Annual growth of the cockle Clinocardium ciliatum in the Norwegian Arctic (Svalbard area)

Summary

The Svalbard Islands are influenced by warm Atlantic water in the south and west, and cold Arctic water in the east. Ice cover, and hence the location of the highly productive marginal ice zone, varies both intra and interannually. Part of the primary production accumulates on the bottom and is utilized by the benthos. In this study, the annual growth of the cockle Clinocardium ciliatum (Fabricius, 1780) from three sites in Svalbard waters is reported. Moffen, the site in the north (80 degrees 01' N, 13 degrees 48' E) is located in the northernmost areas influenced by Atlantic water. The Storfjorden site (77 degrees 10' N, 20 degrees 09' E) is situated in cold Arctic water masses, and the Bear Island site (74 degrees 50' N, 18 degrees 54' E) is in the Polar front area where Atlantic and Arctic water masses meet. Annual growth of cockles was analysed retrospectively by measuring external growth increments, which gave annual growth records from the 1970s to 1996. Shell height for age for different year classes was highest at the Storfjorden site, and lowest at Bear Island. Periods of high growth occurred at Storfjorden and Bear Island during the 1980s while the beginning of 1990s was characterized by low growth. At Moffen, growth was more variable between single years. Several factors are influencing the growth of C. ciliatum in the Svalbard area and growth cannot be coupled to only one environmental factor like ice cover.