Territoriality and condition of chevron butterflyfish ( Chaetodon trifascialis ) with varying coral cover on the great barrier reef, Australia

The chevron butterflyfish, Chaetodon trifascialis, is among the most specialised coral-feeding fish, and while it is known to be very susceptible to extensive depletion of its preferred coral prey (tabular Acropora spp.), their specific responses to changing coral cover are poorly understood. The purpose of this study was to test for variation in territorial behaviour and condition of C. trifascialis relative to spatial variation in coral cover across four mid-shelf reefs on the Great Barrier Reef. Explicit consideration was also given to the territorial arrangement and interactions among sympatric individuals, with a view to better understanding the sociality of this species. Variation in overall coral cover (which ranged from 26.5-73.4% among sites) as well as cover of tabular Acropora (13.3-44.8%) had limited effect on the territoriality or body condition of C. trifascialis. Rather, individual variation in territoriality was attributable to differences in gender and size of fish. Male C. trifascialis were generally larger and also had larger territories than female counterparts. They also interacted with conspecifics (and congenerics) much more than females. Taken together, these results support previous assertions that C. trifascialis is haremic. There was, however, limited evidence of male territories encompassing the territories of >1 female. While the sociality of C. trifascialis is clearly atypical of Chaetodon butterflyfishes, more work is needed to understand their reproductive biology as well as their behavioural responses to changing coral cover.