Why are the Indo-Pacific lion fish, Pterois volitans and Pterois Miles, successful invasive species in the Caribbean and Western Atlantic? – A Literature Review
Introduction
It has been more than 33 years since the invasive lionfish, P. volitans and P. miles, native to the Indo-Pacific have been introduced to the ecosystems of the Caribbean and Western Atlantic (de León et al., 2013). The lionfish species Pterois miles and P. volitans are the first alien marine fishes to settle in the Western North Atlantic (Schofield, 2009). First reported in 1985 (Morris & Atkins, 2009), the lionfish has created established communities across the Caribbean and Western Atlantic in places as far as Trinidad and Tobago (Alemu, 2016) to the Cayman Islands, Bahamas as well as Bermuda, (Betancur et. al, 2011) Florida Keys and Cape Hatteras off the Coast of North Carolina (Schofield, 2009). Grazers and other small prey species struggle to thrive having significant amounts of native populations reduced in reef habitats. On small patch reefs in The Bahamas, Albins and Hixon (2008) experimentally determined that the abundance of small native fish can be reduced by nearly 80% in just 5 weeks by a single lionfish. In addition, Albins (2013) documented on similar reefs in a following experiment, a decline in small fish abundance over 8 weeks by 94%. Having left their native region, leaving behind species that are their natural enemies the “enemy release hypothesis” could be a possible factor of the lionfishes’ success. Not having to contend with co-evolved natural predators, pathogens, competitors and parasites that limit their populations at home could be play a strong role in why invasive species are so successful (Keane & Crawley, 2004). However, the information gap about lionfish and their interactions with their native community members impedes robust analysis of the suggestion of ecological release (Cote et. al, 2013). Nonetheless, applicable observations from the invaded range are being amassed. These dramatic upsurges of lionfish seem to have been developed by several opportune benefits of ecosystem and species qualities, potentially including features of the invaded Atlantic ecosystems, including weak competitors, overexploited naive predators, and, naive prey, and the fundamental life-history characteristics of lionfish, such as ecological versatility, early maturation, prolific reproductive output, and anti-predatory defences (Côté et al., 2013). According to Kulbicki et al., 2012, it is not entirely clear why, while having life-history traits that seem to encourage a high inherent rate of population growth, neither P. miles nor P. volitans is especially abundant in its native range. Currently an unprecedented event in the Caribbean and Western Atlantic, it is difficult to predict whether subsequent predatory invasions will occur there in the future after this invasion. Nevertheless, the lionfish invasion is contributing a model to experiment the importance of fluctuating resources (Davis et al., 2000), propagule pressure (Williamson, 1996), species diversity (Levine, 2000), and habitat heterogeneity (Melbourne et al., 2007) in invaded marine habitats.
Diet
In marine ecosystems, the diurnal light cycle has a strong effect on the hunting habits of most predators, with many species hunting most actively during dawn and dusk ‘crepuscular’ low-light phases (Hobson, 1973; Galzin, 1987). Species feeding in these relatively darker conditions can gain advantages from decreased visual detection from predators, increased prey availability, and increased capture success (Connell 1998; Fishelson, 1975; Helfman,1993). The lionfish, P. volitans in particular, is a generalist predator consuming a wide variety of prey (Côté et al., 2013; Morris and Akins, 2009; Muñoz et al., 2011), seemingly without special preference. This allows the lionfish to thrive in a range of habitat types and also enables prey switching when individual prey species are exhausted over time (e.g., Green et al., 2012). This poses a problem for more specialist predators in the invaded ecosystem that consume specific prey. Lionfish are gape-limited predators, meaning that they can potentially prey on anything that is smaller than their mouth. While not particular about species, the lionfish diet largely consists of crustaceans and teleosts (Morris & Atkins, 2009). Although, the larger sized lionfish primarily tend to have a more piscivorous diet (Green et. al, 2011).
Figure 1. A group of Invasive Indo-Pacific lionfish in New Providence Island, Bahamas, Atlantic. Photo taken in July 2010 (Photograph credit: I.M. Côté).
