Population structure and growth rates at biogeographic extremes: a case study of the common cockle, Cerastoderma edule (L.) in the Barents Sea.

A descriptive study of population structure, growth rates and shell morphometry was conducted on nine intertidal populations of the infaunal bivalve Cerastoderma edule in the Murmansk coast of the Barents Sea. Year-to-year population dynamics was analyzed during 2002-2006 on a tidal flat Dalniy Plaj (eastern Murmansk coast). The region constitutes the northern extremes of C. edule range where populations occupied the middle to low intertidal zone and were characterized by low densities. The distribution of age groups and unstable age structure across years in the cockle populations suggest irregular recruitment. Growth rates and shell morphometry showed little variation across the populations studied, and there were no gradient changes from the west to the east parts of Murmansk coast.