Jay Hemdal
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Fish Medic
Aquatic Invasive Species
Jay Hemdal
Introduction –
Humans have moved plants and animals knowingly (and unknowingly) from one location on Earth to another for tens of thousands of years. The argument can be made that there has never been a translocation of a species that did not in some way, do some harm to the environment that it was introduced to. The magnitude of this harm varies greatly; from a single carp added to small pond that might eat some native aquatic vegetation to the invasive lionfish that are rapidly degrading a huge ecosystem in the Tropical Western Atlantic ocean. Some people mistakenly believe that certain translocations are beneficial (usually to humans) and other people think that at the very least, they cause little harm. Reintroductions undertaken by zoos, aquariums and NGOs, using proper science, have proven to be a very successful method of moving organisms without such a degree of environmental damage. This article examines these issues from the perspective of marine aquariums, for both public and private aquarists.
In addition to intentional translocations, marine species can be moved around the globe after being incorporated in the water held as ballast inside ships, as fouling organisms on the outside hulls of ships, in shipments of fishing bait, in consignments of live food, and through various aspects of the aquarium trade. By the sheer number that have resulted from these pathways, incidental movements through the commercial trade have proven to be the most egregious cause of invasive species.
One might think that since all of the world’s oceans are inter-connected, that aquatic animals already have had the opportunity to travel wherever they wish. Actually, ecological barriers tend to restrict the movement of marine species worldwide. For example, if a fish has a two week larval stage, but the rate of the prevailing currents would cause the larval fish to take four weeks to arrive at a distant shore, that would serve as a barrier to its further distribution in that direction. The Arctic Ocean, Cape of Good Hope and Cape Horn all serve as minimum temperature barriers keeping many aquatic species from negotiating through them to another body of water. The tropics themselves serve as an upper thermal limit keeping cold water animals from crossing the globe pole to pole (although some species can make this trip by staying at depth, where the water is cold enough for them to survive).
Problems develop when people move animals if they lose sight of the simple hierarchy that must govern any such moves: the ecosystem takes precedent over any single population that resides in it, and populations are always more important than individual animals. This means for example, while releasing an unwanted pet fish (as opposed to euthanizing it) may be beneficial to that individual, it risks harming populations or whole ecosystems, so the safety of the population or ecosystem must trump that of the individual animal.
Definitions -
Introduced species –
Any organism that is discovered living outside its normal range can be considered an introduced species, although for some people, there must be a reproductive population in order to fully meet this definition. Routes for these introductions vary from rare natural causes (such as a log floating across the ocean with some animals living on it that become established on distant shores) to deliberate establishment of a population by humans for some presumed benefit.
Invasive species –
An introduced species whose population grows and causes damage to the environment or other populations of organisms, noticeable by even a casual observer, would be considered an invasive species.
Feral species –
These are domesticated species that have either escaped, or were released to the wild. Some may develop reproducing populations (wild hogs) and would then be considered an invasive species. Domestic cats may blur the line of this definition in that house cats that are allowed outdoors may decimate local bird population, yet still return to their owner’s homes. The only real example of a widespread feral fish species would be the domesticated goldfish, Carassius auratus that has become an introduced species in some areas of the United States.
Naturalized species –
These are introduced species that have been present in a given ecosystem for so long that their original mode of entry may be unknown, and their effect on the environment has stabilized to a “new normal”. A prime example of this is the orange cup coral, Tubastraea coccinea in the Caribbean. This coral has been in the region for so long that it wasn’t until a decade ago that researchers determined that it is actually an introduced species from the Pacific Ocean that probably hitched a ride into the Atlantic on the hull of old wooden ships.
Propagule pressure –
Also termed “introduction effort” this simply refers to the number of organisms released to a specific area of a new environment. Certainly, the propagule pressure of a single male fish being released is simply not enough to further develop a population. Natural losses from predation require a larger propagule pressure, as does the inherent need a population has for maintaining genetic diversity. If a population forms that is too inbred (say from just a pair or two fish) it may not have the genetic diversity necessary to persist for long periods. Aquarists should take note that this very same “pressure” can affect the spread of diseases in their aquariums. Release of a few Cryptocaryon tomites into an aquarium from an unwashed net might not cause a disease, but adding a fish acutely infected with the same disease will likely cause a full blown disease episode because many hundreds more parasites are being introduced at once.
