ParaPro Reading Practice Test (Set 2)

📖 Reading Comprehension Passage

Coral reefs are among the most biodiverse and economically valuable ecosystems on Earth, often referred to as the 'rainforests of the sea.' Although they occupy less than 0.1% of the global ocean floor, reefs provide shelter, nursery grounds, and foraging habitats for more than 25% of all known marine species. The structural framework of a reef is built primarily by hermatypic (stony) corals, which maintain a delicate endosymbiotic relationship with microscopic photosynthetic algae known as zooxanthellae. In this mutualistic partnership, corals provide the algae with a protected environment and essential metabolic compounds (carbon dioxide, ammonium, and phosphate). In exchange, the zooxanthellae synthesize carbohydrates and oxygen via photosynthesis, fueling up to 90% of the coral host's nutritional energy requirements and facilitating calcium carbonate skeleton precipitation. However, marine warming trends and atmospheric carbon dioxide uptake threaten this delicate equilibrium. When sea surface temperatures exceed local seasonal thermal thresholds by as little as 1 to 2 degrees Celsius for prolonged intervals, the photosynthetic mechanisms of zooxanthellae malfunction, releasing harmful reactive oxygen species. In response to cellular toxicity, the coral host expels the algae, causing the coral tissues to turn translucent white in a phenomenon known as coral bleaching. Without their photosynthetic partners, corals face severe nutritional starvation and increased vulnerability to lethal opportunistic pathogens. Furthermore, ocean acidification—driven by the chemical absorption of anthropogenic carbon dioxide into seawater—reduces the saturation state of carbonate ions, drastically impeding the calcification rates necessary for reef structural repair.