Ophioblennius atlanticus is a shallow-water, surge zone Caribbean species, invariably as adult found in permanent territories on a solid substrate. As such it controls space within a complex community. Planar dimensions of the territories of adults show a mean area of about 05 m2. Antagonistic reactions of different degree are shown to both transgressing and intruding conspecifics, and to a much lesser extent to other species. It is hypothesized that interstitial territories of immature specimens provide the nuclei of future territories. Non-reproductive, extra-territorial activity is not common, but does occur. Evidence is presented to show that dispossessed adult blennies have great difficulty in establishing new territories. Territories that have been vacated are subsequently shared by neighbouring fish. Territory provides space, food and shelter for its resident, and as an occupied, but not impermeable space, it is an agent of control of distribution of Redlip blennies and other species of fish.