Reintroduction-
Returning a species to an area where it once was found (but now is extirpated) is termed reintroduction. In most instances, this process is developed by scientists, and involves governmental approval. The animals involved are typically captive raised with the specific goal of returning a self-sufficient breeding population to the species historic home range. There are also some reintroduction programs that utilize wild collected animals in a translocation process.
Translocation-
In some instances, the desire to retain a population is so great that the idea is entertained, of moving a sub-population to an area suitable for them to live, but where they had not been previously found. While this goal may be admirable, the final result may be no different than that of any other introduced species.
Augmentation-
If a given population is thought to be too small, or too fragmented to persist without intervention, population augmentation may be attempted. In this case, captive raised or translocated animals are added to areas with some existing animals are still found. The drawbacks to this technique are there is a risk of disease transfer along with the captive animals (putting the remnant natural populations at risk) as well as unknown variables that include possibly damaging the gene pool of the natural populations. A notable example of an augmentation effort is the propagating and restoring of Atlantic Corals by the Coral Restoration Foundation and other groups.
Most importers and some retail pet stores utilize centrally filtered systems to house their animal stock. This affords them better control over water quality parameters and ensures that their customers receive animals acclimated to a common water source. However, by mixing animals from all across the planet, a variety of diseases can be mixed together as well. Once this is done, it cannot be easily undone and aquarium animals housed under these sorts of conditions should never be released into natural waters. An example of this concern in action is seen with Association of Zoos and Aquariums members who are involved with the captive propagation of endangered Atlantic corals. The policy is that if any of these corals have been housed alongside Pacific corals, they can be used for educational display only and never be returned to the Atlantic. The Aquarium Supply Chain: “The Great Melting Pot” for exotic pathogens? |
Case Histories –
Caulerpa algae -
A domesticated strain of algae, Caulerpa cf. taxifolia was shared among public aquariums in Europe during the 1980’s. At some point, some of this algae was sent to the Musée Océanographique in Monaco. They operated their exhibits on a semi-open basis, with water flowing from their tanks back to the Mediterranean Sea. It is alleged that fragments of this algae made its way into the sea and from there became an invasive species. The museum director at the time, the late François Doumenge, denied that the source of the algae was the aquarium itself, and that divers just found it there first because that was where the sampling took place. Dubbed the “killer algae” by reporters prone to hyperbole, this species has none-the-less devastated littoral regions in the Mediterranean. This species is listed in the IUCN’s compilation of the 100 most invasive species on Earth (at least that they know of so far!).
In 2000, this species of algae was discovered in two lagoons near San Diego, California. Laws were quickly enacted forbidding its sale in California, and eradication methods (poisoning and physical removal) were employed that have seemingly been successful in stopping the invasion in Southern California. This species is listed as a “noxious weed” by the United States Department of Agriculture Animal and Plant Health Inspection Service, Plant Protection and Quarantine division (USDA APHIS PPQ), this bars interstate transport of this species in an attempt to quell future invasions.
Lionfish –
Lionfish are tropical reef fish found in the Pacific and Indian oceans, as well as the Red Sea. Popular in home aquariums, (despite their venomous spines) they have been introduced into the Atlantic Ocean and have become a serious invasive species there.
Lionfish are now common in the Atlantic Ocean, where they have no natural predators, although some groupers and sharks may learn to eat them. They can survive water temperatures as low as 50 degrees, so they can flourish year-round as far north as North Carolina, and seasonally can be found as far north as Cape Cod.
Growing to 18” in length, lionfish are active nocturnal predators, hunting small fishes, shrimps and crabs, their widespread side fins to corral their prey into a corner and then swallowing them. Their prey in the Atlantic Ocean has never had to deal with this feeding strategy before, so they make an easy meal for the lionfish.
