REPRODUCTION AND LIFE-HISTORY STRATEGY OF THE HERMIT-CRAB PAGURUS-BERNHARDUS

Hermit crabs use gastropod shells to protect their bodies and developing eggs an inadequate supply of shells of the appropriate size will, therefore, adversely affect their growth, fecundity and longevity. Since the supply of shells is commonly limited, mechanisms that help to reduce these adverse effects will be selectively advantageous. In Pagurus bernhardus it is suggested that two mechanisms have evolved in this respect: Larval settlement is encouraged in the littoral zone where gastropod species are diverse and numerous and where the youngest hermits will find growth potentially unrestricted and females breed within their first year of life and at a size substantially below that which could be attained in the shells commonly available to them. This ‘precocious’ breeding is suggested to be an adaptation enabling hermits to overcome the problems of shell-limitation, since it frees females of the need to attain a specific age or size before reproducing - a situation which would be perilous when large shells are scarce. Males of a similar age are freed from competition for the larger shells as a result of this strategy, since the growth of the females is suppressed while they are ovigerous. Reproduction in north-temperate littoral populations of P. bernhardus is seasonal and asynchronous, occurring during the months of November to May in response to cold water temperatures and reduced photoperiods. Gestation requires some 43 days and more than two broods are possible in a season. © 1990, Marine Biological Association of the United Kingdom. All rights reserved.