Skeletal Mineralogy Research Articles

Temperature Effects on the Distribution of Aragonitic and Calcite‐Secreting Epifaunal Bivalves

ABSTRACTAimTo test if temperature significantly influences the global biogeographic distribution of marine epifaunal bivalves via their skeletal mineralogy.LocationGlobal.TaxaMarine, epifaunal bivalves.MethodsThe skeletal mineralogy of 45,789 epifaunal bivalve occurrences from 669 species from the Ocean Biodiversity Information System (OBIS) was related to sea surface temperatures from Bio‐ORACLE. Binomial regression was used to assess the influence of temperature and seasonality on the distribution of aragonitic and calcite‐secreting bivalve occurrences, aggregated in equal‐area grid cells.ResultsThe proportion of aragonitic bivalve occurrences significantly increases with mean annual temperature in our global analysis and most marine biogeographic realms. A greater prevalence of calcite‐secreting bivalves in seasonal climates could be shown at low mean annual temperatures at the global scale but not within biogeographic realms.Main ConclusionsThe global biogeographic distribution of epifaunal bivalves is significantly influenced by water temperature via their skeletal mineralogy. The mechanism driving this pattern is best explained by the temperature modulation of the effect of Mg2+ on calcite growth. Although this Mg2+ effect predicts an advantage for aragonite secretion at higher temperatures, poleward migration in response to higher temperature extremes will expose tropical taxa to cooler temperatures in the cold season, which may impede aragonite secretion in taxa not adapted to these climates.SignificanceOur results suggest that skeletal mineralogy is likely to influence ocean warming‐induced migration patterns.

Calcium-rich seawater affects the mechanical properties of echinoderm skeleton

Shifts in the magnesium to calcium ratio of seawater in the geological history are thought to have profoundly affected biomineralization of marine invertebrates, including some echinoderms, which changed their skeletal mineralogy from high-magnesium to low-magnesium calcite and vice versa. Here we report on experiments that aimed to investigate the effect of ambient seawater magnesium to calcium ratio on magnesium to calcium ratio and nanomechanical properties in the spines of two echinoid species (Arbacia lixula and Paracentrotus lividus). We found that echinoids cultured in seawater with a low magnesium to calcium ratio produced a skeleton with lower both magnesium content and nanohardness than those of the control specimens incubated under normal (high) magnesium to calcium ratio conditions. These results may suggest that at certain times in the geological past (during the so-called calcite seas) sea urchins with decreased skeletal magnesium contents were more susceptible to damage due to physical disturbances, predation and post-mortem taphonomic processes. Increased skeletal hardness of echinoids from the so-called aragonite seas is expected to enhance their taphonomic potential, thus, to some extent, mitigates the preservation bias related to increased solubility of high-magnesium calcite.

Skeletal mineralogy of marine calcifying organisms shaped by seawater temperature and evolutionary history—A case study of cheilostome bryozoans

AbstractAimQuantify the contribution of environmental factors (water temperature, salinity and depth) and evolutionary history to varied skeletal mineralogy in calcifying marine organisms.LocationGlobal Ocean.Time periodPresent.Major taxa studiedOrder: Cheilostomatida; Phylum: Bryozoa.MethodsWe employed X‐ray diffraction (XRD) to analyse the skeletal mineral composition of 872 individual colonies, representing 437 bryozoan species, in terms of calcite/aragonite ratios. We integrated these data with equivalent published data, thus reaching 981 species, and applied linear models (LMs), generalized linear models (GLMs) and phylogenetic generalized least squares models (PGLSs) to investigate the influences of temperature, salinity, depth and phylogenetic history on the mineralogy of nearly 1000 cheilostome bryozoan species.ResultsCheilostome bryozoans vary considerably in their skeletal mineral composition: in our dataset 65% of the species possess purely calcite skeletons, 15% exclusively employ aragonite and 20% exhibit mixed (i.e. calcite and aragonite) mineralogies. Temperature is the predominant measured environmental factor influencing bryozoan skeletal mineralogy, accounting for 20% of its variability across species, when phylogenetic relatedness is unaccounted for. Bryozoans in lower latitudes, characterized by higher seawater temperatures, have higher aragonite concentrations. By accounting for phylogenetic structure using a subset of 87 species for which we have topological information, 40% of the observed mineralogical variability could be attributed to present‐day temperature. In contrast, depth and salinity played minor roles, explaining less than 1% of the mineralogical variation each.Main conclusionsThis study emphasizes the influence of evolutionary history on the mineralogical variability of calcifying organisms, even when it can be shown that a single environmental factor (temperature) explains a substantial amount of this variability. When confronted with changing temperature, calcifiers such as bryozoans are likely to respond in diverse ways, depending on the species, given their phylogenetic relatedness and the external conditions they meet.

