Invasive Species

Mediterranean Invasion: The Lionfish

Schilling, H.T., Kalogirou, S., Michail, C. et al. Testing passive dispersal as the key mechanism for lionfish invasion in the Mediterranean Sea using Lagrangian particle tracking. Biol Invasions (2023).


Invasive marine species are flooding into the Mediterranean Sea at an unprecedented rate. On average, a new, non-indigenous species is reported every eight days. The Suez Canal and the equalization of salt dissolved in the Red Sea have contributed to species crossing over from the Indo-Pacific region. This is changing coastal ecosystems and disrupting their natural balance by increasing resource competition and shifting predator/prey abundances.

The common lionfish (Pterois miles) is a prime example of this invasion. It has been one of the fastest expanding non-indigenous species in the Mediterranean Sea since its first confirmed sighting in Lebanon in 2012. It can survive in a wide variety of habitats and with no natural predators in the region, populations are difficult to eradicate once established. Adults have limited home ranges, moving no more than a mile across 15 days. This suggests that population expansion occurs during the species’ larval phase.

Common lionfish (Pterois miles) by Alexander Vasenin

Lionfish are broadcast spawners, releasing large amounts of eggs into the water to be fertilized. Once fertilized, these larvae free-float in the water column anywhere from 20 to 35 days before settling to the ocean floor to grow into the adult form. Currents are the primary mode of dispersion, carrying these larvae to new areas to colonize.

Using particle tracking simulations, researchers tested to see if expansion of the common lionfish in the Mediterranean Sea could be explained solely by the passive dispersal of their larvae. The end goal was to assess the reliability of particle tracking simulations for future predictions of passive dispersal to enhance monitoring and response to invasive species.

Follow the Particles

The simulation was able to accurately predict lionfish settlement in the Mediterranean Sea based on observation data from 2012 to 2020. This supported the hypothesis that lionfish expansion is primarily driven by passive dispersion.

However, there were notable differences in the simulation and real world observations. Namely, the northward expansion into the Aegean and Adriatic Seas was not observed to the degree that the simulation predicted. Also, lionfish were observed in Italy several years before the simulation predicted their arrival.

Lionfish presence in the Mediterranean Sea from 2012 to 2020. A: Simulated prediction of lionfish expansion based on passive dispersal. B: Reported observations of a lionfish with each dot representing an independent observation. (Schilling, et al. 2023).

Predicting the Future

The results demonstrate the power of particle tracking simulations in being able to quickly calculate passive dispersion of larvae based on currents in the region. However, a more sophisticated model is needed to fully capture the complexity of the Mediterranean environment. This includes factors such as surface temperature and temporary, extreme currents which could explain the differences between the simulation and observation data.

Incorporating these changes into future analyses can provide more accurate predictions to help improve lionfish monitoring. Therefore, individuals can be observed and removed more quickly before a population can establish itself. This will reduce negative impacts associated with invasive species by preserving the balance of local ecosystems.


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