Environmental and biological controls on Naĝ•Ca ratios in scleractinian cold-water corals

Abstract

Here we present a comprehensive attempt to correlate aragonitic Nag ratios from Desmophyllum pertusum (formerly known as Lophelia pertusa), Madrepora oculata and a caryophylliid cold-water coral (CWC) species with different seawater parameters such as temperature, salinity and pH. Living CWC specimens were collected from 16 different locations and analyzed for their Nag ratios using solution-based inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements.The results reveal no apparent correlation with salinity (30.1-40.57g kg-1;) but a significant inverse correlation with temperature (-0.31±0.04mmol-1°C-1). Other marine aragonitic organisms such as Mytilus edulis (inner aragonitic shell portion) and Porites sp. exhibit similar results highlighting the consistency of the calculated CWC regressions. Corresponding Naĝ•Mg; ratios show a similar temperature sensitivity to Nag ratios, but the combination of two ratios appears to reduce the impact of vital effects and domain-dependent geochemical variation. The high degree of scatter and elemental heterogeneities between the different skeletal features in both Nag and Naĝ•Mg;, however, limit the use of these ratios as a proxy and/or make a high number of samples necessary. Additionally, we explore two models to explain the observed temperature sensitivity of Nag ratios for an open and semi-enclosed calcifying space based on temperature-sensitive Na- and Ca-pumping enzymes and transport proteins that change the composition of the calcifying fluid and consequently the skeletal Nag ratio.