Skeletal Mg content in common echinoderm species from Deception and Livingston Islands (South Shetland Islands, Antarctica) in the context of global change

Echinoderms with high levels of magnesium (Mg) in their skeletons may be especially sensitive to ocean acidification, as the solubility of calcite increases with its Mg content. However, other structural characteristics and environmental/biological factors may affect skeletal solubility. To better understand which factors can influence skeletal mineralogy, we analyzed the Mg content of Antarctic echinoderms from Deception Island, an active volcano with reduced pH and relatively warm water temperatures, and Livingston Island. We found significant interclass and inter- and intraspecific differences in the Mg content, with asteroids exhibiting the highest levels, followed by ophiuroids and echinoids. Specimens exposed to hydrothermal fluids showed lower Mg levels, which may indicate local environmental effects. These patterns suggest that environmental factors such as seawater Mg2+/Ca2+ ratio and temperature may influence the Mg content of some echinoderms and affect their susceptibility to future environmental changes.

Review of skeletal carbonate mineralogy of brachiopods with new material from New Zealand

ABSTRACT We combine published and new mineralogical data on most major taxa of brachiopods from all over the world, to investigate patterns and controls on brachiopod carbonate mineralogy. Measurements of 1726 specimens in 162 species (including 56 fossil species) ranged from 79°N to 74°S and from intertidal to almost 4000 m deep. Calcareous brachiopods mostly create strong resilient valves of very low-Mg calcite ( = 1.3 wt% MgCO3). The substrate-cemented Craniida ( = 8.9 wt% MgCO3) and Thecideida ( = 6.5 wt% MgCO3) are unusual in precipitating calcite with higher Mg content. This is the first study to find bimineralic brachiopods; a few species show a combination of low-Mg ( = 0.8 wt% MgCO3) and intermediate-Mg calcite ( = 7.2 wt% MgCO3) (sensu Smith AM, Key MM Jr, Gordon DP. 2006. Skeletal mineralogy of bryozoans: taxonomic and temporal patterns. Earth-Science Reviews. 78:287–306.). While Mg in calcite varies systematically among valve layers and sometimes along the growth axis, we found no consistent difference between valves of the same individual. A weak latitudinal signal indicates some overall temperature control of Mg, but in general, brachiopods are active calcifiers, precipitating low-Mg calcite even when Mg:Ca ratio in seawater is high. The drivers on brachiopod mineralogy are individual, environmental, and phylogenetic – resulting in complex variability.

Deep resilience: An evolutionary perspective on calcification in an age of ocean acidification.

