Shell Selection and Invasion Rates of Some Pacific Hermit Crabs 
Gordon H. Orians and Charles E. King 1 
ABSTRACT: Three species of littoral hermit crabs from Horseshoe Cove, Bodega 
Head, Sonoma County, California, and three sublittoral pagurids from Chinimi 
Island, Eniwetok Atoll, Marshall Islands, have been examined with respect to their 
shell selection and invasion rates. 
Periodic removal of crabs from marked areas resulted in immigrations of 
surprising magnitude. By comparison of actual collection patterns with those 
predictable from the alternates of density dependence and density independence, 
there Is an indication that the observed immigration rates result from density- 
dependent dispersal. While our data are not conclusive, the method presented is of 
interest and of possible utility for examining problems of this nature. 
Shell selection is discussed from the bases of both laboratory and field observa- 
tions. Each of the species is shown to utilize the shells of different gastropods with 
different frequencies. 
Finally, behavioral aspects are examined as they relate to the distribution of the 
California hermit crabs. 
Shells of various species of gastropod molluscs 
constitute a necessary component in the environ- 
ment of pagurid crabs. In addition to housing 
the crab the shell may act as an important 
determinant of behavior; for instance, several 
species will not feed unless in a shell (Alice 
and Doughs, 1945; Brightwell, 1952). Different 
species of pagurids regularly utilize different 
species of shells and it has been suggested that 
shell availability may be a limiting factor for 
some species (Provenzano, I960). 
This paper reports on observations of shell 
utilization by six species of Pacific hermit crabs 
and on some simple laboratory experiments on 
shell selection. In addition, a number of removal 
and repopulation experiments were performed. 
Orians worked mainly at Horseshoe Cove, Bo- 
dega Head, Sonoma County, California, during 
the summer of 1957, and King at Chinimi Island 
of Eniwetok Atoll during the summer of 1961. 
The study area at Horseshoe Cove consisted 
of a section of rocky, shelving shore partially 
1 Dept, of Zoology, Univ. of Washington, Seattle. 
Manuscript received January 31, 1963. Orians’ research 
was carried out under the auspices of the Dept, of 
Zoology, Univ. of California, Berkeley. King’s research 
was supported by the U. S. Atomic Energy Commis- 
sion at their Eniwetok Marine Biological Laboratory. 
protected from heavy ocean swell, with an abun- 
dance of small tidal pools at high and medium 
intertidal ranges. Twenty-seven pools in the 
tidal range 2. 5-4. 5 ft above datum (which is 
mean low water) and subjected to long periods 
of exposure at low tides, were selected because 
they were easily reached at most tides. They 
ranged in length from 0.43 to 9.5 m and in 
depth from 15 cm to approximately 1 m. Plant 
cover varied from virtually nothing to dense 
algal growth covering the bottoms and sides of 
the pools. During the period of study, tempera- 
tures never rose above 17 C in the lower and 
deeper pools but on warm, sunny afternoons 
temperatures rose to as high as 27 C in some 
of the higher, shallower pools. However, no 
correlation was found between pagurid distri- 
bution and maximum pool temperature. Three 
species of hermit crabs found on this study area 
were Pagurus hirsutius cuius, P. samuelis, and P. 
granosimanus . 
The site of Kings study was approximately 
100 m offshore in the lagoon adjacent to Chi- 
nimi Island of Eniwetok Atoll. At this location 
the depth is 7 m and the substrate is uniformly 
composed of coralline sand mixed with fine 
pieces of dead coral. A 25 6 m 2 area was divided 
with a thin cord into 16 squares of 16 m 2 each. 
These squares were designated by letters from 
297 
