A lionfish (Pterois volitans) rises up from the reef to hunt silversides. Photo taken by Dr. Alex Mustard, you can find more at

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygi
Order: Scorpaeniformes
Family: Scorpaenidae
Genus: Pterois
Species: Pterois volitans

When talking about invasive species, I mentioned the lionfish. Can they hurt you? Yes. Are they devastating Atlantic coral reefs? Yes. However, they are not evil fish, despite one of their other common names: the devil firefish.

Pterois volitans is a beautiful fish native to the tropical waters of the eastern Indian Ocean and the western Pacific Ocean. They can be found in depths of 7−180ft (2−55m) near seagrass beds, coral reefs, artificial reefs, and sunken ships. I’ve seen them hiding in crevasses or overhanging ledges on the reef.

When diving, lionfish can be fairly easy to identify. Along the head and body of the fish are alternating maroon and white strips, stretching from top to bottom. Long, unique, fan-like fins, with the same stipe pattern, help the lionfish corner its prey against a reef or hard surface. Along the top, are long striped spines that you want to avoid.

Lionfish are carnivorous fish that prey upon shrimp, crabs, and more than 50 species of fish. In their native habitats, they help to keep the reef healthy, and their populations are controlled by the few predators that eat lionfish, including a couple of species of moray eels and the bobbit worm.

In the Atlantic Ocean, however, they can eat all the available prey in a given reef if gone unchecked. With no natural predators in the Atlantic, and the fact that they produce a lot of eggs each year, their populations have boomed while the populations of herbivore and commercial fish have decreased.

Despite their invasion of the Atlantic, lionfish are quite important. Whether it’s in the Pacific, Indian, or Atlantic Ocean, Pterois volitans provides food and income to the coastal communities. Divers pay good money to see lionfish, and the fish is often the target of many spearfishing tournaments in the Atlantic. You can win hundreds of dollars, depending on where you sign up! Because they’re so distinctive, lionfish can be easy targets for divers.

P. volitans are also quite popular in home aquariums around the world. Their unique coloring and flamboyant fins make for a great conversation starter at a party! Just a reminder, though: if you’re getting rid of your aquarium fish, please don’t dump them in the ocean closest to you. Take them to your local aquarium and ask for help. You never want to dump a potential invasive species in your ocean.

Another common name for lionfish is tastyfish. When I was studying in Jamaica, our dive teams would always bring spear guns, and we would hunt lionfish while exploring or doing research. When we’d come back to the lab, we’d clean them and give them to the lab’s cafeteria. Let me tell you, those wonderful ladies made some amazingly spicy lionfish!

If we make it more popular to eat lionfish, then that will help solve the population issues in the Atlantic, and it will help take the pressure off some of our commercial fish. So, the next time you’re at your local fish market or restaurant, ask for lionfish and let the owners know you’re interested!

The coloration of a lionfish is a special adaptation called warning coloration, which indicates to potential predators that it’s unsafe to eat the lionfish. In this case, the warning is legitimate. In the spines along the top are glands that store venom. When the spines puncture the skin the glands release the venom into the wound. The venom can cause excruciating pain, sweating, paralysis, and respiratory distress; rarely has it been fatal to humans.

I had a couple of classmates get stung by lionfish. One kid got stung by a live one they didn’t see in the reef, which is why you never reach your hands into areas you can’t fully see. Another kid got stung when handling a dead lionfish. In both cases, they had to be rushed to the doctor, but even after being treated, the wounds remained quite painful for a while. So please be careful while diving around lionfish or when handling them!

Lionfish (Pterois volitans) fritters offered as an after dive snack. Photo taken by Dr. Alex Mustard, you can find more at

Sources and links:
Ocean: The Definitive Visual Guide by the American Museum of Natural History ←lionfish recipes you can try at home!

Invasive Species

Invasive is such a harsh word. How can a natural creature be considered an invasive species? Nobody likes weeds, but everyone likes pretty fish and colorful birds—so, how can those be considered dangerous?

An invasive species is any living organism that is found outside of their native environment and has or will cause harm. The harm it can cause can be to the nonnative environment itself, the economy, or humans, or a combination of the three.

The zebra mussels that I’ve spoken about are an example of an invasive species in the United States. They are native to the freshwaters of Eurasia but somehow made it to the United States in the 1980s. Wherever the zebra mussels have been found, outside of Eurasia, they have outcompeted all native species and have changed the environments that they have invaded.

Another example is the lionfish. Its native habitat is the Indo-Pacific Ocean, however, it has made its way to the Atlantic Ocean. It reproduces rather successfully and has no natural predators in the Atlantic waters, so it has decimated many coral reef populations by devouring the herbivorous fish that help keep the reefs clean of algae. Without the algae eaters, the coral are smothered by the thick blankets of algae that naturally grow on them.

Not all invasive species are easy to comprehend at first. For instance, in many countries, domesticated cats and dogs are considered to be invasive species. How can Mittens or Spike be considered invasive? Humans absolutely love them and they (mostly) love us!

Dogs, and especially cats, are considered invasive species in many countries outside of Europe. They were brought over during the time of colonization, and their populations quickly grew unchecked. Dogs threaten native small animal populations, and cats wreak havoc on the native bird populations. For example, the Galapagos penguin population has been hit hard by the invasive house cat populations in South America.

Invasive species don’t have to look exotic. Sometimes they look normal, or they’re hard to notice at all. Invasive species can include plants, animals, fungi, insects, and microbes. And their effects on the local populations can be devastating, as when settlers first encountered native people, and the germs the settlers brought with them killed a lot of the native people of the land who did not have the same immunities built up as the settlers did.

Invasive species can also cause harm in other ways. New microbes introduced to an area can cause illness in people. Insects that have hitchhiked in shipping containers can run wild in new places and hurt the people there, like invasive species of hornets or spiders. Invasive jellyfish can fill the waters and harm beach goers.

Invasive species can even cause harm economically. Invasive hornets destroy beehives that produce honey to be sold. Zebra mussels clog pipes and encrust boats; it costs a lot of money to remove them, and it’s usually not a one-time expense. Lionfish have made coral reefs barren, reducing the populations of game and harvestable fish to low numbers, and impacting aquatic tourism.
Luckily, there are ways to handle invasive species. The best way is to prevent them from entering delicate ecosystems that they don’t belong to. For humans, that means being more careful when transporting food and supplies over long distances. It means finding new owners for exotic animals when you no longer want or can care for them—don’t just release them into the wild!

There are also ways to reduce invasive species numbers. For instance, many places around Florida and the Caribbean offer cash prizes for lionfish through spear-hunting competitions. Or you can encourage local chefs and restaurants to serve invasive species on the menu. The National Aquarium in Baltimore, Maryland frequently serves invasive fish in their diner.

I’ve eaten lionfish, and it’s pretty tasty! Mine was served Jamaican style, featuring a lot of spices that I wasn’t used to, but if prepared properly, it’s a great fish to eat. I’ve also had invasive catfish that was found in our local waters, and it didn’t taste that different from the native catfish, just maybe a little sweeter. So there are all kinds of ways to deal with invasive species, but it’s up to us to keep them in check!

More information:

Zebra Mussels

Domain: Eukarya

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

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: