Size-based analysis

Mimetic behavior signifies organisms evolving to share behaviors and a common resemblance despite different phylogeny. Relationships in mimicry rely on the characteristics of mimics and models: appearance and size, vertical and geographical distribution, mimic to model abundance, behavioral shifts of the mimic and observed benefits. Using these criteria, species from the Hypoplectrus genus (hamlets) were analyzed as potential aggressive mimics. Using a visual census, the distribution of each mimic and model were surveyed and behaviors of individuals within the mimetic pairs were video recorded. There was 80-94% difference between the population densities of two potential mimetic pairs: Hypoplectrus nigricans (black hamlet) and Stegastes adustus, (dusky damselfish) and Hypoplectrus unicolor (butter hamlet) and Chaetodon capistratus (foureye butterflyfish). Data collected for the potential mimetic pair, Hypoplectrus chlorurus (yellowtail hamlet) and Microspathodon chyrsurus (yellowtail damselfish) does not support the hypothesis because the population density of the supposed mimic was higher than that of the potential model. In addition, for all studied pairs, no notable behavioral shifts were observed, and therefore whether the studied pairs are cases of mimicry is still a question.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 43-50 from CIEE Bonaire.

Hermodice carunculata, commonly known as the Bearded Fireworm, is a corallivorous Polychaete found throughout the Atlantic Ocean and the Caribbean and is noted for its fluorescence. Studies have found that the highest abundance of H. carunculata is in water shallower than 1 m. The present study observed the habitat, size, and fluorescent patterns of H. carunculata in the intertidal zone of Yellow Submarine dive site on Bonaire. Three transects were laid at 55 cm and 110 cm deep, at 20 and 50 minutes after sunset. Additionally, fireworms were caught in wire traps to be more closely observed in the laboratory under a dissecting microscope. There was no significant difference between the depth (110 cm or 55 cm) and the size (less than or greater than 6 cm), nor was there a difference in abundance between the two time periods of data collection (20 minutes and 50 minutes after sunset). Furthermore, there was no significant difference between the fluorescent pattern (GREEN, GOB, OOB, or ROB) and the substrate (algae, coral, rubble, rock, or sand) the individual was found on, or fluorescent pattern and size. There was, however, a significant difference in density of fireworms per square meter over the five-week study period. Fireworm predation can have a large impact on the health of corals. This paper aims to increase the understanding of H. carunculata, so that the corals can be better protected, and the interaction between these two organisms can be better understood.

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 54-60 from CIEE Bonaire.

Abstract:

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.