The Great Lionfish Invasion: What Is the Threat?

As everyone in the dive world knows by now, the Caribbean has been invaded by lionfish – reef fishes indigenous to the Indo-Pacific region.  Sightings have been reported from the mid-Atlantic U.S. coast all the way to S. America and through much of the Caribbean.

That much is scientific fact.  But what are the long-term impacts of this unforeseen event?  Will lionfish simply turn out to be just another interesting fish for reef divers to watch, or will the entire fish population of the Caribbean eventually be reduced to one single lionfish about the size of Aruba waiting patiently for the next cruise ship to pass by?

Speculation runs amuck, and the purpose of this article is to shed some hard light on what is known and what is not regarding the great lionfish invasion.

Impacts of Concern

The main expressed concerns posed by Caribbean lionfishes can be summarized as follows:

1. Ecosystem Change: Because lionfish are highly piscivorous, they may have the capacity to reduce the recruitment of juvenile fishes to reef areas. This has been experimentally confirmed by short-term studies on a few small Bahamian patch reefs. Such impacts could (in theory) lead to declines in Caribbean reef biodiversity, disruption of normal ecological processes, and possibly the local extinction of select species.

2. Economic Impacts: By reducing populations of grouper and other commercially valuable species, lionfish may damage the economies of island communities dependent upon fishing. Lionfish may also impact local tourism, an economic mainstay of many Caribbean island nations.

3. Human health: Lionfish are highly venomous, with the capacity to inject neurotoxins dangerous to humans (and other animals) from stout spines on several of the main fins.  As lionfish populations continue to increase, so does the likelihood of human injuries. Lionfish envenomation is considered a serious injury requiring immediate professional medical evaluation and treatment.

Evaluating the Impacts

While the lionfish is undoubtedly here to stay, this author’s evaluation of the threat is, for the most part, not as dire as some others might believe.

The threat to human health is real and unquestioned, but the number of actual injuries is likely to be relatively small and rarely (if ever) life threatening.

The economic threat to tourism will likely be minimal. In terms of general tourism, the main impacts will probably occur from parents understandably reluctant to allow children to wade or snorkel in reef areas.  But that alone will not deter family travel to the Caribbean.  In terms of dive tourism, based upon the propensity of the dive industry to capitalize on “thrill tourism” (e.g., shark feeding), it is likely that this opportunity will also be used to attract rather than repel scuba divers (e.g., “help count lionfish”; “see a new species”, etc.).

In terms of ecological and commercial fisheries impacts (referred above), the concerns expressed are legitimate. Nonetheless, it should be kept in mind that the scientific basis for these concerns is minimal at best, based upon one or two published short term studies from small patch reefs in a limited area.  How these results might extrapolate to large reef areas throughout the region is purely speculative at this time.

Finally, from the broad perspective we must keep in mind that for millions of years lionfish have been widespread throughout a vast oceanic region that contains at least ten times the biodiversity of the Caribbean.

While fears that modern Caribbean reef communities have never before been exposed to lionfish are not unfounded, it is also true that the Caribbean reef fauna is derived from Pacific reef communities that have “only” been isolated for some three million years.  Most populations of these animals certainly have the capacity to rapidly undergo adaptive changes (i.e., evolution) to face new situations.

In any event, only time will tell what the real threat of the great lionfish invasion really amounts to.

William S. Alevizon, Ph.D.

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10 thoughts on “The Great Lionfish Invasion: What Is the Threat?”

  1. Thank you for a calm yet incitful evaluation of the “Lionfish threat”. I am a grateful but humble visitor to the beautiful underwater realm and cause no harm to the creatures that inhabit it. I feel that an amicable equalibrium will be found.

