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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.

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.

Meet the Mole Crab

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Ocean Acidification

The Strata that Matta

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From Desert to Seafloor

Fig. 1) team Strata That Matta: Victoria C., Maeghan D., Maddie B., Vale B. (from left to right)

The months leading up to OCEAN CORE Academy were filled with another type of adventure for me, surveying the badlands of New Mexico in search of dinosaur bones. Yet, my work in the Gulf Coast Repository consisted of examining ocean cores using a microscope. Although these experiences couldn’t be any more different, the two were similar in that each attempted to answer the same question: what did Earth look like in the past?

I focus much of my research on vertebrate paleontological and geological fieldwork, such as prospecting for fossils, measuring strata, or describing ancient paleoenvironments and faunal assemblages. While I knew about microfossils, I had not fully grasped how much geological history is present in them.

 Fig. 2) fieldwork, NM (May 2026)

History Through a Microscope 

This leads me to one of the most memorable parts of OCEAN CORE Academy, learning to prepare smear slides and identify what existed within the ocean cores. Ocean sediments are fairly recent in that they have not yet been lithified, each layer represents tens to hundreds of years of depositions onto the seafloor. What I looked at was much deeper!

It was a momentous occasion when I first saw a radiolarian beneath the microscope! These tiny fossilized organisms provide surprisingly detailed insights into ancient environments. The conditions in which different groups of microfossils thrive vary, but by tracking how they fluctuate between layers, we can reconstruct climatic shifts over geologic time.

Team Strata That Matta correlated a transition from calcareous to siliceous ooze layers with a cooling climate!

Fig. 3) my first time seeing microfossils

                   

Fig. 4) radiolarian                                                Fig. 5) coccolithophores                                          Fig. 6) sponge spiccules 

Bringing OCA Back to AZ   

Upon my return to Arizona, I will carry this new perspective with me. As I move forward with future projects and field seasons in New Mexico, volunteer at the Arizona Museum of Natural History, and pursue my degree, the skills I developed here will prove to be invaluable for strengthening my own research.

Prior to attending OCEAN CORE Academy I viewed microfossils as existing, yet somewhat separate from my projects. This place has challenged that perspective. I came to understand that many of the most detailed records of Earth’s past are the microfossils hidden within a single grain of sediment!

Fig. 7) class of OCA 2026 

Written by OCA 2026 student, Maddie Baare

The Strata that Matta

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Ocean Acidification

Earth’s History at Every Scale

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From Desert to Seafloor

Fig. 1) team Strata That Matta: Victoria C., Maeghan D., Maddie B., Vale B. (from left to right)

The months leading up to OCEAN CORE Academy were filled with another type of adventure for me, surveying the badlands of New Mexico in search of dinosaur bones. Yet, my work in the Gulf Coast Repository consisted of examining ocean cores using a microscope. Although these experiences couldn’t be any more different, the two were similar in that each attempted to answer the same question: what did Earth look like in the past?

I focus much of my research on vertebrate paleontological and geological fieldwork, such as prospecting for fossils, measuring strata, or describing ancient paleoenvironments and faunal assemblages. While I knew about microfossils, I had not fully grasped how much geological history is present in them.

 Fig. 2) fieldwork, NM (May 2026)

History Through a Microscope 

This leads me to one of the most memorable parts of OCEAN CORE Academy, learning to prepare smear slides and identify what existed within the ocean cores. It was a momentous occasion when I first saw a radiolarian beneath the microscope!

Before, I had been hunting for fossils measured in centimeters/meters, but now I am studying those measured in micrometers. These tiny fossilized organisms provide surprisingly detailed insights into ancient environments. The conditions in which different groups of microfossils thrive vary, but by tracking how they fluctuate between layers, we can reconstruct climatic shifts over geologic time.

Using these changing microfossil assemblages, my team correlated a transition from calcareous to siliceous ooze layers with a cooling climate!

Fig. 3) my first time seeing microfossils

Fig. 4) radiolarian                                           Fig. 5) coccolithophores                                          Fig. 6) sponge spiccules 

Bringing OCA Back to AZ   

Upon my return to Arizona, I will carry this new perspective with me. As I move forward with future projects and field seasons in New Mexico, volunteer at the Arizona Museum of Natural History, and pursue my degree, the skills I developed here will prove to be invaluable for strengthening my own research.

Prior to attending OCEAN CORE Academy I viewed microfossils as existing, yet somewhat separate from my projects. This place has challenged that perspective. I came to understand that many of the most detailed records of Earth’s past are the microfossils hidden within a single grain of sediment!

Fig. 7) class of OCA 2026 

Written by OCA 2026 student, Maddie Baare

Earth’s History at Every Scale

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Ocean Acidification

Microplastic Pollution Research at Sea

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I have been studying plastic pollution for more than a decade. I’ve analyzed hundreds of samples in labs, pored over data and spent years thinking hard about where plastics go once they leave our hands and enter the environment. I love doing work on the water—this was a big part of my previous professional roles in Alaska and in Saipan, Northern Mariana Islands.

