Each summer and fall I spend more time snorkeling, diving, and seining, than I can really afford. I can’t help it. The sea is so full of mystery and wonder, I am utterly powerless to it. After more than 20 years of exploring the waters of New York, I try to tell myself that nothing will surprise me. Nevertheless, every year I see something that completely catches me off guard. I have seen frenzied bluefish chase millions of menhaden into a small harbor, packing them in so tight, that the entire school suffocates. I have snorkeled with ocean sunfish that dwarf my dinner table. I have seen innumerable tropical reef fishes that have no business living in our cold, murky waters: exquisite young french angelfish cleaning parasites off of tautogs and black seabass, aggregations of squirrelfish in the rotted hull of a sunken boat, spotfin butterflyfish in such abundance that they may be the dominant fish species around certain docks and jetties, at least for a few months of the year. Just a few weeks ago I found an octopus living in a submerged toilet bowl – maybe not a strange occurrence in the tropics, but octopus sightings in New York are relatively rare.

Young P. volitans, caught on Long Island, on display at Atlantis Marine World. (Photos by Todd R. Gardner)

Tropical marine life in the Northeastern US is nothing new. Their presence here is simply the result of pelagic larvae, the dispersal mechanism for the majority of marine animals, getting carried hundreds or thousands of miles from a suitable habitat and climate. The Gulf Stream, flowing at a rate approximately equal to all the world’s rivers, combined, provides ample transportation for them. Whereas some of the more oceanic species like jacks and triggerfishes may be able to return to warmer waters before winter sets in, most of the reef species found in our area probably do not.

I’ve grown somewhat accustomed to seeing these brightly-colored wayward fishes in my underwater wanderings, so when I happened upon a tiny lionfish (Pterois volitans) clinging to a wooden piling along the south shore of Long Island in September, 2001, it took a moment for me to fathom the implications. This was not just a stray from the tropical Atlantic. Lionfish are found in the Eastern Pacific, Indian Ocean and Red Sea. This fish was way off course. My first thought was that perhaps someone had released it from his or her home aquarium. Lionfish are certainly popular enough in the aquarium trade. The problem was that this one was no more than an inch long and nearly transparent. I had never seen a lionfish this small (or young) in a pet shop.

NOAA Satellite imagery (from http://www.weatherimages.org) of the Gulf Stream: a major vehicle of dispersal for lionfish (as well as many other species) along the Atlantic Coast of North America.

I decided, before thinking about it any more, I should catch the fish. It would make a fine addition to one of the display tanks in our lab. Besides, I would need evidence if anyone was to believe my story. The fish was using its fins to hold itself against the piling among some calcareous worm tubes, with its venomous dorsal spines facing out toward me. I took my hand net out from under my arm and placed it against the piling, just below the fish. His head was pointed down, and now toward the open end of my net. Holding the net against the piling with my left hand, I reached for his tail with my right hand. The idea was to shoo him into the net, but the lionfish had other plans. He nestled deep into a crevice between the worm tubes and spread his dorsal spines so that I couldn’t touch him without a high probability of getting stung. I thought for a minute and then reached into my pocket and pulled out my car keys. I gently stuck a key into the crevice and touched his tail. He immediately sprung out into open water, but made no attempt to get away. He just hung in the water column with his elegant fin rays swaying in the wave surge, looking not unlike a stinging jellyfish. I was hypnotized by the beauty of this venomous little stray, and mystified by its presence here. I engulfed the fish with my hand net, and then reached into my pocket for a ziplock bag. Once the fish was bagged, I stood up, removed my snorkeling gear and ran down the beach to catch up with the rest of my party.

I was on a field trip with my professor and some fellow graduate students. We were on our way to a rock jetty about a mile from the parking lot. As usual, I was lagging far behind because I can’t walk past a submerged piling, rock, tire, or any kind of artificial reef, without jumping in the water to see what kinds of interesting marine life have settled on it since the last time I checked. As I approached the group, I held the bag out and, trying very hard to conceal my excitement, I said, “Hey guys. Look what I caught.” The string of exclamations that erupted as they passed the bag around is hardly printable, but needless to say, they were surprised. My professor even expressed some doubt as he accused me of buying the fish and smuggling it out to the beach in my bathing suit.

Seine netting for tropical fishes in Shinnecock Bay. (Photo by By Todd R. Gardner)

For the rest of the day the lionfish dominated our thoughts and conversations. We decided that this fish was either spawned somewhere in the Atlantic, or transported here as a larva in ballast water in a ship. Being an aquaculturist, I had my doubts about the ability of a larval fish to survive such a trip in total darkness, unable to feed. If it was spawned in the Atlantic, it seemed that the only reasonable explanation was that its parents were released by aquarium hobbyists, but there were still a lot of unanswered questions. If multiple lionfish were released, what are the chances of them surviving to adulthood, encountering others, and spawning? Certainly, near zero in the Northeast, but suppose a pair had formed from released individuals somewhere south of here. What are the chances of us finding one of their offspring here in New York? Every year we encounter a handful of tropical species here, but that is probably the result of billions of larvae produced from millions of spawning events throughout the tropical and subtropical western Atlantic.

