Ontogenetic pattern of resource use by the tiny hermit crab Pagurus villosus (PAGURIDAE) from the temperate Chilean coast

The biology of hermit crabs in the temperate zone is understudied in comparison with hermit crabs in the tropics and subtropics. Here we provide the first observations of population traits of the smallest South Pacific hermit crab, Pagurus villosus, using descriptive and experimental approaches. The principal emphasis is on ontogenetic and spatio-temporal variation in the breeding season, recruitment, sex ratio, microhabitat use, and shell occupancy pattern. We also experimentally evaluated colonization rates, in order to assess the pattern of habitat use. P. villosus showed continuous reproduction and recruitment, and an unbiased sex ratio. Algae turf was the microhabitat with highest record of individuals, regardless of their ontogenetic stage. Females were smaller and showed less movement activity on experimental trays than did males, for three microhabitat analyses. Early stages colonized higher proportions of artificial algae and shell hash (only juveniles). Diversity of gastropod shells used by hermit crabs (12 in total) decreased during development, but for all stages Tegula tridentata and Nassarius gayi were the most used. Females in different reproductive conditions (ovigerous and non-ovigerous) showed a shift of shell occupancy pattern likely related to the tradeoff between fitness and shape, weight, thickness and internal volume of shells. Population and life-history traits, i.e., continuous breeding and high resource use during all ontogenetic phases (microhabitats and shells), of P. villosus on the temperate Chilean coast seem more similar to pagurid species from low latitudes. These traits may reflect a tropical origin of this species and/or an adaptive strategy of these tiny crabs in a temperate region. (C) 2007 Elsevier B.V. All rights reserved.