Damselfish

The purpose of this research was to determine the level of defensive aggression of the threespot damselfish, Stagastes planifrons, when exposed to intruders of different species using models. Adult S. planifrons were exposed to models of a conspecific, an herbivorous fish, Sparisoma viride, and a predator, Aulostomus maculatus. Attack rates and retreat rates of S. planifrons were determined by observations during exposure to models. It was expected that aggression levels would be highest towards the conspecific model and lowest towards the predator model and that evasive behavior would be highest in the presence of the predator model and lowest with the conspecific. It was found that there is a significant difference in the level of aggression when encountering a predator versus a conspecific, showing more aggression towards the conspecific and more evasion towards the predator. No significant difference was found in the aggression levels shown between the predator and the herbivore. Exposure to the predator elicited the highest number of retreats, also showing a significant difference in the level of evasion when comparing all three models. The results suggest that S. planifrons are able to differentiate between intruder species and react depending on the level of threat posed and perhaps on what is most energy efficient.

This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 13-18 from CIEE Bonaire.

The Threespot Damselfish, Stegastes planifrons, defends a variable territory size depending upon the level of threat posed by the species encroaching upon it. Aggression patterns in the Threespot Damselfish were studied in relation to intruder size, attack duration, maximum distance of attack and intruder species on a reef in Bonaire, Netherland Antilles. Thirteen species were found to intrude upon Threespot Damselfish territories with the Bicolor Damselfish (Stegastes partitus) being the most frequent visitor (37.8%) followed by the Brown Chromis (Chromis multilineata; 20.2%), Blue Tang (Acanthurus coeruleus; 15.1%) and the Stoplight Parrotfish (Sparisoma viride; 9.2%). Analysis showed a positive correlation between intruder size and attack duration as well as maximum distance traveled by the Threespot Damselfish in pursuit of the intruder during the attack. Data supported the hypothesis that the Threespot Damselfish alters its behavior based on intruder size. Data, however, did not support a species specific relationship between the Threespot Damselfish aggression patterns and the variables selected.

This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 7-12 from CIEE Bonaire.

Damselfish are small herbivores that cultivate algal gardens on coral heads throughout Caribbean reefs. These gardens are used to grow specific types of algae that they can digest easily. However, algal gardens can affect coral both physically and physiologically. In addition to competing with coral for light and space, algal gardens cause coral to spend valuable metabolic energy to remove the algae. This study aimed to determine whether there is a correlation between damselfish density, percent dead coral cover, and coral diversity. A total of thirty-two 20 x 1m belt transects were laid out randomly at a highly impacted and less impacted site. The damselfish density, the number of species, and their size distribution were recorded along with percent dead coral present and coral composition of the substrate. Data were analyzed and compared to deduce whether or not there was any significant evidence that high damselfish numbers are correlated with an increased percentage of dead coral. Although no connection was found between high densities of damselfish and increases in dead coral, it is possible that factors not quantified in this study, such as human impact, could have had an influential role on both damselfish densities and the health of the reef.

This student research was retrieved from Physis: Journal of Marine Science IX (Spring 2011)19: 50-56 from CIEE Bonaire.

Damselfish have a considerable effect on benthic composition and have been described as a keystone species because of their role in the maintenance of coral and algal assemblages within their communities. By looking at the different densities of damselfish at varying depths and locations, this study aims to see the effects of damselfish densities on coral reef benthic composition and if the presence of damselfish is beneficial to coral reef benthos. The abundance of all damselfish was recorded within 30 x 2 m belt transects. Random photographs within the belts were taken and still images were analyzed using Coral Point Count software to determine total percent coral cover, total percent algal cover, and coral species richness. A total of 702 damselfishes over 4 species were observed. Thirteen species of coral were identified. Contrary to the predictions, a higher density of damselfish was not correlated to increased coral cover and coral species richness. There was significantly more algae than coral cover throughout the study, but such a trend fits with the theory of phase shifts of coral reefs from coral dominated to algae dominated reefs.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 29-34 from CIEE Bonaire.

Various symbiotic relationships build and maintain coral reefs. Mutualistic relationships provide the organisms involved with an increased chance of survival and reproduction which prove important for the health and function of reef communities. The increasing presence of macroalgae is an indication of declining reef health. In order to maintain the growth of certain species of macroalgae, Threespot damselfish, Stegastes planifrons, cultivate and maintain algae gardens. If there is an abundance of algae in the gardens of S. planifrons, there is a limited opportunity for coral recruitment and growth; this makes them an important species in the ecosystem. Damselfish are very territorial and will defend their gardens by chasing and biting intruders. This study tested whether there is a particular sized territory surrounding the garden that correlates to the size of the garden itself. Attacks by S. planifrons in the gardens toward a laser pointer allowed the determination of garden and territory area. The area of the garden, the point where the attacks ended and the total surrounding territory of the damselfish were measured using a measuring tape. A positive trend between area of garden and area of territory was found indicating that both increased correspondingly. The algae gardens and territorial behavior of S. planifrons can be indicative of the current phase shift from a coral reef to a coral depauperate ecosystem. More algal cover is indicative of decreased coral cover and coral recruitment success. By understanding ecological dynamics, protection of coral reefs from a degrading phase shift can be implemented.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 96-102 from CIEE Bonaire.

