Compositional variability of Mg/Ca, Sr/Ca, and Na/Ca in the deep-sea bivalve Acesta excavata (Fabricius, 1779).

Tim M Conway,Nicolai Schleinkofer,Max Wisshak,Axel Gerdes,Jacek Raddatz,David Evans,Janina Vanessa Büscher,Silke Voigt,Sascha Flögel

doi:10.1371/journal.pone.0245605

Abstract

Acesta excavata (Fabricius, 1779) is a slow growing bivalve from the Limidae family and is often found associated with cold-water coral reefs along the European continental margin. Here we present the compositional variability of frequently used proxy elemental ratios (Mg/Ca, Sr/Ca, Na/Ca) measured by laser-ablation mass spectrometry (LA-ICP-MS) and compare it to in-situ recorded instrumental seawater parameters such as temperature and salinity. Shell Mg/Ca measured in the fibrous calcitic shell section was overall not correlated with seawater temperature or salinity; however, some samples show significant correlations with temperature with a sensitivity that was found to be unusually high in comparison to other marine organisms. Mg/Ca and Sr/Ca measured in the fibrous calcitic shell section display significant negative correlations with the linear extension rate of the shell, which indicates strong vital effects in these bivalves. Multiple linear regression analysis indicates that up to 79% of elemental variability is explicable with temperature and salinity as independent predictor values. Yet, the overall results clearly show that the application of Element/Ca (E/Ca) ratios in these bivalves to reconstruct past changes in temperature and salinity is likely to be complicated due to strong vital effects and the effects of organic material embedded in the shell. Therefore, we suggest to apply additional techniques, such as clumped isotopes, in order to exactly determine and quantify the underlying vital effects and possibly account for these. We found differences in the chemical composition between the two calcitic shell layers that are possibly explainable through differences of the crystal morphology. Sr/Ca ratios also appear to be partly controlled by the amount of magnesium, because the small magnesium ions bend the crystal lattice which increases the space for strontium incorporation. Oxidative cleaning with H2O2 did not significantly change the Mg/Ca and Sr/Ca composition of the shell. Na/Ca ratios decreased after the oxidative cleaning, which is most likely a leaching effect and not caused by the removal of organic matter.

Highlights

IntroductionThe reefs provide shelter for other organisms such as the bivalve Acesta excavata (Fabricius, 1779) as one of the key species associated with CWC reefs
Cold-water coral (CWC) reefs comprise an important contribution to the marine biodiversity on continental margins that is similar to that of warm-water coral (WWC) reefs
This is an effect of increased meltwater supply and increasing northerly winds, which causes the depth of the Norwegian Coastal Current (NCC) to decrease

Summary

Introduction

The reefs provide shelter for other organisms such as the bivalve Acesta excavata (Fabricius, 1779) as one of the key species associated with CWC reefs. These sensitive ecosystems are greatly threatened by the combined effects of ocean acidification and warming [7,8,9,10]. Commonly used proxies such as Mg/Ca and can be influenced by vital effects [19,20,21,22] Other corals such as bamboo corals show more promising results regarding growth patterns and trace element proxies [23,24,25,26] and might provide an alternative archive

Methods

Results

Discussion

Conclusion