Tim Pearce

August 2, 2024 by Erin Southerland

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

Imagine you’re a clam, hanging out in your cozy little hole under shallow ocean water, with your siphon out, just filtering lunch out of the water current, happy as a…you. Then, all of a sudden, something flips you gently out of that hole.

You pull in your siphon and your foot, clamp shut your valves. You’re pretty tough to get open, strong adductor muscles keep your two shells held tightly together, and you’ve survived danger by closing up shop and waiting before. And nothing seems to be trying to pry you open, even though something has wrapped itself around you, and is now pulling you down into the sand with it. Then:

scrape scrape scrape

Or imagine you’re a young moon snail, Neverita duplicata – one of the most common species of moon snails that live on the eastern seaboard of North America. You’re a gastropod with a lovely round grayish shell, such that people call it a “shark eye,” and you’ve got a huge foot that can come out of that shell and cover almost all of your body – or all of your prey’s body! But at the moment you’re just cruising along the sand, slurping at a bit of detritus. Suddenly, you’re enveloped by something. You instinctively pull your body into your shell and tightly close your door-like operculum for safety. Then your aperture is covered by…something familiar? Then:

scrape scrape scrape

It doesn’t matter how tightly the clam clamps, or how mighty the young snail’s foot, both are going to come to the same fate, slowly.

scrape scrape scrape

Eventually, your shell is penetrated. A rasping radula – a mollusk’s organ containing its teeth – has bored a hole through your shell with the help of a gentle acid secreted by a gland by the mouth, and then you feel a burning: gastric juices are being pumped through the hole to begin to digest your flesh. Your killer begins to slurp you up, right where you lie, wrapped up in their hug, as you’re slowly eaten alive.

The young moon snail might have figured out who its killer was before the end: that’s how it eats too. The thing is, moon snails are cannibals, the larger preying on the smaller.

There are hundreds of kinds of moon snails all over the world, but the ones that are probably most familiar to beach goers on the eastern coast of the USA are two species also commonly called “shark eyes” – Neverita duplicata and Euspira heros. From the top, they’re hard to tell apart (the spire on E. heros is a little pointier than on N. duplicata) but once you flip them over, it becomes easy to distinguish them: N. duplicata, the Atlantic moon snail, has a big callus over its umbilicus, and E. heros, the Northern moon snail, doesn’t. Technically, only the Atlantic moon snail has a shark eye shell, but since they’re often mixed up with Northern moon snails, the term shark eye is sometimes applied to them too.

N. duplicata, left; E. heros, right. *Photo credit: Sabrina Spiher Robinson*

These two moon snails aren’t the only marine gastropods that drill their prey and digest them alive to suck them up for dinner – lots of marine gastropods are predatory drills. But moon snails have distinct boreholes that allow people to identify when a shell has been bored specifically by a moon snail – scientists can even tell the difference between the Atlantic and Northern species’ holes. These “countersunk” holes look like little funnels, wider on the outside of the shell than on the inside. Other kinds of drilling snails leave behind straight-sided holes.

These unique boreholes allow scientists to track the evolution of moon snails from the Miocene to recent times. One group of researchers found that moon snail cannibalism might have driven a kind of coevolution between and among moon snail species. Because one moon snail can make dangerous prey for a fellow moon snail predator, over time moon snails seem to have learned to drill other moon snails at a spot on their shells that allowed the predator to cover the prey’s entire aperture, preventing the strong foot of their prey from fighting back. This means boring through a thicker part of the shell, however, so it takes longer to hold down and bore through the prey snail’s shell. But the record of natural selection in fossils throughout time suggests the added cost must be worth the benefit of moving target drilling zones. Meanwhile, small moon snails almost always lose out to larger ones when attacked, so both N. duplicata and E. heros have evolved to get bigger and bigger over time – although a bigger snail is also a more enticing snack target. Same-sized moon snails don’t even bother to attack one another, suggesting that a fellow moon snail is just too dangerous a prey when the winner of the battle between snails is a toss-up. As evidence that these are often battles between predator and prey snails, there are many incomplete boreholes found – a moon snail started attacking another moon snail, but only managed to get the job halfway done before the prey moon snail escaped. [1]

