This story originally published on Fairplay.IHS.com.

Ports are facing slower growth as fundamental structural changes in the container shipping industry and global trade impact throughput volumes, according to new research from global ratings agency Fitch.

Fitch said ports and terminals also face a growing risk from protectionism, which, should current rhetoric on the topic turn into reality, would have significant impact on world economic growth.

Throughput at ports and terminals in many world regions has been on the rise recently with year-on-year growth of about 3.6% in the first quarter of 2017. Africa, Latin America, Oceania, and China all showed stronger first quarter growth figures when compared with last year, prompting shipping consultants Drewry to revise its full year throughput growth forecast for global ports upwards to 4%.

But the longer-term trend is one of slowing growth, as the container volume to GDP multiplier continues to slide. In the 1990s, container volume growth was 3.5 times global GDP growth; from 2000-2009 it was 2.7 times global GDP growth, and since 2010 it has been moving towards par.

"Traffic growth in the ports sector is likely to remain well below historical levels for the foreseeable future, due to fundamental structural changes in the industry and global trade," Fitch said in the research note written by its Global Infrastructure team.

China's growing domestic market, shifting global supply chains, and the maturing container shipping industry in the developed world are identified as key factors contributing to the long-term slowdown in port throughput growth.

The shift from bulk transport to containers has been a major force in the growth of port traffic, as lower end-to-end transport costs enabled firms to more easily benefit from cost differentials in the location of production, Fitch notes.

This shift allowed for the globalisation of supply chains, with goods production increasingly involving components manufactured in different parts of the world and shipped to a final assembly point.

"We believe this shift towards containers is now maturing in developed markets as there are few goods left that can be containerised."

Expansion of internal markets such as China may also mean production is less oriented towards exports; while the convergence of labour costs may reduce the trend for production to relocate to emerging markets, the agency adds.

"Data show that supply chains are shifting, with an increasing proportion of emerging market exports being shipped to other emerging markets. This creates challenges for port operators, but also new investment opportunities.

Ports are also being impacted by requirements to handle bigger ships, the research says. IHS Markit data show that between 2014 and 2016 the percentage of vessels larger than 10,000 teu capacity calling at the world's top 30 ports rose from 11% to 17%. Mega-ship tonnage - or vessels in excess of 10,000 teu capacity - now comprise more than 80% of the global fleet orderbook, the data show.

"In this lower-growth environment, overcapacity will probably linger for longer, resulting in increased competition and price and revenue erosion.

"Vessel sizes have increased and major ports have increased their capacity in response. Smaller ports that are not equipped to handle the biggest ships may therefore suffer price wars if volumes shrink."

The recent increase in protectionist and anti-globalisation rhetoric represents a growing risk for the ports sector, Fitch says.

"While this has not yet translated into higher tariffs or non-tariff barriers, and our base case is that disputes will be resolved within the existing World Trade Organization framework, our analysis suggests broader protectionist measures would have a significant impact on world growth."