Marine Mademoiselle

 

Invasive lionfish by Rachel Louise Gunn

Lionfish represent one of the most successful marine invasions to date. Invasive lionfish have a broad diet, excellent predatory efficiency and a high reproductive rate. Without efficient management, invasive lionfish pose an additional threat to our already struggling oceans. 

What is a lionfish?

Lionfish (Pterois spp.) are members of a diverse group of fish called scorpaeniforms. Lionfish are a highly distinctive species, popular in aquariums, with a brown/maroon body and white stripes covering the entirety of the body and head.  Lionfish have large pectoral fins and spines located on the dorsal and anal sides. Lionfish are venomous, with venom located within both dorsal and anal spines. There are 12 recognised species of lionfish native to the Indo-pacific. Of these 12 species, two are invasive: The red lionfish (Pterois volitans) and the devil firefish (Pterois miles). The two invasive species of lionfish differ in the number of dorsal and anal fin rays.

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Lionfish introduction and invasive distribution

Lionfish are a hugely popular aquarium species. The aquarium trade is the most likely source of the lionfish invasion. For example, there is a documented release of lionfish into waters of the Southeast United States (SEUS) from Biscayne Bay, Florida, following hurricane Andrew in 1992. Lionfish spread into the Caribbean from the SEUS via dispersal on currents (Johnston and Purkis, 2015) and by 2010 lionfish had become well established throughout the Caribbean. Under current climatic conditions, lionfish are predicted to spread throughout South American waters. In 2015, a single lionfish was observed as far south as Brazil.  Furthermore, P.miles, native to the Indian ocean and the Red sea, has been sighted within the Mediterranean sea. It is possible that a second invasion of lionfish into the Mediterranean could progress in the future.

Densities in the invasive range

Global distribution of lionfish. The red lionfish and the devil firefish have different native ranges (green and blue respectively). Both species are present in the invasive range (red), although the red lionfish dominates. Stars represent sightings of P.miles in the Mediterranean. Hatching represents the predicted future distribution of lionfish.   (source: USGS-NAS)

Global distribution of lionfish. The red lionfish and the devil firefish have different native ranges (green and blue respectively). Both species are present in the invasive range (red), although the red lionfish dominates. Stars represent sightings of P.miles in the Mediterranean. Hatching represents the predicted future distribution of lionfish. (source: USGS-NAS)

Across the invasive range, lionfish are both larger and found in greater densities than in the native range. For example, on native reefs off the coast of Kenya, P.miles has an average density of 25.1 individuals per hectare compared to 101.7 individual per hectare on invasive Bahamian reefs. At peak densities have been recorded at up to 326 individuals per hectare in the Caribbean and 350 individuals per hectare in the SEUS. The substantial densities of lionfish across the invasive range pose a threat to native ecosystems through a combination of predation on and competition with native species.

Success and Impact

Lionfish occupy a variety of marine habitats within the invasive range, such as reef walls, reef terraces, patch reefs, mangroves and seagrass beds. They are cryptic, easily concealed from prey species, efficient predators with a broad diet, and have a high reproductive range and strong dispersal capabilities.  Furthermore, native prey species are unable to recognise lionfish as a threat as they are a novel species. Prey species therefore do not elicit a defensive response, a concept known as prey naivety. A combination of all these factors have resulted in the success of lionfish across the invasive range.

Lionfish consume a diverse array of prey, encompassing both fish and crustacea. In  the Bahamas, lionfish predation success rate is 72%, which is equivalent to just over one kill, per lionfish, per hour. Up to 30 different fish species have been identified within the stomach of lionfish.  The consequence of both prey naivety and the broad generalist diet of the lionfish is a substantial contribution to small reef fish mortality. For example, the recruitment of native reef fish on Bahamian reefs declined by 79% in just 5 weeks due to the presence of lionfish on the reefs. Lionfish also consume the juvenile stages of important commercial species, such as groupers and parrotfish. 