It has been reported that on some heavily impacted reefs, lionfish make up 40% of the fish biomass and can consume up to 65% of the available prey species (Green et-al 2012). Lionfish can live in a wide variety of habitats: shipwrecks, coral reefs, sea grass and mangrove areas, so few animals can find an area safe from them.
Control of this invasive species does not seem likely. Lionfish are known to be cannibalistic, but so far, this has not limited their population growth in the tropical Western Atlantic Ocean to any great degree. Only coronet fish and some groupers have been reported to feed on juvenile lionfish in the Atlantic Ocean – other predators tend to avoid lionfish. However, they make a tasty meal for humans, and in many areas “lionfish derbies” are formed where divers catch as many as they can and then prepare them as food.
Since two species, the black lionfish, Pterois miles and the red lionfish, Pterois volitans have been recorded from the Tropical Western Atlantic Ocean, which means that at least two different introductions of these fish must have occurred. A single lionfish was reported to have been found off Dania, Florida in 1985. The first reports of multiple lionfish in the Atlantic were recorded from Biscayne Bay off of Miami in 1992. Rumor has it that a home aquarium housing lionfish was washed out to sea due to Hurricane Andrew in 1992. It is unlikely that lionfish could have survived such devastation, let alone find a mate and reproduce and then be collected. More likely is that the fish found in 1992 was an intentional aquarium release, and probably did not reproduce. Indeed, lionfish were not reported again from Biscayne Bay until 2005 and did not become common there until 2009. After 1992, the next reported occurrence was in 1995 off of Palm Beach County, Florida. This coincides with reports of other Pacific Ocean fish species being found in the same area at that time. One hypothesis as to why this may have occurred is that the fish could have been released by a tropical fish dealer in the misdirected hopes of introducing expensive aquarium fish from the Pacific, closer to home, where divers could then collect and sell them back to the pet trade.
In any event, lionfish then showed up in Bermuda in 1999, more than a thousand miles from Florida. Remember however, that the Gulf Stream current flows north from Florida at an average speed of four miles per hour. Lionfish larva could be transported to Bermuda by this current in a bit more than 10 days. Later that same year, SCUBA divers off of South Carolina began reporting seeing lionfish as well. By the fall of 2001, baby lionfish were being reported from Long Island (although they cannot survive the winter that far north). By 2008 or 2009, the Gulf Stream had spread lionfish clockwise throughout the Tropical Western Atlantic, to central America and then northward to the Florida Keys, just south of where they were first seen. Now that lionfish have come full circle, there is no hope of ever eradicating them from this ecosystem.
Red Sea Fishes in Florida –
Table 1 is an interesting look at the variety of exotic tropical marine fishes that have been sighted in Florida waters since 1990 by the Reef Environmental Education Foundation (REEF) – a well-known environmental citizen action group. In one study of the data (Semmens et-al 2004) the conclusion was drawn that these introductions could have only been made through two pathways; ballast water transfer or from the aquarium trade. They rightly concluded that the latter was the source of these fish introductions, but they did not speculate as to why the introductions were made.
