Research by New Zealand scientists could lead to cleaner and quieter ports.
The National Institute of Water & Atmospheric Research and Auckland University discovered noisy ships act like magnets to sea-dwelling organisms, such as mussels.
When the scientists played recorded ship sounds to mussel larvae at two different intensities, the larvae moved towards the louder noise.
When marine organisms attach themselves to a boat's hull, NIWA says they create drag and slows the ship.
This phenomenon, known as marine fouling, is a huge cost to the shipping industry.
The scientists plan to put forward ways for berthed ships to reduce or eliminate noise - for instance, by switching to a shore-based electrical supply.
NIWA says generators still run when ships are in port and produce a large amount of underwater noise.