Localized Defecation in Territorial Herbivorous Fishes

The spatial patterns of feces deposition have been well studied in many terrestrial organisms, while few studies have examined these behaviors in marine fishes. Territorial animals tend to feed within their respective territories. Thus, individuals are faced with the decision of defecating within their territory, where they live and feed, or outside where they are potentially more susceptible to predation. In this study, we conducted behavioral observations on three species of damselfishes to quantify defecation rates and to investigate the spatial distribution of defecation events relative to territory location on Caribbean coral reefs. Defecation rates were low in the early morning and steadily increased throughout the day, peaking in the late afternoon. All 108 observed defecation events occurred outside of the territory. Additionally, 73% of individuals (n = 52) utilized the same location in successive defecation events, which is a significant departure from what would be expected were they defecating in randomly selected locations. Daily defecation rates follow previously determined rates for diurnal coral reef fishes and are closely linked to feeding behavior. However, the spatial patterns of damselfish defecation are likely related to territory maintenance, predator avoidance, or parasite avoidance. This is only the second study to investigate the spatial distribution of fecal matter in damselfishes.