Mearsk is kind of critical infrastructure - they carry a lot of freight. It's conceivable that if you took out a few major carriers like this for a week, you'd get widespread food shortages.
Even just Maersk could have huge consequences. Some of their ships have capacities of more than 10,000 containers, that's a lot of goods which may not be unloaded for the time being. Many supply chains will be quite sensitive to a delay like this and it could have very visible knock-on effects.
A delay of a day is probably already enough to cause congestion in ports with further delays down the road.