Variations de la croissance de la coquille, et de la structure d'âge du bivalve Macoma balthica (L.) dans une population intertidale de l'estuaire du Saint-Laurent (Québec)

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Abstract
Greater annual shell growth rate and increased mortality are observed in Macoma balthica (L.) with an increase of immersion time in the intertidal zone of the St. Lawrence estuary. There is also a greater annual growth rate in tidal pools, and sediment temperature alone may explain spatial variations in spring and annual growth. Reciprocal transfers of specimens between upper (0.8 m above mean water level) and lower (1.2 m below mean water level) tidal level result in enhanced shell growth for individuals of the upper level transferred to the lower level. There is no corresponding change of shell growth rate for individuals of the lower level. This genotypic difference in short-term physiological responses to environmental changes may be the result of different selective pressures associated with habitat temporal heterogeneity. An opportunistic strategy is associated with the more terrestrial and unpredictable environment (upper tidal level) and a more specialized strategy accompanied by low phenotypic variability is associated with the more marine and stable environment (lower tidal level).