I doubt that the bristle worms are responsible for the crab deaths.
More importantly you need to address the reasons for the abundence of algae, can you describe your tank setup?

 

A maroon in a 20 gal.?

 

Tank setup: 20 gallon, 300 gph marineland powerfilter, whisper 3 powerfilter, counter current protein skimmer, 55w CF, 1.5"-2" live sand bed, 10-15 lbs live rock. Also do 20-50% water change every 4-6 weeks. Oh yea, 1 snail, 2-3 hermits.

this algae came on one piece of rock. It is a nasty algae, cause it spreads fast and you have to destroy the rock to pull it off because the rhizomes are so buried in it. I also have some caulerpa growing as seen int he photo, that I trim regularly.

Here is a photo of this algae, which I have not been able to ID.

The macro algae has even started to grow on my snail, so he cruises around with a forest on his back, which is kinda funny looking.

 

Here is a pic of my snails foliage. He is actually quite a prized possession.

The maroon was about 1" long when we got him, now he is about 2" long and owns the tank. The poor jawfish stays around his burrow entrance and just hangs out. the maroon clown even tries to attack my hand when I do tank maintenance.

Mark

 

looks like u need to get a weed eater on that LR... thats crazy, love your snail though!
sry cant help you w/ the algae problem... im just tagging along to see what i can do about my lil algae prob...