Hamelin Cockle

Domain: Eukarya
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Cardiida
Family: Cardiidae
Genus: Fragum
Species: Fragum erugatum

When I wrote about Shell Beach, Australia, I mentioned the Hamelin cockle, Fragum erugatum. Today, I want to expand on what I wrote.

The Hamelin cockle is a bivalve that belongs to the phylum Mollusca, along with oysters, snails, and squids, to name a few. It’s native to the shallow shores of Western Australia, though it is prevalent in Shark Bay and Shell Beach.

Shark Bay is a hypersaline marine environment. Its seagrass beds restrict tidal movement, and the rate of evaporation is higher than the rate of precipitation, which makes the water really salty. In fact, the water is plankton-deficient because the high salinity makes it hard for plankton to survive.

So what does the cockle do for food? Isn’t it a filter feeder like many of its bivalve brethren?

Hamelin cockles are not strict filter feeders. Instead, they have a partnership with our favorite oceanic BFFs, zooxanthellae. Like coral, the cockle receives leftover food from the zooxanthellae in exchange for protection in well-lit waters. Fragum erugatum will siphon plankton from the water when they can, but it’s never enough to sustain them.

The soft body of the cockle is brown, and the photosynthetic algae live in the soft tissue. The shells are white and appear translucent in the light. Fun fact, zooxanthellae also help to collect calcium carbonate that the cockle uses to make its shell. The entire organism is less than 20 millimeters, which is a little smaller than an inch.

Hamelin cockles are hermaphrodites, meaning they have both male and female sex organs; however, they still need other individuals to reproduce. Between winter and spring, F. erugatum will release their gametes, or eggs, into the water to be fertilized by other Hamelin cockles. The fertilized eggs develop into zooplankton that float around in the water before they settle to the ground and further develop into cockles.

I find these bivalves to be every interesting. They entered Shark Bay over 4000 years ago and really put forth the effort to make the bay and Shell Beach their home. Most living things do not prosper in extreme conditions, especially in areas of high salinity. However, the Hamelin cockle not only adapted to the hypersaline water, but they prospered so beautifully that they left a noticeable mark in the local geology.

Four thousand years’ worth of cockle shells replaced the sandy beach of Shell Beach. Building material was made from the dense accumulation of these shells that, over time, became cemented together. It just blows my mind to think how successful these tiny little organisms are, and that makes them special!

Sources and links:
Ocean the Definitive Visual Guide made by the American Museum of Natural History
https://www.sharkbay.org/publications/fact-sheets-guides/hamelin-cockle/

Zebra Mussels

Domain: Eukarya

A colony of zebra mussels (Dreissena polymorpha), living in freshwater. Photo by Dr. Alex Mustard, find more at www.amustard.com

Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Myida
Family: Dreissenidea
Genus: Dreissena
Species: D. polymorpha

Today, we’re going to talk about zebra mussels. We’re not going to talk about zebra muscles like I had originally written down on my blog schedule. Honestly, why would I talk about the muscles of a zebra? They’re not even aquatic!

I know that was a lame introduction. It just doesn’t have enough strength to land a clever opening—maybe it needs more mussels…

Okay, I’ll stop!

Zebra mussels, D. polymorha, are freshwater bivalves native to Eurasia. Bivalves are shelled creatures; specifically mollusks with two shells that close together, like clams and oysters. Zebra mussels are about an inch long and are shaped liked a stretched out “D”. They are named from the black, zigzag patterning on their shells.

Humans can be so creative with their naming schemes.

Zebra mussels have a relatively short life span, between 2‒5 years, reaching reproductive maturity at 2 years of age. Each female can produce up to a million eggs per year, spewing them into the surrounding water and using the currents to transport the eggs.

The reason I’m bring up D. polymorpha is because it is an invasive species in the United States and Canada. The mussels were first discovered in the early 1980s near the Great Lakes and are believed to have been transported by accident in the ballast water of a ship. Since then they have been found in the Great Lakes, the Mississippi and St. Croix rivers, and the Chesapeake Bay.

Why are the zebra mussels bad for these environments? Don’t they help filter the water in their surroundings, and isn’t that a good thing?

In their natural habitat their job as filter feeders is absolutely amazing; in other habitats, it can have devastating effects. In fact, zebra mussels are so efficient as filter feeders that they can clean a body of water of particulates in record time, faster than the native filter feeders. But this is not a good thing.

The environments that the mussels invade have a special balance that is maintained by the native populations of animals. If you change one aspect of that balance, then it creates a domino effect.

Let’s say that we have an imaginary river, the River Sága, which is home to large, healthy beds of freshwater bivalves called blue purses (not a real bivalve). In this river there are also a few species of fish that go there to spawn and where the juvenile fish live until they’re big enough to move on. One day, an old fisherman dumps water into the River Sága from his boat and unknowingly releases several thousand eggs of the zebra mussel. A couple of years later, the river is no longer the same. The once-healthy beds of blue purses are now completely covered in smaller bivalves, smothering the native species. The water of the river is the clearest it’s ever been, but downstream there are enormous patches of algae, and there are no fish to be seen. What was once a nice fishing spot for man and animal alike is now barren, save for the zebra mussels and the algae.

