Description: Freshwater bivalves of the order Unionoida display an uncommon phenotypic plasticity with high interpopulation and intrapopulation morphological variability, which could be advantageous for coping with habitat modifications. However, unionoids have suffered a marked population decline in different parts of the world in the last decades. A decline in some populations of the South American long‐lived freshwater mussel Diplodon chilensis as a consequence of habitat deterioration has recently been recorded. Ontogenetic allometry and shape variation in shells of D. chilensis from 2 different sites, Paimun lake and Chimehuin river, North Patagonia, Argentina, have been studied. For these purposes, geometric morphometric methods were used. Shell shape shows differences between sites, which the shells from Chimehuin river show less intrapopulation variability; are more elongated, with the anterior part extended upwards and the posterior part downwards; and show a steeper anterior curvature at the umbo compared to those from Paimún lake. These characteristics make shell shape more streamlined to withstand river current. Furthermore, the extended posterior‐ventral part in river shells coincides with higher foot weight that would improve anchoring to the river rocky–sandy substrate. River shells present a bounded eco‐morphotype whereas the higher variability of lake shells includes the “river eco‐morphotype.” Growth is allometric throughout life in both sites and is not sex‐dependent. The success of river repopulation programmes using mussels from lake populations may be increased by transplanting selected individuals that show “river eco‐morphotype.”

Description: The snow crab Chionoecetes opilio and Arctic lyre crab Hyas coarctatus are prominent members of the Chukchi Sea epifaunal community. A better understanding of their life history will aid in determining their role in this ecosystem in light of the changing climate and resource development. In this study, the size frequency distribution, growth, and mortality of these two crab species was examined in 2009, 2010, 2012, and 2013 to determine temporal and spatial patterns within the eastern Chukchi Sea, and to identify potential environmental drivers of the observed patterns. Temporally, the mean size of both sexes of C. opilio and H. coarctatus decreased significantly from 2009 to 2013, with the number of rare maximum sized organisms decreasing significantly to near absence in the latter two study years. Spatially, the mean size of male and female crabs of both species showed a latitudinal trend, decreasing from south to north in the investigation area. Growth of both sexes of C. opilio and H. coarctatus was linear over the sampled size range, and mortality was highest in the latter two study years. Life history features of both species related to different environmental parameters in different years, ranging from temperature, the sediment carbon to nitrogen ratio of the organic content, and sediment grain size distribution. Likely explanations for the observed temporal and spatial variability are ontogenetic migrations of mature crabs to warmer areas possibly due to cooler water temperatures in the latter two study years, or interannual fluctuations, which have been reported for C. opilio populations in other areas where successful waves of recruitment were estimated to occur in eight year intervals. Further research is suggested to determine if the spatial and temporal patterns found in this study are part of the natural variability in this system or if they are an indication of long-term trends.

Description: Biological hard parts and skeletons of aquatic organisms often archive information of past environmental conditions. Deciphering such information forms an essential contribution to our understanding of past climate conditions and thus our ability to mitigate the climatic, ecological, and social impacts of a rapidly changing environment. Several established techniques enable the visualization and reliable use of the information stored in anatomical features of such biogenic archives, i.e., its growth patterns. Here, we test whether confocal Raman microscopy (CRM) is a suitable method to reliably identify growth patterns in the commonly used archive Arctica islandica and the extinct species Pygocardia rustica (both Bivalvia). A modern A. islandica specimen from Norway has been investigated to verify the general feasibility of CRM, resulting in highly correlated standardized growth indices (r〉0.96; p〈0.0001) between CRM-derived measurements and measurements derived from the established methods of fluorescence microscopy and Mutvei’s solution staining. This demonstrates the general suitability of CRM as a method for growth pattern evaluation and cross-dating applications. Moreover, CRM may be of particular interest for paleoenvironmental reconstructions, as it yielded superior results in the analysis of fossil shell specimens (A. islandica and P. rustica) compared to both Mutvei staining and fluorescence microscopy. CRM is a reliable and valuable tool to visualize internal growth patterns in both modern and fossil calcium carbonate shells that notably also facilitates the assessment of possible diagenetic alteration prior to geochemical analysis without geochemically compromising the sample. We strongly recommend the CRM approach for the visualization of growth patterns in fossil biogenic archives, where conventional methods fail to produce useful results.