Chaetodon fasciatus – Red Sea raccoon butterflyfish *
Cromileptes altivelis – Panther grouper
Dascyllus aruanus – Three striped damsel (unconfirmed)
Gramma loreto – Royal gramma
Naso lituratus – Naso tang
Platax orbicularis – Orbicularis batfish
Pomacanthus annularis – Bluering angelfish *
Pomacanthus asfur – Arabian angelfish *
Pomacanthus imperator – Emperor angelfish *
Pomacanthus maculosus – Yellowbar angelfish *
Pomacanthus semicirculatus – Koran angelfish * (unless afflicted with HLLE)
Pomacanthus xanthometopon – Blueface angelfish *
Pterois volitans – Black lionfish
Rhinecanthus verrucosus – Bursa triggerfish
Zanclus cornutus – Moorish idol *
Zebrasoma desjardinii – Red Sea sailfin tang *
Zebrasoma flavescens – Yellow tang
Zebrasoma veliferum – Sailfin tang
Zebrasoma xanthurum – Purple tang *
Table 1. Exotic marine aquarium fish species reported from U.S. coastal waters around Florida. (adapted in part from Schofield et-al 2009, Semmens et-al 2004 and Hemdal 2006)
People familiar with the pet industry will quickly understand why species such as panther groupers, lionfish, orbicularis batfish and Pacific damselfish are on the list. Most pet stores and public aquariums receive requests every month from hobbyists looking to re-home unwanted fishes such as these. Less easy to explain in that fashion are the presence of species such as the Moorish idol and the angelfishes. In 15 years in the pet industry and 25 years with public aquariums, I have NEVER had anyone offer up as a donation, any species in table 1 marked with an asterisk. These fish all retain high value in captivity and would normally be sold back to a pet store, or accepted willingly as a donation by a public aquarium. Why then would people release these valuable fish into the sea as unwanted pets? The epicenter of these releases seems to have been northern Broward County, in South Florida. Any subsequent sightings north of that point (into Palm Beach County) can easily be attributable to the strong Gulf Stream current that flows northwardly very close to shore in that region. Likewise, the paucity of sightings south of that location is possible evidence of the fish being unable to swim long distances against the prevailing currents. One theory is that a marine fish wholesale company released these fish with the intent of developing breeding populations that divers could then exploit for the aquarium trade. There was at least one operation nearby that was importing many shipments of fishes from the Red Sea around this time. A zoo curator familiar with the region offers another hypothesis; that rich “snowbirds” may have released their unwanted aquarium fish before returning north for the summer. Certainly the low numbers of exotic fish sighted could be attributed to having come from even just a few large home aquariums, but the question remains why these people would not have just sold the fish back to a pet store? Maybe the wish to see their fish “be free” overrode common sense?
Rumors have persisted for many years of fish collectors translocating fairy basslets (Gramma loreto) from Cay Sal Bank in the Bahamas into Florida waters in an attempt to establish a breeding population of these fish that are not native to the area, so that these populations could be more easily exploited by local collectors.
Not all fish dealers are part of the problem. One collector in the Florida Keys actually helped round up a stray Pacific batfish that had been living on an offshore reef.
Pet Fish Releases –
With the potentially large adult size of some aquarium fishes, home aquarists who buy them need to consider which steps they will take when the fish outgrow their aquariums. Purchasing a larger aquarium is certainly an option, albeit a costly one. Returning the fish to a pet store might also be a solution, although most stores do not have aquariums all that much larger than that of home aquarists and are usually unwilling to take back the grown fish they sell as juveniles. Donating it to a public aquarium might be an alternative except that most of these large fish are such long-lived creatures; aquariums usually have enough of these fish for their exhibits. More commonly, public aquariums are now using the very structured Institutional Collection Plan (ICP) process to choose the animals for their exhibits. While this results in exhibits that house the best possible diversity of species for their visitors, it does not allow much in the way of a “fudge factor,” where you can call up a public aquarium and try to talk them into taking your over-sized home aquarium fish – if it causes them to deviate from their collection plan.
Not buying a species that you know you will be unable to care for when it reaches adult size is certainly the most prudent course of action. Some people have resorted to euthanizing their over-sized fish out of desperation, not being able to find a better home for it.
One option that must never be considered is releasing these large fish to the wild. Captive fish, used to the confines of a home aquarium, are unlikely to survive, yet the diseases they can carry may flourish. The person releasing the fish is usually not able to identify which aquatic habitat would be best suited for the fish and may just release the fish into the water regardless of the habitat. Finally, if the released fish does somehow manage to survive, and meets up with another released member of the opposite sex, reproduction may occur and an invasive species problem may develop. In no instance should the needs of an individual animal be placed above that of an ecosystem.
