(53) Effect of Colony Size on Dusky Damselfish (Stegastes adustus) Aggressive Behavior

     Some species of damselfish have a mutualistic relationship with turf algae and exhibit different behaviors in order to defend their territories. Among species of damselfish, territory size varies as well as the degree... [ view full abstract ]

     Some species of damselfish have a mutualistic relationship with turf algae and exhibit different behaviors in order to defend their territories. Among species of damselfish, territory size varies as well as the degree to which individuals aggregate into colonies. In this study, we compared aggressive behavior specifically in colonial and solitary dusky damselfish (Stegastes adustus). We hypothesized that individual dusky damselfish that are in colonies will be more aggressive than those that are solitary. After controlling for water depth and type of substrate, we observed damsel fish behavior in 10 minute intervals.  We quantified the number of aggressive behaviors, estimated the distance chased by a damselfish, and the number of successful grazing occurrences by other fish species on the damselfish gardens.  We found that solitary individuals were significantly more aggressive towards other fish as opposed to individuals associated with a colony. We concluded that colonial damselfish were less aggressive due to their strength in numbers and intimidation compared to a single damselfish who protects its garden alone. However, we also discovered that successful herbivory was fairly similar in both colonies and solitary territories, and that solitary individuals chase possible threats much further away than individuals in colonies. Observations associated with our results suggest that aggressive behavior exhibited by dusky damselfish toward herbivorous fishes may vary widely depending on the species involved in the interaction.