And here’s where it took me! I was thrilled to have the opportunity to join the first leg of eXXpedition’s voyage in the South Pacific this past spring, trading my lab coat for a lifejacket to study microplastics at sea. Sailing from Auckland, New Zealand, to the Bay of Islands aboard the 70-foot research vessel Wind Shift over 10 days, our crew of 12 women conducted ocean water-surface sampling via manta tow nets (a long cone-shaped mesh net), cleaned up debris on remote beaches and examined city streets with measuring tapes and field equipment. Our purpose? To collect key data to help us better understand the flow of plastics from land to sea.

Our all-female guest crew—hence the XX in “eXXpedition”—brought aboard expertise from the fields of structural engineering, circular economy strategy, sustainable fashion, plastics research, robotics and more. Together, we represented a remarkable cross-section of disciplines united around a shared concern for the health of our ocean.

Seeing it with my own eyes

We found plastics of all shapes and sizes everywhere we went—in the city streets of Auckland, while crossing the Hauraki Gulf and even at Aotea Great Barrier Island (one of the most remote and protected stretches of New Zealand’s coastline). Our ocean is vast and some of these places felt far removed from the centers of human activity, but this eXXpedition was a good reminder that plastic doesn’t respect remoteness. It moves, accumulates and shows up where we least expect.

Working alongside local NGO Sustainable Coastlines, we arrived on a remote stretch of beach on Aotea Great Barrier Island to audit and clean up any plastics we came across. What we found there told the same story our Auckland street surveys did: We found bottle caps, food packaging, fragments, plastic pellets and fishing debris. The everyday materials of modern life—but weathered, broken and scattered.

Science at sea

One of my favorite parts of the voyage (which was also one of the most challenging, if I’m being honest!) was the sea-surface manta trawl analyses we did onboard. I found out quickly that sorting microplastics from krill-laden seawater samples under a microscope while sailing is not for the faint of stomach.

The most common plastic culprit we found in those samples? Microplastic fibers. This type of microplastic is no wider than a human hair and is the most common type of microplastic found in the environment. Microplastic fibers can come from a variety of sources like cigarette butts, weathered ropes or wet wipes, but actually, most microplastic fibers shed from synthetic clothing and textiles. Laundering is a major source— shockingly, a single load of laundry can generate up to 18 million microfibers.

And yet, we found these tiny plastic fibers floating in the ocean many miles away from the nearest washing machine.

In my lab research, I have found microplastic fibers time and time again, but there’s something even more sobering about hand-picking them out of a seawater sample collected from pristine-looking waters. It was a good reminder of why understanding where plastic comes from, how it moves and where it ends up is so critical to addressing the problem at its roots.

Filter Out NSFW Microplastics
Tell your elected officials to take action against plastic pollution by requiring microplastic fiber filters! Adding your name takes less than two minutes, and goes a long way in protecting our ocean, forever and for everyone.

What I’m bringing back

Studying plastic pollution from the deck of a boat in some of the most remote waters in the Southern Hemisphere made me appreciate the work I do even more. It also made me appreciate how important people are in this giant puzzle of plastic pollution solutions. The plastic pollution crisis is a human problem, and solving it requires all of us. The courage and dedication of the women I shared those 10 days with is something I won’t forget. Going to sea, doing the science and pushing through discomfort to collect data that matters was not easy. We were seasick some days and exhilarated others. Despite that fact, we showed up for it fully, every day.

The plastic is out there, even in far-flung corners of the ocean. And the answer is not to be paralyzed by that fact, but to use it as fuel. Every sample we collected is now a data point in a larger story about where plastic comes from and where it goes. Every cleanup, every surface trawl, every street block walked and every hour spent at a microscope are parts of building the evidence base that informs policies, regulations and systems-level changes that can actually turn this crisis around.

Cleaning up beaches and coastlines is valuable and necessary work. But we also must stop plastic from entering the ocean in the first place—through stronger policy, better product design and real investment in waste management infrastructure everywhere. Luckily, when it comes to the most common microplastics in the ocean— microplastic fibers—there is already an effective, affordable solution to immediately reduce microplastics coming from our laundry by roughly 90%: washing machine filters. These filters act just like laundry lint filters in our dryers, capturing fibers in tightly-woven mesh and effectively preventing them from leaving our homes and leaking into the environment.

What can you do?

There’s no better time to tackle plastic pollution than right now, during Plastic Free July™! Take two minutes to add your name and call on your elected leaders to combat those pesky, dangerous microfibers that are pouring into our ocean daily—like the ones I found from my samples at sea. Together, we can stop plastic pollution at the source and protect our ocean forever and for everyone.

My biggest takeaways from this experience? People are remarkable. Our ocean is remarkable. And our ocean is worth fighting for, including from 70 feet of sailing vessel in the South Pacific, staring down a microscope with a pair of tweezers and a queasy stomach.

The eXXpedition South Pacific I voyage ran from April 27 to May 6, 2026, sailing from Auckland to the Bay of Islands. Learn more about the research team and our itinerary at https://exxpedition.com/voyage/auckland-to-bay-of-islands/.

The post Microplastic Pollution Research at Sea appeared first on Ocean Conservancy.

Microplastic Pollution Research at Sea

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