Sanctioned introductions –
Although historically not very common, government-sanctioned releases of marine animals could take place more often in the future. Caribbean corals are being propagated in captivity for release into the wild through the SECORE project (Delbeek 2011) and arguments have been made that perhaps the Banggai Cardinalfish (Pterapogon kauderni) could be bred in captivity and then released within its native range to augment wild populations. Both of these projects must be mindful of two potential pitfalls; the accidental co-introduction of exotic pathogens along with the target species and the potential change in the genetics of the populations by introduction on novel genes to a natural population. In the case of the Banggai Cardinalfish, a researcher has demonstrated the presence of an iridovirus associated with episodes of mass mortality in newly imported cardinalfish (Weber, et-al 2009). If this disease is unknown in wild populations of these fish, captive stock must never be returned for fear of causing a pandemic in those wild populations.
One notable failed sanctioned introduction was undertaken in Hawaiian waters in 1958 when some bluestripe snappers, known as ta ‘ape (Lutjanus kasmira) were introduced from the Marquesas with the intent of improving local fisheries. Local fishers now find them more of a pest species than an asset to their catches (Hoover 2007). Their populations are also incriminated in causing damage to populations of more desirable food fishes.
Conclusion –
There has never been an instance where the movement of one species to a new location by humans has not caused some change to the environment. The degree of change varies, and such introductions may have a benefit to humans that overshadows the ecological damage, but nonetheless, this harm to the environment is always present. From the collection of a clownfish that leaves its host anemone less protected from butterflyfish predators to the massive invasion of lionfish in the tropical western Atlantic Ocean – every movement of an aquarium animal changes the environment to some degree.
Even reintroductions designed with the conservation of a particular species in mind are fraught with peril. What if the endangered species being reintroduced brings with it some exotic disease that it acquired while in captivity? What if the genetic make-up of the reintroduced species is different than the population that had previously been in the ecosystem?
Humans need to stop being so conceited and provincial in their attitudes towards the movement of animals from one ecosystem to another. Before you acquire any animal, think about all the possible ramifications and be certain that the movement of that specimen is prudent and justifiable!
References –
Delbeek, J.C. 2011. Advanced Aquatics: Project SECORE stalks the spawning stony corals. CORAL Magazine. Nov/Dec: p.130
Firchau, B., Warmolts, D. and Branshaw, P. editors 2012. Marine Fish Taxon Advisory Group (TAG) Regional Collection Plan (RCP), 2nd edition. 2012.. Association of Zoos and Aquariums, Silver Springs, Maryland. (152pp)
Green, S. J., J. L. Akins, A. Maljkovic, I. M. Côté. 2012. Invasive lionfish drive Atlantic coral reef fish declines. PLoS One 7:e32596.
Hemdal, J.F. 2006. Advanced Marine Aquarium Techniques. 352pp. TFH publications, Neptune City, New Jersey
Hoover, J.P. 2007. Hawaii’s Fishes – A Guide for Snorkelers and Divers. 181pp. Mutual Publishing, Honolulu, Hawaii.
IUCN 1998. Guidelines for Re-introductions. Prepared by the IUCN/SSC re-introduction specialist group. IUCN, Gland, Switzerland and Cambridge, UK 10 pp.
Schofield, P. J., J. A. Morris, Jr. and L. Akins. 2009. Field Guide to Nonindigenous Marine Fishes of Florida. NOAA Technical Memorandum
NOS NCCOS 92.
Semmens, B.W., Buhle, E.R., Salomon, A.K., Pattenfill-Semmens, C.V. 2004. A hotspot of non-native marine fishes: evidence for the aquarium trade as an invasion pathway. Marine Ecologial Progress Series. Vol. 266: 239-244.
Weber, S.E., Waltzek, T.B., Young, D.A., Twitchell, E.L., Gates, A.E., Vagelli, A., Risatti, G.R., Hedrick, R.P., and Frasca S. 2009. Systemic Iridovirus Infection in the Banggai Cardinalfish (Pterapogon Kauderni Koumans 1933) J Vet Diagn Invest 21:306–320
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