A LONG-TERM GROWTH RECORD DERIVED FROM ARCTICA-ISLANDICA (MOLLUSCA, BIVALVIA) FROM THE FLADEN GROUND (NORTHERN NORTH-SEA)

Long-term variations in shell growth of the mollusc Arctica islandica (Mollusca, Bivalvia) from the northern North Sea have been assessed re trospectively using the annually deposited internal growth lines. Rela tively young specimens yielded a detailed year-to-year chronology whil e the growth record of specimens older than 30 y yielded a time series with a length exceeding 100 years. The long-term growth trends demons trated a marked alternating sequence of periods in which growth was be low and above expectation. A 33-y long cycle could be discerned. Since the 1960s the growth patterns in Arctica from two nearby locations we re opposite, while they resembled each other in the period before 1960 . Although expected, no significant correlations were found between sh ell growth and local bottom water temperature or CPR (Continuous Plank ton Recorder) phytoplankton variables. The alternative hypothesis to e xplain the variations in shell growth is the existence of a link betwe en local hydrographical phenomena and the occurrence of the Arctica be ds. The stations from where the specimens were collected were discover ed when a drogue was caught by a local eddy. It is speculated that thi s distribution pattern is the consequence of import and accumulation o f organic matter by the eddy system. This idea is supported by the cor relation between the variations in the influx of North Atlantic water into the North Sea which determines the existence of the eddy.