Which marine creatures often attach themselves to the bottom of boats?

Marine creatures that often attach themselves to the bottoms of boats include barnacles, mollusks like mussels, and various types of algae. These organisms can cling to surfaces underwater, forming biofouling communities. Barnacles, in particular, are known for their hard shells and can accumulate in large numbers, impacting the boat's performance and increasing maintenance costs. Regular cleaning and anti-fouling coatings are often used to manage these attachments.