    Rating: 5.0/5. From 3 votes.
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  2. I made about 250 dives off Okinawa 1985-90. I saw from one to twenty lionfish on every dive. They have no fear of divers and stand their ground. I know of only one person who was stabbed by one (on his finger tip, a small fish about 4 inches long) He said it was worse than sticking his finger into a 110V outlet. The pain was intense and worked its way up to his shoulder in a few minutes. By the time he exited the water and climbed the 147 steps to the parking lot the pain had started back down his arm. They started for the Navy hospital but turned around and made a second dive. A few days later all he had was a tiny hole in the end of his ring finger. A large lionfish might do more damage though. Don’t mess with them. They’re fast as lightning. We also had stonefish, scorpion fish and sea snakes around Oki. No one was ever hurt by them.

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  3. Hi Bill,
    I apologize for the confusion. I thought you were another diving noob (like me) but you most definitely are not.

    I know that coastal development is on the rise in the Canary Islands and has wrecked havoc on the ecosystem in other parts of Spain (Alicante, Balearic Islands), but unfortunately I don´t know the extent of the problem nor how large of an impact this has had on the water quality.

    My Oceanography professor has a sister who works in a Dive Center in Valencia and is somewhat of an expert when it comes to these matters. I´m going to shoot her an email and maybe next week I can give you a better answer :D.

    Btw, do you have a Twitter?

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  4. Hi Michael

    Perhaps I was not clear what I meant by “water quality” in my reply. It has been shown that in coastal seas, increases in dissolved nitrates in the micromolar range can trigger algal blooms.

    I would think that the Spanish Ministry of Health and Consumer Affairs is probably more concerned with the safety of the public water supply than regularly monitoring the surrounding oceans for miniscule levels of dissolved nitrates and phosphates.

    I probably should have asked a different question, namely, has the coastal human population (or human activities along the coast, such as building, dredging, coastal development, etc.) changed much in recent years?

    That is usually the root cause of coastal ocean water quality declines, which can trigger algal blooms and thereby greatly increase food supply for herbivores such as urchins.

    Even in cases where extensive studies have been done, researchers can rarely pinpoint the exact cause for urchin population booms.

    In the words of one expert on urchin “population booms”; “Initially biologists blamed the overfishing of lobsters, thought to be an important urchin predator, but that idea has since been shown to be incorrect…Although there has been much speculation as to the causes of these and other urchin outbreaks, we still don’t know for certain what caused them. However, human alteration of the marine environment probably played a role in creating the conditions that led to the increases in urchin abundance”.

    For more in-depth discussion, I refer you to the article I briefly cited above:


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  5. Hi Bill,
    According to an official report releaased in 2007 from the Spanish Ministry of Health and Consumer Affairs, The Canary Islands have maintained high quality water levels.
    I´ve also done a few Google searches and have not found any news regarding the water quality.

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  6. Michael

    Overfishing has been theorized by some to explain similar population “booms” of sea urchins in the Caribbean area. However, the actual scientific support for such speculation is tenuous at best. Relatively few Caribbean reef fishes feed on urchins.

    I believe that it is at least as likely that sea urchin population explosions maybe the result of a decline in water quality – specifically, increased nutrient loads in the water leading to rapid algal growth (the food of sea urchins), followed by a population increase in urchins as a result of a much greater supply of available food.

    Has the water quality declined in the Canary islands coastal regions in recent years?


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  7. The Canary Islands are suffering a similar problem. Sea urchins have exploded in population and have caused biodiversity to decline in various sites and have whitened reefs, blanquizales as it is called in Spanish, all over the islands. The cause of the problem is speculated to be overfishing which has made predators dissappear and has allowed for the urchins to overpopulate.

    Is overfishing also the cause of this problem?

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  8. Digger

    The article was written to provide a perspective – namely, no one really knows what the outcome of this invasive species will be.

    There have been other things written about this topic in various sources – some warning of near doomsday scenarios. I wanted to provide what I feel is a more rational evaluation of the available evidence.

    That is reason enough in itself, at least in my mind.

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  9. The last sentence begs the question,”So, why did you write this article?”.

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  10. Hey Bill,

    Long time.

    Thanks for the thoughtful and sensible piece.


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