The Tremendously Invasive Lionfish

Lionfish are in the news again! Only two weeks ago, a lionfish was reportedly fished up out of the waters off Dorset’s Chesil Beach in the U.K. Of course, this may just be a one-off aquarium release. Still, the question remains: How can a fish possibly survive in an ocean over 10,000 km away from its natural home?

Here we will look beyond the venomous spines to what makes these fish such tremendous survivors.

An invasive lionfish found in the U.K. would be over 10,000 km from home!

Photo Credit: Alexandra Ward

It’s hard to be a scuba diver and not hear about the lionfish invasion. However, to truly grasp their current impact, we must understand what lionfish are and where they came from.

Basic Facts About Invasive Lionfish

• Lionfish have 18 venomous spines for defence.

• They prey on small reef fish and crustaceans.

• With no natural predators within their invasive ranges, they are a severe threat to native fish populations.

The History of Invasive Lionfish in the Atlantic

• Lionfish originated from the Indo-Pacific region.

• They were first discovered in Florida in 1985.

• Thought to have been released from multiple sources, lionfish went on to populate the entire Caribbean over the next 30 years.

• By 2015, lionfish were reported off the coast of Brazil for the first time.

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How Lionfish Survive

Believe it or not, the process of foreign species being transplanted from one ocean to another is not uncommon. In most cases, the stress of the journey makes it difficult for these poor creatures to survive. Differences in temperature, salinity, and food availability in the new location also limit the spread of other sea life between oceans.

Invasive lionfish, on the other hand, are extremely good at surviving:

• Temperature range – Optimally between 25-30° C, lionfish can survive temperatures as low as 12.5° C.

• Salinity – Although native to regions where the salt concentration is very high, lionfish can tolerate very low salinity for extended periods. This potentially allows them to colonise riverine estuaries.

• Food – Lionfish are binge eaters. Capable of eating up to four times their own body weight during a single day, they accept a wide range of food, from small fish to crustaceans, and can store a lot of fat. This means they are perfectly equipped to survive a long journey between suitable habitats when food might be scarce.

A Lionfish’s Habitat and Depth Range

Lionfish have been found in depths ranging from 0.5 meters to over 100 meters on hard bottom, mangrove, seagrass, coral reefs, and artificial reefs such as shipwrecks. Unfortunately, this means that divers’ efforts to cull lionfish are unlikely to ever be 100% successful. Invasive lionfish can hide in many places that divers simply don’t go or don’t have access to.

The deepest invasive lionfish sighting to date was during a coastal survey off the coast of Bermuda in 2016, where a lionfish was recorded at a depth of 304 m. A second 21 cm long individual was spotted at 297 m.

The deepest invasive lionfish found to date was at a depth of 304m! (This is not it, by the way) Photo Credit: Alexandra Ward

The Adaptive Behaviour of Lionfish

Lionfish can adapt their behaviour to suit their new circumstances. Studies have found that although lionfish are naturally nocturnal, in the Atlantic Ocean, they feed around the clock and are often seen out on the reef in the daytime.

They have also learned that humans are predators. Lionfish that have been hunted before are more alert and more likely to hide deep inside the reef when divers are present. This causes concern that in the future, lionfish sightings may be ‘missed’ on these reefs.

Where are they? Looking for invasive lionfishPhoto Credit: Alexandra Ward

The Spread of Invasive Lionfish in the Mediterranean

During the last 35 years, invasive lionfish have progressed acrossthe Caribbean at a steady pace. However, this issue is not exclusive to one region.

Since 2012,repeated sightings of lionfish have also been reported in the Mediterranean.
•In 2015, lionfish were first sighted off Cyprus and Turkey,
•In 2018 lionfish were first sighted off mainland Greece.

In this region, over100 sightings have already been reported. These invasive lionfish are thought to have migrated from the Red Sea via the Suez Canal.

The above map was created by the U.S. Geological Survey, Nonindigenous Aquatic Species Database.

The original can be found here: USGS Reported Lionfish Sightings.

Lionfish in the U.K.?

Invasive lionfish are extraordinarily adaptable and scarily good at surviving conditions that would kill most other fish. So, was the recent U.K. catch an advance scout of a new invasion or just an escapee from an aquarium? We will undoubtedly be watching the news with interest.

About the Author

Alexandra fell in love with the underwater world when she was 10 years old. A fish ID expert and keen marine conservationist, she is now a PADI Master Instructor with 12 years of experience working in the Caribbean.

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