The success of today's calcifying organisms in tomorrow's oceans depends, in part, on the resilience of their skeletons to ocean acidification. To the extent this statement is true there is reason to have hope. Many marine calcifiers demonstrate resilience when exposed to environments that mimic near-term ocean acidification. The fossil record similarly suggests that resilience in skeletons has increased dramatically over geologic time. This "deep resilience" is seen in the long-term stability of skeletal chemistry, as well as a decreasing correlation between skeletal mineralogy and extinction risk over time. Such resilience over geologic timescales is often attributed to genetic canalization-the hardening of genetic pathways due to the evolution of increasingly complex regulatory systems. But paradoxically, our current knowledge on biomineralization genetics suggests an opposing trend, where genes are co-opted and shuffled at an evolutionarily rapid pace. In this paper we consider two possible mechanisms driving deep resilience in skeletons that fall outside of genetic canalization: microbial co-regulation and macroevolutionary trends in skeleton structure. The mechanisms driving deep resilience should be considered when creating risk assessments for marine organisms facing ocean acidification and provide a wealth of research avenues to explore.

Fibrous or Prismatic? A Comparison of the Lamello-Fibrillar Nacre in Early Cambrian and Modern Lophotrochozoans.

The Precambrian-Cambrian interval saw the first appearance of disparate modern metazoan phyla equipped with a wide array of mineralized exo- and endo-skeletons. However, the current knowledge of this remarkable metazoan skeletonization bio-event and its environmental interactions is limited because uncertainties have persisted in determining the mineralogy, microstructure, and hierarchical complexity of these earliest animal skeletons. This study characterizes in detail a previously poorly understood fibrous microstructure-the lamello-fibrillar (LF) nacre-in early Cambrian mollusk and hyolith shells and compares it with shell microstructures in modern counterparts (coleoid cuttlebones and serpulid tubes). This comparative study highlights key differences in the LF nacre amongst different lophotrochozoan groups in terms of mineralogical compositions and architectural organization of crystals. The results demonstrate that the LF nacre is a microstructural motif confined to the Mollusca. This study demonstrates that similar fibrous microstructure in Cambrian mollusks and hyoliths actually represent a primitive type of prismatic microstructure constituted of calcitic prisms. Revision of these fibrous microstructures in Cambrian fossils demonstrates that calcitic shells are prevalent in the so-called aragonite sea of the earliest Cambrian. This has important implications for understanding the relationship between seawater chemistry and skeletal mineralogy at the time when skeletons were first acquired by early lophotrochozoan biomineralizers.

Temperature as a likely driver shaping global patterns in mineralogical composition in bryozoans: implications for marine calcifiers under global change

The Southern Ocean is showing one of the most rapid responses to human‐induced global change, thus acting as a sentinel of the effects on marine species and ecosystems. Ocean warming and acidification are already impacting benthic species with carbonate skeletons, but the magnitude of these changes to species and ecosystems remains largely unknown. Here we provide the largest carbonate mineralogical dataset to date for Southern Ocean bryozoans, which are diverse, abundant and important as carbonate producers, thus making them excellent for monitoring the effects of ocean warming and acidification. To improve our understanding of how bryozoans might respond to ocean warming and acidification, we assess latitudinal and seafloor temperature patterns of skeletal mineralogy using bryozoan species occurrences together with temperature data for the first time. Our findings, combining new mineralogical data with published data from warmer regions, show that the proportions of high‐Mg calcite and bimineralic species increase significantly towards lower latitudes and with increasing seawater temperature. These patterns are consistent with the hypothesis that seawater temperature is likely a significant driver of variations in bryozoan mineralogy at a global scale.

