Coral Bleaching: Loss of Symbiotic Algae

Coral bleaching is a phenomenon where corals lose their vibrant colors and turn white.

Understanding Coral Symbiosis

Corals have a crucial symbiotic relationship with microscopic algae called zooxanthellae (or symbiotic alga). These algae live within the coral tissues.

• The zooxanthellae photosynthesize, providing the coral with essential nutrients and up to 90% of its energy needs.
• The algae also give corals their characteristic colors.

Cause of Bleaching

When corals experience stress, primarily due to increased sea temperatures but also from pollution or changes in light, they expel their symbiotic algae.

• This expulsion causes the coral to lose its color, revealing the white calcium carbonate skeleton underneath – hence, "bleaching".
• While corals can survive a bleaching event, prolonged stress can lead to coral death.

Analysis of Options

• Loss of epithelial membrane: This is not the primary cause of bleaching.
• Loss of symbiotic alga: This is the direct and primary cause of coral bleaching.
• Loss of surficial polyps: Polyps are the coral animals; losing them signifies death, not bleaching itself.
• Rapid calcification: Calcification is the process of skeleton building and is unrelated to the *cause* of bleaching, although it can be affected by coral health.

Therefore, the primary reason for coral bleaching is the loss of symbiotic algae.