To be fair, moon snails aren’t just vicious cannibals – they also enjoy the snail equivalent of a nice salad. Another study that analyzed the tissues of moon snails revealed that their bodies have the chemical signatures of omnivores. The technique is called stable isotope analysis, wherein scientists use the ratio of carbon and nitrogen isotopes in an animal’s body to determine its diet, in broad terms. Carbon exists in three isotope forms, meaning the number of protons is the same in all three atoms, but the number of neutrons is different in each (carbon-12, carbon-13, and carbon-14); Nitrogen also has three isotope forms, nitrogen-14, nitrogen-15, and nitrogen-16. The vast majority of carbon on Earth is carbon-12, which is a stable isotope, as is carbon-13, meaning they do not decay over time; nitrogen-14 and -15 are stable, and make up the vast majority of nitrogen atoms. Different plants and animals have different ratios of carbon and nitrogen isotopes. The ratios of isotopes in plants and animals differ and these differences transfer to the body of the consumer, and so the isotope ratios of a meat-eating animal will differ from those of a vegetarian animal, and an omnivorous animal will be different again. Scientists were surprised to find that wild moon snail isotopes suggested they also ate non-animals, so to check their findings they fed captive moon snails nothing but clams, and then tested their isotopes – which looked exactly as one would expect in an all-meat diet. Apparently the wild moon snails were actually eating things other than meat, probably algae. This was a big deal, since so much of the literature on moon snails is about their predatory drilling! [2]

Moon snail shells are a relatively common find on east-coast beaches (and another moon snail, Euspira lewisii, is a common find on the west coast), but if you’re at the beach this summer, there’s more to look for than just shells – moon snails also leave behind very distinctive egg nests, often called “sand collars.” The fertilized female snail nestles into a little hole in the sand (as all moon snails do during the day when they’re not feeding) and produces a sheet of mucus, which she mixes with sand and pushes up to the surface, as she does so, the sheet curls around her shell and eventually right around to form a ring. This fusion of mucus and sand grains solidifies, she attaches her thousands of eggs to it, and then covers those with another layer of mucus and sand. Once the eggs are ready to hatch after a few weeks, when the next high tide comes along the eggs let go thousands of little larvae called veligers, which will drift off to finish developing into baby snails who will eventually settle into the intertidal zone and start lives for themselves. Once the eggs hatch, the collar becomes brittle and disintegrates, but if you find one that’s still plastic-y on the beach, leave it! There are thousands of tiny baby vicious predators in there waiting to hatch! Awww.

*A sand collar full of shark eye eggs. Image credit: Blenni, Public domain, via Wikimedia Commons.*

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks and Tim Pearce is Head of the Section of Mollusks at Carnegie Museum of Natural History.

References

[1] Gregory P. Dietl and Richard R. Alexander, Post-Miocene Shift in Stereotypic Naticid Predation on Confamilial Prey from the Mid-Atlantic Shelf: Coevolution with Dangerous Prey PALAIOS Vol. 15, No. 5 (Oct., 2000), pp. 414-429

[2] Casey MM, Fall LM and Dietl GP, You Are What You Eat: Stable Isotopic Evidence Indicates That the Naticid Gastropod Neverita duplicata Is an Omnivore. Front. Ecol. Evol. 4:125. (2016) doi: 10.3389/fevo.2016.00125

The Busyconidae Whelks, Homebodies of the East Coast

by Sabrina Spiher Robinson and Tim Pearce

We try not to have strong favorites among the mollusks of the world in the CMNH Section of Mollusks, but it’s hard not to love the whelks. They leave behind big, beautiful shells for shell collectors on our east coast and Gulf beaches; they’re instantly recognizable as a family— Busyconidae — and pretty easy to tell apart at the species level by an amateur. Some of the species are sinistral, left-coiling snails, which are otherwise rare among gastropods. They live long and move slowly, reminding us all that slow and steady is an optimal way to approach life. They taste good! The traditional Italian American dish scungilli is often described as “conch,” but conchs only live in our warm southern waters, and what is usually sold in American markets for scungilli is actually whelk meat. (In Italy, they also eat sea snails, under a lot of different names, but the Mediterranean has different families of marine gastropods.)

three view of a lightning whelk — *The lightning whelk,* Sinistrofulgar perversum, a left-coiling gastropod. Public domain, via Wikimedia Commons.

Now, whelks are maybe not the most sophisticated of marine snails: unlike some gastropods with eye stalks and relatively good sight abilities, whelks have eye spots, which don’t do much more than detect light and dark. Studies of their sense of smell reveal them to have a tenuous ability at best to follow scent trails of prey in the water, and they’ve been observed just kind of slowly zig-zagging back and forth in the mud, apparently hoping to run into a clam. Once they find a clam, some whelks wedge the edge of their own shell between the valves of their prey, and just pry for as long as it takes to pop it open. Other species of whelk rock the edge of their own shells back and forth against the opening of a bivalve, slowly chipping its valves apart.

I mean, look: it isn’t much, but it’s honest work. Whelks are just a great family of sea snails. And Busycon whelks are endemic to the east coast of North America, meaning they’ve only ever been found here. Hometown heroes, if you will.

Our east coast whelks are committed homebodies partly because they evolved relatively late among mollusk families, in the Oligocene, a period spanning from 33.9 – 23 million years ago. The family Busyconidae first emerged in the fossil record in the Mississippian Sea, which had been a shallow extension of what is now the Gulf of Mexico that reached far inland along the route of what is now the Mississippi River. At the end of the Oligocene, the planet’s climate cooled and as ice formed at the poles, sea levels fell, eliminating this inland sea in North America — the whelks then found themselves in the Gulf.