Calcitic shells in the aragonite sea of the earliest Cambrian

Abstract The initial acquisition of calcium carbonate polymorphs (aragonite and calcite) at the onset of skeletal biomineralization by disparate metazoans across the Ediacaran-Cambrian transition is thought to be directly influenced by Earth's seawater chemistry. It has been presumed that animal clades that first acquired mineralized skeletons during the so-called “aragonite sea” of the latest Ediacaran and earliest Cambrian (Terreneuvian) possessed aragonite or high-Mg calcite skeletons, while clades that arose in the subsequent “calcite sea” of Cambrian Series 2 acquired low-Mg calcite skeletons. Here, contrary to previous expectations, we document shells of one of the earliest helcionelloid molluscs from the basal Cambrian of southwestern Mongolia that are composed entirely of low-Mg calcite and formed during the Terreneuvian aragonite sea. The extraordinarily well-preserved Postacanthella shells have a simple prismatic microstructure identical to that of their modern low-Mg calcite molluscan relatives. High-resolution scanning electron microscope observations show that calcitic crystallites were originally encased within an intra- and interprismatic organic matrix scaffold preserved by aggregates of apatite during early diagenesis. This indicates that not all molluscan taxa during the early Cambrian produced aragonitic shells, weakening the direct link between carbonate skeletal mineralogy and ambient seawater chemistry during the early evolution of the phylum. Rather, our study suggests that skeletal mineralogy in Postacanthella was biologically controlled, possibly exerted by the associated prismatic organic matrix. The presence of calcite or aragonite mineralogy in different early Cambrian molluscan taxa indicates that the construction of calcium carbonate polymorphs at the time when skeletons first emerged may have been species dependent.

Recent Ostracod Fauna of the Western Ross Sea (Antarctica): A Poorly Known Ingredient of Polar Carbonate Factories

Ostracoda are a minor but recurrent component of Southern Ocean marine carbonate factories, and their low-Mg calcitic skeletal mineralogy helps in ensuring a noteworthy post-mortem resilience. Our study, based upon surface sediment occurrences, contributes to the better definition of their distribution vs. potential controlling factors in Antarctic waters. The ostracod fauna from the Western Ross Sea Shelf appears dominated by Australicythere polylyca, Australicythere devexa, Xestoleberis rigusa, Loxoreticulatum fallax, Cativella bensoni, Austrotrachyleberis antarctica and Patagonacythere longiducta, colonizing a variety of shelf environments along a wide bathymetric range. The abundance and richness values correlate well to nutrient distribution and sediment supply, primarily related to the circulation of different oceanographic regimes affecting the floor of the Ross Sea Shelf. Circumpolar Deep Water could represent the main factor controlling the distribution of ostracods. Similar results (high abundance and richness in ostracod values) were also recorded in the Terra Nova Bay and in a nearby area characterized by warm water rich in nutrients and composed of water of circumpolar origin flowing from the open ocean southwards onto the continental shelf. Particulate Fe (pFe), in suspended particulate matter (SPM), and other particulate trace metals in TNB could support the hypothesis that biogenic iron may significantly contribute to the bioavailable iron pool, sustaining both primary production and ostracod fauna richness in this area.

Global assessment of coralline algae mineralogy points to high vulnerability of Southwestern Atlantic reefs and rhodolith beds to ocean acidification

Coralline algae constitute one of the main groups of highly vulnerable calcified benthic organisms to ocean acidification. Although damaging effects of seawater acidification on the coralline algae skeleton have been widely demonstrated, the susceptibility to dissolution varies according to the Mg2+ in the calcite lattice. Even though the Southwest Atlantic Ocean exhibits the world’s largest rhodolith beds, which occupies 20,902 km2, there is no information regarding the coralline algae species mineralogy in this area. Here, we provide mineralogical data of twenty-four coralline algae species, examine the similarity in taxonomic groups, spatial occurrence and the vulnerability of these algae to seawater acidification. Mineralogy revealed that coralline algae skeletons were mainly composed of high-Mg calcite (> 70%) with minor presence of aragonite (< 30%) and dolomite (< 3%). There were no similarities between the skeletal mineralogy of taxonomic groups and sampling regions. Remarkably, the mean Mg-substitution of encrusting coralline algae from the Brazilian Shelf was 46.3% higher than global average. Because of the higher mean Mg-substitution in calcite compared with worldwide coralline algae, these algae from Southwest Atlantic Ocean would be highly susceptible to dissolution caused by the expected near-future ocean acidification and will compromise CaCO3 net production across the Brazilian Shelf.

