Predator-prey interactions are a driving force for many identifying features of ecosystems. Predation pressure not only strongly influences population structure and distribution but also influences prey behavior. Predator avoidance behavior may play a large part in self-defense. In marine systems, there are many cases of organisms which are not capable of changing physical location as a predator avoidance technique (e.g.,, sponges, corals). In this study, Bispira variegata was used as an indicator for consumer impact on behavior in a benthic, sessile organism. Primarily, population structure (i.e. size, density) was assessed. Paired clipped and unclipped populations were used to quantify an increase of potential predators based on exposure and the impact that they may have on worm response. In order to determine the impact of predation pressure, worms were observed and video recorded to assess the distance from simulated predation that caused worms to react. There was a mean density of 12 worms m-2. The population was variably distributed with no bias towards the large nor the small end of the size range represented. There was significant difference in the number of potential predators which entered the clipped plots (p = 0.005). For the predator simulation, there was extreme variation on the distance from the simulated predator that triggered a reaction, specifically retraction. The results of this study can be used as a stepping stone for understanding the effect of predation pressure on benthic, sessile organisms by showing the impact of three-dimensional habitat as well as the behavioral reactions to simulated predation.
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.