I just came across this paper shared on LinkedIn with some cool results. Shipping causes multiple impacts on the marine environment, one of them is due to the noise of the engines. And underwater noise travels fast and wide. One ship, two ships may not be a major issue, but when tens or hundreds of ships pass through an area each year, their noise may become unbearable to some organisms. Cetaceans are, in particular, known for their sensitivity to acoustic disturbance (but fish can also suffer, for instance on coral reefs, see this interesting paper). Shipping traffic also concentrate near coasts where ships have narrower areas to operate compared to the open ocean or all aim for the same ports follwoing the same route.
Blair et al. 2016 show how humpback whales' behaviours are affected by ship traffic noise. There have not ben many studies able
to show the direct impacts of shipping traffic noise on large whales, but we already know that impacts of sonars exist.
We definitely need more work on the impacts of shipping traffic on marine life, in particular in the coastal areas.