Bryozoan carbonate skeletal geochemical composition in the White Sea compared with neighbouring seas

A fundamental question underlying skeletal mineral secretion in marine invertebrates is the extent to which the physico-chemical parameters of seawater (e.g., salinity, temperature) and animal physiology influence their skeletal mineralogy and chemistry. Groups with more complex mineralogies, such as bryozoans, have the ability to actively control their own skeletal composition in response to environmental conditions and could be considered indicators of global environmental change. Thus, this study aims to reveal how the unique environmental conditions of low salinity (circa 24–26), prominent seasonality and semi-isolation of the White Sea (WS) subarctic region caused by the last glaciation (12,000 ya) affect the carbonate skeletal geochemical composition of bryozoans. X-ray diffraction analysis of 27 bryozoan taxa (92 specimens) revealed a completely monomineral calcite composition of skeletons with a mean value of 6.9 ± 1.8 mol% MgCO3 and moderate variability at the species and family levels. Most specimens (43.5%) precipitated skeletal magnesium within the range of 7–8 mol% MgCO3. Regional analysis of the mineralogical profile of the White Sea bryozoans shows that they differ statistically from bryozoan species living in the neighbouring Arctic and temperate Scotland regions in terms of magnesium content in calcite (approximately 7 mol% MgCO3 in the White Sea versus 5 mol% MgCO3 in other regions). We suggest that the effect of low salinity on magnesium content was compensated by relatively high summer temperature causing rapid growth and calcification and possibly resulted in the increased Mg contents in the White Sea (WS) bryozoans. However, on a local scale (between sampling locations), the influence of temperature and salinity could be excluded as a source of observed intraspecific variability. The concentration of MgCO3 in skeletons of the studied bryozoans is controlled by other environmental variables or is species-specific and depends on the physiological processes of the organisms.

A Review and Meta-Analysis of Potential Impacts of Ocean Acidification on Marine Calcifiers From the Southern Ocean

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the global oceans. Average surface seawater pH levels have already decreased by 0.1 and are projected to decline by ~0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many resident marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). Ocean warming could further exacerbate the effects of OA in these particular species. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make projections about how OA might affect a broad range of SO taxa. We consider a species' geographic range, skeletal mineralogy, biological traits, and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate illustrates that the response variation is largely dependent on mineralogical composition. Species-specific responses due to mineralogical composition indicate that taxa with calcitic, aragonitic, and HMC skeletons, could be at greater risk to expected future carbonate chemistry alterations, and low-Mg calcite (LMC) species could be mostly resilient to these changes. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits, and physiological processes are also expected to influence species-specific responses.

Palaeozoic stromatoporoids and chaetetids analysed using electron backscatter diffraction (EBSD); implications for original mineralogy and microstructure

Palaeozoic hypercalcified sponges were ubiquitous Ordovician—Devonian reef builders but, despite their rich fossil record, their original skeletal mineralogy and microstructure remain poorly understood. This study provides the first application of electron backscatter diffraction (EBSD) to analyse skeletal structure of Silurian and Devonian stromatoporoids. The two Silurian and two Devonian stromatoporoid taxa selected are typical of stromatoporoids in showing poor preservation. A reference sample of an exceptionally well-preserved hypercalcified chaetetid sponge from the Carboniferous Buckhorn Asphalt Quarry (a fossil lagerstätte renowned for its preservation of skeletal microstructures) contains evidence that its skeleton comprised distinct bundles of single-crystal fibres, similar to modern hypercalcifying sponges. Similar bundles of crystal fibres are proposed here as the original microstructure of stromatoporoids, and acted as precursors to the coarse fibrous calcitic overprinting recrystallisation that is orientated normal to the growth layers, seen in all stromatoporoids viewed in cross-polarised light. The studied stromatoporoids show pronounced microporosity and micro-dolomite inclusions which are circumstantial evidence of an original composition of high-Mg calcite (HMC). We propose that the evidence of fibrous structures might be linked to inclusions of hydrated amorphous calcium carbonate (ACC·H2O) in the skeleton at the time of early diagenesis, as occurs in modern calcified sponges. The possible HMC skeletal composition of Palaeozoic stromatoporoids supports earlier views that the mineral composition of hypercalcifying reef builders is linked to Phanerozoic oscillations in the ratio of Mg:Ca, expressed as aragonite-calcite seas; stromatoporoids thrived in times of calcite-seas.

