Invasives Blog

By Rebecca Quarterman and Hannah Fielder


Lionfish populations continue to expand, threatening the well-being of coral reefs and other marine ecosystems (Image: Pixabay)

The majestic, unusual looking Lionfish could be seen as harmless to the untrained eye. Yet, this invasive species has multiplied aggressively over the last two decades to become a serious threat to biodiversity in the marine setting.

The red lionfish (Pterois volitans) and the devil firefish (Pterois miles) are native to the Pacific Ocean and the Indian Ocean respectively, though their ranges overlap in the waters around Indonesia. These two species are collectively known as lionfish and are so similar in appearance that scientists usually rely on genetic analysis to tell them apart. Thriving on coral reefs and among mangroves and seagrass, lionfish have distinctive white and red/brown striped bodies and venomous spines on their fins to protect them from predators.

Lionfish scare their prey – small fish and shrimp – by boasting their venomous spines and blowing water at them. This allows the Lionfish to corner, disorient and then attack their prey in an aggressive manner. They can grow to over a foot long and can survive for around 15 years, making them a worryingly invasive species.

Their invasive agenda has been made apparent due to their colonisation of Western seas around the USA, Caribbean, and the Mediterranean. Their distinctive appearance makes them popular in aquariums and some speculate that exotic pet owners dumped adult Lionfish in the Atlantic after realising they could not cope with their predatory nature. It is believed that a small number were released from captivity in the mid-1980s along the coast of Florida, USA. Their population has since exploded, invading over 7.3 million km2 in the western Atlantic Ocean and Caribbean Sea with severe consequences for native coral reef fish populations.

More recently lionfish have also been found thriving in the Mediterranean. It is thought that they migrated through the Suez Canal, and with the Canal’s recent expansion, along with rapidly rising sea temperatures in the Mediterranean Sea, lionfish numbers are likely to soar. This is particularly true in the waters surrounding Cyprus, close to the Suez Canal, but other recent reports from more distant locations such as Italy, Libya and Tunisia are a further cause for concern.

There are a number of factors which have made the Lionfish invasion of multiple coastal areas so prolific.

Firstly, the Lionfish breeds at an alarming rate. They reproduce all year round, with females releasing approximately 2 million eggs a year. They have invaded many different areas, discharging eggs into open water every two or three days. These eggs then move freely to various bodies of water, continuously colonising new environments.

Also, its physicality means there are few natural predators willing to attack it. The cautionary spines and threat of venom makes its defence almost impenetrable. The only known occasional predators are sharks and eels, and some research suggests that predators do not travel beyond the Indo-Pacific sea.

Few creatures want to attack it, and it reproduces constantly over an immense area. It also feeds constantly on native fish species, upsetting the ecosystem whilst also affecting local fisheries and tourism. Many prey fish do not recognise it as a threat, making feeding an easy task for the Lionfish. Its stomach can even expand to 30 times their normal size. Dr Gretchen Goodbodly-Gringley, Chief Investigator at the Bermuda Institute of Ocean Sciences, states that some Lionfish actually overeat, causing them to grow fatty liver deposits and increase in size. And now, in some places, they outnumber native species.

An understanding of the biology and behaviour of lionfish leaves no doubt as to why they are such successful invaders. They spawn every four days, producing approximately two million eggs per year that spread over large distances on ocean currents. They have high growth rates, can live in a wide range of habitats and are not picky when it comes to their prey, eating a variety of fish and crustaceans.

To combat the very real threat that they pose, scientists are now encouraging the public to get involved in controlling lionfish populations. Scientists at the University of Cyprus, in collaboration with the University of Plymouth, the Cyprus Department of Fisheries Marine Research and others, are working to establish Cyprus as a ‘first line of defence’ against lionfish invasion through the European Union funded project, RELIONMED-LIFE. To do this, they are recruiting local divers to form ‘Removal Action Teams’ that will target lionfish hotspots and ‘at risk’ protected areas. Local derbies are also being organised where diving teams compete to remove the most lionfish, with prizes also going to teams with the smallest and largest fish.

Luckily, Lionfish can be eaten, meaning their meat doesn’t go to waste. They can be found in restaurants and even in supermarkets. In fact, one of the more unusual strategies encourages local restaurants to offer lionfish on their menus, creating a niche market and economic incentive for local divers and fishermen to catch them; strategies that are already used along the coast of Florida, USA. Will their newfound demand help balance out the marine ecosystem?

Humans are now the only real predator who can remove the Lionfish threat from our seas, before it damages the marine environment even further. Specially trained scuba divers are attempting to cull these predators, but there is inherent danger in this job. Some are trialling traps to remove larger numbers of Lionfish at once. A “Robotic Zapper” or Lionfish Terminator has been deployed in the Caribbean to dispose of the Lionfish as they often swim at a level too deep for most scuba divers.

This invasive species proves that human intervention is necessary now more than ever to ensure our seas are restored to a healthy balance. Marine invasions have the potential to cause huge environmental and economic problems, destroying habitats, threatening native species and affecting tourism and fisheries. Increasingly, scientists are turning to projects that increase public awareness and create a willing workforce of volunteers, equipped with the knowledge and skills to help protect their environment and livelihoods. When looking for sustainable solutions to large scale conservation challenges, such as this, could harnessing the power of the volunteer help to turn the tide?

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