Practice Tests
IELTS Reading (AC) Task 1 #113

A. Coral reefs, often referred to as the "rainforests of the sea," are among the most biodiverse and productive ecosystems on Earth. These vibrant underwater structures are built by colonies of tiny animals called coral polyps, which live in a symbiotic relationship with microscopic algae known as zooxanthellae. This partnership is vital: the algae live within the coral''s tissues, providing them with up to 90% of their energy through photosynthesis and giving them their brilliant colours. However, this delicate symbiosis is under severe threat from a phenomenon known as coral bleaching.

B. Coral bleaching occurs when corals become stressed by changes in environmental conditions, such as temperature, light, or nutrients. The primary driver of mass bleaching events today is rising sea temperatures caused by global climate change. When the water becomes too warm, the symbiotic relationship breaks down, and the corals expel the colourful algae from their tissues. Without the algae, the corals lose their major source of food and their colour, revealing their transparent tissues and the white calcium carbonate skeleton underneath, hence the term "bleaching."

C. While a bleached coral is not dead, it is in a severely weakened and vulnerable state. If water temperatures return to normal relatively quickly, the corals may be able to regain their algae and recover over time. However, if the stress is prolonged or severe, the coral will starve and die, leaving behind just its skeleton. The dead reef is then quickly overgrown by other types of algae, making it difficult for new coral to settle and grow.

D. The consequences of widespread coral bleaching are catastrophic, extending far beyond the loss of the corals themselves. Reefs provide essential habitats for approximately 25% of all marine species, and their collapse triggers a devastating loss of biodiversity. Furthermore, hundreds of millions of people worldwide depend on coral reefs for food, income from tourism and fishing, and coastal protection from storms and erosion. The ongoing threat of coral bleaching represents a critical environmental crisis, underscoring the urgent need for global action to mitigate climate change and protect these invaluable marine ecosystems.