http://www.biologynews.net/archives/2010/10/07/volcano_fuels_massive_phytoplankton_bloom.htmlSummary:

In 2008 the Kasatochi volcano in the Aleutian Islands erupted. When it erupted it spewed iron-laden ash over a great portion of the North Pacific
The ash actually helped in it made the number of phytoplankton rise. The bloom was the biggest number ever recorded since 1997. Phytoplankton is free floating single celled plants that basically start the marine food chain.

Opinion:
I think it’s just all in chance. You would thing the ash would actually kill not help the phytoplankton. Maybe that area is just a good spot for it to grow.
Yes the eruption might have had a little to do with it. Not all off the bloom is based on the eruption I think. Maybe there was something else that could have trigured such a massive bloom.
Shelby G