Calcification in marine molluscs: how costly is it?

Area of Science:

• Marine biology
• Evolutionary biology
• Biochemistry

Background:

• Calcification is vital for marine invertebrate skeletal evolution.
• The metabolic cost of calcium carbonate (CaCO3) deposition is difficult to isolate from other metabolic expenses.
• Previous studies often overlooked calcification costs, attributing shell expenses solely to organic matrix.

Purpose of the Study:

• To quantify the metabolic cost of calcification in marine gastropods.
• To determine the energy expenditure required for CaCO3 shell formation.
• To investigate the evolutionary implications of calcification costs.

Main Methods:

• Utilized natural variation in shell thickness in Nucella lamellosa and Nucella lapillus.
• Conducted experiments in both field and laboratory settings.
• Calculated calcification cost by measuring extra energy assimilated per unit of extra shell produced, accounting for organic matrix costs.

Main Results:

• Snails producing thicker shells consumed more food, indicating a direct metabolic cost.
• The estimated cost of calcification is 1-2 J/mg of CaCO3.
• Calcification cost is approximately 5% of the cost of the organic matrix in molluscan shells.

Conclusions:

• The metabolic cost of calcification is a significant factor in skeletal evolution.
• The relatively low cost of calcification may explain the reduced prevalence of organic-rich calcareous microstructures evolutionarily.
• This research provides a quantitative basis for understanding the energetic trade-offs in shell formation.