What is the purpose of ballast water exchange in tankers?

Ballast water exchange serves a critical environmental purpose by helping to limit the spread of non-indigenous species. When tankers take on water as ballast, they can inadvertently transport organisms from one region to another. If this water is not properly managed or exchanged, these organisms can be introduced to new habitats, where they can disrupt local ecosystems and outcompete native species. By conducting ballast water exchange, tankers replace coastal ballast water with oceanic water while at sea, significantly reducing the risk of transporting these non-indigenous species. This practice is essential for protecting biodiversity and maintaining ecological balance, which is why it is the correct answer in this context.