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MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS?
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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.