Influence of Diet on Element Incorporation in the Shells of Two Bivalve Molluscs: Argopecten irradians concentricus and Mercenaria mercenaria

Recently, biogenic carbonates have received much attention as potential proxies of environmental change; however, a major pathway of elemental incorporation is often overlooked when making interpretations or designing experiments. This research experimentally examines the influence of diet on elemental composition in juvenile shells of the bay scallop, Argopecten irradians concentricus, and the northern quahog, Mercenaria mercenaria.\nExploratory trials were conducted using Argopecten irradians concentricus juveniles fed different algal diets: Isochrysis, Chaetoceros, Pavlova, Tetraselmis, or a mix of all four in a 2:1:2:2 ratio. No differences between the left and right valves were revealed, thus, subsequent analysis of the dietary influence on shell chemistry utilized both valves. Only Mg/Ca and K/Ca were significantly different between the diet groups, though different influences were determined.\nExperiments with juvenile Mercenaria mercenaria compared shell chemistries among clams fed unicellular diets of Isochrysis sp. (CCMP1324), Pavlova pinguis (CCMP609), Chaetoceros mulleri (CCMP1316), Isochrysis sp. (CCMP1611) culture, Pavlova sp. (CCMP1209), or Chaetoceros galvestonensis (CCMP186), a mixed diet of all species in equal ratios (Mixed), or no food (starvation control). The results indicate that diet can influence shell chemistry either directly or indirectly, with degree of influence varying by diet and mollusc species.\nAdditional information concerning the use of alternative element ratios and changes in the shell chemistry due to starvation-induced stress are also presented. Altogether, the present research provides valuable information concerning shell dynamics and potential diet-associated fluxes, thus demonstrating the need to consider the composition of dietary inputs when assessing environmental associations with elemental shell chemistries.