Mollusks have existed on Earth clear back to the Cambrian Era, 540 million years ago. Most modern marine gastropod families began evolving earlier than the Busycons, which meant they were around when all the continents on Earth were one giant supercontinent called Pangea. But Pangea had already broken apart before the Busycons appeared in the fossil record.

Now, here’s the thing, if you are a marine gastropod only suited to shallow, intertidal waters, and you come into being along the coast of a supercontinent, given enough time, your family can spread around the entire coastline of that supercontinent. Then, as it begins to break up, your populations break up with it, and in a few dozen millions of years, your family has populations all over the Earth. But if you are a marine gastropod only suited to shallow, intertidal waters, and you come into being when the North Atlantic has already split from Europe, your family can’t make it across the open sea to go anywhere else. And so, the Busycon family of whelks found themselves in the Gulf of Mexico, near the shore, and began to spread from there, east and west, south and north, until today they exist from the Yucatan Peninsula up to about Cape Cod (it gets too cold for them further north).

five views of a knobbed whelk — *Knobbed whelk,* Busycon carica. H. Zell, CC BY-SA 3.0, via Wikimedia Commons.

Buccinidae whelks, however, can handle arctic cold. They first evolved in the Northeast Pacific Ocean, and they eventually spread along the coastlines across the Bering Strait and down onto the North American west coast, across the Canadian Arctic to the North American east coast and the European eastern Atlantic. They’ve actually made it almost everywhere! But Buyscons can’t take that kind of cold.

There are other factors that limit their spread, one is the ocean currents around the Gulf and western Atlantic. Although Cuba is just 90 miles from the Florida Keys, whelks, which are plentiful in Florida, have never managed to cross the Gulf Stream to colonize Cuba. But one of the main things that keep Busycon whelks from getting anywhere is that, unlike most marine mollusks, they never have a free-swimming larval form, in which they could disperse more widely on ocean currents. Most marine snails have a life cycle that starts with an egg and then proceeds after hatching to a free-swimming larva. Basically, most baby marine mollusks are plankton. And in this state, they can float around and sometimes disperse pretty far afield on ocean currents. As long as they end up in suitable habitat when it’s time for them to metamorphosize into their adult forms, marine mollusks can theoretically end up living hundreds of miles from where they were spawned.

But whelks don’t have this free-swimming period in their youth. Adult females are inseminated directly by males and then lay strings of egg cases (which are also reliably common finds on our eastern beaches) in which the little baby whelks grow and hatch as fully formed miniature snails. Then they just crawl off.

knobbed whelk egg case — *The egg case of a knobbed whelk,* Busycon carica. Gtm at en.wikipedia, Public domain, via Wikimedia Commons.

And they’re not very fast crawlers, even for snails. Whelks make their living by eating bivalves, but they’re never in a hurry to find them — in multiple observational studies over many decades, no one has ever seen a Busycon whelk move further than 150 meters in a day, and those go-getters were the outliers; many days whelks barely move at all. Many factors conspire to keep whelks close to their birthplace.

*The channeled whelk,* Busycotypus canaliculatus. Credit: Skye McDavid, CC BY-SA 4.0, via Wikimedia Commons.

Whelk populations are so localized that some researchers think it’s important to identify and treat separately groups of whelks in distinct geographic locations not at all far from each other. In 2022, several scientists at the Virginia Institute of Marine Science (VIMS) published a paper on channeled whelks (Busycotypus canaliculatus) documenting their genetic diversity in different geographic locations. They did this as part of a study of the channeled whelk population in general, to recommend how to manage the whelk fishery. (Whelks are increasingly harvested and sold as “conch” – and sometimes as clam strips!) In America, individual states manage their own fisheries of all kinds, but this isn’t always done well. In order to keep the fishing of any species (fish, mollusk, crab, shrimp, what have you) productive and sustainable, it’s important not to take more from the sea than can be replenished, and not to take animals that haven’t lived long enough to have reproduced (which is why some fisheries have size limits, as a proxy for the age and sexual maturity of the animal being harvested). But without good data on population size as well as age and size at sexual maturity, effective management and limit setting is basically impossible, and too often states don’t err on the side of caution. When allowable takes are too large, or allowed to include juvenile animals, the population of the fishery will plummet, and this has happened in different places and different times among the whelks. So, the VIMS project was meant to contribute data to help manage the whelk fisheries along the east coast sustainably.

