Factors Influencing Shell Shape in the Mussel Mytilus Edulis

Abstract

An attempt is made to explain the great variations in gross shell morphology noted in field populations of Mytilus edulis.In any one mussel population, variation in shell form can be attributed to differences in age, old mussels having proportionately heavier shells where width often exceeds shell height. This is invariably accompanied by down-turned, divergent umbones and varying degrees of incurvature of the ventral shell margin.Variations in the age structure of mussel populations from different habitats can also account for local variability in shell morphology. Localities where the life expectancy of mussels is increased due to absence of predators (especially in the upper shore) reveal a high incidence of old ' ungulate' individuals, whereas populations in which the mussel turnover is more rapid show a preponderance of relatively young mussels.Shell morphology is greatly influenced by growth rate and density. These probably exert their effect through physical compression which is maximum in localities of fast growth and high density and least in areas of slow growth and low density. High compression leads to an elongate form whereas low compression results in higher, more triangular shaped shells. Growth rates and densities, even within the same habitat, are, however, exceedingly variable.Since all environmental conditions vary in both time and space, wide variation in shell morphology is to be expected, even in animals from the same locality.Transplantation experiments indicate that variation in shell morphology is essentially phenotypic, older animals being more likely to exhibit a form which is characteristic of their particular habitat. Smaller mussels from widely different habitats show remarkable similarity in shell morphology. The plasticity of Mytilus in this respect renders shell morphology a doubtful criterion for taxonomic studies.

The occurrence of Mytilicola intestinalis Steuer, an intestinal copepod parasite of Mytilus, in the south-west of England

“…Whitsand, Cawsand, Maenporth, Porthmeor, Westward Ho) albeit at a relatively low level, even when compared to recently infested estuarine populations of mussels. Seed (1968) has shown that mussels from estuarine sites are considerably larger than mussels of the same age on open coast sites. The differences in infestation levels, therefore, between mussels from these two types of site may be associated with differences in host size.…”

Domoic acid uptake and elimination kinetics in oysters and mussels in relation to body size and anatomical distribution of toxin

“…Bivalve shell size was measured as the maximum long axis from the umbo to the ventral margin of the shell, which represents the shell height (SH) in oysters (Carriker, 1996) but is commonly referred to as the shell length (SL) in mussels (Seed, 1968). Oysters, C. virginica (SH = 15-78 mm), were obtained from Bay Enterprises Ltd., Malagash, and mussels, M. edulis (SL = 16-45 mm), from Indian Point Marine Farms Ltd., Mahone Bay, NS, Canada in May 2007.…”

Colonization of an artificial hard substrate byMytilus edulisin the German Bight

“…On tidal coasts, duration of air exposure of intertidal mussel beds is considered to be one of the most crucial factors controlling mussel growth (e.g. Baird & Drinnan 1957;Faldborg et al 1994;McGrorty 1997) and may lead to considerable variations in size and shape between intertidal and subtidal M. edulis (Baird 1966;Seed 1968).…”