This article says that the dangerous type of algae are indeed away from the coast, and it appears it is encouraged by the limited iron fertilization experiments that have taken place to date:
They joined Ken Bruland, professor of ocean Sciences at UCSC, on a research cruise to study iron chemistry in oceanic waters of the Gulf of Alaska. During this expedition, they collected water samples and found the algae and its toxin in nearly all of the natural oceanic environments throughout the region. This prompted them to examine older, stored samples from other sites around the Pacific, and again they found the toxin in most samples.
OK, so it probably happens naturally too. That's not to say it's such a good idea to cause more widespread toxic waters than what we see already.Then, with the help of Kenneth Coale, director of Moss Landing Marine laboratories and principal investigator on several cruises that conducted classic iron enrichment experiments in the Pacific, they retrieved samples and found both Pseudo-nitzschia and substantial amounts of toxin. Their findings show that iron enrichment indeed promotes high levels of toxins in the open sea, sometimes as high as those in coastal regions, where deaths of seabirds and mammals occur. The authors of this PNAS paper also noted that iron enrichments can occur naturally, suggesting that the high levels of toxins may also have occurred when iron was added by wind-blown dust and other climate and geological processes.
And in other worrying news, another study suggests that elkhorn coral has its reproductive success greatly limited by ocean acidification. It's not that coral reefs will ever start fizzing due to an acid ocean, but as they are worn down by mechanical action, warm water bleaching and other damaging factors, they may not grow back.
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