We returned to our lab at Hofstra University around noon. I placed the lionfish in a quarantine tank, fed the rest of my fish and sent out a few e-mails about our catch. Around 1:00 PM we logged onto fishbase.org to check the range of Pterois volitans. We wanted to see just how far away the closest population was from here. Viewing a map that displays data points at confirmed collection sites for the species, we were surprised to see a single point in the eastern Atlantic Ocean where two specimens were reportedly collected in the 1930s. This was a particularly exciting piece of information. For the first time since seeing the wayward fish early that morning, I began to consider the possibility that lionfish were in the Atlantic as part of a natural range extension. I acknowledged that this was very unlikely, especially considering the fact that there hadn’t been a single report of an Atlantic lionfish in more than 70 years.

After lunch I checked my e-mail to see if I had received any responses to my initial messages. To my surprise, there were more than 20 responses. One of the people who received the message, forwarded it to a fish ecology list server and sent me all the replies. Almost all of them said essentially the same thing: “Lionfish don’t live in the Atlantic ocean. Obviously, you’ve caught someone’s released pet.” A few were more along the lines of: “Are you sure it was a lionfish? Maybe it was a sculpin or a sea robin.” I resisted the temptation to write back in defense of my fish-identification skills and to explain that when people release their pet fish, it’s usually because they’ve grown too large for their tank or for the owner’s food budget. This fish was tiny! You can’t even buy a lionfish this small.

With each response, my hopes of solving this puzzle shrank a little bit more – until I got to the very last message in my in-box. It was from Jon Hare at the National Marine Fisheries Service (now called NOAA fisheries). He explained that NOAA (the National Oceanographic and Atmospheric Administration) had been receiving reports of lionfish sightings off the coasts of Florida, Georgia, and North Carolina for the last two years. In fact, he and some colleagues were just about to submit a paper documenting the reports and suggesting that they may represent the successful introduction of a non-indigenous fish species into the Atlantic Ocean. There was only one problem with this hypothesis. All of the individuals sighted and caught over the last 2 years had been large adults. So it was conceivable that each one could have been a released pet and that no reproduction was taking place – until now. This little post-larval fish that showed up on a dock piling in Fire Island inlet on September 16, 2001, was the first young-of-the-year lionfish ever found in the Atlantic Ocean and the first evidence of successful reproduction. It appeared that the lionfish paper would need to be revised.

The author, diving in the murky waters of Long Island, in search of tropical fishes. (Photo by Matthew Ajemian)

The next day I was contacted by Paula Whitfield, the primary author on the Lionfish paper. She asked if I would be interested in co-authoring the paper and I happily agreed. As Paula filled me in on the details of the invasion, I listened in amazement to stories of numerous Atlantic lionfish sightings and captures over the summer of 2001. Most of them were observed by recreational SCUBA divers on shipwrecks off the coast of North Carolina, but several were also reported from Florida, and one was speared by a diver on a reef in Georgia. She told me about a dive shop that had video footage of a lionfish on a North Carolina shipwreck displayed on its website. I couldn’t believe it. They were actually using the lionfish invasion as a promotion for their business. How did I not hear about this until now? I mentioned to Paula that Fishbase was reporting two lionfish collected from the Atlantic in the 1930s. She told me that she had already looked into it and that those data points were the result of a mistake in the data entry process. Those specimens had actually been collected in Indonesia.

Over the following weeks, reports of lionfish encounters continued to come in at an alarming rate and one week after our capture at Fire Island inlet, I found another post-larval lionfish at the very same dock. A few weeks later, my friend, Chris Paparo at Atlantis Marine World put me in touch with one of his volunteer divers who had found two juvenile lionfish in Shinnecock bay (also along the south shore of Long Island) around the same time as I found mine. In all, 34 lionfish were verified from 12 Atlantic locations in 2001 (up from 6 lionfish at 3 locations in 2000). By now (2006), lionfish sightings along the Atlantic coast have become so commonplace that attempts to count them have become futile. Not long after our initial discovery of P. volitans on Long Island, I began working as an aquarist at Atlantis Marine World where I keep an exhibit devoted to local lionfish. It’s never a problem keeping it filled to capacity and when we catch more lionfish than we can house, we send some off to other aquaria.

