According to researchers at Nova Southeastern University’s (NSU) Oceanographic Center, hurricanes help the spread of marine invasive species throughout a region, via their dramatic effect on ocean currents.

NSU researchers looked at the distribution of lionfish in the Florida Straits and how under normal weather conditions, currents represent a potential barrier to the transport of lionfish eggs and larvae across the region. The researchers found that as a hurricane passes, the flow of water shifts from a strong, northern flow to a strong, eastern flow and it’s these changes in flow direction and speed that likely carry lionfish larvae and eggs from Florida to the Bahamas and can explain how lionfish were able to cross the Gulf Stream so soon after their introduction to South Florida waters. It’s believed lionfish were first introduced into marine waters off Florida in the early 1990s from local aquariums or fish hobbyists.

Lionfish belong to the genus Pterois, venomous marine fish native to the Indo-Pacific. Two of the nine species of Pterois, the red lionfish (P. volitans) and the common lionfish (P. miles), have established themselves as significant invasive species off the East Coast of the United States and in the Caribbean. About 93% of the invasive population in the Western Atlantic is P. volitans and they have been described as “one of the most aggressively invasive species on the planet”. Pelagic larval dispersion is assumed to occur through oceanic currents, including the Gulf Stream and the Caribbean Current, as well as translocation of larvae via the ballast water of shipping vessels.

Matthew Johnston, Ph.D., one of the research scientists at NSU’s Oceanographic Center who conducted the study says that once they were established in the Bahamas, hurricanes have allowed lionfish to spread quickly against the normal, northwestern direction of water flow in the area. In addition, such storms helped increase the spread of lionfish by approximately 45% and their population size by 15%.

“This is the first-ever study that shows hurricane-altered ocean currents are able not only to help, but actually accelerate the invasion of non-native marine species of any kind,” said Johnston. “Lionfish are pretty sedentary, so this is like creating express lanes on a superhighway — otherwise, that’s a pretty long swim for lionfish babies.”

“The study has broader implications in that global climate change may cause an increase in storm frequency and/or intensity, perhaps further accelerating the spread of marine invasives,” Johnston said. “Given that South Florida is a hotspot for marine invasive species, the transport of marine larvae from Florida to the Bahamas on hurricane-altered water flow may become commonplace for invasive and native species alike.“

The primary concern relating to lionfish invasions is that they pose a major threat to reef ecoystems in these areas. A potential ecological impact caused by Pterois is their effect on prey population numbers by directly affecting food web relationships, which could could ultimately lead to reef deterioration and negatively influence Atlantic trophic cascade. There has been numerous studies on the potential impacts of invasive lionfish species in the last two decades. A 2010 study conducted by Mark Hixon, an Oregon State Univeristy professor of zoology and expert on coral reef ecology determined that a single lionfish per reef reduced young juvenile fish populations by 79% in only a five-week period. Hixon’s data showed many species to be affected, including cardinalfish, parrotfish, damselfish and others, with one large lionfish observed consuming 20 small fish in a 30-minute period 1.

Control and eradication of invasive lionfish

Measures to control the population of non-native lionfish species are currently implemented by many marine conservation organisations in affected regions, with organised hunting expeditions for Pterois such as the Environment Education Foundation’s ‘lionfish derby’ held annually in Florida. Rigorous and repeated removal of lionfish from invaded waters could potentially control their exponential expansion.

Such controlling methods are currently of the upmost importance, as in addition to the ecological impacts of invasive lionfish in the Florida region, potential economic impacts have also been reported. According to an economic commentary from Florida TaxWatch 2, invasive lionfish pose a serious threat to Florida’s saltwater fishing industry — the second largest in the nation — and the thousands of jobs it supports, as a result of the negative impact lionfish have on fish populations. Some 109,000 jobs are tied to recreational fishing in the region, and more than 64,000 dependent on the commercial fishing industry, all bolstering the state economy. Florida Fish Wildlife Conservation Commission is working to control the population of lionfish by encouraging lionfish removal from reefs around the state, promoting a lionfish reporting smartphone app, and prohibiting lionfish from being imported for aquariums, with ten lionfish derbies also planned this year starting in May throughout the state. The Reef Environmental Education Foundation (REEF) is a marine conservation organisation based in Key Largo, Flordia that has been working with Federal and State partners as well as divers, public aquaria, and foreign fisheries departments to enact rapid response protocols and to assist with scientific investigations related to non-native lionfish species and other invasives. REEF has maintained an on-line educational section on non-native species as well as an on-line exotic species reporting page. Since 2006, REEF has been working in close partnership with government agencies and partners throughout the region to help develop lionfish response plans, train resource managers and dive operators in effective collecting and handling techniques and conduct cutting edge research to help address the invasion.

NSU’s findings are being published in the journal Global Change Biology and is available here.

For more information and materials on invasive lionfish species, visit: http://www.reef.org/lionfish

– JK

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