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Smith AM, Clark DE, Lamare MD, Winter DJ, Byrne M
Risk and resilience: variations in magnesium in echinoid skeletal calcite
Sea urchins (echinoids) make their spiny skeletons from magnesian calcite (Ca,Mg)CO3. Calcite is usually resistant to dissolution but the partial substitution of calcium carbonate with magnesium carbonate makes calcite more soluble. A New Zealand/Australian team added 382 new measurements of skeletal composition to the 261 already published, developing a numerical model describing global patterns in 73 echinoid species. Smith and colleagues found that, in general, teeth and jaw parts were highest in Mg, whereas adult tests and spines had less, and larvae the least. Mg also varied with latitude; higher Mg content in warmer waters could reflect increased growth rates. Patterns in skeletal composition could contribute to resistance of urchins to ocean acidification over the next century, and consequent ecosystem changes in coastal marine environments.