The VIMS scientists caught whelks in ten different locations, from Buzzards Bay in Massachusetts down to Charleston, South Carolina, and sequenced their DNA. They found significant genetic divergence between the three sampled populations from the Carolinas and the populations in Virginia and north. But the scientists also found pretty big divergences across all the locations, even in populations as geographically close to one another as Virginia Beach, VA, and the Virginia Eastern Shore, about a hundred miles away across the mouth of the Chesapeake Bay.

Morphologically, all these whelks look pretty much alike, but genetically, they’re very isolated and distinct populations, with very little breeding among locations. Busycon whelks stay so close to home that each of their little geographically specific populations genetically diverge from one another since they never get far enough to meet and mate with whelks in other relatively close locations. The VIMS authors suggested that different whelk populations in different places might require different fishery management based on size at age of maturity, which seemed to change across genetically different populations. And so, it isn’t as simple as managing the “whelk fisheries on the east coast,” or even the “whelk fisheries in Virginia.” Because Channeled whelk populations are so isolated from one another, they might need to be managed as fisheries in Charleston, SC and Ocean City, MD, and so forth, specifically. [1]

After all that, I should tell you, though, that there is one exception to this east coast endemic story: at some point about a hundred years ago, a population of channeled whelks was introduced to San Francisco Bay. They’ve been prospering there ever since, but they can’t spread any further on the west coast because the water outside the bay is too cold for them. That’s an extremely genetically isolated population, in an unusual environment for Busycon whelks – maybe someday it might become distinct enough from its east coast forebears to become its own species?

[1] Askin, Samantha E.; Fisher, Robert A.; Biesack, Ellen E.; Robins, Rick; and McDowell, Jan, Population Genetic Structure in Channeled Whelk Busycotypus canaliculatus along the U.S. Atlantic Coast (2022). Transactions of the American Fisheries Society. DOI: 10.1002/tafs.10374

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks and Tim Pearce is Head of the Section of Mollusks at Carnegie Museum of Natural History.

Type Specimens: What are they and why are they important?

by Timothy A. Pearce and Rachel Thomas Beckel

What do we mean when we say we have type specimens in the Carnegie Museum of Natural History (CMNH) collections?

Type specimens are (usually) the specimen(s) a person describing a new species looks at as they write the description (it’s this tall, this wide, this color, sculptured with bumps like this, etc.) and type specimens are the official name bearers for the whole species.

There are many kinds of type specimens, but the most important kind is the holotype. Paratypes (other specimens the original describer believes are the same new taxon) are also important, but holotypes are the most important. Two other kinds of type specimen are lectotypes (selected from the paratypes if the holotype is lost) and neotypes (selected from any specimen if all type material is lost). Every time we add another holotype it bolsters the significance of CMNH’s already significant collections. It raises our visibility on the “radar” of researchers and puts us on the map for that taxon.

Carnegie Museum collaborator Dr. Aydin Örstan recently named a new subspecies of snail Albinaria coa tek (Örstan & Yildirim 2023). He deposited the holotype and 12 paratypes of the new subspecies in the Mollusks collection at CMNH.

*Holotype of* Albinaria coa tek *Örstan, 2023. Image from Örstan & Yildirim (2023).*

If a researcher wants to know if they have found another specimen of Dr. Örstan’s new subspecies, they could read his description. However, to be absolutely sure, a researcher might need to compare their finding to the type specimen.

Think of types as the gold standard. Because of their importance to nomenclature and taxonomy (the science of naming species), most museums (including CMNH) keep their type specimens securely locked in a special cabinet.

With regard to this land snail holotype, for Carnegie Museum to have the holotype of Albinaria coa tek means that people studying that subspecies or closely related taxa might need to travel to the museum to examine the type specimen or ask for additional information about it. For their research paper to be complete, they would need to refer to that holotype specimen. In addition to the holotype, Dr. Örstan gave CMNH paratypes of Albinaria coa tek, which can be important for understanding the range of variation in the subspecies.

Albinaria are land snails that occur in SE Europe and the Middle East and are typically found on limestone. In some cases, they appear to have been able to form new colonies when ancient humans moved limestone around for buildings (the snails likely hitchhiked on the limestone blocks). That means we can trace trade routes over which ancient humans were moving limestone.

The family Clausiliidae (which contains the genus Albinaria) are of interest because they bear a clausilium, a kind of door for closing the shell (hence the common name “door snails”), which is unique to the family and is very different from the operculum, which is a different kind of door in many sea snails and some land snails. Furthermore, most snails in the family Clausiliidae coil counterclockwise, which is the opposite direction of more than 99% of all other snails. Additionally, Clausiliidae have a peculiar global distribution, being found in western Europe, Eastern Asia, and northern South America. People who study biogeography (how species came to be living where they are now) scratch their heads wondering how Clausiliidae came to be living in those three separate places without any individuals being found in between – for example, if they migrated from Europe to northern South America, why don’t any Clausiliidae occur in North America?

