The war in Ukraine has severely hobbled shipping in the Black Sea, with broad consequences for international transport and global supply chains. Dozens of cargo ships are stranded at the Ukrainian port of Mykolaiv, shipping trackers said. An estimated 3,500 sailors have been stuck on some 200 ships at Ukrainian ports, according to London-based shipping tracker Windward Ltd. More ships are stranded around the globe than at any point since World War II, maritime historians said.

The result is a shutdown of the world’s second-largest grain exporting region. Ukraine accounts for 16% of global corn exports, and together with Russia, 30% of wheat exports. Global wheat prices have jumped more than 55% since the week before the invasion.

“This shock to global grain supply is the biggest supply shock since the OPEC oil cuts in the 1970s,” said Salvatore Mercogliano, a professor at Campbell University in North Carolina and former merchant mariner. “It will mean food shortages in the Middle East and Africa, and inflation across the world.”

Making matters worse for global shippers, thousands of Ukrainian and Russian seafarers are stuck in ports around the world, leaving shipowners scrambling to find replacement crews to keep strained supply chains rolling.