What do you call the wooden bridge-like structures that make up a harbor?

Solution 1:

It’s a pier or a dock or a wharf.

From Wikipedia:

In American English, a dock is technically synonymous with pier or wharf—any human-made structure in the water intended for people to be on.

The structure shown is clearly a human-made structure in the water intended for people to be on. Therefore, it is a dock in American English. Whether it is also a pier or wharf may vary depending on what part of the world you live in. Here it would also be called a pier.

Yes, it’s floating. But it’s still a floating pier or floating dock.

Solution 2:

One word is jetty.

A landing stage or small pier at which boats can dock or be moored:
Ben jumped ashore and tied the rowboat up to the small wooden jetty

[ODO]

It appears that this is a British-English usage of the word and American English uses different words for various marine structures — or uses the same words in different ways. Despite that, Google images for jetty include the sort of thing illustrated in the question:

^{xlibber via Wikimedia Commons}

...and some rather larger structures:

^{Luke Roberts via Wikimedia Commons}

Solution 3:

I'd usually refer to them as a "pontoon".

Jetty, dock, quay and pier all tend to be non floating. The OP's original picture is a device that floats with the tide but is kept in place by the upright poles so the boats are always at the same level as the "artifical ground level" created by pontoon.

The floats under the decking are often referred to as pontoons (much like the pontoon on a sea plane) but the decking and floats combined are what I would call a Pontoon