Lionfish vs. Sharks: The Battle for the Reef

Watch your step!

If you’re visiting the beaches of Florida you may encounter a sign like the one below or, if you are unlucky, the fish the sign is warning you about.

Lionfish warning sign from the Florida Keys National Marine sanctuary. Image from (Morris, 2011)

If you step on the small and beautiful Red Lionfish (Pterois volitans), you’ll find your foot impaled by large, venomous spines. As soon as the spine enters your skin, the needle-like point will passively inject a neurotoxin into your bloodstream. While usually not deadly, the venom can be extremely painful.

Originally from the South Pacific and Indian Oceans, Red Lionfish are an invasive species in the Atlantic Ocean. They have few predators in the Atlantic and tend to settle on coral reefs, displacing local fish and invertebrate species. This can have huge consequences for the already fragile reef ecosystem. Studying these fish and learning how they may be removed has major ecological implications.

Red Lionfish. Photo by Alexander Vasenin.

To this end, Dr. Kate Galloway and Dr. Marianne Porter from Florida Atlantic University decided to study the lionfish and how they might interact with would-be predators; the Blacktip Shark, Black Grouper, and humans. Their goal was to understand if an attack by one of these predators on the lionfish would cause more damage to the fish, or to the attacker.

Their study, published in Integrative Organismal Biology, involved dissecting out lionfish spines from different regions along the body and measuring the force and energy it takes to stab them into skin samples from the predators (don’t worry, they used porcine skin to represent humans). They also measured the damage to the spine after stabbing to see who would sustain the most injury after a stabbing event.

They found that sharks are much more resistant to damage from the spines. This is probably because sharks are covered in tooth-like scales called denticles which protect them from puncture. The spines used to puncture shark skin also had a lot more damage then spines stabbed into grouper or porcine skin.

SEM images of shark and grouper skin used for puncture test. Figure modified from Galloway and Porter (2021)

In addition to resistance to stabbing, they also measured the energy needed to stab. Lionfish don’t actively stab their predators. Instead, it’s the predators bite (or step) onto them, the force of which causes the spine to be injected into the skin. Galloway found that it generally takes much more energy to stab into shark skin then it did to stab into either grouper or porcine skin. This means that the lionfish spine might not even puncture the shark’s mouth unless the shark decides to bite much harder than the grouper.

Even though their skin is more puncture resistant, we still don’t know how badly a lionfish spine hurts a shark. Dr. Galloway proposed a future study to investigate how deeply the spine would need to go to inject the venom. 

This research along with future related studies could inform local ecologists and conservation biologists about which predators are best suited to handle the lionfish invasion. If we know who’s up for the challenge, we can do a better job at protecting them as well. Teaming up with large predators like sharks could even help us restore the reef communities to their pre-lionfish diversity.

Dr. Cassandra Donatelli is post-doctoral researcher at the University of Ottowa interested in the ways fish and robots move.

References

Impacts of Invasive Lionfish. (2020). NOAA Fisheries. https://www.fisheries.noaa.gov/southeast/ecosystems/impacts-invasive-lionfish

Images

Moris, James. (2011). Invasive Lionfish: A Guide to Control and Management. Gulf and Caribbean Fisheries Institute. 

Vasenin, Alexander (2010). Red lionfish in Indonesia. Wikipedia.

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