Interpreting space use and behavior of blue tang, Acanthurus coeruleus, in the context of habitat, density, and intra-specific interactions Brice X. Semmens a , Daniel R. Brumbaugh b & Joshua A. Drew c a Department of Biology, University of Washington, 24 Kincaid Hall, Box 351800Seattle, Washington, 98195- 1800, USA (e-mail: semmens@u.washington.edu) b Center for Biodiversity and Conservation, American Museum of Natural History, Central Park West at 79th Street, New York, NY, 10024-5192, USA c Boston University Marine Program Marine Biological Laboratory, Woods Hole, MA, 02543, USA Received 4 May 2004 Accepted 5 April 2005 Key words: movement, coral reef, behavior, space, territory, home range Synopsis We hypothesized that blue tang, Acanthurus coeruleus, territories on sites with low biogenic structure would be larger than territories on sites with relatively high biogenic structure due to differences in the amount and distribution of resources. We tested this hypothesis by tracking blue tang over uncolonized pavement and reef crest, two habitat types at opposite ends of the habitat structure spectrum. We recorded density, feeding rates and aggression events in order to evaluate our findings in the context of a territory model and the ideal free distribution model. Territories of A. coeruleus averaged nearly four times larger on pavement sites than on reef crest sites. Conversely, densities of A. coeruleus were significantly lower on pavement sites. While there was no significant difference in the average rates of movement between habitats, average turning angles were significantly higher on reef crest. There were no significant differences in feeding rates between habitats, suggesting that higher territory sizes and lower densities may allow fish on uncolonized pavement to match resource acquisition of fish on reef crest. The insignificant difference of aggression encounters between habitats suggests that movement and density differences among habitats are not solely legacies of differential settlement. Introduction Habitat structure and quality in the marine environment are in a state of flux globally (Watling & Norse 1998). Nowhere are these changes more obvious than in coral reef systems, where alarming reports of reef destruction and degradation from anthropogenic and natural disturbances are com- mon (Ginsburg 1994, GCRMN 2002). In Carib- bean reefs, the cumulative effects of disease, bleaching, and anthropogenic disturbance have significantly reduced coral cover, resulting in decreased biogenic structure (GCRMN 2002, Gardner et al. 2003). In addition to these impacts, increases in atmospheric carbon dioxide will likely decrease coral calcification rates, resulting in weaker skeletons, reduced extension rates, and increased susceptibility to erosion (Kleypas et al. 1999, Kleypas et al. 2001). Changes in habitat structure are known to affect the movement of organisms in other systems (e.g., spotted owls in patchy forests) (Lande 1988). Thus effective long- Environmental Biology of Fishes (2005) 74: 99–107 Ó Springer 2005 DOI 10.1007/s10641-005-6467-z