Aspects of the ecology of Pagurus bernhardus are examined and the strategies which enable this species to exploit two quite different habitats are determined. The area of shell selection is reviewed and mathematical indices of shell adequacy are rejected as biologically flawed. A subjective index is proposed to more accurately describe the quality of a hermit crab shell resource. Shell preference is considered to be an artificial phenomenon and shell selection is demonstrated to be an essentially random process. Shell-limitation is considered one of the most common problems facing all populations of hermit crabs, detrimentally affecting growth, fecundity, and longevity. The reproductive cycle of Pagurus bernhardus is examined, and the period spent in the littoral zone is considered critical in the life history. Breeding is shown to occur only during the winter months in littoral populations, and is shown to require two interacting stimuli. Low temperatures affect egg production in the female; while reduced photoperiods affect breeding behaviour in the male. Gestation is shown to require some 43 days at temperatures of 8-10°c, and most females will produce two broods during a breeding season. Females are sexually mature in their first year and precocious breeding is seen as a vital strategy to overcome the restrictions of shell-limitation. The monitoring of marked individuals indicates that Pagurus bernhardus is not territorial, and that the distribution of individuals on a shore is essentially random. The patterns of movement, the non-breeding interactions between individuals, and the residence times of these animals on a shore are suggested to be most strongly influenced by the quantity and quality of their shell contacts. Migration into the sublittoral is seen as an inevitable consequence of this behaviour.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 98-102). Also available via the Internet.

Thesis (Honors)--College of William and Mary, 2008. / Includes bibliographical references (leaves 35-40). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Delaware, 2008. / Principal faculty advisor: Charles E. Epifanio, College of Marine & Earth Studies. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1994. / Typescript. Includes bibliographical references (leaves 92-94).

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Charles E. Epifanio, College of Marine & Earth Studies. Includes bibliographical references.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 54-57.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984. / Bibliography: p. 152-163.

Behavioural responses of the colour forms of Carcinus maenas to salinity variation were investigated, and related to their physiology and distribution in an estuary. Red males, characterised by a thicker carapace were unable to survive in as low salinities as green males; this was reflected in their poorer osmoregulatory capabilities. Haemolymph osmolality and ion concentrations of red crabs decreased at a faster rate and reached lower levels than in green crabs. Haemolymph osmolality and choice behaviour did not vary with size. In the tidally mixed estuary male and female crabs occurred in roughly similar proportions. Most were green and generally smaller than their open shore counterparts. Migration out of the estuary in winter was reversed in late spring. Differences in salinity tolerance of red and green crabs were reflected in salinity preference behaviour. Green crabs persisted longer in the lowest range of salinities tested, especially if a shelter was available. Prior acclimation affected the timing of choice behaviour; the lower the salinity of acclimation the faster the time of exit from the lowest range of salinities tested, and vice versa. Estuarine green crabs exhibited endogenous locomotor activity of circatidal periodicity and were less responsive to episodes of low salinity than open shore red and green crabs. Constant low salinity initiated a rhythm of circatidal periodicity in arhythmic red and green crabs; red crabs reacted faster and were more active upon salinity change than green crabs. The amount of locomotor activity induced after prior acclimation was similar within each acclimation salinity tested. Carcinus detected salinity variation by responding to the concentrations of Na and Cl in seawater, and was able to differentiate between salinities separated by as little as 0.5ppt., - General physiological changes appear to occur before behavioural responses are mediated; they probably act as cues for the behavioural responses, which appear not to be triggered by specific receptors. Behavioural and physiological responses combing to enhance, the survivability of crabs in changing salinities.