Intrinsic over extrinsic: Species identity shapes spatial and interannual Mg/Ca patterns in Arctic marine calcifiers

Abstract

Marine calcifiers incorporate magnesium into their calcium carbonate skeletons through processes influenced by both ambient environmental conditions and species-specific physiological regulation. As a result, their carbonate structures can serve as valuable archives of past and present oceanic conditions, provided that biological controls are explicitly considered. This study investigated how skeletal magnesium-to-calcium (Mg/Ca) ratios vary in space and time among three Arctic benthic invertebrates differing in phylogeny, evolutionary history, and biomineralization strategy: the barnacle Semibalanus balanoides, the spirorbid Paradexiospira violacea, and the bryozoan Harmeria scutulata. Mg/Ca ratios were quantified using inductively coupled plasma atomic emission spectroscopy (ICP-AES) across three Svalbard fjords and over a four-year temporal interval (2006–2009). Kruskal–Wallis analyses revealed that species identity was the dominant factor controlling Mg/ Ca ratios among the studied taxa. S. balanoides exhibited the lowest values of mean Mg/Ca ratios but highly variable (mean = 35.2 mmol/mol ± 16.8 SD), whereas P. violacea (62.5 mmol/mol ± 14.3) and H. scutulata (65.3 mmol/mol ± 14.1) showed higher and more consistent Mg/Ca ratio. Significant differences in Mg/Ca ratios were observed among sites for all species, following a consistent Hornsund < Kongsfjorden