Increased pCO2 and geographic origin on purple sea urchin

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Ocean acidification will likely have negative impacts on invertebrates producing skeletons composed of calcium carbonate. Skeletal solubility is partly controlled by the incorporation of " foreign " ions (such as Mg and Sr) into the crystal lattice of these skeletal structures, a process that is sensitive to a variety of biological and environmental 5 factors. Here we explore the effects of life stage, oceanographic region of origin, and changes in the partial pressure of carbon dioxide in seawater (pCO 2) on trace elemental composition in the purple sea urchin (Strongylocentrotus purpuratus). We show that, similar to other urchin taxa, adult purple sea urchins have the ability to precipitate skeleton composed of a range of biominerals spanning low to high magnesium 10 calcites. Mg/Ca and Sr/Ca ratios were substantially lower in adult spines compared to adult tests. On the other hand, trace elemental composition was invariant among adults collected from four oceanographically distinct regions along the US west coast (Oregon, Northern California, Central California, and Southern California). Skeletons of newly settled juvenile urchins that originated from adults from the four regions ex-15 hibited intermediate Mg/Ca and Sr/Ca between adult spine and test endmembers, indicating that skeleton precipitated during early life stages is more soluble than adult spines and less soluble than adult tests. Mean skeletal Mg/Ca or Sr/Ca of juvenile skeleton did not vary with source region when larvae were reared under present-day, global-average seawater carbonate conditions