What is primarily affected by rising sea temperatures in the Great Barrier Reef?

Rising sea temperatures have a significant impact on coral polyps, which are the building blocks of coral reefs. Coral polyps are small, soft-bodied organisms that live in colonies and secrete calcium carbonate to form the hard structures of the reef. Increased water temperatures can cause stress to these coral polyps, leading to coral bleaching, a phenomenon where coral expels the symbiotic algae (zooxanthellae) that provide them with color and nutrients. If the temperatures remain elevated for prolonged periods, it can result in weakened coral health, reduced growth, and even mortality. This impact is critically important for the ecological balance of the Great Barrier Reef, as healthy coral systems support a large diversity of marine life and protect coastal areas from erosion.

Other options such as marine mammals, sand and sediment, and ocean currents may be affected indirectly by temperature changes in the ocean, but the direct and immediate consequence of rising temperatures is primarily on the coral polyps themselves.