Living in future ocean acidification, physiological adaptive responses of the immune system of sea urchins resident at a CO2 vent system

The effects of ocean acidification, a major anthropogenic impact on marine life, have been mainly investigated in laboratory/mesocosm experiments. We used the CO2 vents at Ischia as a natural laboratory to study the long-term effects of ocean acidification on the sea urchin Paracentrotus lividus population resident in low-pH (7.8 ± 0.2) compared to that at two control sites (pH 8.02 ± 0.00; 8.02 ± 0.01). The novelty of the present study is the analysis of the sea urchin immune cells, the sentinels of environmental stress responses, by a wide-ranging approach, including cell morphology, biochemistry and proteomics. Immune cell proteomics showed that 311 proteins were differentially expressed in urchins across sites with a general shift towards antioxidant processes in the vent urchins. The vent urchin immune cells showed higher levels of total antioxidant capacity, up-regulation of phagosome and microsomal proteins, enzymes of ammonium metabolism, amino-acid degradation, and modulation of carbon metabolism proteins. Lipid-hydroperoxides and nitric oxide levels were not different in urchins from the different sites. No differences in the coelomic fluid pH, immune cell composition, animal respiration, nitrogen excretion and skeletal mineralogy were observed. Our results reveal the phenotypic plasticity of the immune system of sea urchins adapted to life at vent site, under conditions commensurate with near-future ocean acidification projections.

Investigating marine bio-calcification mechanisms in a changing ocean with in vivo and high-resolution ex vivo Raman spectroscopy.

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio‐calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non‐classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high‐resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio‐calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.

Mineralogy of Deep-Sea Coral Aragonites as a Function of Aragonite Saturation State

In an ocean with rapidly changing chemistry, studies have assessed coral skeletal health under projected ocean acidification (OA) scenarios by characterizing morphological distortions in skeletal architecture and measuring bulk properties, such as net calcification and dissolution. Few studies offer more detailed information on skeletal mineralogy. Since aragonite crystallography will at least partially govern the material properties of coral skeletons, such as solubility and strength, it is important to understand how it is influenced by environmental stressors. Here, we take a mineralogical approach using micro X-ray diffraction (XRD) and whole pattern Rietveld refinement analysis to track crystallographic shifts in deep-sea coral Lophelia pertusa samples collected along a natural seawater aragonite saturation state gradient (Ωsw= 1.15–1.44) in the Gulf of Mexico. Our results reveal statistically significant linear relationships between rising Ωsw and increasing unit cell volume driven by an anisotropic lengthening along the b-axis. These structural changes are similarly observed in synthetic aragonites precipitated under various saturation states, indicating that these changes are inherent to the crystallography of aragonite. Increased crystallographic disorder via widening of the full width at half maximum of the main (111) XRD peaks trend with increased Ba substitutions for Ca, however, trace substitutions by Ba, Sr, and Mg do not trend with crystal lattice parameters in our samples. Instead, we observe a significant trend of increasing calcite content as a function of both decreasing unit cell parameters as well as decreasing Ωsw. This may make calcite incorporation an important factor to consider in coral crystallography, especially under varying aragonite saturation states (ΩAr). Finally, by defining crystallography-based linear relationships between ΩAr of synthetic aragonite analogs and lattice parameters, we predict internal calcifying fluid saturation state (Ωcf = 11.1–17.3 calculated from b-axis lengths; 15.2–25.2 calculated from unit cell volumes) for L. pertusa, which may allow this species to calcify despite the local seawater conditions. This study will ideally pave the way for future studies to utilize quantitative XRD in exploring the impact of physical and chemical stressors on biominerals.

Skeletal carbonate mineralogy of Scottish bryozoans.

