I assume by polychaetes you mean the clam worms.
They really are nasty looking little beggars, especially when they stick out their fangs.
Some people recommend them as fish bait but I found the stinking pile worms worked better.

Red tide only affects the clams, not the crabs.
The clams concentrate the poison and depending on the type of clam they can cause paralytic shellfish poisoning for a long time after the Red Tide is over.

20 years ago they used to track the red tide blooms and issue warnings for the areas it appeared in.
It seems the Ministry of Fisheries still does it.
Here is a site.
http://www-ops2.pac.dfo-mpo.gc.ca/xnet/c...id=recreational

I am certain they also have a page explaining what red tide is.
The warning sign of tingling lips is not something you can trust either.

There are other problems beside red tide though. There are lots of places where the shellfish beds have been contaminated by pollution.

One of my favourite seafoods while I was there was sea urchins.
Urchins graze on seaweed so they are not affected by red tide.
You find them just below the low tide level.
By now it is likely illegal to harvest them because of overfishing (Asian market?).
There are 5 fingers of roe in them clinging to the inside of the shell. The rest of the mess inside them is just water and seaweed to be dumped out.
To me they taste somewhat like strawberry and lemon raw but just like scrambled eggs cooked. I prefer them raw.

Octopus was another real treat.

Vancouver Island is good for the Dungeness crabs too.
You can get them by setting a crab pot at low tide and checking it when the tide goes out again.
I have even had crabs grab onto my fishing line when fishing on a beach for sole. There are size limits so you need to measure and release the ones that are too small.

There are a lot of fish besides salmon. Many of them are easily caught from shore. Ling cod, greenling and rockfish are all good catches. There are other sculpins like red irish lord that are good and of course there are flatfish like flounder, sole and of course halibut. (but for halibut you really need a boat to fish effectively)
The small sharks are good eating too, the one they call the dogfish.
I understand there are more mackerel appearing on the west coast now.

In the spring there is a herring run and there are smelt runs too.
Herring are jigged for with small white jigs that are almost like fly fishing flies. You usually have 4 or more tied to your line above a weight and jig vertically. Sometimes you can get a herring on each hook each time you drop the line in.
One part of the herring fishery is for the herring roe.
When the run is on the herring eggs glue themselve to seaweed or anything else in the water.
People sometimes hang tree branches in the water to collect the roe on.

Smelt, oolichan and anchovies are often caught on the beaches with smelt nets.

Bull kelp makes nice pickles, there are other seaweeds that are like the stuff from Japan. (Sea lettuce, rockweed)

If I start talking about forest produce like berries, roots, fruits and mushrooms I could write another chapter.
So I will stop now.