The effects of environment on &amp;lt;i&amp;gt;Arctica islandica&amp;lt;/i&amp;gt; shell formation and architecture

Gernot Nehrke,Irene Ballesta-Artero,Bernd R Schöne,Stefania Milano,Alan D Wanamaker Jr,Thomas Brey

doi:10.5194/bg-14-1577-2017

Abstract

Abstract. Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly understood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and interpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional proxies not influenced by multiple environmental variables or animal physiology would be a great asset in the field of paleoclimatology. The aim of this study is to investigate the potential use of structural properties of Arctica islandica shells as an environmental proxy. A total of 11 specimens were analyzed to study if changes of the microstructural organization of this marine bivalve are related to environmental conditions. In order to limit the interference of multiple parameters, the samples were cultured under controlled conditions. Three specimens presented here were grown at two different water temperatures (10 and 15 °C) for multiple weeks and exposed only to ambient food conditions. An additional eight specimens were reared under three different dietary regimes. Shell material was analyzed with two techniques; (1) confocal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment distribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization. Our results indicate that A. islandica microstructure is not sensitive to changes in the food source and, likely, shell pigment are not altered by diet. However, seawater temperature had a statistically significant effect on the orientation of the biomineral. Although additional work is required, the results presented here suggest that the crystallographic orientation of biomineral units of A. islandica may serve as an alternative and independent proxy for seawater temperature.

Highlights

Biomineralization is a process through which living organisms produce a protective, mineralized hard tissue
Shell material was analyzed with two techniques; (1) confocal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment distribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization
Our results indicate that A. islandica microstructure is not sensitive to changes in the food source and, likely, shell pigment are not altered by diet

Summary

Introduction

Biomineralization is a process through which living organisms produce a protective, mineralized hard tissue. Different architectures at the micrometer and nanometer scale and different biochemical compositions determine material properties that serve specific functions (Weiner and Addadi, 1997; Currey, 1999; Merkel et al, 2007) Besides these differences, all mineralized tissues are hybrid materials consisting in hierarchical arrangements of biomineral units surrounded by organic matrix, known as “microstructures” Previous studies conducted on mollusks show that environmental parameters can influence microstructure formation (Lutz, 1984; Tan Tiu and Prezant, 1987; Tan Tiu, 1988; Nishida et al, 2012) These results set the stage for research that focuses on the use of shell microstructures as proxies for reconstructing environmental conditions (Tan Tiu, 1988; Tan Tiu and Prezant, 1989; Olson et al, 2012; Milano et al, 2017)

Objectives

Methods

Results

Discussion

Conclusion