Recruitment
One of the main contributing factors to high rates of growth in marine fish populations is early maturation (Denney et al., 2002). According to Côté et al., 2013, lionfish appear to outgrow some native western Atlantic mesopredators. Several papers make reference to the unpublished data of Pusack et al. (Côté et al., 2013; Albins & Hixon, 2011), which expresses that lionfish show more rapid growth in the invaded Atlantic than in their native Pacific range. In addition to this, they appear to become sexually mature earlier than comparable mesopredators on Atlantic coral reefs (Côté et al., 2013), having the ability to become sexually mature within their first year of life (Morris, 2009). Frequent, year-round reproduction combined with early age of maturity creates a persistent stress of lionfish propagules on habitats (Côté et al., 2013). With the advantage of their faster growth rate, Albins (2013) proposed that lionfish might rapidly become predators of their modern group of native groupers and that they are capable of achieving significantly faster growth rates than already established native.
Behaviour
While the behavioural and physical defences of the lionfish are less effective in their native range because of co-evolution, this makes lionfish unlikely targets for consumption by Caribbean predators. However, even in the native range, there have been few reports of predation on lionfish. This is most likely because lionfish have been poorly studied throughout the Indo-Pacific region. It has been suggested by some studies that invaders may have higher competitive proficiency compared to species native to the invaded habitat (e.g., Keane and Crawley, 2002; Vilà and Weiner, 2004). Moreover, the common flight response of most Atlantic fishes to perceived threats is not exhibited by lionfish, but rather they assume a bold reaction, with a defensive pose, pointing their venomous dorsal spines towards the threat (Green et al., 2011; Whitfield et al., 2007). Additionally, native prey being naïve is an advantage that likely adds to lionfishes’ success in the invaded habitats (Cure et al., 2012). This benefit is probably due to the fact that their appearance (i.e., conspicuous morphology of broad pectoral fins and pronounced striping) and behaviour are not observed as a predation threat (Côté et al., 2013). Moreover, the lionfishes’ capture tactic of stunning prey by blowing jets of water at them (Albins and Lyons, 2012), as well as its slow, hovering hunting style (Côté and Maljkovic, 2010; Green et al., 2011) is unique among the fish of the Atlantic. This may be a factor for a substantial increase in the lionfishes’ capture rates in the invaded range comparison to native range. Presently, there is no evidence to imply that lionfish obviously compete with native mesopredators, but the naiveté of their prey, their hunting style and trophic flexibility may make lionfish successful long-term exploitation (Côté et al., 2013).
Figure 2. Identified lionfish incidences in the Caribbean Sea and Western North Atlantic (USGS-NAS, 2009). The panels serve to depict the cumulative spreading of P. volitans and P. miles throughout the invaded region. Data from USGS-NAS database and is accessible online taken from (Schofield, 2009).
Figure 3. The distribution of the Indo-Pacific lionfish Pterois miles and P. volitans in the Caribbean and North-western Atlantic as of December 4, 2018. Data taken from U.S. Geological Survey, 2018, Specimen observation USGS Nonindigenous Aquatic Species Database.
Mitigation
Now that these invasive predators are firmly established in the Western Atlantic and Caribbean basin, many queries remain concerning how best to cope with the lionfish invasion. Leaders from across the Caribbean region have identified a list of research interests that are needed (Morris and Green, 2012). Based on their review, Côté et al., 2013, highlights what they believe are the most important, among these holes in research, needed to support lionfish management. These include but are not limited to: 1. The need to measure propagule pressure, as it may be one of the most vital factors of lionfish abundance. Proper estimations could assist in prioritising reefs for local removal (e.g., where removals on reefs could be efficient for longer periods of time) 2. There is currently no data for lionfish <2 cm TL (total length), as lionfish larvae are infrequently captured. Recognising the habitat needs of the settlement-stage larvae could introduce opportunities for larval removal and trapping programs at a local scale. 3. Understanding of initial post-settlement mortality could feasibly identify and promote population limitation. 4. Comprehending why adults move, if movement is habitat-dependent and how far they move could benefit the spatial design of removal plans. 5. Identification of the most optimal frequency and intensity of lionfish removals to attain the best ecological influence per unit time and finance invested. The efficiency of such programs can be further enriched if done in tandem with strategies to restore populations of potential lionfish predators (Arias-González et al., 2011). Viewing past the result of lionfish management actions, the invasion has emphasised the serious need for efficient prevention, early detection, and prompt response to every introduction of exotic species within our oceans, taking special interest in the predators.