Final answer:
Marine iguanas undergo body size shrinkage as an unusual adaptation during El Niño events.
Step-by-step explanation:
During El Niño events, marine iguanas have been documented to undergo an unusual adaptation of body size shrinkage. This is because El Niño causes a decrease in marine productivity, leading to a scarcity of food, particularly the brown algae that marine iguanas feed on. As a result, the iguanas reduce their body size to conserve energy and survive with limited food resources.