Combining genotypic and phenotypic variation in a geospatial framework to identify sources of mussels in northern New Zealand

The New Zealand green-lipped mussel aquaculture industry is largely dependent on the supply of young mussels that wash up on Ninety Mile Beach (so-called Kaitaia spat), which are collected and trucked to aquaculture farms. The locations of source populations of Kaitaia spat are unknown and this lack of knowledge represents a major problem because spat supply may be irregular. We combined genotypic (microsatellite) and phenotypic (shell geochemistry) data in a geospatial framework to determine if this new approach can help identify source populations of mussels collected from two spat-collecting and four non-spat-collecting sites further south. Genetic analyses resolved differentiated clusters (mostly three clusters), but no obvious source populations. Shell geochemistry analyses resolved six differentiated clusters, as did the combined genotypic and phenotypic data. Analyses revealed high levels of spatial and temporal variability in the geochemistry signal. Whilst we have not been able to identify the source site(s) of Kaitaia spat our analyses indicate that geospatial testing using combined genotypic and phenotypic data is a powerful approach. Next steps should employ analyses of single nucleotide polymorphism markers with shell geochemistry and in conjunction with high resolution physical oceanographic modelling to resolve the longstanding question of the origin of Kaitaia spat.

Building amorphous calcium carbonate into geochemical biomineralisation models

<p>Amorphous calcium carbonate (ACC) has been observed, or inferred to exist, in the majority of the major phyla of marine calcifying organisms. The CaCO<sub>3</sub> produced by these organisms represents one of the largest long-term carbon sinks on Earth’s surface, such that identifying how calcification will respond to anthropogenic climate change is an urgent priority. A substantial portion of our knowledge of the biomineralisation process of these organisms is derived from inferences based on skeletal geochemical data, yet such models typically do not include an ACC component because little is known about trace element and isotope fractionation into ACC. In order to address this, we present, to our knowledge, the first structural and geochemical data of ACC precipitated from seawater under varying carbonate system conditions, seawater Mg/Ca ratios, and in the presence of three of the most common intracrystalline amino acids (aspartic acid, glutamic acid, and glycine). Based on these data we identify the carbonate system conditions necessary to produce ACC from seawater [Evans <em>et al</em>., 2019], and identify the dominant controls on ACC geochemistry. As an example, we utilise these data to build a simple biomineralisation model for the low-Mg (e.g. planktonic) foraminifera, based on precipitation of low-Mg calcite through an ACC precursor phase in a semi-enclosed pool. This exercise demonstrates that the observed shell geochemistry of this group of organisms can be fully reconciled with a model that includes an ACC component, and moreover that constraints can be placed on the degree of ACC utilisation and the ACC-calcite transformation process. More broadly, the exercise demonstrates that knowledge of the characteristics and geochemistry of ACC is important in the development of a process-based understanding of marine calcification.</p><p>Evans, D., Webb, P., Penkman, K. Kröger, R., & Allison, N. [2019] The Characteristics and Biological Relevance of Inorganic Amorphous Calcium Carbonate (ACC) Precipitated from Seawater. <em>Crystal Growth & Design</em> <strong>19</strong>: 4300.</p>

Zooglider-Based Measurements of Planktonic Foraminifera in the California Current System

Spines and rhizopodia play an important role in the feeding behavior, symbiont ecology, shell geochemistry, and density and drag of planktonic foraminifera. However, there are few empirical data on planktonic foraminifera in situ, and these delicate structures are disturbed on capture. Here, we report spine and rhizopod measurements from underwater images obtained in the California Current System near La Jolla, California by Zooglider, a new autonomous zooplankton-sensing glider. Across all observed species, we find that spine length and flexibility correlate with test size and that spines increase the effective prey encounter volume of spinose foraminifera by two to three orders of magnitude. Our data also yielded several novel observations regarding hastigerinid foraminifera (Hastigerinella digitata and Hastigerina pelagica), a group of unusually large planktonic foraminifera that are abundant in our dataset below 250 m. First, the effective encounter volume of hastigerinid foraminifera can be very large: our largest specimen occupies almost 40 cm3 (about the size of a golf ball), while the median specimen occupies 5.3 cm3 (about the size of a cherry). Second, the majority of hastigerinid foraminifera in our dataset have asymmetric bubble capsules, which are most frequently oriented with their bubbles on the upward side of the test, consistent with the hypothesis that the bubble capsule is positively buoyant. Third, 16% of hastigerinid foraminifera in our dataset have dispersed bubble capsules with detached bubbles distributed along the spines and rhizopodia, consistent with a regular source of natural disturbance. Taken together, our observations suggest that hastigerinid foraminifera play a larger role as mesopelagic predators in the California Current System than previously recognized.

New petrographic and geochemical insights on diagenesis and palaeoenvironmental stress in Late Cretaceous inoceramid shells from the James Ross Basin, Antarctica

New petrographic and geochemical insights from inoceramid bivalve shells of lower Campanian (Marambio Group, James Ross Basin, Antarctica) show that they suffered significant palaeoenvironmental stress just before their disappearance in the southern high latitudes. Inoceramid data have mainly been derived from shell fragments of the large form Antarcticeramus rabotensis Crame & Luther, collected at stratigraphical levels marking the early disappearance of inoceramids in the James Ross Basin (10 m.y. before the Cretaceous/Tertiary boundary in Antarctica). Cathodoluminescence studies and minor and trace element intra-shell variations in A. rabotensis shells, along with their whole shell geochemistry (major, minor, and trace elements, including REE), have revealed evidence of only weak diagenesis but significant palaeoenvironmental stress. The most relevant evidence of such adverse palaeoenvironmental conditions in A. rabotensis shells is reflected by marked growth interruptions in the normal shell layering, including the occurrence of a previously undetected inner aragonitic nacreous layer formed of alternating aragonitic and calcitic sublayers. The weak diagenesis produced characteristic geochemical intra-shell variations, which have subsequently been detected in the inoceramid shell microstructure, especially in the inner aragonitic nacreous layer.