Skeletal Mineralogy of Marine Bryozoans

Marine bryozoans form calcareous exoskeletons that are predominantly composed of calcite, aragonite or a combination of both. This mineralogical diversity is influenced by evolutionary lineage, seawater chemistry and environmental factors such as temperature, salinity and depth. Cheilostome bryozoans often exhibit a wide range of skeletal compositions—pure calcite, pure aragonite or bimineralic frameworks—whereas cyclostomes tend to rely on low-magnesium calcite. Microstructural analyses reveal distinct crystal habits, including tabular, platy and granular assemblies in calcite, and fibrous or granular-platy textures in aragonite. The sequence of mineral deposition, the role of the extrapallial space and organic templates are central to biomineral formation. Phylogenetic controls modulate mineralogical plasticity, determining how species respond to ocean warming and acidification. At a global scale, latitudinal gradients in temperature correlate with shifts in aragonite content, with warmer waters favouring higher aragonite proportions. Understanding bryozoan skeletal mineralogy is essential for reconstructing past ocean conditions, predicting vulnerability to ongoing climate change and informing conservation of bioconstructional habitats.

Research from Nature Portfolio

Detailed correlative microscopy and diffraction techniques have elucidated the architecture of Anoteropora latirostris, showing asymmetric layering of platy calcite overlain by fine-grained aragonite on lateral walls. NanoSIMS mapping identified an organic interfacial layer that serves as a template for aragonite nucleation, while electron backscatter diffraction revealed stronger crystallographic preferred orientation in calcite than in aragonite and high levels of twinning in aragonite grains. Mechanical modelling of these textures suggests directional flexibility that facilitates colony fragmentation as a mode of clonal reproduction. This multi-scale investigation provides a novel paradigm for remote biomineralisation within a broad extrapallial space, distinguishing cheilostome bryozoan skeletogenesis from that of other marine invertebrates.

Skeletal Mineralogy of Marine Bryozoans publication trend

The graph below shows the total number of articles in skeletal mineralogy of marine bryozoans across all publications each year (not limited to Nature Index journals).

Technical terms

Calcite: A stable polymorph of calcium carbonate commonly found in bryozoan skeletons.

Aragonite: A denser polymorph of calcium carbonate that is more soluble than calcite and often favoured in warmer waters.

Bimineralic skeleton: A skeletal framework comprising both calcite and aragonite mineral phases.

Extrapallial space: The narrow fluid-filled region between the living tissue and the forming skeleton where biomineralisation occurs.

Crystallographic preferred orientation (CPO): The non-random alignment of crystal axes within a mineral phase, influencing mechanical properties.

High-Mg calcite (HMC): Calcite containing significant magnesium substitution, which increases solubility and affects vulnerability to acidification.

References

1. Skeletal mineralogy of marine calcifying organisms shaped by seawater temperature and evolutionary history—A case study of cheilostome bryozoans. Global Ecology and Biogeography (2024).
2. Skeletal microstructures of cheilostome bryozoans (phylum Bryozoa, class Gymnolaemata): crystallography and secretion patterns. Marine Life Science & Technology (2024).
3. Architecture of Anoteropora latirostris (Bryozoa, Cheilostomata) and implications for their biomineralization. Scientific Reports (2019).
4. Temperature as a likely driver shaping global patterns in mineralogical composition in bryozoans: implications for marine calcifiers under global change. Ecography (2022).
5. Spatio-temporal variation of skeletal Mg-calcite in Antarctic marine calcifiers. PLOS ONE (2019).