Coral reefs are one of the most complex ecosystems on the planet, and every creature that lives on them has a role to play however when these creatures start being eaten this is bad news for the reef. There are currently two species of lionfish destroying western coral reefs in the Bahamas and Caribbean Pterois volitans and Pterois miles. Between them, these two fish are decimating reef fish populations due to their voracious eating habits and rapid breeding rates.
Lionfish originate in the Indo-Pacific from the east coast of Africa to the eastern edge of Micronesia, however it is thought that these lionfish were introduced into the Atlantic ocean from Florida during hurricane Andrew in 1992. Since then they have taken overmost coral reefs in the Bahamas and Caribbean bringing catastrophe to the coral reefs they inhabit. With the ability to extend their stomach to over 30 times its usual volume and large fin rays that make them appear larger than they are, they can prey on large fish given them a much broader range of fish to eat. Female lionfish also spawn once every 4 days all year round releasing approximately 2 million eggs a year, with females reaching sexual maturity at around a year old. This means lionfish numbers increase rapidly to the point where they completely take over an ecosystem or reef.
From 2004 to 2010 lionfish went from being rare in the Bahamas to making up over 40% of the total predator biomass (the total weight of predatory organisms) in the area while causing a biomass decrease of 65% in the lionfishes 42 prey fish in only 2 years. This massive reduction in reef fish biomass is obviously extremely bad for the reef, as this reduces the number of prey fish available for other predators and causes some food chains to be completely destroyed.
One of my other blogs (How Overfishing Is Destroying Coral Reefs) talks about the danger overfishing poses to coral reefs, and lionfish essentially have the same effect. By dramatically reducing the numbers of herbivorous grazing fish (fish that eat algae on coral reefs) then it allows the algaes growth to run wild, spreading across the reef like a plague, releasing nutrients into the water. This in turn causes massive bacterial growth which eventually kills off the corals.
This invasion has been a problem in western Atlantic reefs for many years now but now this whole process is repeating in the Mediterranean, and while there numbers seem low at the moment due to their rapid spawning rates and high growth rates these small numbers could soon rapidly increase to the kind of epidemic we see in the Bahamas and Caribbean.
However as long as there is a fast response to growing lionfish populations in the Mediterranean they may not gain a foothold as they have done in the past, with more and more people becoming aware of the threat they pose, and more people hunting the lionfish to reduce its numbers there may still be hope for Atlantic and Mediterranean coral reefs yet.
Kletou, D. Hall-Spencer, JM. Kleitou, P. (2015) A lionfish (Pterois miles) invasion has begun in the Mediterranean Sea: https://doi.org/10.1186/s41200-016-0065-y [Accessed 7th Feb. 2018]
Green, SL. Akins, JL. Maljković, A. Côté, IM. (2012) Invasive Lionfish Drive Atlantic Coral Reef Fish Declines: https://doi.org/10.1371/journal.pone.0032596 [Accessed 7th Feb. 2018]
Albins, MA. Hixon, MA. (2008) Invasive Indo-Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral-reef fishes: https://doi.org/10.3354/meps07620 [Accessed 7th Feb 2018]
Lionfish Facts: https://lionfish.co/lionfish-facts [Accessed 7th Feb 2018]