[2026] PTE Academic Reading - Multiple Choice, Multiple Answers

Ocean acidification is often referred to as 'the other carbon dioxide problem,' as it is a direct result of the ocean absorbing approximately 25% of the CO2 released into the atmosphere.When carbon dioxide dissolves in seawater, it forms carbonic acid, which lowers the pH level and makes the water more acidic.This chemical change reduces the availability of carbonate ions, which are essential building blocks for calcifying organisms.Species such as corals, oysters, clams, and some types of plankton rely on carbonate ions to construct their protective shells and skeletons.Studies have shown that in more acidic water, these structures become thinner, more brittle, and can even begin to dissolve.The impact on these 'calcifiers' has a ripple effect throughout the entire marine food web, as many larger species depend on them for food or habitat.For instance, the decline of coral reefs can lead to the loss of biodiversity and the collapse of local fisheries that millions of people rely on for protein.Furthermore, researchers have discovered that ocean acidification can alter the behavior and sensory systems of some fish, making it harder for them to detect predators or find suitable habitats.While some marine species may be more resilient or even benefit from higher CO2 levels, the overall speed of the chemical change is faster than what most organisms have experienced in millions of years.Reducing global carbon emissions is considered the only effective long-term solution to stop and eventually reverse the acidification of the world's oceans.