Habitat selection and shelter use by Octopus tetricus

The ecology of a shallow-water benthic octopus (Octopus tetricus) in northeastern New Zealand was examined. Spatial and temporal patterns of abundance, habitat association, and shelter use were quantified. Octopus were abundant on the reef during summer, during which time females brooded eggs. Numbers declined rapidly at the end of summer. Octopus were not evenly distributed across sites, and were more abundant in patch reef habitats than in broken or flat reef habitats. The role of reefal factors in habitat selection, both abiotic and biotic, was examined using multiple regression and partial correlation analyses. Octopus were more abundant near the reef edge, and in areas with high numbers of small boulders. No relationships between octopus and potential reefal predators (eels) or reefal prey (crayfish) species were found. Soft-sediment bivalves occurred in the majority of shelter middens, suggesting that octopus were foraging over adjacent soft-sediments rather than on the rocky reef itself. The degree of shelter modification varied with habitat, sex, and brooding status. Shelters were more likely to be modified in patch reef habitats than in broken and flat reef habitats. Brooding females were more likely to modify their shelters than non-brooding females and males, and often completely barricaded shelter entrances. This study suggests that Octopus tetricus are associated with rocky reef habitats during the breeding season, while a considerable portion of their life may be spent in soft-sediment habitats.