In addition to this new holotype (and paratypes) in the Section of Mollusks, holotype specimens of new species of vertebrates and paratypes of a new species of insect were named in 2023 and deposited in the relevant sections of the CMNH collection:

Pietro Calzoni, from the Universitá di Padova, Italy, and colleagues designated a CMNH Vertebrate Paleontology fossil as the holotype of a new bony fish species, Rhamphosus tubulirostris (Calzoni et al. 2023).

Three new species of the insectivore mammal genus Plagioctenoides (P. cryptos, P. dawsonae, and P.goliath), and one new species of Cuetholestes (C. acerbus), were recently named from CMNH Vertebrate Paleontology fossils (Jones and Beard 2023).

A CMNH Vertebrate Paleontology gekko fossil was designated as the holotype of Limnoscansor digitatellus (Meyer et al. 2023). CMNH visitors can view this specimen on display in the Solnhofen case in the Dinosaurs in Their Time exhibition.

A male and six female moths from the CMNH Invertebrate Zoology collection were named the new moth species Meganaclia johannae (Ignatev et al. 2023). The moths were collected between 1918 and 1925 in Cameroon and were housed in the Invertebrate Zoology collection awaiting discovery as new species.

While CMNH welcomes hundreds of thousands of visitors per year to the public galleries, scores of researchers work behind the scenes to expand our understanding of the different kinds of organisms, as evidenced by their type specimens, that are present in our incredible world. As the moth example demonstrates, Carnegie Museum of Natural History (and other museums around the world) hold specimens that have yet to be recognized as new species!

Timothy A. Pearce is Curator of Mollusks and Rachel Thomas Beckel is Administrative Coordinator for Science & Research at Carnegie Museum of Natural History.

References

Calzoni, P., J. Amalfitano, L. Giusberti, M. Carnevale, and G. Carnevale. 2023. Eocene Rhamphosisdae (Teleostei: Syngnathiformes) from the Bolca Lagerstätte, Italy. Rivista Italiana di Paleontologia e Strigrafia, 129(3): 573-607.

Ignatev, N., G.M. László, A. Paśnik, Z.F. Fric, H. Sulak, and G.C. Müller. 2023. Five new species of the genus Meganaclia Aurivillius, 1892 (Lepidoptera: Erebidae: Arctiinae: Syntomini). Zootaxa, 5296: 457–474.

Jones, M., and K.C. Beard. 2023. Nyctitheriidae (Mammalia, ?Eulipotyphla) from the Late Paleocene of Big Multi Quarry, southern Wyoming, and a revision of the subfamily Placentidentinae. Annals of Carnegie Museum, 88(2): 115-159.

Meyer, D., C.D. Brownstein, K.M. Jenkins, and J. Gauthier. 2023. A Morrison stem gekkotan reveals gecko evolution and Jurassic biogeography. Proceedings of the Royal Society B., 290: 20232284.

Örstan, A., and M.Z. Yildirim. 2023. A new insular land snail, Albinaria coa tek Örstan, from Marmaris, Türkiye (Clausiliidae: Alopiinae). Archiv für Molluskenkunde, 152(2): 175-182.

The Hermit Crab and the Moon Snail

by Timothy A. Pearce and Mandi Lyon

When a snail needs a larger shell, it simply grows its shell larger, continuing the spiral. However, when a hermit crab needs a larger shell, it must find a larger shell to move into. Consequently, hermit crabs depend on snails to provide housing. Hermit crabs have soft abdomens, which are vulnerable to predators, so they keep their abdomens protected inside of snail shells.

There are amusing stories of several hermit crabs lining up in order of shell size, in a type of pecking order. When a new shell becomes available, the hermit crab highest on the pecking order holds onto the new shell and keeps a tight grip on its current shell as well. It tries out the new shell, and if it is an improvement, the crab will quickly move from one shell to the other, releasing the old shell. The old shell then becomes available to the next crab in the pecking order who examines it, and so on down the line.

Apparently, hermit crabs don’t kill snails to get the shells, but instead appear to move into already empty shells.

This series of photos was taken in the evening of August 12, 2017, at Amherst Shore Provincial Park on the Northumberland Strait in Nova Scotia. The photos show a hermit crab wearing the shell of a Dog Whelk (Nucella lapillus) encountering a Spotted Northern Moonsnail (Lunatia triseriata). The entire interaction took about a minute or so. The hermit crab approaches (Fig. 1) and climbs onto the moon snail (Fig. 2). The snail pulls its body into its shell and blocks the shell opening with its horny operculum, like a door that shuts the opening tightly (Fig. 3). The crab flips the shell over and the reddish colored operculum is visible (Fig. 4). The crab probes into the aperture (Fig. 5). Then the crab walks away (Fig. 6), evidently convinced that the shell is not available.

