The introduction of huge container ships, together with the mechanisation and computerisation of many operations, has had a tremendous impact, both physically and socially. Large areas of waterfront, often at the very heart of these cities, have been abandoned and the workforce has shrunk.
Substantial investment has been necessary to regenerate these derelict areas of former docks and quaysides. Within the mix of redevelopment, the inclusion of a significant cultural offer has been crucial, and has often included a maritime museum.
Traditionally, maritime museums were about ships and technology and very male orientated. They were full of model ships, navigational instruments and explanations of shipping rigs that people admired, but didn't understand, or even the development of the compound steam engine that bored the pants off virtually everyone.
A change in emphasis, telling the story through the people involved, concentrating on the wider maritime experience and examining the personal association of objects, spoke to those nostalgic for their recent past.
A couple of decades ago, most people in cities such as Liverpool were either directly employed in port-related activities, or had family and friends who were. That is no longer the case. For the present generation, that maritime connection is rapidly disappearing. The danger is that as these personal links diminish, maritime museums will lose their audiences.
Further, as port cities continue to diversify and the impact of the maritime sector declines further, there is a danger that maritime museums will be left telling a purely historical story, one which is continually receding from the experience of its visitors. They will also find it hard to reflect contemporary activity and issues.
The National Maritime Museum's (NMM) Maritime London gallery, which opened in 1999, tried to explain the role of present-day maritime business in the city, which is still very important to the British economy. But it failed to engage visitors and was rapidly replaced with a more historical survey of the capital's maritime experience.
Representing the work of contemporary shipping and port activity is also challenging. It is hardly feasible to preserve a container ship or the tools of the trade, such as one of the 320-tonne cranes that were recently blown up in Birkenhead docks.
These are concerns that have not only worried maritime museums in this country, but have been a constant theme at gatherings worldwide, such as the International Congress of Maritime Museums.
I think the low point came in the past decade and the tide has now turned. Maritime museums are finding new ways to engage audiences. For some, this means embracing community interests or local leisure pursuits. Others have focused on global matters, such as ecological issues, climate change or the natural history of the sea.
In the case of Merseyside Maritime Museum, we have picked up on some of the global issues that have local relevance, such as transatlantic slavery and migration, but which also have strong contemporary resonances.
Indeed, the commitment to the subject of slavery has been so successful that it has developed into a new museum in its own right - the International Slavery Museum.
But we have also embraced other socially diverse subjects, such as producing the first exhibition on gay seafarers, and we are planning exhibitions on black seafarers and, in conjunction with the Australian National Maritime Museum, on the experience of child migrants.
Across the world, there are multimillion- pound maritime museum projects. A national museum has just opened in Finland, new national museums are at the detailed planning stage in Belgium and Denmark, and the national museum in Amsterdam is being completely refurbished. The largest single project, the China Maritime Museum in Shanghai, opens in July 2009 and is expected to attract 10,000 visitors a day.
Closer to home, the refurbishment of the ss Great Britain and the new museum alongside it has been a fantastic success, while the NMM, Cutty Sark and Mary Rose have major projects in hand. My own museum has had more than 750,000 visitors in the first eight months of this European Capital of Culture year, which makes it the most visited museum in Liverpool.
There will be challenges ahead, but I believe that the best maritime museums are flexible, can and do move with the times, and will continue to interpret and contribute to maritime heritage, which is an important part of communities across the world.
Tony Tibbles is the director of the Merseyside Maritime Museum. He is a speaker at On the Waterfront: Culture, Heritage and Regeneration of Port Cities, Liverpool, 19-21 November 2008