Mesophotic Coral Ecosystems

Figure 6.15. Invasive lionfish ( Pterois volitans ) on a MCE at 60 m off Utila, Honduras (photo Ally McDowell).

6.7.2. Lionfish Lionfish— Pterois volitans (Figure6.15) and P.miles —originally native to the Indian andPacificOceans andRed Sea, are believed to have been introduced into waters around Florida, USA in the 1980s from home aquariums (Whitfield et al. 2002, Schofield 2009). Over the past decade they have rapidly spread, from their few initial sightings to colonizing shallow and mesophotic reef habitats across the Western Atlantic, where they can reach at least five times their natural population densities (Darling et al. 2011, Kulbicki et al. 2012). Their current Western Atlantic range stretches from Bermuda and North Carolina in the north, to Brazil in the south, encompassing the Caribbean Sea and Gulf of Mexico (Schofield 2009, 2010). Lionfish have been observed at 55 m in Puerto Rico (Bejarano et al. 2014), deeper than 100 m in the Bahamas (Lesser and Slattery 2011), 112 m in the northwestern Gulf of Mexico (Nuttall et al. 2014) and 120 m in Honduras (Schofield 2010). Lionfish are voracious, gape-limited predators, feeding on a wide variety of fish and invertebrate species. As invasive species, their presence on reefs has been observed to cause declines in prey fish biomass of up to 65 per cent (Green et al. 2012) and to reduce native fish recruits by up to 79 per cent (Albins and Hixon 2008). Lionfish are highly successful invaders due to a combination of prey naivety (native prey species do not recognize lionfish as predators), a lack of predators, defensive venomous spines and a broad thermal tolerance (Morris et al. 2009). Furthermore, lionfish are highly fecund, spawning all year round at a maximum rate of once every 2–3 days (Gardner et al. 2015). Lionfish produce buoyant egg bundles, aiding dispersal and new site colonization by drifting in surface currents.

In addition to the direct effects on native reef fish and invertebrate abundance and recruitment, lionfish have also been linked with indirect MCE shifts. In the Bahamas, it is suggested that lionfish are associated with a shift in MCEs from coral- to algal-dominated states by altering the balance in the food chain, known as a trophic cascade. Lionfish feed upon mesophotic herbivorous and omnivorous fish, leading to a reduction in grazing pressure on the alga Lobophora variegata , and hence, an increase in algal abundance relative to corals and sponges occurs (Lesser and Slattery 2011, Slattery and Lesser 2014). Thus, the lionfish invasion may contribute to major MCE shifts over relatively short timescales of several years. Lionfish exhibit ontogenetic migrations, with older lionfish found at greater depths on reef habitats (Claydon et al. 2012). Juvenile lionfish tend to use shallow reef environments, mangroves and seagrass beds as nursery grounds (Barbour et al. 2010, Claydon et al. 2012). It is likely that lionfish populations on MCEs form an extension of this ontogenetic migration, although this requires further research. Current control measures for lionfish focus on hand culling with spears, often using dive volunteers (Figure 6.16). Culling is known to reduce the abundance of lionfish on shallow reefs (Frazer et al. 2012), and has been shown to aid the recovery of native shallow reef fauna (Green et al. 2014), although continuous culling is necessary to maintain low lionfish populations. There has been limited culling on MCEs, and there is no assessment of its effect. Across the Western Atlantic, the International Coral Reef Initiative has a regional lionfish strategy aimed at fostering collaboration between governments, scientists and reef-reliant industries in the management of lionfish.

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 79