The additional source of mortality from predation by lionfish on herbivorous species such as parrotfish could have a knock on effect on the recruitment of coral on native reef systems. Parrotfish feed on algae that competes with coral for space. A reduction in the number of herbivorous fish would encourage a build up of algae, resulting in a phase shift from a coral dominated to an algae dominated community. Lionfish predation therefore has knock on effects throughout the food web, from threatening commercially valuable species to reducing the resilience of coral structures. It is therefore apparent that something needs to be done to reduce lionfish numbers across the invasive range.

Lionfish Management 

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Lionfish management is fundamental to reducing the negative impacts on native marine ecosystems. The key to efficient lionfish management is early detection. Where this fails, a rapid response is needed. Lionfish management consists almost exclusively of direct removals via culling, often through specific control plans. Control plans in lionfish management allow limited resources to be allocated effectively and specific targets for removal efforts to be proposed.   Research has shown that areas where lionfish culling is instigated immediately following sightings is more effective at reducing lionfish densities than when there is a delay in culling after sightings have been made. In the Cayman Islands, a No Dive Zone is in place on Grand Cayman, where no culling occurs. Lionfish densities within this zone are substantially higher than in  surrounding, culled regions.  Key to culling programmes is ongoing monitoring. Effective monitoring of lionfish culling allows successes and failures to be identified and dealt with accordingly.

Culling programmes are now in effect across the invasive range, with affected areas utilising dive centres to promote culling activities. In general, culling involves the use of pole spears and collection buckets. Individuals are often licensed to use the pole spear for lionfish culling purposes only. This is generally accepted to be an effective method of lionfish removal. For example, in Trinidad and Tobago, monthly culling has resulted in a 30% decline in lionfish biomass. Lionfish derby events, such as those conducted around Utila and the Cayman Islands, can yield hundreds of lionfish in a single day. Public contributions and citizen science approaches to lionfish management such as through derby style event, are an effective way to educate local people about the importance of lionfish management whilst removing hundreds of lionfish in the process.

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Lionfish Containment Unit

Unfortunately, lionfish management is not as simple as culling lionfish until they have been completely eliminated. The high reproductive dispersal rates of lionfish mean that complete elimination of the invasive species is impractical. Instead, culling aims to reduce lionfish densities to a point at which the negative impacts on native communities are minimal. This can be achieved by inducing recruitment overfishing in lionfish populations. Recruitment overfishing is the point at which the number of lionfish removed is approximately equal to the number of recruits in the lionfish population, so lionfish numbers neither increase nor decrease. Estimations suggest that a removal rate of 35-65% of lionfish populations in any given region is necessary to induce recruitment overfishing. The primary problem associated with culling is the recruitment compensation of lionfish after a culling event. Lionfish that remain unculled act as population recruits , allowing lionfish populations to recover rapidly. Sources of recruits include lionfish occupying depths greater than can be reached by SCUBA, or individuals from areas of high larval connectivity.  With all the issues associated with lionfish culling, alternative sources of management may be necessary. One possible option is biocontrol, whereby native predators, such as sharks and groupers, learn to predate upon lionfish, resulting in a  natural reduction in lionfish numbers.

What can you do?

If you live in an area affected by lionfish, it is a huge help to both dive centres and research stations if you record and report any sightings of lionfish to help monitor lionfish densities over time. To learn more about how you can assist with the control and monitoring of invasive lionfish, or to get involved with lionfish culling events, visit reef.org and the Invasive Lionfish Web Portal.

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Rachel Louise Gunn

Rachel is a Marine biologist, Divemaster and Scientific Diver specializing in Invasive Lionfish. After completing her Divemaster she went on to complete a Masters degree in Marine Biology at Bangor University in Wales. During this times Rachel gained a Distinction on her thesis researching invasive lionfish in Cayman Islands. Most recently she presented her work at the 2017 European Coral Reef Symposium (ECRS) in Oxford, UK. We look forward to hearing more from Rachel and following her  journey.