Prey naïveté, or the failure of prey to recognize non-native predators due to a lack of co-evolutionary history, is thought to underpin the large impact of invasive Indo-Pacific lionfish (Pterois sp.) on coral reef fish populations in the western Atlantic. Most previous studies of lionfish recognition have taken place in experimental tanks that did not mimic natural conditions or used bottle or cage field designs that constrained natural behaviour. To alleviate these issues, we compared the homing patterns of experimentally translocated Caribbean bicolor damselfish (Stegastes partitus) in the presence and absence of standardized models of a lionfish, of an ecologically similar native piscivore (black grouper; Mycteroperca bonaci), and of a native non-piscivore (French grunt, Haemulon flavolineatum) in the field. The native grouper model elicited a strong predator avoidance response: translocated damselfish became unlikely to home when released beyond ~ 2 m from their territory and took longer to do so. In contrast, damselfish facing a lionfish model exhibited similar homing behaviours to those of damselfish in the presence of a non-piscivorous grunt and in the absence of any model. Fish length and translocation distance also influenced homing: damselfish stopped homing when released more than 5.6 m away from their territory and larger individuals crossed wider sand gaps. Overall, our findings are consistent with the idea that bicolor damselfish are naïve to the threat of predation presented by lionfish, but also with the notion that damselfish might be assessing, but deeming to be low, the threat of a stalking predator hunting over open sand. Both mechanisms point to inaccurate risk perception in relation to invasive lionfish. More broadly, we highlight a novel experimental translocation approach to evaluate behavioural responses of native prey species to novel predators under realistic field conditions.
Global sea-level rise of up to 0.6 m is predicted in the next 100 years. In areas where coastal structures prevent landward mi- gration of beaches, a major impact of sea-level rise will be a loss of beach habitat, with repercussions for beach-dependent organ- isms such as sea turtles. Setback regulations, which prohibit construction within a set distance from the sea, have the potential to mitigate loss of beach area by providing a buffer zone which allows for the natural movement of beaches in response to perturbation. The potential impact of a rise in sea level on 11 important sea turtle nesting beaches in Barbados under a range of setback regu- lations was determined. Three sea-level rise scenarios were modelled under five different setback regulations (10, 30, 50, 70 and 90 m). Beach area was lost from all beaches under all sea-level rise scenarios with a 10 and 30 m setback, from some beaches with a 50 m setback and from one beach with a 70 m setback. No beach area was lost with a 90 m setback distance. Sea turtles nest within a range of beach elevations and there was an overall loss of beach habitat within the preferred nesting elevation range with both a 10 and 30 m setback under all sea-level rise scenarios. Considerable variation in the extent of beach and nesting area loss was observed. The implementation and enforcement of adequate setback regulations have the potential to maintain the ecological and economic function of beaches in the face of extensive coastal development and sea-level rise.
Culling can be an effective management tool for reducing populations of invasive species to levels that minimize ecological effects. However, culling is labour-intensive, costly, and may have unintended ecological consequences. In the Caribbean, culling is widely used to control invasive Indo-Pacific lionfish, Pterois volitans and P. miles, but the effectiveness of infrequent culling in terms of reducing lionfish abundance and halting native prey decline is unclear. In a 21-month-long field experiment on natural reefs, we found that culling effectiveness changed after the passage of a hurricane part-way through the experiment. Before the hurricane, infrequent culling resulted in substantial reductions in lionfish density (60–79%, on average, albeit with large uncertainty) and slight increases in native prey species richness, but was insufficient to stem the decline in native prey biomass. Culling every 3 months (i.e., quarterly) and every 6 months (i.e., biannually) had similar effects on lionfish density and native prey fishes because of high rates of lionfish colonization among reefs. After the hurricane, lionfish densities were greater on all culled reefs compared to non-culled reefs, and prey biomass declined by 92%, and species richness by 71%, on biannually culled reefs. The two culling frequencies we examined therefore seem to offer a poor trade-off between the demonstrated conservation gains that can be achieved with frequent culling and the economy of time and money realized by infrequent culling. Moreover, stochastic events such as hurricanes can drastically limit the effectiveness of culling efforts.
The projected rise in sea level is likely to increase the vulnerability of coastal zones in the Caribbean, which are already under pressure from a combination of anthropogenic activities and natural processes. One of the major effects will be a loss of beach habitat, which provides nesting sites for endangered sea turtles. To assess the potential impacts of sea-level rise on sea turtle nesting habitat, we used beach profile measurements of turtle nesting beaches on Bonaire, Netherlands Antilles, to develop elevation models of individual beaches in a geographic information system. These models were then used to quantify areas of beach vulnerable to three different scenarios of a rise in sea level. Physical characteristics of the beaches were also recorded and related to beach vulnerability, flooding, and nesting frequency. Beaches varied in physical characteristics and therefore in their vulnerability to flooding. Up to 32% of the total current beach area could be lost with a 0.5-m rise in sea level, with lower, narrower beaches being the most vulnerable. Vulnerability varied with land use adjacent to the beach. These predictions about loss of nesting habitat have important implications for turtle populations in the region.