It’s hard to tell whether the hermit crab feels crowded in its current shell; it looks fine to us, but maybe hermit crabs are always on the lookout for better accommodations. The crab approached from the snail’s backside, so perhaps the crab didn’t notice that the snail is alive. The crab flipped the shell over, probed into the aperture where it bumped into the operculum.

How fortunate to be able to witness such an interaction, and to have a camera to record the episode!

*Fig. 1. Hermit crab approaches snail. Photo by M. Lyon.*

*Fig. 2. Hermit crab climbs onto snail. Photo by M. Lyon.*

*Fig. 3. Snail withdraws into shell blocking opening with operculum. Photo by M. Lyon.*

*Fig. 4. Hermit crab flips the shell over (note reddish operculum). Photo by M. Lyon.*

*Fig. 5. Hermit crab probes into the shell aperture, knocking on the door-like operculum. Photo by M. Lyon.*

*Fig. 6. Hermit crab walks away. Photo by M. Lyon.*

Mandi Lyon is the Program Manager for Schools & Groups and Timothy A. Pearce is Curator of Mollusks at Carnegie Museum of Natural History.

Oysters Swim Towards a Siren Soundscape

by Sabrina Spiher Robinson

illustration of a walrus and a person on a beach looking at oysters with feet — *Illustration by Sir John Tenniel. Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License.*¹

“’O Oysters, come and walk with us!’

The Walrus did beseech.

‘A pleasant walk, a pleasant talk,

Along the briny beach:

We cannot do with more than four,

To give a hand to each …

Four other Oysters followed them,

And yet another four;

And thick and fast they came at last,

And more, and more, and more—

All hopping through the frothy waves,

And scrambling to the shore …

‘O Oysters,’ said the Carpenter,

‘You’ve had a pleasant run!

Shall we be trotting home again?’

But answer came there none—

And this was scarcely odd, because

They’d eaten every one.”

In 1872, Lewis Carroll included the poem “The Walrus and the Carpenter” in his classic book Through the Looking Glass. The Walrus calls out to the oysters to join him and the Carpenter on a walk along the seashore; the young oysters don’t know any better and come to join him. Eventually, all the oysters are eaten up. But can one really sing a siren song to make an oyster come to them? An informed answer to this question requires some background knowledge information about an underappreciated form of wildlife.

oyster shells on cultch in a box — *The favored subsurface described as “cultch” is depicted in this cluster of oyster shells of the species* Crassostrea virginica.

Oysters live in reefs, submerged ridges or mounds of stable material, and baby oysters prefer to settle on a base — called “cultch” — of old oyster shells. Where conditions are favorable, oysters have plenty of company. When a team of researchers investigated the diversity of oyster reefs in the Gulf of Mexico, they detailed the incredible number of creatures that live on the reefs where oysters form: 115 species of fish and 41 species of crustaceans made the Gulf oyster reefs their homes, at very high densities and in communities containing up to 52 species at a time. Other researchers have documented multiple corals, mollusks, and worms that live primarily on oyster reefs. Unfortunately, erosion from coastal development, wetland destruction, unsustainable harvesting, and pollution have decimated populations of the Atlantic coast’s native oyster, Crassostrea virginica, which is bad news for coastal marine habitats in general.²

The importance of oyster reefs as marine habitats for multiple species is only one reason to preserve and reconstruct them. Oysters, as filter-feeding animals, provide an incredible service to the water quality of the estuaries they inhabit. They are also, of course, an important food source along America’s east coast.

The complications of rebuilding and repopulating oyster reefs are many. Pollution must be reduced, especially the run-off of agricultural fertilizers. Such fertilizers “enrich” underwater environments in a process called eutrophication.

Eutrophication causes massive blooms of algae that set off a chain of events disastrous for bodies of water and their inhabitants: the algae can release toxins on its own, but most commonly it overwhelms host ecosystems by blocking sunlight and killing all of the other plants in the water. Eventually the algae die too, and as all these dead plants decay, eaten away by multiplying bacteria that use up what little oxygen is left, dead zones form that suffocate underwater animals. This decay also lowers the pH of the water, leading to acidification that harms and kills animals (especially mollusks, whose shells dissolve in a very acidic environment). Additionally, if sediment erosion is not reduced, these water-borne materials eventually bury and suffocate oysters.

Oyster bed substrates that have been destroyed by human construction or aggressive commercial dredging can be replaced with cultch that is attractive to baby oysters. However, baby oysters must be recruited to the rebuilt reefs, either from the natural population of oyster larvae, or from hatchery-grown larvae reintroduced to the environment.