This paper describes the skeletal carbonate mineralogy of 156 bryozoan species collected from Scotland (sourced both from museum collections and from waters around Scotland) and collated from literature. This collection represents 79% of the species which inhabit Scottish waters and is a greater number and proportion of extant species than any previous regional study. The study is also of significance globally where the data augment the growing database of mineralogical analyses and offers first analyses for 26 genera and four families. Specimens were collated through a combination of field sampling and existing collections and were analysed by X-ray diffraction (XRD) and micro-XRD to determine wt% MgCO3 in calcite and wt% aragonite. Species distribution data and phylogenetic organisation were applied to understand distributional, taxonomic and phylo-mineralogical patterns. Analysis of the skeletal composition of Scottish bryozoans shows that the group is statistically different from neighbouring Arctic fauna but features a range of mineralogy comparable to other temperate regions. As has been previously reported, cyclostomes feature low Mg in calcite and very little aragonite, whereas cheilostomes show much more variability, including bimineralic species. Scotland is a highly variable region, open to biological and environmental influx from all directions, and bryozoans exhibit this in the wide range of within-species mineralogical variability they present. This plasticity in skeletal composition may be driven by a combination of environmentally-induced phenotypic variation, or physiological factors. A flexible response to environment, as manifested in a wide range of skeletal mineralogy within a species, may be one characteristic of successful invasive bryozoans.

Evaluating potential factors influencing branch diameter and skeletal Mg-calcite using an Antarctic cyclostome bryozoan species

Environmental and biological factors play important roles in determining the skeletal morphology and mineralogy of modular colonial organisms such as bryozoans. The broad bathymetrical ranges of Antarctic bryozoans make them useful organisms for evaluating depth-related changes in colony morphology, including branch diameter, which has been shown to decrease with depth in various ramose colonial animals. The current study focuses on the bryozoan Fasciculipora ramosa, using 32 specimens collected at East Antarctica from 185 to 597 m deep during the CEAMARC cruise (2007–2008). In order to test for the expected inverse relationship between depth and branch diameter, measurements of branch diameters were made. Levels of Mg in the calcite skeleton were determined as this was also predicted to follow changes in branch diameter. A significant negative correlation was found between branch diameter and depth. No significant relationship was detected between branch diameter and skeletal Mg, suggesting that these variables are driven by different factors. The thickest branches were found in current-influenced sites on Adelie Bank where temperature and salinity are both lower and planktonic food supply may also be different from the other sites. Further studies are needed along a wider bathymetrical range to clarify which factors influence branch diameter as well as Mg content in F. ramosa and to test its potential as an environmental indicator.

Interactive effects of temperature, food and skeletal mineralogy mediate biological responses to ocean acidification in a widely distributed bryozoan.

Marine invertebrates with skeletons made of high-magnesium calcite may be especially susceptible to ocean acidification (OA) due to the elevated solubility of this form of calcium carbonate. However, skeletal composition can vary plastically within some species, and it is largely unknown how concurrent changes in multiple oceanographic parameters will interact to affect skeletal mineralogy, growth and vulnerability to future OA. We explored these interactive effects by culturing genetic clones of the bryozoan Jellyella tuberculata (formerly Membranipora tuberculata) under factorial combinations of dissolved carbon dioxide (CO2), temperature and food concentrations. High CO2 and cold temperature induced degeneration of zooids in colonies. However, colonies still maintained high growth efficiencies under these adverse conditions, indicating a compensatory trade-off whereby colonies degenerate more zooids under stress, redirecting energy to the growth and maintenance of new zooids. Low-food concentration and elevated temperatures also had interactive effects on skeletal mineralogy, resulting in skeletal calcite with higher concentrations of magnesium, which readily dissolved under high CO2 For taxa that weakly regulate skeletal magnesium concentration, skeletal dissolution may be a more widespread phenomenon than is currently documented and is a growing concern as oceans continue to warm and acidify.