Seasonal Growth Studies of Intertidal Gastropods From Shell Micro-Growth Band Measurements, Including A Comparison With Alternative Methods

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Abstract
Tidal micro-growth bands were used to study the annual cycle of shell growth of individuals dated predominantly by the immersion mark technique, in three common intertidal gastropodsNucella lapillus(L.),Littorina littorea(L.) andPatella vulgataL. growing naturally in the Menai Straits. Growth in all three species approximated to the von Bertalanaffy type. All three species grew throughout the year,N. lapillusandL. littoreawith early autumn and summer maxima, respectively, andP. vulgatawith two maxima, one in late spring and the other in early autumn.P. vulgataalone were observed during exposure to a 6-day period of sub-zero air temperature in January 1982 when shell growth was totally interrupted. InNucellaandLittorinashell growth was found to be closely related to ambient temperature but inPatellathere was a summer depression in growth. The file technique when combined with the immersion mark technique in date marking, was found to be inferior to the immersion mark technique on its own, since filing occasionally affected growth adversely.From among the factors determining the seasonal changes in growth rate, temperature was of major importance. Seasonal reproduction may also have an influence, especially inP. vulgatawhere gametogenesis coincides with the depression in growth rate during summer months.Alternative methods used in gastropod growth studies were compared. In the light of inadequacies associated with other methods of measuring growth, micro-growth band measurements in gastropods offers a new method with high resolution suitable both for short and long-term growth studies. It has potential also for ecological and physiological aspects of growth measurements.
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