The appearance of P. volitans in the Atlantic has sparked some lively controversy over possible means of introduction. The two active hypotheses today are essentially the same ones we discussed on that day in 2001 when we found our first baby lionfish. If you think about it, there really aren’t any other reasonable explanations. The first one is that lionfish larvae or eggs were drawn into the ballast of a ship somewhere within their native range and discharged along with the foreign ballast water when the ship reached its destination port in the southeastern United States. The second, and in my opinion, more reasonable hypothesis is that lionfish from a home aquarium, or somewhere along the commercial supply chain, were released, intentionally or otherwise, into the wild. Although a number of aquatic invasions have been attributed to ballast water transport, it is a relatively rare means of marine fish introductions. One reason for this is that most marine fishes have a relatively long larval stage and very little yolk reserve in their eggs, so they need to start feeding soon after hatching. Furthermore, they are primarily visual feeders, so if a larval fish of any kind is drawn into a ship’s intake and makes it past whatever filters are in place to prevent debris from entering the ballast tank, they would likely starve to death in the dark chamber during the two week trip from the home range of P. volitans, to the eastern United States.

In a recent paper, Semmens, et al. (2004) examined this question in detail. They looked at records from ships traveling between ports within the home range of P. volitans, and the southeastern United States. Fish population data from the ports of origin were compared to the results of exotic fish surveys along the east coast of Florida and marine ornamental fish trade data. The process of drawing in ballast water can essentially be thought of as a random sampling technique in terms of capturing fish eggs and larvae from the water surrounding a ship. Therefore, if ballast water was the means of transport for these fishes, we should expect to see a strong correlation between the most abundant species in the ports of origin and the most common exotic species to turn up in fish surveys near destination ports. No such relationship was found in the case of the Florida fish surveys; however, all of the 16 exotic fish species found within the survey area are among the most commonly imported species in the marine ornamental fish trade. Whereas these statistics may not offer any definitive answers, they certainly don’t support the ballast water hypothesis as a means of introduction for P. volitans into the Atlantic Ocean.

We may never know how lionfish came to inhabit the Atlantic Ocean, and their impact, if any, on their new ecosystem may not be clear for many years; however as keepers of exotic species, aquarium hobbyists need to be conscientious about all of the environmental and moral issues that our activities touch on: the chemicals we use, the wild harvest of marine life, invasive species, the ethics of keeping animals in captivity, just to name a few. For although we are a part of the global ecosystem and our actions may be no less natural than those of any other organisms, we bear the burden of having at least a partial understanding of our impacts on it. I believe that the positive effects of aquarium keeping, in terms of its educational value and the appreciation it fosters for aquatic life, far outweigh any negative impacts it may have on the environment, however there are some things we should keep in mind. One is that the introduction of non-indigenous species into new locales is widely considered to be second only to habitat destruction as a cause of extinction. Another is that there are people out there who would love to see our hobby shut down and if we refuse to ponder and discuss these issues, we will be ill prepared to defend ourselves. We owe it to ourselves as well as to the planet to be responsible aquarists.

Further Reading

1. Hare, Jonathan A. and Paula E. Whitfield. 2003. An Integrated Assessment of the Introduction of the Lionfish (Pterois volitans/miles complex) to the Western Atlantic Ocean. NOAA NOS Technical Memorandum CCFHR 1 Available online at:http://shrimp.ccfhrb.noaa.gov/lionfish/lionfish_ia.pdf.
2. Robins, Robert H. Date unknown. “Biological Profiles: Red Lionfish.” Ichthyology at the Florida Museum of Natural History. Available online at: http://www.flmnh.ufl.edu/fish/Gallery/Descript/RedLionfish/RLionfish.html.
3. Whitfield, P.E., T. Gardner, S.P. Vives, M.R. Gilligan, W.R. Courtenay, Jr., G.C. Ray, and J.A. Hare. 2002. Biological invasion of the Indo-Pacific lionfish Pterois volitans along the Atlantic Coast of North America. Marine Ecology Progress Series 235: 289-297. Available online at: http://www.int-res.com/abstracts/meps/v235/p289-297.html.
4. Whitney, Dawn. 2003. Introduced Species Summary Project–Lionfish (Pterois volitans). Available online at: http://www.columbia.edu/itc/cerc/danoffburg/ invasion_bio/inv_spp_summ/ Pterois_volitans.html.
5. Semmens, Brice X., Eric R. Buhl, Anne K. Salomon, Christy V. Pattengill-Semmens. 2004. A Hotspot of Non-native Marine Fishes: Evidence for the Aquarium Trade as an Invasion Pathway, Marine Ecology Progress Series, vol. 266. Available online at: http://www.reef.org/data/meps_exotic.pdf)