So, how to attract a baby oyster to your newly constructed oyster reef? First, let’s consider the life cycle of C. virginica, and the critical importance of age range in young oyster populations. In the first year of their adult lives, oysters are male. At certain times of the year, in response to pheromonal cues from their fellow oysters on the reef, they release clouds of billions of sperms. Older oysters on the reef, creatures transitioned into females after a year or two of life, release millions of eggs into these clouds of sperm. About two days after an egg is fertilized, the oyster larvae have become what are called veligers, and they begin to feed on particles in the water and to seek a place to call home. During this time, they develop a foot, and once they arrive on some promising substrate, they can crawl around, looking for just the right spot. At this point they are called spat. Soon the spat lose their feet and cement themselves to the spot they will call home for the rest of their lives, which can be more than a dozen years in the wild.

small boxes of oyster shells — Crassostrea virginica, from the CMNH collection, multiple shells that look completely different, but represent a single species. Epicures report taste differences according to where exactly each oyster lived.

It was long unknown how much choice an oyster veliger had in determining where it landed. Until the 1990s scientists thought that baby oysters had very little control over their movement in the water. In 2022, Australian scientists studying the Australian flat oyster, Ostrea angasi, proved that oyster veligers could very deliberately move to get to a surface they preferred to make their permanent home on.³

How this discovery occurred is of particular interest. The Australian researchers were testing the effects of soundscapes on oyster larvae, following experiments conducted in America in Pamlico Sound in North Carolina. Soundscapes are the collective sounds of a given environment: all the noises of human and non-human animal activity, along with environmental sounds of wind and water and precipitation. In 2014, researchers in North Carolina were experimenting with ways to attract oyster larvae to their newly built conservation reefs. They discovered that by recording the soundscape of a healthy oyster reef and playing it in the water, they attracted a much higher number of spat on experimental tiles near the recordings. Apparently, the baby oysters heard the sound of a healthy oyster reef and headed towards it to make their homes.⁴

How do oysters hear? Humans and other land animals hear through a system of air compression. Sound waves compress air in certain patterns, and tiny hairs within our ears translate those compressions into electrical signals that are then sent to the brain for further interpretation as sound. Underwater, animals hear through particle vibration: sound waves vibrate from particle to particle in the denser medium of water, where the particles are in direct contact with one another, even the water contained in the bodies of fish and invertebrates. Underwater animals have sensing structures that translate these vibrations into electrical signals that the animal then interprets in some way.⁵

Following up on the work of the North Carolina scientists, the Australian scientists confirmed in lab studies using underwater speakers in a completely currentless body of water, that oyster larvae were deliberately swimming towards the sounds of a healthy reef to settle. When they tried this technique on human-made conservation reefs, oyster recruitment increased on the artificial cultch — an important finding, since if baby oysters don’t find the newly deployed conservation reefs quickly, the reefs become covered in algae, making it very difficult for oyster spat to attach to them.⁶

And so, recording and replaying the soundscape of a healthy oyster reef — populated by snapping shrimp, oyster toadfish, and many other creatures that call a healthy oyster reef home — can help with the recruitment of baby oysters to human-made reefs for the purposes of conserving and growing the endangered population of C. virginica. Not only can oyster larvae “hear,” they can — and will — very deliberately swim toward the sounds of a healthy reef. And truly, who amongst us could deny the siren song of the snapping shrimp and the oyster toadfish?

Listen:

Coastal Conservatory

Center for Marine Sciences and Technology (CMAST)

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks at Carnegie Museum of Natural History.

Notes:

Science Museum Group. Magic lantern slide depicting Alice’s Adventures in Wonderland, Walrus, Carpenter and Baby Oysters. 1951-316/11Science Museum Group Collection Online. Accessed 9 January 2024. https://collection.sciencemuseumgroup.org.uk/objects/co8362656/magic-lantern-slide-depicting-alices-adventures-in-wonderland-walrus-carpenter-and-baby-oysters-lantern-slide.
La Peyre Megan K., Aguilar Marshall Danielle, Miller Lindsay S., Humphries Austin T. Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis Frontiers in Marine Science, Vol. 6, 2019 https://www.frontiersin.org/articles/10.3389/fmars.2019.00666
Williams, B. R., McAfee, D. & Connell, S. D. Oyster larvae swim along gradients of sound. Journal of Applied Ecology, Vol 59, 2002, pp. 1815–1824 https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.14188
Ashlee Lillis, David B. Eggleston, DelWayne R. Bohnenstiehl Oyster Larvae Settle in Response to Habitat-Associated Underwater Sounds PLOS ONE 9(1). October 30, 2013 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079337#amendment-0
Nedelec, S.L., Campbell, J., Radford, A.N., Simpson, S.D. and Merchant, N.D. Particle motion: the missing link in underwater acoustic ecology. Methods Ecol Evol vol 7, 2016, pp. 836-842 https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12544
McAfee, D., Williams, B. R., McLeod, L., Reuter, A., Wheaton, Z., & Connell, S. D. Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations. Journal of Applied Ecology, vol. 60, 2023, pp.111–120 https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.14307

Shark-ish Beasts Versus Cephalopods: Which is Predator, Which is Prey, and is One an Artist?

by Sabrina S. Robinson and Timothy A. Pearce

We’ve all heard the legend of the sperm whale and the giant squid, locked in epic battles in the waters of the deep, like that imagined in Jules Verne’s 20,000 Leagues Under the Sea (and yes, sperm whales do love to eat giant squids). If one substituted a shark for the whale, most of us would think the squid — or its relation, the octopus — wouldn’t have much chance. But that assumption might be wrong…and in fact, evidence from nearly one hundred million years ago hints at surprising mortal interactions between shark-like vertebrates and cephalopods.

