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Abstract Coastal Indigenous communities that rely on subsistence harvests are uniquely vulnerable to declines in nearshore species. The basket cockle Clinocardium nuttallii is among the favored foods of Indigenous people along the northwest Pacific coast of North America, yet localized declines in their abundance have led to interest in stock enhancement efforts. We used a population genomics approach to examine potential risks associated with stock enhancement of C. nuttallii in the southern Salish Sea, a large inland estuary that includes Puget Sound. More than 8000 single nucleotide polymorphisms across 349 individuals at 12 locations were assembled de novo using restriction site‐associated DNA sequencing. Results indicated that C. nuttallii within the southern Salish Sea were distinct from those along the outer Pacific coast (FST = 0.021–0.025). Within the southern Salish Sea, C. nuttallii populations appear to be well‐connected despite numerous potential impediments to gene flow; Hood Canal, which experiences the lowest flushing rates of all Puget Sound sub‐basins, was a minor exception to this strong connectivity. We found evidence of isolation by distance within the southern Salish Sea, but the slope of this relationship was shallow, and FST values were low (FST = 0.001–0.004). Meanwhile, outlier analyses did not support the hypothesis that southern Salish Sea sub‐populations are locally adapted. Estimates of effective population size had no upper bound, suggesting potentially very high adaptive capacity in C. nuttallii, but also making it difficult to assess potential reductions in effective population size resulting from stock enhancement. We present several strategies to augment cockle populations for subsistence harvest that would limit risk to the genetic diversity of wild cockle populations.

Coastal Indigenous communities that rely on subsistence harvests are uniquely vulnerable to declines in nearshore species. The basket cockle Clinocardium nuttallii is among the favored foods of Indigenous people along the northwest Pacific coast of North America, yet localized declines in their abundance have led to interest in stock enhancement efforts. We used a population genomics approach to examine potential risks associated with stock enhancement of C. nuttallii in the southern Salish Sea, a large inland estuary that includes Puget Sound. More than 8000 single nucleotide polymorphisms across 349 individuals at 12 locations were assembled de novo using restriction site‐associated DNA sequencing. Results indicated that C. nuttallii within the southern Salish Sea were distinct from those along the outer Pacific coast (FST = 0.021–0.025). Within the southern Salish Sea, C. nuttallii populations appear to be well‐connected despite numerous potential impediments to gene flow; Hood Canal, which experiences the lowest flushing rates of all Puget Sound sub‐basins, was a minor exception to this strong connectivity. We found evidence of isolation by distance within the southern Salish Sea, but the slope of this relationship was shallow, and FST values were low (FST = 0.001–0.004). Meanwhile, outlier analyses did not support the hypothesis that southern Salish Sea sub‐populations are locally adapted. Estimates of effective population size had no upper bound, suggesting potentially very high adaptive capacity in C. nuttallii, but also making it difficult to assess potential reductions in effective population size resulting from stock enhancement. We present several strategies to augment cockle populations for subsistence harvest that would limit risk to the genetic diversity of wild cockle populations. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of Clinocardium californiense shell were investigated in relation to the different parts of shell. It is found that the shell can be divided into three parts, that is, the dorsal side, body part, and marginal side based on the variation of microstructures along the longitudinal cross section. Specifically, all areas exhibit a cross-lamellar structure on the dorsal side, and a hierarchical structure comprising three layers including inner (with a cross-lamellar structure), middle (with a complex cross-lamellar structure), and outer (with a prismatic structure) layers was observed on the body part, whereas on the marginal side, the orientation of aragonite sheets shows an obvious deflection. The structural architecture, the dimensions of different-order lamellae in the same kind of structure and the orientation between the indenting direction and aragonite sheet all contribute to the unique mechanical properties of this shell. It is also found that a low value of the ratio of hardness-to-Young's modulus ( H/ E) corresponds to an improved indentation toughness. The middle layer with the densest and most complicated structure on the body part shows the lowest H/ E ratio and the highest hardness and Young's modulus. [ABSTRACT FROM AUTHOR]

Abstract: The correlation between microstructures and indentation toughness of Clinocardium californiense shell was characterized by a fractal method. It is found that the shell exhibits a hierarchical structure comprising three layers, i.e., the inner layer with a cross-lamellar structure, the middle layer with a complex cross-lamellar structure, and the outer layer with a prismatic structure. The microstructure in the middle layer with fine and complex arrangement of aragonite sheets corresponds to the largest fractal dimension for indentation-induced cracks, and consequently to the highest indentation toughness. [Copyright &y& Elsevier]

Growth patterns of two common circumpolar bivalves, the Greenland cockle ( Serripes groenlandicus), and the hairy cockle ( Clinocardium ciliatum) have been used in previous studies to reconstruct environmental conditions in the arctic. To date, there has been no direct determination that growth lines in either species are deposited periodically, and there has been no examination of factors affecting growth. We placed calcein-marked individuals of both species on oceanographic moorings in two fjords (Rijpfjord and Kongsfjord) in the Svalbard archipelago for one and two (Kongsfjord only) years. Growth patterns were compared with concurrent in situ temperature and fluorescence data in order to assess environmental controls on growth. Dark growth lines are evident on the outer shell surface and internally in shell cross section in both S. groenlandicus and C. ciliatum, and both species deposited only one line per year, unequivocally confirming that internal lines are deposited annually. Growth line deposition in both species began in late summer to early fall, before the seasonal decline in temperature. There was no difference in growth of S. groenlandicus between the two fjords despite differences in water temperature (3°C), fluorescence (nearly threefold) and the onset and duration of the winter season. C. ciliatum, however, grew approximately 2.8 times faster in the warmer, more food-rich Kongsfjord than in Rijpfjord. Subannual lines were counted in two individuals of each species from each fjord, but deposition of these lines was not clearly related to number of growing days estimated by temperature and fluorescence. [ABSTRACT FROM AUTHOR]

Abstract: 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 (6–13years) 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. [Copyright &y& Elsevier]