Bathymetric distribution of hermit crabs (Crustacea : Decapoda : Anomura) from the Otago region, southeastern New Zealand

Abstract

An account of the distribution and abundance of 16 species of hermit crabs in the Otago region is given, based on semi-quantitative trawl samples from subtidal stations off the Otago Peninsula and adjacent coast, and on intertidal samples. Intertidally, hermit crab population density is very low (0–0.08 crabs m-2). Subtidally, population density is highest between 20 and 120 m (1. 6–13.1 crabs m-2). Beyond the shelfbreak (at c. 200 m), population density is again low (0.1–2.5 crabs m-2). Three major species assemblages are present: an intertidal assemblage with two species, a continental shelf assemblage with ten species, and a slope (canyon) assemblage with seven species. For the majority of shelf species, a Nearshore zone (0–20 m) and an Outer Shelf zone (120–200 m) represent respectively their upper and lower distributional limits and few hermit crabs live in these transitional zones. Some shelf species appear to have more limited distributions: Pagurus n.sp.A between depths of 4–12 m on well sorted sand in association with large populations of the gastropod Umbonium zelandicum; Paguristes pilosus between depths of 14–40 m on high energy coarse sand bottoms; Pagurus n.sp. B in water shallower than 120 m; and Pylopagurus stewarti at depths greater than 40 m. Some shelf species spill over beyond the shelf break, but only one species (Pylopagurus stewarti) attains large population densitites on both shelf and slope. Four species are found exclusively in the canyon zones.