Climatic regulation of Clinocardium ciliatum (bivalvia) growth in the northwestern Barents Sea

We examined the growth of the Arctic bivalve Clinocardium ciliatum in the Barents Sea to evaluate the effect of oceanographically distinct water masses on growth and to assess the influence of climatic forcing on ecological processes over decadal scales. Analysis of annually-deposited growth lines in shells of 22 individuals from 3 stations allowed us to assess growth conditions from 1977–2006, encompassing both warmer and colder climatic phases of the 20th century. Growth rates of juvenile specimens (6–13 years) were highest in Atlantic water, resulting in a 20% greater average shell size compared to similarly aged individuals from Arctic water or at the Polar Front. This may reflect comparatively warmer sea temperatures and/or greater food supplies in regions of the Barents Sea dominated by Atlantic water. Despite different absolute growth rates, temporal patterns of ontogenetically-adjusted incremental growth (i.e. Standard Growth Index = SGI) were similar at all sites, with low but increasing SGI throughout the 1980s and peaking in 1994 or 1995. An abrupt decline starting in 1996 led to low SGI values for most years from the turn of the century to the last year of bivalve growth in 2006. The decline in SGI coincides with abrupt phase shifts in two hemispheric oscillatory indices: the North Atlantic Oscillation (NAO) and the Arctic Climate Regime Index (ACRI). The strongest statistical relationships were found between standardized growth and the ACRI and its local manifestations through precipitation and sea ice cover. The ACRI explained 51% of the variation in growth from all the samples, while ACRI, annual precipitation, and ice-free days together explained 65% of the growth variability. Using a two-year running mean of the ACRI improved these relationships substantially and indicates a possible lag in the relationship between external forcing and bivalve growth. These results show that benthic communities in this area are intricately linked to regional climatic forcing and that the predicted increase in Atlantic water influence in the Barents Sea in response to climate change will impact growth of benthic organisms.