As a result of being hunted, animals often alter their behaviour in ways that make future encounters with predators less likely. When hunting is carried out for conservation, for example to control invasive species, these behavioural changes can inadvertently impede the success of future efforts. We examined the effects of repeated culling by spearing on the behaviour of invasive predatory lionfish (Pterois volitans/miles) on Bahamian coral reef patches. We compared the extent of concealment and activity levels of lionfish at dawn and midday on 16 coral reef patches off Eleuthera, The Bahamas. Eight of the patches had been subjected to regular daytime removals of lionfish by spearing for two years. We also estimated the distance at which lionfish became alert to slowly approaching divers on culled and unculled reef patches. Lionfish on culled reefs were less active and hid deeper within the reef during the day than lionfish on patches where no culling had occurred. There were no differences at dawn when removals do not take place. Lionfish on culled reefs also adopted an alert posture at a greater distance from divers than lionfish on unculled reefs. More crepuscular activity likely leads to greater encounter rates by lionfish with more native fish species because the abundance of reef fish outside of shelters typically peaks at dawn and dusk. Hiding deeper within the reef could also make remaining lionfish less likely to be encountered and more difficult to catch by spearfishers during culling efforts. Shifts in the behaviour of hunted invasive animals might be common and they have implications both for the impact of invasive species and for the design and success of invasive control programs.
Biotic resistance, the process by which new colonists are excluded from a community by predation from and/or competition with resident species, can prevent or limit species invasions. We examined whether biotic resistance by native predators on Caribbean coral reefs has influenced the invasion success of red lionfishes (Pterois volitans and Pterois miles), piscivores from the Indo-Pacific. Specifically, we surveyed the abundance (density and biomass) of lionfish and native predatory fishes that could interact with lionfish (either through predation or competition) on 71 reefs in three biogeographic regions of the Caribbean. We recorded protection status of the reefs, and abiotic variables including depth, habitat type, and wind/wave exposure at each site. We found no relationship between the density or biomass of lionfish and that of native predators. However, lionfish densities were significantly lower on windward sites, potentially because of habitat preferences, and in marine protected areas, most likely because of ongoing removal efforts by reserve managers. Our results suggest that interactions with native predators do not influence the colonization or post-establishment population density of invasive lionfish on Caribbean reefs.
Species invasions have a range of negative effects on recipient ecosystems, and many occur at a scale and magnitude that preclude complete eradication. When complete extirpation is unlikely with available management resources, an effective strategy may be to suppress invasive populations below levels predicted to cause undesirable ecological change. We illustrate this approach by developing and testing targets for the control of invasive Indo-Pacific lionfish (Pterois volitans and P. miles) on Western Atlantic coral reefs. We first developed a size-structured simulation model of predation by lionfish on native fish communities, which we used to predict threshold densities of lionfish beyond which native fish biomass should decline. We then tested our predictions by experimentally manipulating lionfish densities above or below reef-specific thresholds, and monitoring the consequences for native fish populations on 24 Bahamian patch reefs over 18 months. We found that reducing lionfish below predicted threshold densities effectively protected native fish community biomass from predation-induced declines. Reductions in density of 75- 95%, depending on the reef, were required to suppress lionfish below levels predicted to over-consume prey. On reefs where lionfish were kept below threshold densities, native prey fish biomass increased by 50-70%. Gains in small (<6cm) size classes of native fishes translated into lagged increases in larger size classes over time. The biomass of larger individuals (>15cm total length), including ecologically important grazers and economically important fisheries species, had increased by 10-65% by the end of the experiment.
Crucially, similar gains in prey fish biomass were realized on reefs subjected to partial and full removal of lionfish, but partial removals took 30% less time to implement. By contrast, the biomass of small native fishes declined by more than 50% on all reefs with lionfish densities exceeding reef-specific thresholds. Large inter-reef variation in the biomass of prey fishes at the outset of the study, which influences the threshold density of lionfish, means that we could not identify a single rule-of-thumb for guiding control efforts. However, our model provides a method for setting reef-specific targets for population control using local monitoring data. Our work is the first to demonstrate that for ongoing invasions, suppressing invaders below densities that cause environmental harm can have a similar effect, in terms of protecting the native ecosystem on a local scale, to achieving complete eradication.
User fees can contribute to the financial sus- tainability of marine protected areas (MPAs), yet they must be acceptable to users. We explore changes in the fee system and management of Bonaire National Marine Park (BNMP) from the perspective of users. Responses from 393 tourists indicated that 90% were satisfied with park conditions and considered current user fees reasonable. However, only 47% of divers and 40% of non-divers were prepared to pay more. Diver willingness-to-pay (WTP) appears to have decreased since 1991, but this difference could be due in part to methodological differences between studies. Although current fees are close to diver maximum stated WTP, revenues could potentially be increased by improving the current fee system in ways that users deem acceptable. This potential surplus highlights the value of understanding user perceptions toward MPA fees and management.
The invasion by Indo-Pacific lionfish (Pterois volitans and P. miles) of the western Atlantic, Caribbean and Gulf of Mexico is emerging as a major threat to coral reef communities across the region. Comparing native and introduced populations of invasive species can reveal shifts in ecology and behaviour that can accompany successful invasions. Using standardized field surveys replicated at multiple sites in Kenya and the Bahamas, we present the first direct comparisons of lionfish density, body size, biomass and behaviour between native and invaded coral reefs. We found that lionfish occur at higher densities with larger body sizes and total biomass on invaded Bahamian coral reefs than the ecologically equivalent species (P. miles) does on native Kenyan reefs. However, the combined average density of the five lionfish species (Pterois miles, P. antennata, P. radiata, Dendrochirus brachypterus and D. zebra) on Kenyan reefs was similar to the density of invasive lionfish in the Bahamas. Understanding the ecological processes that drive these differences can help inform the management and control of invasive lionfish.