One of the great pleasures of scuba diving is having the opportunity to view the spectacular life that exists under the waves.  Lionfish are certainly amongst those most beautiful, with each of the eleven species of lionfish having highly conspicuous shades of red, white, black, and creamy bands.  Their myriad tentacles and venomous spines add to their ornate and captivating beauty. 

Yet when a group of divers out spear fishing in south-eastern Brazil came across a lionfish in May 2014, they immediately speared it, and alerted the local authorities.  Lionfish are native to the Indo-Pacific.  Their presence in the western Atlantic has been described by Graham Maddocks, president and founder of the Bermuda-based Ocean Support Foundation as “probably the worst environmental disaster the Atlantic will ever face.”

Whilst Maddock’s view may be a little extreme, there is no doubt that the two species of lionfish now present in the Atlantic are having a huge impact on Atlantic coral reefs.  Exactly how the red lionfish (Pterois volitans) and the common lionfish (Pterois miles) established themselves in the Atlantic is uncertain, but it is almost certainly a result of human actions. 

The first confirmed sighting of the red lionfish, which makes up approximately 93% of the invasive population, occurred in Florida in 1985.  Introduction via ballast water discharge has been proposed as one vector for the lionfish, as has deliberate introduction from aquarium enthusiasts who simply want rid of these beautiful but highly voracious fish.  Interestingly, a study published in April indicates that contrary to previous thinking, red lionfish populations in the Atlantic haven’t all originated from Florida.  Lead by John Butterworth from the US Geological Survey, genetic analysis from 214 red lionfish from 9 countries/territories found two genetically distinct populations, separated north and south around the Bahamas, likely arising from multiple releases.  To date, lionfish have been confirmed as far north as New York and as far south as Arraial do Cabo, Brazil. 

There are a number of factors that may have allowed lionfish to become so successful in the western Atlantic.  Lionfish become sexually mature at one years old, with females able to produce 10,000 – 40,000 eggs per spawning event.  Whilst this is lower than many similar native Caribbean predators, lionfish are able to produce eggs almost continuously when conditions are favourable.  Work lead by NOAA’s James Morris Jr. in 2008 suggests that during the summer months, lionfish in North Carolina and The Bahamas are likely to spawn approximately every four days.  The average annual fecundity of female lionfish, Morris calculated, may exceed 2 million eggs.  Whilst transference via ballast water may have helped spread some of the lionfish eggs and larvae along the western Atlantic, ocean currents -particularly the Gulf Stream, the Gulf of Mexico loop current, and the Caribbean current, are thought to be the primary mechanisms of dispersal. 

The larval stage of many species involves wide dispersal, but if there is not suitable habitat for the larvae to settle, then their ability to establish populations greatly diminishes.  Movement ecology of lionfish is still an area of research, but we do know that although lionfish are largely associated with coral reefs, they are not limited to them.  In their native range red lionfish are also found on rock and sand substrate, down to depths of 50 meters, and the common lionfish is also found in seagrass beds.  In the Atlantic, both species have been recorded down to depths of 80 meters, and in mangroves, seagrass beds, and estuaries - even those with low salinity.  With sightings of primarily smaller lionfish in seagrass beds and larger ones on deeper coral reefs, it is thought that lionfish may use different habitats during different stages of their life cycle. 

Perhaps unsurprisingly for a species that can occupy a variety of different habitats, lionfish also predate on a variety of vertebrates and invertebrates.  In the Atlantic they appear to eat a greater diversity of species than in their native habitat.  Their voracious appetite is one of the primary reasons conservationists and managers are so concerned about their presence in the Atlantic.  Research lead by PhD student Stephanie Green (Simon Frasier University) focusing on native fish communities on reefs off New Providence Island, Bahamas, found that lionfish abundance increases to 40% of the total predator biomass coincided with a 65% decline in 42% of the lionfish’s Atlantic prey in just two years.  In Belize, research led by Luiz Rocha which looked at lionfish stomach contents found that half of the lionfish diet was comprised of social wrasse (Halichoeres socialis), an endemic to Belize’s inner barrier reef and a critically endangered species.  In their new range the lionfish appear to have fewer natural predators, likely in part due to their aggressive defensive strategies and neurotoxins in their spines, but also possibly as a result of a decline in top predators due to overfishing. 

Effectively dealing with any invasive species is a challenge but in the oceans, the challenge is all the more difficult.  We cannot prevent lionfish or their eggs moving by fencing them in.  We cannot apply a pesticide to kill them off.  Nevertheless there are a number of initiatives being tested and used to attempt to keep the numbers down.  Hunting by recreational ocean users has been actively encouraged throughout the Western Atlantic.  In the Florida Keys National Marine Sanctuary, permits are being issued to remove lionfish using hand nets or slurp guns from Sanctuary Preservation Areas – areas in which fishing is otherwise banned.  In the Cayman Islands, where spearfishing is prohibited, the Department of Environment imported short lionfish hand-spears which they sold to licenced hunters.  In Antigua, lionfish hunts, involving prizes for the number of fish caught have proved popular.  The fish don’t just have to hunted for removal, argue NGO Reef Environmental Education Foundation (REEF), who are based in Key Largo, Florida.  Instead, we could “consume it [the lionfish] out of existence”.  In 2010 the foundation launched the first book of lionfish recipes, with the aim of creating consumer demand for the fish.  It is described as a flaky white fish with a firm texture and not an overly powerful taste. 

Today, lionfish can be found on the menu of many a restaurant throughout east-coast USA and the Caribbean.  Non-human consumers are also being encouraged to eat lionfish.  In the Rotan Marine Park, Honduras, local and experienced dive masters have begun feeding lionfish on the end of spears to reef sharks in the hope of giving the sharks a taste for the fish, and encouraging them to see lionfish as prey.  Similar efforts have also been tried in the Gardens of the Queen National Marine Park, Cuba.  In the Indo-Pacific, sharks do predate on lionfish, apparently with no ill-effects from the lionfish’s toxic spines.

Regardless of the method use, complete lionfish eradication is likely to be an impossible task.  In a hunting derby organised in Rotan Marine Park in 2011, more than 1,300 lionfish were removed, yet the number of lionfish present in the park does not appear to have declined permanently.  As for encouraging natural predation by sharks, reports that lionfish numbers appear lower in shark-areas may be the result of the number of lionfish being speared and fed to sharks as oppose to the sharks hunting the fish themselves. 

There is also a concern that the sharks will associate divers with food, eventually ending up in tragedy.  Lionfish eradication many be unobtainable, but there is some evidence that sustained removal efforts can keep numbers low.  One piece of research led by Ramón de León from the Bonaire National Marine Park noted that “local removal efforts using volunteers represent a cost-effective, rapid-response option that is successful at significantly reducing the density and biomass” of the lionfish in Bonaire. 

This story appeared in The Marine Professional, a publication of the Institute of Marine Engineering, Science & Technology (IMarEST).