Octopuses vs. Sharks

In 2000, with some trepidation, a Giant Pacific Octopus was placed in a large tank with sharks at the Seattle Aquarium. At the time, some aquarium staff wondered whether the octopus would be attacked by the sharks. It turned out that the trepidation was justified, but for precisely opposite reasons: sharks started disappearing (and perhaps the octopus began to look too self-satisfied). Several years later a video, which subsequently went viral, was filmed at the aquarium showing an octopus attacking and eating a dogfish shark. As in many videos produced for nature documentaries, the creatures were subject to human interference (not to ruin nature documentaries for you); divers directed dogfish toward the octopus. Despite this meddling, the fact remains: sharks, beware.

*Credit: A sperm whale attacks a giant squid. Colour line block after A. Twidle. Wellcome C o llection. Public Domain Mar*k

Ammonites vs. Mosasaurs

Ammonites and ammonoids were ancient cephalopods that became extinct at the end of the Cretaceous. Fossilized ammonite shells have been found with indentations that some paleontologists interpret as bite marks from mosasaurs. (An alternate explanation is that the mosasaur bites were holes made by limpets, marine gastropods, some species of which scrape holes into calcium carbonate surfaces, such as other shells [Seilacher 1998], although some paleontologists continue to defend the mosasaur bite hypothesis [Tsujita & Westermann 2001]. Mosasaurs were part of a group of extinct ocean-going reptiles, having the body form and presumably the behaviors of sharks. In other words, this mollusk vs. shark(ish) conflict might be a blood feud going back 90 million years or more.

So, let’s say that it was mosasaurs (and not nibbling limpets) snacking on the ammonites, and that all of this adds up to a pattern, leaving the question: do the mollusks or the sharks and shark-like reptiles have the intellectual advantage in the fight? Modern squids and octopuses, collectively classified as coleoids, are famous for their intelligence and quick wit. It’s difficult to know whether ammonites shared this cleverness — coleoids and ammonites descend from a common ancestor known as a bactritid, and we don’t know how intelligent this ancestral creature was. The modern chambered nautilus, resembling ammonites though not closely related to them, does not seem to be very smart (but it does have a remarkable memory).

Squids vs. Ichthyosaurs

Here is additional possible evidence of ancient intelligence shaping the feud between mollusks and shark-like reptiles. Fossils of shell-less cephalopods are rare, but the creatures’ presence in the fossil record is sometimes detectable through their preserved bird-like beaks and gladii (singular is gladius), a hard pen-shaped internal structure of squid. The beak remains of a large fossil squid with a body length estimated to be at least 10 meters were found in Nevada near multiple ichthyosaur vertebrae arranged in an unusual pattern. This peculiar circumstance, which had been seen elsewhere in the fossil record, led at least one paleontologist to speculate that the bones had been deliberately arranged by a large squid (who presumably killed the vertebrate), perhaps as a self-portrait! Ichthyosaurs, like mosasaurs, are shark-like in body plan and (presumably) behavior.

Of course, this is a highly controversial idea — but creatures making art on the seabed has at least some precedent. In 2011, Matsura Keiichi solved a mystery in the sands of the sea floor around the Ryukyu Islands, a chain of Japanese islands on the boundary between the East China Sea and the Philippine Sea. Complex and beautiful circular patterns had been found by divers in these underwater sands for years. It was finally discovered that the white spotted pufferfish (Torquigener albomaculosus), was making these works of art as a courtship display, carefully constructing and maintaining them, until a female, enticed by their sculpture, spawned in the center of the circle, leaving the artistic male to care for the eggs. (See a video of one adorable little guy making his art on PBS.) So underwater art is a known explanation for strange seabed arrangements.

We’re reminded of the Arnold Schwarzenegger movie Predator, in which the Predator’s trophies from its kills were spinal columns. Could this ancient kraken have been the original Predator, collecting its victims’ spinal columns? Constructing displays with them to attract mates??

Which reminds us of a joke. Tim’s friend called him on the phone to say he was changing his name to Spinal Column. Tim asked, “Umm, can I call you Back?”

Sabrina Robinson is a volunteer in the Section of Mollusks. Tim Pearce is Curator of Collection in the Section of Mollusks.

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

References

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