Bicolor damselfish, Stegastes partitus, are well known for their aggressive nature. They are known to attack almost any species threatening their food, territory or spawn, often regardless of the size of the intruder. Studies show that three spot damselfish are even able to identify certain species based on the threat they present by displaying different aggressive behaviors. However, little is known on how, and if, these aggressive displays are species dependent in bicolors. The purpose of this study was to test for species dependent aggression in bicolor damselfish during reproductive season to determine if this behavior relates to increased egg protection during reproductive season. Four damselfish individuals were analyzed over the course of five weeks during one reproductive and one non-reproductive cycle using underwater video camcorders. S. partitus was shown to increase frequency of aggression toward egg threatening intruders while guarding eggs. Conversely, they were shown to decrease in frequency of aggression towards intruders threatening their food resources. Lastly, the frequency of intrusion for eggeating intruders was not shown to significantly increase while bicolor damselfish eggs were present.

This student research was retrieved from Physis: Journal of Marine Science XV (Spring 2014)19: 9-14 from CIEE Bonaire.

Among fish that lay their eggs on the ground (demersal) and have external fertilization (oviparous), typical parental care includes building a nest, then cleaning and guarding it as an investment in the fitness and survival of their offspring. Male Caribbean sergeant major damselfish, Abudefduf saxatilis, take on a darker coloration when they prepare a nest and engage in mating rituals, then guard and aerate their nest. Aggression of the guarding A. saxatilis could be linked to a number of factors. Nest size, size of the guarding fish is, or age of the nest may all affect nest guarding territoriality. Based on observational data collected in Bonaire in the Dutch Caribbean, there was no association between aggression (attack rate or average response distance) the guarding fish size (fork length), nest area, number of eggs, or age of the nest. Aggression was found to correlate with time of day, which may have been due to higher abundance of egg predators later in the day. Nest guarding aggression and parental care are complex behaviors that are largely species and context specific, making it difficult to make true predictions about aggressive behavior.

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 58-68 from CIEE Bonaire.

Abudefduf saxatilis, or sergeant major damselfish, are a common reef fish in the Caribbean and western Atlantic that form large feeding aggregations. Abudefduf saxatilis are primarily planktivorous, with zooplankton making up over 50% of their diet. Zooplankton are known to have diel movements to avoid predation, which have been shown to be triggered by the presence of ultra violet radiation. Beneath boats along the coast of Bonaire, aggregations of A. saxatilis have been observed, but why they prefer these areas over the open water column had not previously been examined. The abundance of zooplankton was estimated beneath boats as well as in the open water, up-current from the boats. Both the abundance and bite rates of A. saxatilis were also estimated beneath the boats that corresponded to the estimates of zooplankton abundance. In addition, the bite rates of A. saxatilis were estimated in the open water. It was found that the zooplankton abundance (p<0.001) and the bite rate of A. saxatilis (p<0.001) were both significantly greater beneath boats than in the open water. Also, a significant correlation was found between increasing abundances of zooplankton and A. saxatilis (p<0.01). These results demonstrate that one of the main drivers for the aggregation of A. saxatilis beneath boats is likely to feed on the zooplankton, which are in high abundance. In turn, this could alter community structure on the reef due to a decrease in the amount of algae grazing by A. saxatilis

This student research was retrieved from Physis: Journal of Marine Science XVII (Spring 2015)19: 51-57 from CIEE Bonaire.

Bonaire’s coral reefs remain among the healthiest in the Caribbean. Although the island’s reefs have suffered bleaching disturbances similar to those plaguing reefs throughout the Caribbean, they uniquely show signs of recovery. Here we highlight key findings from our March 2015 biennial coral reef monitoring expedition. We put the findings in the context of both the trends recorded since 2003 when we began our regular monitoring and the most recent research related to the factors controlling the structure and functioning of healthy coral reef ecosystems. 

On Bonaire, we studied the effects of predator abundance and habitat availability on the abundance of the threespot damselfish Stegastes planifrons, a species that creates algal gardens at the expense of live coral cover. Across 21 sites, predator biomass ranged from 12 to 193 g m−2 (mean = 55.1; SD = 49.1) and benthic cover of S. planifrons’ preferred habitat (corals of the Orbicella species complex) ranged from 2.2 to 38.0% (mean = 14.3; SD = 9.6). Across these gradients, the local abundance of S. planifrons was significantly and negatively related to preda- tor biomass, but not to habitat availability. Increased local abundance of S. planifrons corre- sponded to an increasingly larger proportion of coral colonies affected by its ‘farming behavior’, resulting in an increased prevalence of coral disease. Thus, predators indirectly affected the com- position of reef communities around Bonaire by controlling damselfish abundance. Furthermore, the abundance of S. planifrons could not be correlated with its preferred habitat, despite such cor- relations having been observed elsewhere in the Caribbean.