Description: Optic technologies and methods/procedures are established across all areas and scales in limnic and marine research in Germany and develop further continuously. The working group “Aquatic Optic Technologies” (AOT) constitutes a common platform for knowledge transfer among scientists and users, provides a synergistic environment for the national developer community and will enhance the international visibility of the German activities in this field. This document summarizes the AOT-procedures and -techniques applied by national research institutions. We expect to initiate a trend towards harmonization across institutes. This will facilitate the establishment of open standards, provide better access to documentation, and render technical assistance for systems integration. The document consists of the parts: Platforms and carrier systems outlines the main application areas and the used technologies. Focus parameters specifies the parameters measured by means of optical methods/techniques and indicates to which extent these parameters have a socio-political dimension. Methods presents the individual optical sensors and their underlying physical methods. Similarities denominates the common space of AOT-techniques and applications. National developments lists projects and developer groups in Germany designing optical high-technologies for limnic and marine scientific purposes.

Description: 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 un- derstood, 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 in- terpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional prox- ies not influenced by multiple environmental variables or an- imal physiology would be a great asset in the field of paleo- climatology. The aim of this study is to investigate the poten- tial use of structural properties of Arctica islandica shells as an environmental proxy. A total of 11 specimens were ana- lyzed to study if changes of the microstructural organization of this marine bivalve are related to environmental condi- tions. In order to limit the interference of multiple parame- ters, 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) confo- cal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment dis-tribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization. Our results indicate that A. islandica microstructure is not sen- sitive to changes in the food source and, likely, shell pig- ment 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 alterna- tive and independent proxy for seawater temperature.

Description: This study investigated to what extent the extrapallial fluid (EPF) of the marine bivalve Arctica islandica (Linneaus, 1767) is involved in shell formation. With in situ pH microscopy, pH gradients were identified between inner shell surface and outer mantle epithelium (OME). pH at the OME varied rapidly between neutral and values above 9, suggesting active H+ pumping. Microsensor measurements showed also remarkable short-term dynamics in pH and Ca2+ concentrations, again suggesting active ion pumping. Further focus was on pH, Ca2+, and dissolved inorganic carbon dynamics within the EPF to determine whether calcium carbonate precipitation is possible within the EPF. The data show that the bulk of the inner EPF rarely reaches calcium carbonate saturation and, thus, cannot be the site of shell formation. At the OME surface, however, pH levels of up to 9.5 were observed, corresponding to a 30-fold carbonate supersaturation. Thus, ion pumping by the OME can drive calcification when the OME is just a few mm distant from the inner shell surface, as it is the case in the outer EP