Seasonal growth variation in Chlamys islandica (Bivalvia) from sub-Arctic Greenland is linked to food availability and temperature

In order to assess the role of different environmental parameters in the population dynamics of marine invertebrates in the Arctic, we examined seasonal variation in individual biomass, shell growth, and mass production of somatic and reproductive tissues of immature and maturing scallops Chlamys islandica suspended in culture nets at 15 and 30 m depth in SW Greenland from May 2007 to October 2008. All 3 parameters varied both seasonally and between depths. Individual shell growth rate and biomass were poor proxies for the actual mass growth rate on a seasonal scale. Minimum and maximum mass growth rates were observed from November to February and in April-May, respectively. Simultaneous monitoring of biotic and abiotic parameters in the water column made it possible to establish a growth model relating variation in mass growth rate to variation in environmental conditions. The best-fit model (R-2 = 0.71) indicated that total mass growth rate depended on chlorophyll a concentration, carbon-to-nitrogen ratio of seston, and water temperature. While availability of high-quality food items affected growth positively, the growth model indicated a negative effect of increasing temperature on the mass growth rate of C. islandica. These results indicate that scallops in SW Greenland are resource-limited and that elevated temperature through its effect on metabolic costs reduces growth efficiency. Hence, it is most likely that the growth capacity of C. islandica in SW Greenland is either never realized or only attained for short periods of time (hours to days) under the present conditions.