate makes the future well-being of wondrous places like the Mariana Trench uncertain. What’s more: More than 70% of the global ocean has yet to be mapped. And what we don’t yet know about, we cannot wisely work to protect.
It’s up to us to work together to defend our ocean, from the sandy shores of our favorite beaches to the deepest, darkest parts of the sea. Together, we can work to protect our ocean as a whole, which ultimately helps protect treasured places like Challenger Deep.
Find out how you can join Ocean Conservancy’s wave of momentum to secure a healthy ocean and a thriving planet, forever and for everyone!
The post The Mysteries of the Mariana Trench appeared first on Ocean Conservancy.
Intro
At the western tip of Luzon, which is the biggest island of the Philippines, lies the small coastal town of Bolinao. Tourists seldom find their way here as it takes around seven hours to get here by bus from Manila. Still, you can spot foreigners walking around every now and then, but they really stand out among the Filipinos. A reason for their presence is often that they study or work at the Bolinao Marine Laboratory (BML), which belongs to the University of the Philippines (UP). It is one of the seven research institutions participating in the GAME project 2026. Every year, GAME brings together Master’s students from all over the world to experience different cultures and conduct globally replicated experiments in marine ecology.
This year’s Team Philippines consists of Jona, a Filipino master student of Marine Biology at the University of the Philippines, and Konstantin, a German student who is enrolled in the Master programme „Ecology and Evolution“ at Freiburg University. As part of GAME 2026, we are currently staying at BML for 6 months to run experiments about the influence of underwater soundscapes on the colonization of marine hardbottoms.
Where are we?
At the BML, we live in a dormitory together with many other students and scientists mostly from the Philippines and a few international interns. At almost any time of the day there is someone in the kitchen to hang out with, eat together, or simply have a chat. It is easy to make friends in this little community. The way to work is just a short walk along a forest path, where we can pick mangos for a snack and spot butterflies, birds, or even wild macaques climbing through the trees. After crossing a street, we reach the institute. But instead of enjoying the cool temperatures of the laboratories, we spend most of our working days outside, doing fieldwork in or near the water.
On Fridays, Konstantin experiences real Filipino culture during an almost weekly party at the institute with karaoke and lots of food and drinks. And Jona even brought some German culture to the Philippines by baking German bread for everyone.
