Effect of population density and aggressive behavior of Three Spot Damselfish (Stegastes planifrons) on macroalgae cover and parrotfish grazing activity

When overly abundant, macroalgae can be a major threat to the health of a coral reef ecosystem due to its capability to smother live coral and reduce the rates of recruitment. Several factors can contribute to macroalgal growth, one of the controlling elements being a lack of herbivorous grazing. When grazing pressure is high the ecosystem remains balanced, but when grazing pressure is low reefs can experience macroalgal blooms that have a lasting negative effect. This study examined the indirect causes of macroalgal cover change through assessing damselfish aggression. Stegastes planifrons, also known as the Three Spot Damselfish, are highly aggressive and territorial fish that will defend their territories against a number of intruding species. This study looked at the relationship between damselfish abundance and aggression and the grazing behavior of parrotfish, as well as the relationship between damselfish abundance and macroalgal cover on Bonaire, Dutch Caribbean. Video transects were implemented over the chosen study stations and then analyzed with Coral Point Count (CPCe) software to attain the percentages of macroalgae cover at each station. Aggressive behavior of the three spot damselfish as well as the grazing behavior of parrotfish were observed and recorded using SCUBA diving. It was found that damselfish aggression and parrotfish grazing were negatively correlated, and that parrotfish grazing followed the same trend line as the macroalgae cover. Based on the findings of this study it was concluded that S. planifrons aggression has no considerable effect on the grazing behavior of parrotfish,and it can be assumed that it does not contribute to increased macroalgal cover.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 16-21 from CIEE Bonaire.