Marine Organisms and Calcium Carbonate

Marine Organisms

• Pteropods, macroalgae, and mollusks also deposit aragonite, while other organisms like calcareous algae, echinoderms, crustaceans, and forams deposit CaCO3 as calcite.
• Aragonite has a stronger and more resistant structure.

Carbonate Production

• Typical rates of carbonate production: 10 kg/m2/yr on productive coral-rich forereef zones, 4 kg/m2/yr on reef flats, and 0.8 kg/m2/yr in lagoons and rubble substrates.
• Global map of coral reef carbonate budgets: values indicate estimated net reef carbonate budgets, in kg CaCO3 m-2 year-1.

Coral Reefs Around the World

• Coral reefs cover approximately 300,000 km2 of the Earth's surface, less than 0.1% of the ocean's surface.
• The Indo-Pacific region (including the Red Sea, the Indian Ocean, Southeast Asia, and the Pacific) represents 91.9% of the world's coral reefs.
• The Southeast Asian region represents 32.3%, while the Pacific, including Australia, represents 40.8%.
• The Atlantic and Caribbean regions represent 7.6% of the world's coral reefs.

Classification

• Atolls: a type of coral reef structure.
• Barrier reef: a coral reef growing parallel to the coastline, separated from it by a lagoon, characterized by a shallow seabed and coral growth.
• Fringing reef: a type of coral reef structure.

The Animal

• Coral is a carnivorous animal that feeds on microscopic animals that fall from above, filtering the water at night.
• Coral has a white, calcium carbonate structure, and the different colors it presents are due to microalgae called zooxanthellae that live in symbiosis with the coral polyps.
• Coral needs transparent waters to develop, as the zooxanthellae perform photosynthesis.
• Coral polyps are a few millimeters in diameter and have the ability to fix dissolved calcium in the water, forming rigid structures.

Zooxanthellae

• Zooxanthellae are microalgae that live in symbiosis with coral polyps and provide them with energy in the form of carbon compounds.
• They can provide more than 90% of the coral's energy requirements.
• Zooxanthellae live in other protozoa and invertebrates and are mostly autotrophic.

Coral Bleaching

• When coral is under stress, it loses its zooxanthellae and turns white, leading to coral bleaching and eventually death.

CaCO3 Producers

• Coral
• Calcareous algae
• Mollusks/gastropods

Reef Types

• Platform reefs: form on the continental shelf or in the open ocean, variable in size, and can grow in all directions.
• Fringing reefs: extend only seaward.
• Barrier reefs: grow parallel to the coastline, separated from it by a lagoon.

Elements of a Reef

• Coral polyps
• Zooxanthellae
• CaCO3 structures
• Other organisms

Factors Conditioning the Existence of Reefs

• Temperature: 18°C – 20°C
• Oxygen levels
• Salinity
• Turbidity
• Dissolved carbonate
• Nutrients
• Hydrodynamic conditions
• Light

Origin and Evolution

• Modes of reef growth in response to sea-level changes: reef growth oscillates between 1 cm/year for slow-growing massive corals and 30 cm/year for fast-growing, branching forms.

Impacts

• Human activities affecting coral reefs: e.g., climate change, pollution, overfishing.