There are very few areas of US coastal waters that are unaffected by HABs. The New England states are subject to recurring PSP problems. Fish kills in the middle Atlantic states have recently been linked to a newly discovered organism called Pfiesteria. Florida and other Gulf Coast states are subject to fish kills and NSP from Karenia brevis red tides. The West Coast including Alaska has a continuing PSP problem and more recently domoic acid (ASP) problems have been discovered in the region. Even the tropics of the Florida Keys, Hawaii, and Puerto Rico are not immune as Ciguatera Fish Poisoning (CFP) has been reported there for some time.
One question that scientists ponder is "Are HABs spreading and is the problem getting worse?" A growing body of evidence suggests that HABs are increasing around the globe.
Maps of the expansion of HABs in the US since 1972 indicate the scale of the problem now compared to 30 years ago. We have more toxic algal species, more algal toxins, more areas affected, more fisheries resources affected, and higher economic losses.
Why is this? There are many reasons. The first thought of many is that pollution or other human activities are involved. On close inspection, however, many of the "new" or expanded HAB problems in the US occurred in waters where pollution is not an obvious factor. The organisms responsible for HABs have been on earth for a long time, so new bloom events may simply reflect better detection methods and more observers rather than new species introductions or dispersal events. The 1987 NSP event in North Carolina is a good example, as that was a Florida bloom carried by the Gulf Stream to North Carolina waters - a totally natural phenomenon with no linkage to human activities. Likewise, a massive 1972 red tide was responsible for introducing dormant cysts of the PSP-producing species Alexandrium tamarense to southern New England waters, where it has persisted to this day. Those coastal waters have seen an increase in pollution over the years, but the actual introduction and colonization of the species is the result of natural currents and environmental forcings, including a hurricane which occurred immediately prior to the 1972 bloom. It may be that subsequent blooms of this species are enhanced by pollution, but this has not yet been demonstrated. The appearance of ASP along the west coast after 1991 is also not a result of pollution, but rather to communication among scientists and improved chemical detection methods that led to the identification of a toxin that was surely present in those waters for many years. Some believe that man may have contributed to the speading problem by transporting toxic species in ship ballast water, but this also remains an unproven hypothesis in the United States with respect to HAB species. Another causative factor is that we have dramatically increased aquaculture activities, and these lead to increased monitoring of product quality and safety, revealing indigenous toxic algae that were probably always there.
The linkage to pollution should not be ignored, however, as the increase of nutrient inputs into our coastal waters will stimulate "background" populations of microscopic and macroscopic algae (seaweeds) by fertilizing them into bloom proportions. Harmful or toxic species will thus be more abundant and more noticeable. Some scientists even argue that the nutrients that humans supply to coastal waters are delivered in proportions which differ from those that naturally occur, such that we then alter the species composition of the algae by favoring certain groups better adapted to our nutrient supply ratios. Among the favored groups are some HAB species. One example where nutrient inputs have been linked to harmful blooms is with the ambush predator dinoflagellate Pfiesteria. That organism and many closely related fish-killing species, seem to thrive in polluted waters.
One way to view the expansion of HAB phenomena in the U.S. is that we are better defining the boundaries of the problem - boundaries that may be expanding somewhat due to pollution or other global change issues, but which were always bigger than we thought. As we identify new toxins and new toxic species, we begin to see the nature and extent of the problem as it always was. This does not negate our concern about the expansion at all, nor does it alter the manner in which we must mobilize resources to attack it. The national and global HAB problem is serious and large - much larger than we thought. If it is also growing due to human activities, then our concerns are even more urgent.
The maps showing the change in the HAB events since 1972 are useful, but they give no information about the frequency of the events. A single outbreak will look the same as an annually recurrent bloom. A series of maps has thus been generated which depict the frequency of specific HAB problems along the U.S. coast over the last 10 years. These charts will be updated on an annual basis allowing a time series of the events to emerge.