But the answer is probably no. The toxic algal blooms (Red Tide is only one of them) that occur periodically in all the world's coastal waters are due to organisms which are a natural part of the environment. For some reason, conditions suddenly favor explosive growth of one species, and it goes berserk, often causing severe but temporary damange to the local environment.

You should also be very wary of thinking in terms of "purpose" in nature, as your question implies. There is no purpose in nature, things happen for a reason, but not because they have a purpose. After a while, natural environments adjust to conditions, and you will note that in areas where red tides are frequent, the local ecosystem is pretty resilient and recovers quickly. It's not that the bloom served a purpose, it's that the environment evolved a response to it. Just like the Florida scrubland has evolved a quick response to wildifres because it has selected for fire-resistant species that quickly repopulate a burn, or plants that need fire to spread.

The wildfires don't serve a purpose, they are a blind and random phenomenon, the environment has learned to work around them. Only those plants and animals that are fire-tolerant are left. I know it sounds like I'm nit-picking, but this is a very important point. Nothing in nature happens for a purpose, but everything happens for a reason.