Shipworms

https://en.wikipedia.org/wiki/Teredo_navalis

The common shipworm is a severe enemy of wood in the sea, including ships. On the coast of Holland it became a big disaster about 1730, and so likely about then in the North Sea and around. What would have happened if the shipworm in its modern form had become widespread about 100 BC?

Or as a future story, with Earth run out of oil and coal and back to pre-industrial, trying to go back to wooden sailing ships, and the copper used up in the time of industry so preventing copper-bottoming most ships?

As to why it came around 1730?:-
(1) It came from elsewhere in ships' bottoms.
(2) It became resistant to a parasite or predator that kept it in check before.
(3) A ship brought an organism that attacked that parasite or predator, so freeing the shipworm from control.
 
Copper

You would see docks and major ports built out of stone/concrete along with dikes. Copper would become a valuable commodity like aluminium/gold that is worth the expense of recycling/digging up old landfills. I would also think that the population of shipworms would expand until it exhausts the available resources and crashes.
 
From what I understand common shipworm (you had more ancient, but less destructive shipworms beofre the XVIIth) came from "hot seas", especially from Guinean Golf (at least according scholars of the concerned era) and associated with magniolias family tree.

So, the "why" should be an earlier and more important trade between Europe and Western African coast.
 
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