Zebra mussels, like any invasive species, are horrible for the environments that they infiltrate because they have no natural predators, and they often outcompete the native species. Because zebra mussels are so good at filtering the water, it makes it easier for predators to find their prey in the water, whether it’s a larger fish or a bird hunting the juveniles that have spawned there. And because zebra mussels reproduce so much, they can easily smother their competitors, becoming the dominate species of the environment and changing it for the worse.

Zebra mussels also have an impact on human property. They have been known to block the drainage pipes of factories. They can incapacitate boats by clogging pipes and engines, or even by covering the sides of the boat and making it too heavy to float properly. It can take an absurd amount of money to remove them, and we have to do it often because they regularly come back and are so hard to eliminate.

I wanted to talk about zebra mussels because they have been noticed in the Chesapeake Bay, which is an important part of my life, and because it helps introduce the topic of invasive species. From what I understand, there is not much you can do once the zebra mussels appear, only that we must strive to prevent their spread elsewhere. But this also means that there is a potential opportunity for you, because maybe you can find a way to remove them from their nonnative habitats.

More information can be found:
https://www.chesapeakebay.net/discover/field-guide/entry/zebra_mussel
https://www.tn.gov/twra/fishing/twra-fish-species/zebra-mussel.html
https://www.invasivespeciesinfo.gov/profile/zebra-mussel
https://www.usgs.gov/faqs/what-are-zebra-mussels-and-why-should-we-care-about-them?qt-news_science_products=0#qt-news_science_products
https://www.nps.gov/articles/zebra-mussels.htm

Flamingo Tongue

A flamingo tongue (Cyphoma gibbosm) feeding on a seafan (Gorgonia ventalina). Cyphomas feed on corals and concentrate the toxic chemicals into their mantle, which they then wrap around the outside of its white shell. The mantle is brightly coloured to warn predators of its toxicity. The mantle also absorbs oxygen from the water. Photo and caption by Dr. Alex Mustard. Find more photos at www.amustard.com

Domain: Eukarya
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Order: Littorinimorpha
Family: Ovulidae
Genus: Cyphoma
Species: Cyphoma gibbosum

Please note: no flamingos were harmed in the making of this creature.

Honestly, I don’t know how they got they got their common name. These mollusks look nothing like flamingo tongues, and I should know because I’ve been staring at flamingo pictures for the past several minutes!

Cyphoma gibbosum are interesting mollusks to find on a reef. They have bright orange spots that are outlined in black on a creamy background, but the mollusks aren’t terribly big, averaging about 1‒1.5 inches long. When they’re young, they don’t have many rectangular spots, but as they get older, the spots get smaller and more numerous.

Flamingo tongues can be found on coral reefs in the Western Atlantic, from North Carolina to Brazil, in the Gulf of Mexico, and in the Caribbean Sea. They make their homes on gorgonian corals (soft corals), which is the only thing they consume—eating the soft tissue of the coral they sit on. Flamingo tongues use the chemicals from their prey in their own natural defense against predators by storing the chemicals in their soft tissue, the mantle, making them taste disgusting to most fish. Their predators include pufferfish, hogfish, and the Caribbean spiny lobster.

For those who don’t know—which until recently included myself—the bright spots that you see aren’t part of their shell. In fact, their shell is a very basic-looking cream color, and the spots that you’ll see when diving and snorkeling at a reef are actually the fleshy bits that hide the shell, called the mantle. When frightened, a C. gibbosum will retract into its creamy shell, pulling its colorful patterned mantle inside.

Unfortunately, the populations of C. gibbosum have decreased rapidly in recent years due to the increase activity of humans. Specifically, divers and snorkelers see these cool guys on the reef and think that the spots are part of their shell, so they decide to bring them back as a neat souvenir. When the creature dies, all that’s left is a simple shell sans the color and the spots.

Flamingo tongue shells have also boomed in popularity in the coastal jewelry business, so people will collect a lot of them to make their jewelry. As far as I’m aware, there is no data that can determine if the species is threatened or endangered and there are no regulations in place to protect them. However, that still shouldn’t stop us from being more aware of the situation and doing what we can to help, for instance know where the shells on your jewelry come from before you buy it.

I was lucky enough to spot a few of these guys while diving in Jamaica. I saw them the most when we went to a gorgonian-heavy reef, naturally, and the C. gibbosum were one of the cooler things to spot while swimming by. They’re small and can be easy to miss, but whenever I found one, I was mesmerized by it for a few beats before moving on. I think the coolest thing about them is their ability to be unaffected by the toxins the soft coral produce to deter predators, and they can use it to make themselves distasteful too.

Sources:
Ocean: The Definitive Visual Guide made by the American Museum of Natural History
Reef Creatures Identification: Florida, Caribbean, Bahamas 3rd Ed. By Paul Humann, Ned DeLoach, and Les Wilk
http://www.marinespecies.org/aphia.php?p=taxdetails&id=432297#links
http://species-identification.org/species.php?species_group=caribbean_diving_guide&id=410
http://www.thecephalopodpage.org/MarineInvertebrateZoology/Cyphomagibbosum1.html
https://oceana.org/marine-life/cephalopods-crustaceans-other-shellfish/flamingo-tongue
https://www.lamar.edu/arts-sciences/biology/marine-critters/marine-critters-1/flamingo-tongue.html